Tuning issue?

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Tuning issue?

Post by bumblebuggy on Mon Feb 01, 2010 8:52 am

OK I've been having a problem that I can't sort out.

I'm currently running my buggy engine in the bus while I work on getting my bus engine rebuilt. It's a 1776 running dual 40mm Kads with a 009. Everything is new on the engine as I just got it runnning this past summer.

In an effort to get the kinks worked out, I tuned everything this past week. Valve adjustment, new fuel filter, timing, carb sync, mixture dialed in, linkage adjusted, ect.

Here's my problem. Asside from not wanting to start in the cold (which I expect running a mild cam and these carbs), the engine seems to run great with only one problem. While cruising the engine will "spit" or miss. This only happens while little gas is being applied or in transition from a level cruise to applying slight gas to climb a hill. With the hammer down or with my foot off the gas it does just fine. It only spits when in a level cruise.

There are only a few things I can think of which I haven't checked yet...
1. The accel pumps on the carbs may be out of whack.
2. Maybe a Vac leak somewhere?
3. Too much fuel pressure for the carbs?

Any ideas would be great!
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Re: Tuning issue?

Post by Hobug on Mon Feb 01, 2010 12:21 pm

It could be too much pressure, or when mine acts like yours is, it is usually an idle jet getting plugged.
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Re: Tuning issue?

Post by vwtattooed on Tue Feb 02, 2010 7:40 am

what fuel pump are you running? dual kads will handle 6psi. my first instinct was a vacuum leak...but when i had dual kads and had the same problem it turned out to be the rubber balance tube between the two intakes collapsing on acceleration. once the skinny pedal is mashed it creates enough vacuum to clear the fuel out. scratch
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Re: Tuning issue?

Post by bumblebuggy on Tue Feb 02, 2010 8:23 am

No balance tube installed. Maybe that's the problem.
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Re: Tuning issue?

Post by camch on Tue Feb 02, 2010 8:51 am

have the carbs been syncronized,or has the points been reset to be on the safe side
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Re: Tuning issue?

Post by bumblebuggy on Tue Feb 02, 2010 10:39 am

Yea carbs are in sync. Electric points.

Think I'm going to shim the pump. AJ Sims says kads should run 1-2 PSI. I don't have a gauge that can measure that at the moment but I do have an extra gasket to throw in there. He also said you don't have to run a balance tube. But after reading many posts on thesamba, I might try the balance tube thing.

So I'm going to try things in this order...

1. Check for vac leaks.
2. Shim fuel pump with an extra gasket.
3. Install balance tube.
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Re: Tuning issue?

Post by DiggerD on Tue Feb 02, 2010 11:16 am

FWIW, I'm running the same setup with no balance tube and none of the problems you are seeing. My bet is a vacuum leak or a plugged idle jet like Jon said.
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