Bogging under full throttle
 

Hey guys, so my 71' GMC wants to bog down under full throttle. It'll accelerate to about 45 then will just stay there but if you let off the gas it then has no problem going on to 70+ and runs great otherwise. Any ideas on what could be causing this? The 350 was just rebuilt and it has a new q jet and hei distributer along with new everything on the outside of the engine. Thanks in advance.

Re: Bogging under full throttle
 

When you plant the throttle and it bogs, does it "catch up" with itself and take off in a few seconds or does it stay completely bogged out?

Normally this would be:

a) Accelerator pump not working or undersized
b) Vacuum doors opening too quickly

Re: Bogging under full throttle
 

It will catch up with its self up until 45 or so then completely bogs down. Its hardly smooth up until then though its a slight bog then go and does this repeatedly until it completes bogs out.

Re: Bogging under full throttle
 

Could it be running out of fuel, like a weak pump or dirty filter? Sounds like it can't keep up with the demand somehow....

Re: Bogging under full throttle
 

Thats what I was thinking but the fuel pump is brand new, like put on today brand new haha. The fuel filter was also just replaced. The only thing I can think of to change out is the small inline filter right before the carb. Its also fairly new but I guess it could have something in it.

Re: Bogging under full throttle
 

Do you hear the secondaries open when it's bogging? Also you say that if you get off the gas, and ease into it, you can get it to go up to 70+.

Sounds like the jetting is too rich on the secondary metering rods when the secondaries kick in. I think that if it couldn't get enough fuel, you'd get lean backfire through the carb as it was running out of fuel.

Re: Bogging under full throttle
 

Well it does seem to be backfiring as well under full throttle.

Re: Bogging under full throttle
 

Where's the timing set at, maybe too much advance. I had to change out the bushing in my MSD because it was doing similar to yours. It would run fine until the timing advance came in then it would bog.
My crate engine only has 0 marks, no degree marks on the tab or balancer so I set it by ear. Runs great though.

Re: Bogging under full throttle
 

I'm not sure honestly, I'll have to check

Re: Bogging under full throttle
 

Just try backing off on the timing some and see if it helps. If so you will know you are on the right track.

Re: Bogging under full throttle
 

Update: Looks like this new fuel pump is bad. This is the second new pump thats gone bad within about 25 miles if that. Now I'm thinking it might have not been feeding the carb enough gas under heavy load. Anyone have any suggestions for a good mechanical pump? Seems like I'm having bad luck with the ones from the local parts stores.