Holley Carb Help Needed

[NewUser]

i put a new Holley 670 Truck Avenger on my truck about 3months ago and have been having a recurring issue with it

it starts up fine when cold, idles like a new truck, and runs great up to a point...when riding with the windows open i run up to about half throttle and it starts running like it has a dead plug or wire and starts smelling VERY rich...runs a little rich at idle....i can let off the gas and it will stop missing...i can open the secondaries and it will clear up and go but when i lift of the pedal just a fraction you can feel the truck pick up even more...like its slightly bogging at WOT but clearing up below it

could it be a bad power valve?...stuck vacuum advance?....its driving me nuts because its my daily driver and because im scare to take my kids for a ride because of the fumes

 

[shaun89]

ya thats what im thinking, maybe a power valve

 

[Mike D]

Maybe the centrifigal advance weights in the distributor are sticking or binding ( maybe on the rotor ), thus not allowing the correct amount of spark advance the engine wants.
If you have a timing light that with an advanve adjustment knob, Have a buddy slowly accelerate ( in neutral, with the vacuum advanced disconnected and plugged )
go to 1000rpm check timing degree, then 2000 - check timing,then 3000check timing degree. Return to idle, while you are checking the timing advance at idle have your buddy connect the vacuum advance to a full manifold vacuum. If the vacuum advance only slightly moves the timing advance, the vac advance has a hole in the diaphram and should be replaced.
Concerning the mechanical advance, I think it should be about 36(?) degrees at 3000rpm. from 1000 - 3000rpm it should ramp up smoothly. If it doesn't, check for rust or binding. Carefully inspect the bottom of the rotor for extra plastic that might prevent free operation.
I am not sure ( can't remember ) what the total timing should be. I hope others chime in to clarify if I am wrong.
The bottom line is - when the advance timing curve is correct your engine will run like the devil himself is chasing it!

 

[ryoken]

most small block chevys like at least 32... more depending on how lopey the mill is...

funny, I just rebuilt a pair of dizzy's on some 318's last week... it had sat so long, all the springs had turned to dust...

I ALWAYS check timing at idle and full curve.... At work all I really care about is how they're gonna run at 4 g's...

 

[rcamacho]

Timing: verify 32-36 total mechanical advance in by 3000rpm. + vacuum advance <50 degrees.
Carb: check for vacuum leak at base of carb and fittings. Set idle mixture for highest vacuum @600-800 RPM. If it's still rich off idle you'll likely need to tune primary and secondary main jets and perhaps power valves. Pick up a good Holley book and check our the forums on innovative motorsports for the really advanced stuff. Most tuning of idle and jets can be done by a methodical approach with a stopwatch and copilot.

The truck avengers are calibrated very rich off idle and require some specific design changes to deal with the main circuit check valves in the blocks.