350 falls on its face

[mike's 86 c10]

I just had my 350 rebuilt. Put a street perf cam in it and a dual plane intake on at the same time. It had a 600 holley on the stock intake and old cam set up. The motor runs fine once I get going but off the line it falls on its face then it gets with the program. any ideas?

[cableguy0]

First thing to check is the timing. What is the timing set at? Has the distributor had the advance curve set? Generally falling on its face when you stand on the throttle indicates a lean condition from the accelerator pump shot being too small its a cheap easy fix. Just want more background before you go messing with the carb. If timing isnt right the engine can do the same thing.

[Big Port Jimmy 6]

Gear, tire size, stall in convertor, cam specs, all things we need to know to make a guess.

[mike's 86 c10]

I checkd the timming 3 times, I have it set at 12 degrees. it's a new msd distributor i just bought, there is no stall. It's a stock converter, the gears are 3.73 and the tire size is 31x10.5x15. I put a comp cam part num 12-210-2
valve lift is .454 on int & .454 on exh
tappet lift is 268 268
duration at .050 is 218 218
the cams power range is from 1500 to 5500
its supposed to be a street performance cam that will work with stock converter
the intake is idle to 5500
the 600 holley is a reman i got about 8 mos ago

[cableguy0]

Ok that cam CAN work with a stock converter. Its definately not optimal. That cam would work best with an 1800-2000 or so stall.I wouldnt worry about that yet though. Accelerator pump would be the first thing I would go after. first thing to check is if its squirting like it should. When you open the throttle you should be able to look down into the primaries and see fuel squirt. Nice steady streams. If it is than its likely just an issue of not enough of a pump shot or not coming in soon enough. You can change the cams on the throttle linkage to get a bigger pump shot quicker. Does it ever pop through the carb if you stand on the throttle from a stop?

[mike's 86 c10]

no, ive not had any poping or backfires, it just falls on its face real quick
then once that has past it comes alive.
i will check the pump in the morn and see how much fuel is coming out.
thanks for the help

[cableguy0]

Does the problem exist if you ease into the throttle slowly? Or does it seem fine under normal driving until you stand on the throttle really hard?

[mike's 86 c10]

no, Its only if i get on it a little or all the way to the floor. if i ease in to the throtle its fine. It was doing it while i was driving at 30 up to 65. if i let off then got back on it then it would fall then too.

[mike's 86 c10]

I was thinking be for i put the motor back in that i might need to put a stall in. Can you recommend a good one? The only thing is the trans has about 20,000 on it and im afraid it might not hold up to the abuse, i might have to wait and get it rebuilt at the same time.

[cableguy0]

The stall isnt going to fix the problem your having now.Your issue now is likely in the accelerator pump. The stall converter will improve overall performance. I would look for something from tci,ati,hughes,bte etc. I dont care for b&m stuff personally.Theres a lot of other higher end converters that I didnt mention but will be overkill for your application. A higher stall isnt really going to be any harder on the driveline. If the tranny is in good shape 20k miles isnt much. I personally would throw in a shift kit and get a decent converter and call it good.

[ruffrida2005]

I had the same problem as you do with my 350, and they are built about the same. I have a little more lift and running a 625 demon. I know I had trash in the carb before I had it rebuilt.

Sometimes when I would give it a little more advance it would run fine when I got into it. I have not ran the motor yet since tear down. but I'm wondering how you fix yours.

[ruffrida2005]

Oh I was running a stock convertor out of a 77 sub T350, Now I'm going to run a 2400 B&M tourqemaster.

[mike's 86 c10]

I will try both, the accelarator pump and bump the timeing up a degree or two and see what it does.

[68GMCCustom]

I was going to guess the same...your stumble might be fuel (as in lack of/need a bigger squirt) related

[mike's 86 c10]

10 4 thanks for the help i will check it out in the morning and post the outcome tomorrow.

[mike's 86 c10]

ok, i didn't touch the timing, i left it at 12 degrees. I did adjust the accelerator pump and it solved the problem. now it comes off the line like it should.
thanks for the help

[cableguy0]

Your welcome glad it was an easy fix. figured that was your issue. As a side note that thing will respond even better with a converter if the budget allows in the future.

[gchemist]

Connect a vacuum gauge to it. What does the needle do when you go above idle? Try slowly and then WOT.

[Pyrotechnic]

I had that issue a couple of times. In one case, I did a cam swap and the primaries were too lean afterwards. In another case, the secondaries were opening way too early resulting in a bog.

[Wideopenracing15]

Didn't mean to post

[MR .T]

\If the stumble is on tip in than its an accelerator pump issue. if its at wot well after tip in its likle fuel delivery. bad line or pump.

[mike's 86 c10]

The problem came back after i ajusted the accelerator pump so i just went and got a new 600 edlbrock and put it on now theres no prblem.

[ruffrida2005]

I wonder if you had a blown power valve.

[cableguy0]

Not quite the solution I woulda went for but ok. Theres a bunch of other stuff thats very cheap and easy to fix. How did you adjust the accelerator pump? Did you change the cam on the throttle shaft?