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Sticky throttle sort of

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Stewart

Stewart

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I've run into a slight annoyance. On occasion the engine will maintain 2k rpm with the throttle at idle. If I blip the throttle once or sometimes twice it will return to the normal idle. Its been doing this only since the rebuild. The cable is not sticking and I've gone through the carbs hif4's and both are solidly retuning to idle and the dashpots are topped off. Front carb mixture wise was dead on and the rear carb was slightly rich from reading the plugs. Any ideas on where to look?

The only thing I noticed that was off were the position of the pistons while I was dialing the mixture in. The rear piston was high enough at idle that I could not lift it with the pin however as I continued the process this no longer became a problem and I don't know if this is an issue or not.

Otherwise the car is running fantastic with 200 miles on it so far and it kills me that its in the break in period as it really wants to GO and keeping it limited to 60mph and under 4k rpm is tough.
 
The next time it does this, look at the pistons. My bet is one of them is not returning down in sync with the other. They need to move as a pair. Could you have possibly mixed the two pistons up when you had everything apart? As you know the pistons wear to the bodies and should not be interchanged for this reason. So you might have a sticky piston or a needle that's getting hung up back on it's way down into the jet to cut the fuel off. (hence the high idle issue)

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]The only thing I noticed that was off were the position of the pistons while I was dialing the mixture in. The rear piston was high enough at idle that I could not lift it with the pin however as I continued the process this no longer became a problem and I don't know if this is an issue or not.[/QUOTE]

This is carb balancing my friend. Are you using a unisyn? When I set up SU's, I rough balance then use the colortune. Then I recheck the balance again. Back and forth a couple of times and I'll nail it.
 
I know you said the cable is not sticking...but you still might retrace the entire linkage.

I had a similar problem recently with my '73 Midget...cable seemed OK when I checked it under the hood at the carbs. BUT, before tearing into the carbs, I reached into the driver's footwell and discovered some binding in the accelerator linkage (bent rod through a couple retainers. A squirt of some WD40 on each and some manipulation by hand verified the sticky problem. Some good penetrating oil as a follow-up has eliminated it altogether.

Hope this helps...if nothing else, just to eliminate one easily fixed possibility.

Ray
 
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