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Discussion Starter #1
Good evening everyone. My ‘75 2000 gtv has had an engine rebuild, been run in, timing done, carbs balanced etc. I am running gta trumpets on delorto carbs.
However, between 2,000 and 3,000 rpm when on a light throttle it stutters like mad. Not smooth at all. Any suggestions as to what may be the cause?
Thanks in advance
Rich
 

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Are you running the same idle jets with the trumpets on as you did with the original airbox ?
Shouldn't make that much difference, but it's been known. On Webers, they sometimes like a slightly bigger idle jet when moving to trumpets.
Easy way is to refit the original airbox & filter, & see if it goes away.
Also check to see if you have an accelerator pump jet blocked.
If all is ok with the carbs, then looks like you have an ignition issue.
 

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Depending upon the cam timing you may have some flow reversion through the carbs at certain rpm. When that happens the air flowing backwards picks up some fuel. If you have long air horns the fuel rich air is held in the horns and then passes through the carb a second time which results in a rich dip in the AFR and a loss of torque.
On the other hand you may have a lean mixture due the carburetor issues. An air/fuel gauge is a big help in resolving these problems.
 

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Discussion Starter #4
Thanks for the posts guys. I’m going to try fitting the original air box first and see if that makes a difference.
 

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Hi, just if anyone stumbles upon this thread with the same problem.

For me, the stuttering was almost completely gone when I switched the ignition leads from the standard repro ones (red) to the Lumenition ones (blue, transparent). I also suspected problems with the carbs (which I might still have), but the stuttering was reduced by 80% with this rather cheap solution.
 

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And it didn't do that before the rebuild? Were the carbs touched at all in the rebuild? Carbs can be very sensitive to setting the idle mixture screws. It is also my experience that things smooth out with the stock air cleaner system in place.
Andrew
 
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