I recently put a new 350 into my Camaro and am having trouble getting it to run right under load. If I accelerate smoothly, it runs pretty good (and pulls to at least 6,000 RPM - granted, not as hard as I think it should). But, as soon as I give it full throttle from any speed, anywhere in the throttle range, it just completely dies. It seems like the RPMs are stuck at 3000 RPM and it won't go anywhere - like it is just misfiring and sitting around 3k any time I go to WOT.

Here are the specs on the motor:
Gen-I 350, 10.2:1 CR
AFR 195 Eliminator heads
Comp XR-282 (hydraulic roller)
--Adv. Duration - 282/288
--Duration @ .050" - 230/236
--Lift - 0.510"/0.520"
1.6 Pro-Magnum rockers
Edelbrock Performer RPM intake
D.U.I. Distributor
Carter mechanical fuel pump w/ light weight pushrod
Quick Fuel Super Street 750 Mech. Secondaries, annular boosters
Pro-built 700r4
PI Vigilante converter - 2800 stall

I've just replaced the wires and plugs (NGK FR5) and it didn't help at all. I re-adjusted the valves last week. The distributor was in my 305 for a while first, but was working fine when it was pulled. Timing is set to 12* initial, 22* mechanical and the vacuum advance is hooked up. Carb has not been modified (68 pri jet, 82 sec jet, 6.5 PV) - just set the floats and the four idle screws (using a vacuum gauge). I'm not really sure where to go from here. I'm getting pretty frustrated and could just use some guidance as far as what I should be looking at next.

Thanks.

 

Here is a little more information to add. I just went out and capped the vacuum advance at the distributor and at the carburetor. It actually seemed to make a difference. There is still an initial stumble when I go to WOT, but after a second or 2, it now will recover and continue accelerating. Before, it wouldn't recover after at least 5 seconds (didn't hold it open for longer than that).

 

I dont know dude, I'm about to post my own thread, I have a similar problem in a totally different engine though. I have just put a 383 with a stock tpi in my car and have the under load/ intake back fire problem, is yours an exhaust backfire? and you might want to check for vacuum leaks, I warmed up my car last night and turned off the lights and my driver side header was glowing read hot as if it was running too lean, so I guess that means there is a vacuum leak on that side.
Im going to adjust the valves tomorrow since I also have a lot of valve chatter and see if that helps

 

Same problem in mine...randomly. I did a 350 swap in mine as well. First today it did it in second gear, but only after hitting 4500 rpms while trying to pass someone. Then again did it in "OD", when it kicked down at hit 5000rpms. But, first gear I ran it all the way to 6k and it was fine. Then later on I did it in 3rd gear, and it ran fine to 5k... so I'm confused as well. It almost seems to me like it's hitting a rev limiter...like when the limiter kills the spark but there seems to rhyme or reason to it. It's..well random. .

 

if your headers are turning red red you have a timing issue ive run inyo thids problem once before and after i set timing a thousand times ,set valves ,indexed plugs and so forth i found the problem to be one tooth was sheard off the dist gear .just a thought good luck bigzeke92bird

 

i'm having the same problem as the first guy basically same motor mine falls all over itself as soon as you give it gas it backfires and pops like crazy and yet with no load it runs and revs great. i've tried changing the timing about thirty times by ear by timimg light by vaccum gauge but it won't go away doesn't even change

 

Im having the same issue! Replaced vaccum lines, changed plugs and rotors, replaced distributor and cap. still no success!

 

new plugs, new plug wires, new fuel pump........... still no change misses like crazy under load runs great with little or no load.

 

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Good to see some research for the issue done. What type of carb are we running? It may be a carb issue carb just going lean WOT. Also a few years ago I built a 351W for a friend everything under the hood was new and performance oriented. It sounded great like yours except when you would put it under load it would fall flat pop and do all kinds of crazy crap. Turned out 2 problems brand new distrubutor was fubard internally and the brand new edelcrap had some serious issues as well. Replaced the dizzy and carb and the truck ran great. 150 shot of N20 and it outran his dads modded 07 vett at the track.

 

It's not often I'll blame the carb right away, but it certainly sounds like your problems are starting when the secondaries open.

It's tough to tell through the pedal when that happens so I often disconnect the secondary linkage so it's running only on the primaries. Then take it for a spin. If the problem is in the secondary side you should be able to smack it wide open and it'll pull smooth. Obviously, power won't be what it should higher in the RPMs, but as a diagnostic test it helps to figure out which side of the carb the problem is on.

 

Found my gremlin! Replaced my mallory billet distributor for an old HEI i had sittin around. Not sure what went wrong with the mallory yet. Nothing obvious i can see but at least the problem is fixed. Starts instantly and pulls like a champ Thanks SSC