Hints for setting up carb linkage

paul_f · Post by **paul_f** » Tue Sep 07, 2004 4:07 pm

Just finishing up reinstalling my engine - but having setting up the carb so they linkages are the same is turning out to be a real witch..

The left hand side carb has a about 3mm less rotational travel than the right carb - and no matter how I play about with the horizontal position I can't seem to improve it.

There are 40 DRLAs off an Alfa (later type if it makes any difference) with a 2 year old type 1 offset baseplates and a shortened cross bar.

The small plates are definately drilled exactly the same

Any tips??

Thanks
Paul

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Tue Sep 07, 2004 4:09 pm

You may need to shorten one of the rods more than the other. The alfa carbs seem to have these issues worse than any others.

davygrvy · Post by **davygrvy** » Tue Sep 07, 2004 4:36 pm

Got a pic of the system?

I'm having a similar issue with dual weber 44IDFs and the CB performance hexbar system. the right side has less rotational gain compared to the right. The reason is because the pivot of the hexbar happens to be about 5mm more forward than the left side creating different geometry. Redoing my mount brackets is on my todo list.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Tue Sep 07, 2004 4:47 pm

I never see these issues, it seems very odd. Looks like I need to work more on that bellcrank system.

davygrvy · Post by **davygrvy** » Tue Sep 07, 2004 5:19 pm

MASSIVE TYPE IV wrote:I never see these issues, it seems very odd. Looks like I need to work more on that bellcrank system.

Don't forget that I'm a freak... A freak perfectionist... Or at least trying to be one. I just want a more progressive (logarithmic) pedal feel than how you delivered mine. I'm not unhappy with it, just want mine different.

What's the bellcrank system?

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Tue Sep 07, 2004 5:24 pm

A bellcrank throttle that attaches to the case or shroud and allows rotation that rotates the carbs more simultaneously. It has no hex bar.

I have tried to make it work twice but hit problems..

paul_f · Post by **paul_f** » Wed Sep 08, 2004 1:08 am

Which bellcrank linkage have you tried to use before? I might have a go with a CSP type linkage and fab up a mount for it.

I think I am gonna add a return spring onto both carbs to see if that helps - I think it will help setting them up any way

Paul

samcat · Post by **samcat** » Wed Sep 08, 2004 2:58 am

The problem with the alfa carbs is that one of the throttle arms is longer than the other. Not by much, but enough to make a difference.
On mine we removed both the arms, and cut and shut one so that it exactly matches the other.

Works great

Cya,
Sam C

paul_f · Post by **paul_f** » Wed Sep 08, 2004 3:57 am

samcat wrote:The problem with the alfa carbs is that one of the throttle arms is longer than the other. Not by much, but enough to make a difference.
On mine we removed both the arms, and cut and shut one so that it exactly matches the other.

I am not using the alfa arms though - I am using the ones that came with the CB kit.

What linkage are you running

samcat · Post by **samcat** » Wed Sep 08, 2004 5:24 am

CSP bellcrank.

I had the same problem, but it was down to different lengths of the arms, if your using a CB kit I am guessing they are correct, so it must be something else.

Weird!

Sam C

paul_f · Post by **paul_f** » Wed Sep 08, 2004 5:39 am

It was fine on my 1600 - it seems although the problem is due to the angle of the hex bar - anyone got a pic of their linkage from the top?

Cheers
Paul

paul_f · Post by **paul_f** » Wed Sep 08, 2004 5:48 am

Ah I think I have found my problem....

Looking at this picture on Jake's website http://www.aircooledtechnology.com/cust ... /2270b.jpg my linkage is different - mine runs diagonally across the engine (compared to the backing plate) - where as this one is parallel to the backing plate.

Should it be parallel with the backing plate?

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Sep 08, 2004 7:15 am

yes, it should be parallel...

Also ensure that the arms of the linkage that come off the hex bar are an equal distance away from the center of the velocity stacks. If one is further in, or out the ratio of opening will be accelerated on one side..

paul_f · Post by **paul_f** » Wed Sep 08, 2004 7:27 am

Ar crap, thats my problem then...

The base plates I have are mirror images of each other - I guess they are supposed to be different - and then I have an extension piece for one of the pieces on the throttle spindle.

A friend has just torn down an old 911 type 4 with a hex bar linkage - that would be the same except just swapped to the back side wouldn't it?

Paul

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Sep 08, 2004 8:03 am

yep..

Sit down and look at it all closely and you will notice how it all jives as throttle increases. The worst part is just off idle- the first 1/3 of throttle plate rotation.