Holley 750 CFM Ultra Double Pumper or Quick Fuel Technology SS-750-AN 750 CFM Street?

[blykins]

Took me 5 minutes to figure out how to get onto Club Cobra. I hardly check on here anymore because it's such a pain to get on from a PC.

So how did you reach out to him? Best way is to call and I would suggest that you try him again if you couldn't get a hold of him. I've never received an email from him and I think he's on Facebook and IG, but I don't see him post much.

When you dropped altitude, you added air, and so you'll have to add fuel to compensate. Any time you have a stumble or hesitation, it's most likely a lean stumble or hesitation. Where that hesitation occurs determines on which circuit you have to modify. Changing jets doesn't always work, because you also have an idle circuit, a power enrichment circuit, and air bleeds that help get the mixture right.

If it's doing it at lower rpms, then it's probably in either the transition from idle circuit to main circuit, or it needs an extra shot of fuel when you're tipping into the gas. If you're getting into boost at that point, then it could be the fuel pump not referencing the boost signal correctly.

Can you give an rpm at which this stumble occurs?

As far as what we do with the carbs (I say 'we' because I take responsibility for what I send out, even if Scott does work for me), it's on an order-to-order basis. A lot of times, we order parts in and custom build the carburetors. Other times, we order from Quick Fuel, get the carbs, completely disassemble them, inspect, sonic clean everything, then reassemble with the correct calibration for the engine that it's going on. Most of the issues that we've seen come from QFT involve debris in the carb, boosters that weren't drilled, etc.

Scott will often hand write the parts used if they don't jive with what QFT sent with the carb. If the parts jive, then it's just easier to throw the same card in.

As far as your carburetor being rich to begin with, it was intentional. Anytime boost is involved, it's better to be rich than lean. The amount of boost is often a variable instead of defined and we never know the state of condition that the engine is in. Also, if an engine is worn out, then it won't pull on the carburetor as hard, which means that we need to push more fuel through. Engines that are new and are sealed up well will normally need fuel pulled out because they pull harder on the carburetor.

Again, I would suggest giving Scott a call tomorrow and he can help you dial it back in for a lower altitude.

[RedHawk]

Okay understood.
Stumbling at lower RPM at say 2000 to 2500 while in 5 and running about 65 to 70 mph and doesn't improve above that. If I am simply cruising no real issue.

I have a new Aeromotive fuel system including regulator AN hoses send and return with fittings and phantom fuel cell. At idle and it hovers around 5.5 then when pulling throttle up to 3000 it climbs to 6.5ish sonit looks like fuel pressure is adjusting but I don't have gauge inside the car so don't know for sure.
Should I check vacuum pressure to inspect whether PV is correct. I ask because I don't want to start changing a
Umch of stuff that Scott may have done. Early on Scott did say to adjust idle screws which I did and that helped in Co but haven't messed with that.
Is there a heirchy checklist to go through when messing with tuning.
Like check plugs then vacuum pressure change jets and inspect plugs then to something else and so on?
Thanks Brent for the quick reply and lol I just posted this so my timing was great.

I will call Scott too. Fyi I sent him a text a week or so ago.
Scotty