Supercharged Stock 1600 DP

[Clonebug]

Solex carbs are drilled to mm decimal sizes.

For example a 130 main is 1.30 mm drill size.

I bought a set of drills and they were cheap but worked great. They ranged from 0.30 mm to 2.00 mm

The 0.30 mm drill bit is TINY!!!!

Here is a link....

http://www.widgetsupply.com/product/BBL50.html

[trbugman]

How about rerouting the belt like this?

[Clonebug]

How about rerouting the belt like this?

Bingo!!!!

Nice job there!!!

[T-34]

Yes I guessed that was what Clonebug was explaining, I will measure up the belt length and try this out. There is less contact around the alternator / fan pulley which was my initial concern but I guess I will not know if this is an issue until I try it. Routing the belt this way also gives me more room to fit a sprung idler as well.

Looks like I will go get a set of metric drills this arvo.

[MarioVelotta]

How about rerouting the belt like this?

That looks beautiful!

[Buggin_74]

Your timing needs to be known also.....you don't want to be guessing what it is.
Put a degree pulley on it and then check it at 3000 rpm to see what max advance is.
Standard max is 24 degrees for forced induction but each engine is different of course.

Definitely need a degreed pulley.
This setup is pretty much a carbon copy of my old one but I used an SC12, on both my 1776 and stock 1600s I found them happiest at max 22degrees with a 009.

[T-34]

Your timing needs to be known also.....you don't want to be guessing what it is.
Put a degree pulley on it and then check it at 3000 rpm to see what max advance is.
Standard max is 24 degrees for forced induction but each engine is different of course.

Definitely need a degreed pulley.
This setup is pretty much a carbon copy of my old one but I used an SC12, on both my 1776 and stock 1600s I found them happiest at max 22degrees with a 009.

Thanks for the heads up on the timing. I've red through some threads on your old SC12 build - nice work What boost were you seeing with this setup?

I will try to source a cheap degree pulley. I was going to go old school and use an old scooter trick - scale and print out a 'degree wheel' and stick it to the front of the pulley (obviously ensuring that the piston is at the top of it's stroke and the scale is aligned properly) - then once the timing is set cut in the new timing mark at the appropriate place.

timing.disc.jpg

I managed to buy a set of micro drills today but they only go up in .1 increments, not sure if this is ideal or if I need to look at smaller increments. I currently have 130 (1.3mm) mains, the next size drill is 1.4mm so I will try this next. After that I can go 1.5 / 1.6 / etc but not sure if these jumps are too large. CB performance & Dellorto list jets in much smaller increments -

.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.22, 1.25, 1.28, 1.30, 1.32, 1.35, 1.38, 1.40, 1.42, 1.45, 1.48, 1.50, 1.52, 1.55, 1.58, 1.60, 1.62, 1.65, 1.68, 1.70, 1.72, 1.75, 1.78, 1.80, 1.82, 1.85, 1.88, 1.90, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.35, 2.40, 2.45 or 2.50

Dellorto also list a special set of reamers that look to be tapered - I guess so that you can dial in the size even better. Hopefully the sizes I have will get me in the ballpark so that I can take it to the dyno.

[andy198712]

If you go too big solder and re drill

The new proposed belt location looks like it wraps around the charger less though? Fingers crossed

[Buggin_74]

That was how I got mine dialed in, spare set of jets, just kept soldering them up and redrilling till it was running sweet then bought new ones in the right size.

Mine originally was good for 6psi but once i put the smaller pulley on the blower it was happy at 10psi.

[T-34]

Well I set the timing at 22 degrees overall mechanical advance (vac disconnected) and was pleased to see that the idle is down at 7.5 degrees which seems spot on, so well chuffed there.

I also removed the jets which involved unbolting the carby. I initially drilled them out to 1.4, which made a small difference but still ending up stalling trying to get out of the driveway. So I took the carby off again and redrilled them out to 1.5. I also wound the accelerator pump out. These changes made quite a difference and I was actually able to take it for a spin up the road. However it was still pinking under load and I could only drive it on a partial throttle or else it would stall, so the carby had to come off again.

After drilling the mains out to 1.6 the bus was starting to feel a lot more responsive, it revs much easier and even though it's still pinking under load it pulls quite nice and I can definitely feel the difference over how it was before. The stalling has also decreased - it's still occurring if I open the throttle fast but at least I can drive it on a partial throttle. I am also starting to believe that the boost reading I am seeing is as a result of the engine stalling and not the other way around.

Unfortunately the drill set I bought only went up to 1.6mm so I ran out of holes to drill. I was tempted to go for the 2mm drill I have knocking around the drill drawer but decided to be patient and buy some more drills tomorrow plus I was running out of light. Taking a wild guess I would say that it still needs quite a bit more; the incremental changes seem to be pointing to about 1.8 / 1.9 before it will be somewhere where it needs to be but it could need even more. (complete crystal ball gazing on my part of course).

I didn't take a look at the belt yet, I re-tensioned it and seems fine unless the engine is revved hard, so until I get the jets sorted it can stay as it is. I am however on the lookout for a suitable bolt on sprung loaded tensioner - any recommendations greatly welcomed.

Will see how things go tomorrow, if it's looking good and I can get the belt issue sorted I will book some dyno time to get it tuned properly and find out how much power it's generating.

Mick.

[Buggin_74]

Have you tried playing with the accel pump jet sizes?

When i first got mine running it was doing similar, would boost up with gentle throttle but nailing it would just fall flat on its face.
idle and main jets wouldnt fix it, took changing the accel pump jets.

I'll have to hunt around my old notes but I think from memory they were around 0.4mm


You shouldnt need bigger than 1.6mm mains, from memory thats what I ran with my 1776.

[gearheadgreg]

Where is the vacuum pickup for the blower? Is it set to retard under boost?

[T-34]

Have you tried playing with the accel pump jet sizes?

When i first got mine running it was doing similar, would boost up with gentle throttle but nailing it would just fall flat on its face.
idle and main jets wouldnt fix it, took changing the accel pump jets.

I'll have to hunt around my old notes but I think from memory they were around 0.4mm


You shouldnt need bigger than 1.6mm mains, from memory thats what I ran with my 1776.

Not sure what the accelerator jet size is, I should probably have made a note when I stripped the carby down. Will take a look tomorrow when I take it out. Interesting that you were running 1.6 - mine is still pinking indicating too lean, would be very interested to catch a look at those notes of yours

The other thing I was considering this evening is the air correction jet size - If I understand this correctly, the air correctors bleed air into the emulsion tubes which in effect controls how soon the mains kick in. My pondering led me to wonder that if I've been increasing the size of the mains maybe the air correctors also need to go bigger? Are the two related?

Where is the vacuum pickup for the blower? Is it set to retard under boost?

Vac pickup is stock location adjacent the throttle plate (Dellorto DHLA). It won't retard the ignition but the advance / vac should drop off when the throttle is opened. I can disconnect it to test - will try it tomorrow and see what happens.

[Steve Arndt]

How long was the bus parked with old fuel? If it was over a month then a fresh load of gas may help with the ping.

[gearheadgreg]

Another thing to consider - since you are running 2 barrels into a siamesed intake, you can always mis-match them to get the total flow correct. e.g. a 1.6 drilled main in one barrel, and a 2.0 drilled main in the other. Maybe not ideal for referencing and making adjustments later (esp if you don't mark the jets and your notes aren't good) but the air and fuel don't care which barrel they came from after they combine a few inches later.