Still tuning out that flat spot

Asa

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Since these, I had to replace the fuel tank, that took up most of my time. I'm not trying to remember where I was at and what I was doing with this.

I did rejet the carb as I mentioned in this post, seems to be better, but still a flat spot.
viewtopic.php?p=591901#p591901

Video
Hard to hear, but at 8 seconds or so I floor it and you can hear/see the flat spot. (yes X, I picked up a Gunson unit. Its neat, but I'm not 100% on how to use it.)

I recognize that the flat spot might not be taken out completely, but hopefully I can do a little better than this.
 
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"...you can hear/see the flat spot. (yes X, I picked up a Gunson unit. Its neat, but..."
I haven't seen Dean for months.

(now, on an entirely different post - same topic?)
"...To tune that accelerator pump, there's a welch plug..."
Lookin @ ur other post (quoted here) on this topic - I C 4 depressions drilled around the top of air horn - U sayin turn a screw down in oneada holes to adjust the pump? "Yes", 4 'i got it'; further explanation if not correct:unsure::
 
Yeah there's a definite pause there before the rev. Sucking air. It's in the transition is my guess. Which would point to metering rod size and/or adjustment, or jet size or the two being too different when vacuum drops and the rod lifts. If the the rod is out of adjustment it will only get richer right? What jet and rod are you running now and what is you're idle vacuum? If you're confident the rod is adjusted to spec, I'd be inclined to lower the main jet size a bit or try a larger rod. But the real question is, assuming no vacuum leaks, is it rich stumble or is it going lean? I'm assuming it's a rich stumble iow it's puking and purging. I like that colortune plug. I don't know how to read a color-tune but that's seems to be what it's conveying.

Here's my Chinese YFA clone before I ended up adjusting the metering rod to fix it. It didn't really stumble then and it doesn't stumble now. It was bogged down on power and running rich at low throttle until I adjusted the metering rod. It'll sh it and get for a little 6 banger ;)

Good luck

 
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Did your engine with these components ever run good???
What are your ignition settings?? Initial & total advance. Vacuum advance ported or manifold vacuum??
Have you run an A/R ratio at idle, transition, cruise & WOT??
 
wsa111 said:
Did your engine with these components ever run good???
What are your ignition settings?? Initial & total advance. Vacuum advance ported or manifold vacuum??
Have you run an A/R ratio at idle, transition, cruise & WOT??
Uhh... when it was still automatic? Maybe? I can't remember when that was.

I haven't checked those recently, but its a "new" Duraspark II system with a GM HEI module. Less than 10000 miles on the distributor, it was accurate when I installed it and later on when I had to replace the balancer for being bad. (and it was an automatic.) Ported.

Don't have an A/R gauge.
 
Econoline said:
Yeah there's a definite pause there before the rev. Sucking air. It's in the transition is my guess. Which would point to metering rod size and/or adjustment, or jet size or the two being too different when vacuum drops and the rod lifts. If the the rod is out of adjustment it will only get richer right? What jet and rod are you running now and what is you're idle vacuum? If you're confident the rod is adjusted to spec, I'd be inclined to lower the main jet size a bit or try a larger rod. But the real question is, assuming no vacuum leaks, is it rich stumble or is it going lean? I'm assuming it's a rich stumble iow it's puking and purging. I like that colortune plug. I don't know how to read a color-tune but that's seems to be what it's conveying.

Here's my Chinese YFA clone before I ended up adjusting the metering rod to fix it. It didn't really stumble then and it doesn't stumble now. It was bogged down on power and running rich at low throttle until I adjusted the metering rod. It'll sh it and get for a little 6 banger ;)

Good luck


I've been playing around with the jet and rod. I might have to change them out again, which sucks
 
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