[Tracer64]

I've been tuning my Holley 4777. I'm running quick fuel metering blocks. I've the Idle feed restrictors dialed in and it runs best with 40IFR's. All was good untill I put my new flowmasters on and now I have a miss at highway cruise speed (65mph @ 3100RPM) I can speed up a little and it will go away, if I back down it misses all the way to about 1500rpm. Do you think its jetting (71 prime 81 sec), timing, or need to increase the IFR's again. Like I said this started after the new mufflers.
Thanks
Tracy

 

[351ciofgrunt]

I'm not sure that i understand what it is you're missing but i've realised over the years thats its always in the last place you look...

 

[wildosvt01_OLD]

Check the timing. Make sure its where you left it.

 

[FEandGoingBroke]

I agree with 351cio... Once youve tried everything and it finally works... It was the last one you did...

FE

 

[igo1090]

play with the idle mix screws just a little. maybe richer a slight amount.

 

[My427stang]

AT 3100 rpm you are well out of the idle circuit

4777's are stock at 67/76 jetting, so I would guess you are pretty close to where you want to be. Maybe even a smidge rich, but that wouldnt cause a stumble

I would check float level first, a low float level can delay fuel to the main boosters and make it go lean for a second like you are saying. Run them on the high side, in other words, make sure they come out of the threaded hole, not just if you lean on the fender hard.

Second, depending on your build, maybe you need to raise the number of your power valve by 1 number. Sounds like it could be opening a smidge late. The best bet would be to see what a vac gauge is doing when it stumbles. If its stumbling at 7.0 in vac, and your PV is a 5.5, there is your answer, its going lean.

Feel free to email if you have questions

 

[Beoweolf]

freeing up the exhaust will tend to make the fuel mixture (carb) go lean. If the carb was "dialed-in", then I suspect it to be lean now.

does this happen all the time, some of the time?

 

[Tracer64]

Sorry, I need to make myself clearer. I dont have a stumble per say, its actually missing but only at a steady cruise around 3100 rpm. The PV is set at 5 because I anly have 7.5 inches of vacuum at an idle. It accelerates smoothe, even if I stand on her hard. It will do it everytime because thats where the motor runs at 65mph. If I crusie at a little higher rpm it wont do it.

 

[FEandGoingBroke]

PLUG WIRE.... You have a plug wire arcing out somewhere at highway speeds... Get some ISOPROPHYL Alcohol, mix it 60% to 40% water and put it in a squirt bottle, set it for MIST, start the car set the idle around 1,500 rpm, and slowly spray around the plug wires from cap to plug and watch for Green and or Blue Fire... There's your bad wire causing your on the road Miss.

FE