Tried jetting but still lean at WOT

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UOP

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Hopefully some of you guys can help me with a little problem I'm having. I went to the track on Friday to dial in my new combo, but no matter what I did I couldn't get the wot a/f ratios any richer than 13-13.5. I'm currently running 78 jets in the rear, but tried going up to 82 jets with no luck. I'm not quite sure where to go from here. Smaller high speed air bleeds maybe? I'd appreciate the input.

Specs:

QFT 650 dp
71/78 jet
rear jet extensions
80 idle air bleed
28 hs air bleed
.037 idle restriction (primary), .031 idle restriction (secondary)
100 needles
8.5 primary power valve
rear power valve delete
milled choke tower

255 lph Walbro fuel pump (67 gph)
5/16" fuel line
return style regulator
6.5 fuel pressure
Float bowl fuel level in center of sight glass

I've never dyno'd the motor but I'd bet it makes somewhere in the range of 350-400 hp.

Timing currently set at 18 initial / 33 in by 2500
 
Just a guess. If you aren't losing fuel pressure during the run, I'd step up the needle and seat assemblies to the .120's or bigger. Jetting up with no change in afr's is pretty indicative of a restriction in volume before the jet.

A quick test to try is bring the float level up some and test it. It may blubber around a bit at low speeds, test it and reset it to normal again. See if that helps or makes the leaning out stage a bit later. If it does, then you likely have a fuel delivery problem.
 
crackedback said:
Just a guess. If you aren't losing fuel pressure during the run, I'd step up the needle and seat assemblies to the .120's or bigger. Jetting up with no change in afr's is pretty indicative of a restriction in volume before the jet.

A quick test to try is bring the float level up some and test it. It may blubber around a bit at low speeds, test it and reset it to normal again. See if that helps or makes the leaning out stage a bit later. If it does, then you likely have a fuel delivery problem.
Click to expand...

2x on the float level...

what does your fuel system consist of? pump, line, filter('s), regulator, pressure...
 
UOP said:
255 lph Walbro fuel pump (67 gph)
5/16" fuel line
return style regulator
6.5 fuel pressure
Float bowl fuel level in center of sight glass
Click to expand...

805moparkid said:
2x on the float level...

what does your fuel system consist of? pump, line, filter('s), regulator, pressure...
Click to expand...

Fuel filter is a stock replacement unit for a Turbo RX7.


I'm not 100% sure but I don't think I'm losing fuel pressure during the run. The last run on Friday night (solo run) I basically stared at the a/f gauge after the 1-2 shift and it didn't get any worse, it just seemed to stay about the same. If it were losing fuel pressure wouldn't it get progressively worse?
 
Ok, I went out and checked the float level and to my surprise they were high (haven't checked them in a while). The fuel was over 3/4 to the top of the sight glass. I adjusted them down to where they're supposed to be but it started raining again so I couldn't do a wot pull to test. I did notice the engine seemed to run crisper so at least that's one good point. I'll have to wait until tomorrow.
 
Try turning the fuel pressure up to around 8 psi.

Try to find the max point the n&s will stand before blowing past them.
 
Nothing about this carb has been plug and play. I like it, but at the same time I don't.
 
I don't suppose your air cleaner lid or hood is very close to the vent tubes?
 
Well, it turned out to be a dumb problem. The secondary float was sticking at a lower point than it was set. I stumbled upon it while messing with the rear accelerator pump, so I pulled the bowl, took everything apart, blew it out with carb cleaner, and put it all back together. The next pass was practically blowing black smoke out the back it was so rich, lol. Problem solved.
 
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