360 stumbles when going from full idle to full throttle.

-
flathead5173

flathead5173

Active Member
Joined
Feb 13, 2011
Messages
43
Reaction score
0
Location
wadsworth ohio
I need help. I have a LA 360 that came with roller cam from the factory. I put a Hughes engines Whiplash roller in it. I also put on magnum heads with a airgap intake. I have a Edlebrock 750 on it with stock Chrysler electronic ignition. When I'm at a dead stop and floor it, it stumbles very bad or kills the engine. I went through the carburetor, checked the float settings and accelerator pump. I set everything like the manual said. If I ease into the throttle in runs good and has great power for a low compression engine. I have the timing set at 22 degrees at idle and 38 at full advance. I'm really impressed with the whiplash cam. I had another 360 in this truck (which by the way is a 57 chevy) that had 10 to 1 compression and a flat tappet mutha thumpr cam. This low compression 360 feels like its has more power than the high compression 360 and I'm not having to run a high stall convertor with it or 93 octane gas. The whiplash cam don't have as good a sounding idle as the mutha thumpr has but still sounds good. Thanks in advance for any help.
 
remove edelbrock 750...bolt on holley 750 double pumper....
 
70aarcuda said:
remove edelbrock 750...bolt on holley 750 double pumper....
Click to expand...

xx2,, maybe vac secondary

It sure sounds like your accel pump,,

Take your air cleaner lid off,, with engine off,, look to see if you get a firm shot of gas the instant you move the throttle,.. ANY delay,, sputter,, weak shot,, is your stumble..

Move the acc lever to the closest hole to carb body,
Sometimes there is slack in the linkages,, or the ball checks get crap on it,,

hope it helps
 
May need bigger accelerator pump squirters, and/or as mentioned, adjusted for longer squirt. Make sure secondaries aren't adjusted too light and flopping open.

Is brisk, part throttle acceleration ok? (Nailing it, just not to the floor.)
 
If this thing does this at a stand still (as in nail it and it stumbles)
You can partially cover the intake with your hand and pop the throttle open.
If the problem goes away with your hand over it a little, it's not getting enough fuel on the accelerator pump shot.
I have drilled them as much as 10 thou over to clean this exact problem up.
 
I've got a 360 LA that had the same issue. Mine is also a low compr. engine that we shaved the heads drastically and put big valves in and played around with porting them. Its got a thumpr cam and a Holley 750 vac sec. Once warm she idled good and as long as I eased into in then stomped it ran great, but from idle to floored it would stumble. :banghead: My timing is like yours 20 initial 34 all in. Ended up being the accelerator pump shot, I changed the plastic cam on the accelerator for a quicker and larger acc pump shot and fixed it. With the low comp. pistons the 750 is a little big carb. but will work, it does for mine but it takes a little longer for the air velocity going through the carb to get the jets pulling the way they should so you will need a larger pump shot to give the jets time to catch because the velocity through the carb horn is reduce due to the bigger size.:burnout:
 
Yes, if it's the squirter size, bigger can help cover up the lean spot/bog caused by the vacuum drop. But be careful about going too big on the duration of the squirt. Any squirt past the point of the main metering system starting up will cause a temporary rich condition that will slow you down, even if you don't feel it in the seat of your pants. Gotta sneak up on it.
 
To the OP, I know you said you checked the acc. pump shot and got gas.

BUT it must be instant as in right now! I agree with the others, go back and check that. If you get any movement in the throttle and then see gas try adjusting it.
 
When I snap it, it appears there is no delay. The stream is continuous and smooth. It last all the way to wide open throttle
 
I agree with Locomotion here(squirter size). It sounds like your duration & volume is ok. Make sure the linkage is adjusted correctly with no delay in the shot (as Badsport suggested). And don't make all the changes at once. Smaller increments of change one at a time will save you time & money in the long run. HTH.
 
You must log in or register to reply here.
-

Back
Top