Supercharged Stock 1600 DP

[Buggin_74]

The accelerator jets were indeed .42mm so I opened them up to .5mm However, this seemed to make no difference at all. Not sure if this is because the change was not significant enough or if this simply isn't the cause.

I made the mistake of going bigger and bigger with mine when it was falling on its face at full throttle when it turned out I needed to go the other way.

I've still got the whole setup sitting in the shed, I ended up buying new accel pump jets too, If I can get them out ill see what size they are but 33 (0.33mm) rings a bell.

[T-34]

I hate to say it Mick..... But have you considered fitting a WBX crank pulley and a multi-groove alt and charger pulleys?....

I haven't had anything to do with WBX stuff. Didn't realise that they had grooved pulleys - That might actually be the missing link!! - Was thinking that I would have to get them made up.

V belts are not designed to run via complex tracts such as your project has... You are potentially limiting the life span of the belt as a result....

This is true, and something that I am aware of. The route suggested a few posts back is a little less stressful on the belt and one I aim to try once I've sorted the throttle linkage issue out. Ultimately I need to get some miles on the setup to see how it wears. However that said - I think I've sorted the belt issue - more later....

And get a damn wideband in there will ya!?

Yeah yeah - never needed one in my day I was orignally just going to get the guys on the dyno to tune it but I'm quite enjoying the challenge. If I carry on the way that I'm going there will be little left for them to do. I will have to dig the O2 sensors out that I've had squirrelled away for the Type 4's EFI. Have a feeling that they are narrow band tho (3 wire). I did have a look on epay for a complete AFR kit but it's all a bit spendy for me at the mo - work is very slow. For the time being it's just going to be good old seat of the pants stuff.

Back to this arvo's antics - I managed to pick up an 80mm pulley from my local machine shop, pretty lucky really as most of the stuff he has is industrial and not automotive. It was not exactly the right size so I ended up turning the hub down to fit.



One thing I noticed when measuring up the new pulley was that the belt profile on the old pulley was incorrect - in fact is it for an A series belt - like the ones you find on Mills / Lathes etc. I only really noticed this by coincidence as whilst I was visiting the machine shop looking for a bigger pulley I decided to also get some new drive belts for my milling machine. After a conversation about drive belts they were fresh in my mind. Otherwise I probably would have picked up the pulley and not noticed that it was different (like every other time I have picked it up). It seems that the custom blower pulley I bought is likely little more than an off the shelf power transmission pulley. No wonder the belt slipped - it would have only been gripping on the very tip of the vee.



Whilst annoying, at least it was looking like the cause of the belt slipping might be solved, I think I might have been more pissed off had I not needed to change the pulley for a different ratio. Ahhh well. another thing to chalk down for experience.

Back to the new pulley. I decided to remove the second pulley from the hub to save a bit of weight and also help me to turn the hub down to the correct size (my boring tool wasn't long enough)



I fitted the pulley up on the bus and decided to leave out the additional idler wheel so see what happened. I started the bus up and lo and behold - no slip!! Seems that the issue was the pulley profile.



I was a bit worried that having reduced the boost I was now too big on the jets so decided to take a step back and check everything out. I read back through my notes and tried to figure out what's what.

Reviewing my notes I originally through that the engine was too rich as it was hunting, I was a bit confused as to why it appeared to be too rich yet I was still seeing high temps. Gearheadgreg's comments about timing also stuck in my head, plus with no real way of being able to actually measure or see the vac advance whilst driving I was not sure if I was getting some overlap between the vac and boost which would not be a good thing. So to eliminate one issue I pinched the vac hose with a cable tie to take it out of the equation.

I let the engine warm up and then set my Idles. I initially set them to 2 1/2 turns. The engine was still hunting. I then wound them in until the engine stumbled and then would them back out again by half turn. They are currently sitting on about 1 1/2 turns. From this I deduce that the idles are almost near where they need to be - from recollection any more than 2 turns from the initial 2 1/2 setting means going up or down a jet size.

Took the bus for a drive - No pinking under load - just heaps of torque. Stick it in a high gear and gradually press the loud pedal - normally the bus would just stall but this time it picked up nice and smoothly until throttle was quarter open (mains coming in??). Seems like reducing the boost has made massive difference, only issue was that I am only seeing about 3 or 4 psi on the gauge. ahh well - baby steps.

Whilst everything has improved massively I was still getting hesitation when stamping on the pedal - to the point where it bogged down pretty bad so decided it was time to look at those accelerator jets.

Originally I only opened the accelerator jets up a little and it seemed to make no difference so I decided to go to the next drill size that I had - 0.55mm This improved the hesitation quite a bit so I decided to go up another size and see what this would do - 0.6mm This was a further improvement and the bus was now accelerating much better. However, the power would seem to die off at higher revs. I 'feathered' the throttle to introduce more fuel from the pump jets whilst accelerating and as long as I did this the bus kept pulling so I put this down to the mains being too small.

Next I opened up the mains to 1.8mm (previously at 1.75mm) This improved the situation and the bus has been the most drivable it has been since installing the blower. As the bus was actually really drivable I decided to take the bus for a longer run. Still dying at higher revs and picking up if I feathered the throttle. I also found that the temps were still slowly creeping up and after returning home the oil temp was up at 200 which considering that it was evening time was pretty high, the engine also smelled hot and there was a little oil mist coming from the breather (it's not connected at the moment). By this time I had lost the light and so decided to call it a night.

So as things currently stand: Belt slipping is now a non-issue, but belt longevity is still something to be determined. No more pinking under heavy load - just heaps of torque but still have hesitation under a fast throttle. Engine is still running much hotter than I would like.

I'm pretty confident that the idles are now okay. I think that the mains might still be a little under sized. Accelerator jets might also need to be increased but really want to nail the mains first. I think tomorrow I will try to go up another size on the mains and see what happens. Maximum boost I have seen is now only about 3 or 4 psi which is a little disappointing so I need to source another pulley. Might look to make one up from scratch.

Other ponderings...

I am also considering limiting the advance some more. I was pretty happy with where my dizzy adjustments ended up but I find that if I try to retard the overall advance a little, it is too retarded at idle. I think I need to close the gap. Would really like to try and retard the overall advance a little to see if this addresses or helps the heat issue. I would also like to reinstate the vac at some point but need to figure out what to do to retard the vacuum under boost. That said, there is heaps of torque and it is actually very drivable without the vac so I could just swap it out for a 009 and be done with it.

Another consideration that I am pondering is whether to swap out the chokes to a smaller size. The useable throttle range seems to be from closed to slightly open position - I'm not sure if this is due to; a/ only driving on the idle circuit, b/ boost or c/ chokes. From what I have read centre mounted carbs like a smaller choke to keep the velocity up, which in turn helps keep the fuel in suspension. I cannot help but think that this might also make the throttle response a little better.

Ahh well, some food for thought.

Will try the mains tomorrow and see what happens.

Mick.

[T-34]

Hmmnnnn Interesting reading.... http://oto.to/schematy/gazniki.pdf

[gearheadgreg]

Great work - and good result, I think. Fixing the belt slip and making the thing driveable is a huge step. Bravo.

Now - back when I was messing around a lot more with watercooled VWs, there were some fairly 'common' steps to run a simple old 1.6-1.8L CIS 8 Valve engine with boost. The additional fuel I won't talk about because it's of no convern here, but the ignition might have some relevance.

Many of the old Rabbit/Golf/Scirocco distributors had one simple vacuum cannister screwed onto the side of it. IIRC, some in the 80s added a dual vacuum cannister to retard timing under decel for emissions or something - can't really remember. However, what worked a treat was to use that retard cannister port to run it to manifold pressure so that the timing would retard under boost. Very, very simple, very easy, and factory parts. Here's a pic I stole off the intraweb to show what I mean - notice the 2 vac ports?



I don't know the model number, but probably a 205 DVDA? or something would have the same cannister. Otherwise, I used to add and swap cannisters between Rabbit dizzys all the time. It might swap onto your dizzy as well, but the fat cannister like this should have 2 ports to do what you are thinking. I think.

[T-34]

I think you might be right there. Originally when I was putting the stock engine I ran into the issue of the dreaded flatspot caused by using a 009 dizzy with an PICT34/3 carby. After reading up I found that the correct dizzy to use was the SVDA. However, in my hours of googling I did come across a DVDA carby that operated in a similar manner to how you describe. only issue is that these are not easy to find or are a bit spendy. (there goes that budget again).

I've been pondering running a boost connection from the manifold and connecting it to the vac line. This way when the manifold pressure goes positive it should cancel out the advance. (assuming that the vac is not greater than the boost). Would obviously need a one way valve to stop pushing boosted charge into the vac port of the carby but I already have a few of these from my aquarium air pump setup.

[Clonebug]

The only problem you will have making that distributor work on the retard side is letting it see only pressure.

With a turbo it is easy due to hooking a hose up the the pressure side of the turbo. There is no vacuum to speak of when in cruise or no load conditions.

On the supercharger there will more than likely be vacuum at any time there is no boost and pulling Vac on that side of the canister will not give you a reliable timing curve.

The only thing you might be able to do is put a check valve in place and a very tiny bleed hole so it can not see vacuum.

I ran that distributor for less than a week on my blow through turbo and gave it up due to not trusting the advance curve and not being able to know where I was with the advance.

The MS-1 Extra I upgraded to was worth every penny I paid.
Fully mappable advance and retard.

[T-34]

On the supercharger there will more than likely be vacuum at any time there is no boost and pulling Vac on that side of the canister will not give you a reliable timing curve.

Ahh yes, didn't think of this.

Been doing some reading and found a helpful thread on the samba - http://www.thesamba.com/vw/forum/viewtopic.php?t=396930 it gives some alternatives for the dizzy...

Bosch made a "turbo" dist for the Volvo 240. It shares the same cap/rotor as the 009 and I am sure with some mods the guts could be swapped to a 009. It has a vacuum advance/boost retard canister on it.
Do some research on it...... A lot of retrofit turbo kits use it. I tried finding a pic on the net but came up dry. I am sure there are many 240 turbo's in the boneyards. You are looking for the dist on the B21 engines.

to the xthousend's time....bosch turbo dizzi:
saab 900, saab 9000..both habe bost retart vacuum tins on them. go to a junkyard and get a tin out of these. or spend some time on _BAY and get one für 1 dollar or so. the early adusting is nearly the vw. performs very good.
retart is up to 0,6 bar of boost. i changed mine to retart up to 1,2 bar and a friend to retard all the time.
i run 1,2 bar on a nearly stock 36hp and he on a 40hp with 1300cc doubleport heads and 1,6 bar..fucking 23 psi..no intercooling both.
thats the clever cheap way. i never understood locking a dizzy. it works for sure but on a stupid way. at my friends car we could make much much more performance without boost, and could get 0,3-0,4 bar more out of it via just changing to the retard tin.

So looks like Saab or Volvo 240 cans could be made to do the job and I'm guessing that these are more available than the DVDA cans. There's some further info on using the Saab can here - http://www.shoptalkforums.com/viewtopic.php?p=958187 although this is on an early dizzy.

However, whilst this is great for me to modify it for my own car it is a complete nightmare for supplying in a kit. Adding a dizzy into the mix adds cost, it also means that I need to either invest in a dizzy machine or pay someone to set them up. I might as well just thrown an EDIS setup in the box and be done with it. Ironically replacing the dizzy with EDIS would allow me to mount the blower in a different configuration so that the stock carby could be used (and the same kit would fit both a bus and a bug!), plus it's probably cheaper to supply an EDIS setup with megajolt than it is to supply a DCOE, not to mention that it's far superior. Only thing is that this adds complexity and might scare some people away from the kit.



Last night I actually took the time to read through the whole of the carby book I linked to above (http://oto.to/schematy/gazniki.pdf) it is actually very interesting and explains everything in very good detail. It seems that much of the info that I had previously read on the web was not 100% accurate, it would appear that whilst basically accurate it's been diluted through the 'chinese whisper' effect. I now have a much better understanding of how to set up the carb, especially in relation to the idle jets...

Basically the idle jets need to be sized to give the correct A/F ratio during progression (not idle), the 'at-idle' mixture is then tuned using the adjuster. The progression holes are upstream of the needle in the carby and so the progression circuit can only be dialled in by changing the idle jets. Once set the at-idle setting can then be dialled in using the idle needle. The expression 'idle jet' in this case was a little misleading to me. The book then further goes on to say that if the progression circuit stumbles a little, the idle mixture can be increased to help a little but only up until a point - any further than this and the idle jets / idle air bleed will need to be changed.

Additionally, the at-idle setting should be in the region of 3 1/2 to 5 1/2 turns, if (like mine) it is less it points to the idles jets being too large. I currently have no stumbling on progression and have been incorrectly thinking that it is too lean due to the heat. What I really think is causing the heat issue now is the timing.

I have also learned why the carby I have (an emissions model) is harder to dial in. Most of the internet just say things like 'crap' / 'avoid' / 'etc' about emissions models, the book actually explains that in these models the air bleed on the idle circuit is actually fixed and not interchangeable. It's also 2mm which is excessively large. This can result in a lean idle. They prescribe fitting a small plug into the air bleed to reduce the orifice size to counter this.

So, where to go from here with my new found knowledge...

I think I need to look at reducing the overall advance in my timing so that I can increase the idle timing setting with the vac disconnected. This is obviously only for running a mech only dizzy. I know it is a compromise, but I am interested to learn the limitations of using a 009 as most people will probably already have one or will (mistakenly / foolishly) want to run one.

Ultimately if running with a dizzy I think that the vac is needed for off boost timing control but it needs to be set up to work properly with on boost conditions - for example by using a DVDA dizzy or similar. I also need to do some work to find out a reliable source for this kind of setup.

So, I will adjust the dizzy and give it a test to see how this has affected the temps. I then think I need to solder up the idles - reduce the idle air bleed size and start again with dialling them in. I think my previous deduction that the idles were good is now inaccurate. Once I have the idles dialled in I will then look at the mains and then the pumps.

Looks like I have some work to do.

Mick

[gearheadgreg]

Since the ignition timing looks to be the stumbling block here, and indeed, if you sell it as a kit and customers hole some pistons - that's the end of the kit, I bet.

So - check out this and some other options - I think there is likely a cheap, replacement dual-port vacuum cannister out there that will solve the problem and take you to the next stumbling block!

http://www.ebay.com/itm/VW-1971-Type-1- ... ccessories

[Buggin_74]

You could try a one way/non return valve on the vac can hose so it only gets boost and shuts off when there's vacuum there.

That's what I had planned to do with mine, except I couldnt find a dual action vac can.
They were only fitted to bugs in Aus in 71 but the factory recalled them and put SVDA on as they ran so terribly.

[T-34]

Greg I think the can you've linked to is an SVDA can as it only has one connection. Although if I could find a source for these I would definitely buy them. As Joel mentions, they are pretty hard to come by over here and my search for DVDA's only seems to return pages of DVD's

Anyhows, I did manage to make some progress. I'm pretty sure I've got the timing licked. I took the dizzy off and adjusted the advance stops a little more. I set the overall timing at 24 degrees and checked where the idle sat. It's now 10 degrees. The heat issues now seem to be solved and after taking it for a drive the temps were down at 160. I also invested in a fancy timing gun. Wanting to get this right I figured that if I was going to spend $150 to buy a degree pulley from the local VW shop I might as well cough up a few extra dollars and get a programmable gun. So I did.



Took me a while to track one down as Adelaide doesn't have too much in the way of anything but I eventually found one at the Repco main depot in Wingfield.

So I'm figuring that the heat was due to driving the car around on load stuck at a static 7.5 degrees timing, it simply didn't like it. Obviously the vac would fix this issue as well but for the time being the timing is one less thing to worry about. I will return to it later as there is obviously room for improvement but at the moment there's no pinking and no heat issue.

So with the timing sorted I moved on to setting up the carby. The flat spot / stutter / stumble / hesitation is still present but other than that it is drivable. So I decided to put into practice what I had read last night. First thing to address is the air bleeds on the idles. I took the carby out and stripped off the float bowl cover.



The two small angled holes that you can see are the air bleeds for the idle circuits. These are fixed at 2mm. The recommendation was to plug the holes up with a small tube with an inner diameter of 1.2mm. This helps to limit the air bleed and prevent off idle lean conditions it basically brings the size into line with the air correction jet of a non-emmisions model. I didn't have any suitable material to make some plugs up from so after looking at the idle jets and pondering a little I decided to try something a little different. I decided to solder up 2 of the 4 holes in the idle jet holder as this seemed like it would achieve a similar thing (limiting the air flow). After some more road testing I determined that this had made no difference at all. I tried winding out the idles a little to see if this compensated but this also had no effect.

So - on to the next thing. If it is a too lean condition that was causing the on progression hesitation perhaps the accelerator jets were too small. So I opened them up to 0.65mm. This actually made a massive difference, only not for the better. Instead of stumbling it actually coughed back. Obviously too much fuel this time.

(There is a point to note here regarding belt type. With the vee profile belt the cough back simply makes the belt slip. No need for a pop-off valve and no danger of launching the blower.)

So carb off once again. I soldered up the accelerator jets and redrilled them to 0.4mm This cured the most recent issue but did not improve the overall hesitation problem.

What next??

I figure that if changing the accelerator jets isn't making any difference, except when introducing too much fuel, then maybe there is simply too much fuel to start with. I tried to back off the accelerator pumps to see what happened but even with the adjustment slackened right off the actuator spring still operated the pump lever. So the next logical step - reduce the size of the idles.

Previously I had gotten the best improvement by increasing the idle jet size , but after changing the blower drive ratio I was wondering if these were now too large. Reading through the Dellorto book it certainly seemed to imply that if the best idle was achieved at less than 3 1/2 to 5 1/2 turns the idle jets were probably too large. So I removed the carby once again, soldered up the Idle jets and re-drilled them to 0.6mm

Again this was a massive difference - for the worse. The bus was now almost undriveable. The hesitation was present from almost just off of idle. This was obviously not a good choice.

I also had a bit of an issue with my alternator connection shorting out on the inlet manifold - this is something that is addressed in the revised design but not on the prototype, so to counter this I moved the blower and carby up a little, which had the effect of slackening the belt. So I re-tensioned the belt by repositioning the idler pulley. Only issue was that I forgot to tighten the idler bolt properly and when driving around the pulley ended up moving upwards to the point where the belt was shredded between the idler and alternator pulleys. Oops



So with a shredded belt I decided that it was time to try out the other belt configuration. I made a small adjustment to the accelerator linkage so that it cleared the belt and refitted the idler adjuster. Looks great but there is only about a quarter of a pulley contact on the alternator which was causing it too slip a little. I will pick up another belt tomorrow and get it back in action in the previous configuration. I will also revise the tensioner pulley location so that it cannot move near to the alternator pulley.

One thing that I noticed with the belt shredded was the bus still ran fine. That and the same hesitation / flat spot was still present so the hesitation issue is obviously not related to boost.

Tomorrow I think I will take the idle jets up another size. Increasing the idles jets has been the biggest improvement so far and perhaps taking them up another size might be the key. Although the changes I made today made everything a little worse, when I was driving it last night and feathering the throttle I could feel the engine's potential. If I can get the jetting figured out I think this thing will pull like a train. Larger idle jets seem logical based on the results I have experienced, although I have got to admit that it doesn't seem right based on how the engine idles - it still seems to sound way too 'rich'. Guess tomorrow I will find out.

Mick.

[T-34]

Okay, now that I am knees deep into this I've decided that maybe I should really take the plunge and invest in a wideband. I know i really wanted to save the expense but if I am really going to get these kits off of the ground I guess I need to get the thing dialled in properly. If I pay the dyno guy to do the tuning it will cost me $90 an hour. So from a financial perspective I might be better off investing in the right tools and doing it myself, Plus then I have the tools for other projects.

So, with this in mind I've been taking a bit more of a look at widebands. The two sensors that I have 'in stock' are narrow band so not really of any use other then with my archaic DTA EFI system. So my initial idea of just buying a gauge is not feasible.

Ultimately I'm not really interested in a permanently installed system as I will definitely get use out of it with my other projects so
I've been looking at the Innovate LM-2's.

What's everyone opinions on these? anyone use them? I've found the basic kit for sale at a shade over $300 - a bit more expensive than a separate gauge and sensor but as it is just plug and play it seems to be a better bet in the long run. Very interested to hear your opinions and any alternatives.

Mick.

[gearheadgreg]

Greg I think the can you've linked to is an SVDA can as it only has one connection. Although if I could find a source for these I would definitely buy them. As Joel mentions, they are pretty hard to come by over here and my search for DVDA's only seems to return pages of DVD's

More meaningful progress - good on ya.

I think that one I linked to is a DVDA canister, I just think the 2nd nipple is hidden. Snicker.

Here's another - http://www.ebay.com/itm/VW-Type-3-1972- ... 9f&vxp=mtr

So, if these are available new for $50/ea, then I would think a wholesale price or non-Bosch version might be had cheaper. I also think those look a heck of a lot like the Scirocco/Golf watercooled VW ones as well, etc. There's got to be an 'easy' way to adjust the timing according to boost and engine load. I think it is key to getting good performance, as well as reliability.

[T-34]

Totally agree. From what I have experienced with my SVDA I would never go back to running a 009 and from what I have seen so far with this setup it would definitely benefit from the vac advance being hooked up.

Anyhows. The DVDA vac can is now mine Now I just need to wait until it arrives.

I am also very nearly at the point of hitting the buy it now button on the LM-2 kit.

Ahh why is spending it so much easier than earning it?!

[T-34]

So after some pondering I decided not to increase the size of the idle jets. I decided instead to reduce the size of the idle air bleed as recommended in the tuning guide. I had a bit of a eureka moment and figured out that the tips for my MIG welder would make a perfect base from which to make the tiny little plugs needed to plug up the idle air bleeds.

For those who haven't read the rest of the thread the carby I am using is a Dellorto DHLA 40H. This is what they refer to as an emissions model and it has some differences from the stock 'universal' DHLA's that supposedly make it hard to tune. The main difference is that the idle circuits don't have a separate air bleed nozzle / jet and so the air bleed cannot be swapped out to tune the idle circuit - as you can on the normal 'universal' models. Whats worse is that this air bleed is pre-set at 2mm. The other main difference is the emulsion tubes.

My ponderings revolved around the reason for the air bleed being 2mm. I figured that if the air bleed was too large then the carby would have a tendency to go lean whilst on progression. This lean condition is pretty much what I have been trying to address with the ever increasing idle jet size. But what if the issue was not the jets but the air bleeds.

So armed with a new found direction I turned down one of the MIG tips in the lathe. Unfortunately trying to turn a 2mm piece of copper is not an easy thing to do on a 1948 lathe so it ended up catching and bending. Not perturbed I decided that maybe 2mm was too small. so I counter bored the air bleed hole in the carby to 3mm and turned another MIG tip down to suit. I then opened up the hole to 1mm, figuring that I can always go bigger if needs be.







It has got to be one of, if not THE smallest thing I have ever turned. After cutting it down I pressed the two new idle air bleeds into place in the carby



So, the test drive...

Considering that the car was previously almost undrivable it made an instant difference. It was much smoother all the way through the range, however it was waaay too rich with plenty of black smoke. This seemed logical as now that less air was being bled through it was obviously drawing through more fuel. Whilst smoother it still wants to die if I stamp on the pedal fast.

Ok so next - reduce the size of the Idle jets, I also decided to bring the mains down as well. Previously the mains were at 1.8mm and the idles were at 0.6mm so I brought them down to 1.5mm and 0.4mm

Now it would only drive on a partial throttle and spluttered when opened up. Could still only accelerate very slowly to overcome the (now larger) hesitation when opening the throttle too fast.

So I figure that the spluttering (lean) means the mains are now too small, and figure I will try reducing the idles some more to see what happens.

Opened mains to 1.5. Idles down to 0.4.

No more spitting on mains
Idles nicer but the hesitation is now happening on less throttle.
Overall it drives smoothly but only on a very low throttle which makes it feel like it's down on power. (opening up the throttle any more than a smidge causes the engine to die due to the hesitation).

So figuring that this might be due to the pump jets being too large I soldered jets up and re-drilled to .35 still same hesitation. Doesn't look like it is due to pump jets.

Thats about where I got to this evening. Here's where things currently stand.

Mains 1.5
Main Air bleeds - 180 (still same as when I got the carb)
Idles 0.4
Idle air bleeds - 1mm
Pumps 0.35

The tuning guide recommends 45 idles and 7850.1 or 7850.2 air bleeds (idle holders). It also mentions somewhere else that a 7850.1 air bleed has one 1.4mm hole - mine has four holes - not sure what size but possibly about 1.4mm although having plugged up the main bleed hole it's now only seeing the 1mm.

For mains the guide is a little woolly. For normal one barrel per cylinder applications it gives the main jet size based on the cylinder capacity and choke size - much as you would expect. For 'siamesed' applications it simply gives a jet size based on the choke size - in my case with 30mm chokes it recommends 135's - quite a bit smaller than the current 150's. This recommendation doesn't seem right to me based on the spluttering that I experienced with the 140's. I can only think that the main difference is the emulsion tubes.

The 7772.11 emulsions that I have are only fitted to the emissions carbs. I'm now starting to wonder if these may be the cause of the hesitation that I get. No matter where the idles and mains are the hesitation is still present. I've had them too lean, too rich and in both cases the engine wants to die if the throttle is opened too fast. Changing the jets only seems to move where it happens. No matter what I have done to the accelerator jets the hesitation has remained the same. Recommendations for the main air correction jets seem to be the 180's that I have - or possibly 190's in some applications so I don't think that these are the issue. The more I think about it and try to get my head around it, the more I keep thinking that it can only be related to the two things that I have yet to play with - the emulsion tubes and chokes.

I can only liken the stumbling to turning the ignition off. (ha - i just wondered if it IS actually the ignition ). it's not a too lean condition or too rich it is literally like turning the engine off. No coughing, no spluttering, no hesitation that if you keep your foot down will pick up. it literally dies.

I'm not really sure where to go from here. I'm almost on the limit of how small I can test the idles - I could possibly go to .35mm as this is the smallest drill my pin chuck will hold - the 0.3mm drill does not fit. However, having already snapped a few of the sub 0.5mm drill bits it's not something that I relish doing, plus I'm not convinced that this is the issue. The performance has got steadily worse as I have decreased the idle jet size. Obviously there have been a few other parallel changes such as the air bleeds, but all in all if I map out the changes I am not 100% convinced that any combination of idles / mains / pumps will cure the issues I am seeing as I think I've almost tried them all.

Think I really need to get my hands on an O2 sensor and see what's happening with this 'flat spot'. My guess is that is is going lean, if it was too rich it would simply splutter a bit and carry on (air + lots of fuel = some unburned fuel = still running) whereas what appears to be happening is that it simply dies (air + no fuel = nothing). Will order an LM-2 but as this isn't going to be here for a while I've still got some time to play.

Joel, did you get a chance to look at your setup and find out what jets you were running? I'm also interested to learn if you had to change it much when you changed the boost from 6psi to 10psi.

Also if anyone has the jetting from a normal single weber application on a 1600 I would be interested to learn what it is.

Open to suggestions / pointers / wild stabs in the dark

Mick.

[gearheadgreg]

I wouldn't doubt the ignition - try changing where the vacuum advance pulls off of just for shits and grins, to see if it makes any difference, and if so, what? Maybe?