i need some help before i load up the 100 round drum in my ak and start blasting my car. 91 rs, 383, 10.89:1 cr, lt headers, edelbrock performer rpm heads, cam, dual plane intake, holley 750dp, holley blue elec fuel pump. my problem is that when i take it out and run for a few minutes it runs fine. but after a few miles or when i hit it REAL hard the a/f meter reads lean, it starts losing power and runs like crap, then i shut it off and it diesels. i have a clear fuel filter next to the carb and its full of gas, the carb isnt even warm to the touch. right now its jetted to run rich because of this leaning problem. help!

 

your electric fuel pump -> carb, how is the pressure lowered?
your power valve setup is right?

then, have you hooked up a gauge, in line at the carb inlet, then did a test run, to see if you're losing pressure at WOT? (for whatever reason?)
after that...:

hmm, this makes me suspicious... lean - dieseling, makes sense, as it's getting hot in the combustion chamber.... how do your plugs look after one of these runs? I'd shut 'er down right after a WOT blast, where it does this, and inspect ALL of your plugs. Just to make sure that all cylinders are on the same page, and indeed lean.

 

i have the regulator that came with the pump hooked up. i have 2 gauges hooked up, 1 at the regulator(i needed something to plug the extra hole) and 1 at the carb inlet. both read 8-9 pounds which is a little high. i havent messed with the power valve yet, i cant get past this leaning out problem to try to do some fine tuning. it makes really good power and the a/f is right on the edge of stoich and rich. then it just goes lean and stays there, the a/f meter reads all the way to the left(not digital readout, analog sweep scale) lean. i tried bringing it back to idle, just in case it was a fuel pressure problem to let the bowls fill back up but it doesnt do any good. the only other thing i can think it would be is possibly heat soak into the carb boiling the fuel. when i parked it i immediately took off the filter and touched the side of the carb, it felt pretty cool but it looked like some of the gas in the carb was evaporating. the base plate was pretty warm though. i ordered a phenolic spacer that im gonna install, possibly fab up a heat shield.

 

Check for an intake leak that opens up when the engine heats up.

You have an air/fuel gage, have you done the trick with the unlit propane torch?

 

I highly doubt you're boiling your fuel. I think the spacer will be a waste of time.

vacuum leaks, worth checking for. but if they only occur under power or something, then it's hard to find.

if your power valve is non-functioning, that would definately get you lean when you trounce the throttle. Any holley experts out here?

Perhaps do the WOT blast, and when it stutters, shut 'er right off, and pull over, and check your float levels. This would work with your electric fuel pump setup right? If your bowls are dry, then maybe there is a restriction in the line somewhere...

 

fuel presure
yes it is you may be flooding out the motor please drop the fuel presure to 5 psi or 6 psi-- don't take my word for it check your carb manual and call holly. if you are going to run that kind of fuel presure you will have to rebuild the carb to handle it.


later and

GB

rick

 

what is the unlit propane torch trick?????


nevermind, i did some research and found the answer

 

heres the update. now my problem has progressed. it begins after warming up for a while just idling with slight engine revving. i replaced the intake manifold gaskets about 2 weeks ago chasing this problem, didnt fix it. manifold vacuum reads about 10" at idle. i unhooked every vacuum line and capped them all except the one hooked to my vacuum gauge. it holds between 9-10" until it warms up, then drops to 5-6" and starts reading lean on the a/f meter. i tried spraying carb cleaner on all the places i figured it could be leaking, no response. so i went and got a propane torch, still same result. as soon as it went lean, i shut it off and checked the fuel level in the bowls, dead on where it needs to be. the only thing i have done to the carb is install a set of quick jet change bowls and they arent leaking. any thoughts?

 

i think i have it fixed. i pulled the intake off AGAIN and started polishing the gasket surfaces to make sure i had no place to leak. i got to the last set of intake runners and lo and behold, there was a crack between the ports. ordered a holley street dominator dual plane intake and put it on this morning. reset my timing, and let it idle for about 15 minutes, no problem. took it down the road and burned the rubber off the tires, lots of power with no leaning!