engine stumbles

[blackchevy3de]

i have a 385 gm fast burn engine , why'll seating still with my foot on brake and stepping slowly on gas pedal at about 15 to 2000 rpm engine stumbles and will stall if i dont let up , also when driving down the road and steping down it will do the same but onces past that stumble car will run great.

[1970C10truck]

After you have made sure your timing is dialed in I would suggest looking at the accelerator pump. Sounds like it might not be getting that initial squirt of fuel quick enough while under a load.

[70c10]

I just went thru this exact thing. My truck was sitting from the gas I put in 6 months ago. The bogging down right before my secondaries kicked in was driving me crazy! I filled it with fresh 93 octane and had to use up all the old gas. The more I burned the better it ran. It sounds crazy but it's true. How old is the gas?

[scum1]

im having this same issue as well..runs fine but sometimes when i punch it it bogs down..or if i sit at a light and get on it fast it cuts out...i got a 350...how do you check the accelerator pump??

[geezer#99]

Originally Posted by scum1

im having this same issue as well..runs fine but sometimes when i punch it it bogs down..or if i sit at a light and get on it fast it cuts out...i got a 350...how do you check the accelerator pump??

With the motor shut off look down in the carb below the choke plate and when you stroke the throttle you should see 2 shots of fuel out of the accelerator transfer slots. One on each side.

[scum1]

well i did a couple tests messing with the accelerator pump linkage and the vacuum line hookups..moved the accelerator from the lowest to the middle hole and moved from manifold vacuum (full) to the ported vacuum..it runs killer now..im still gonna take the carb off and give it a lil cleaning since i havent done that yet and also take a look at the mechanical advance and make sure thats all good..but as of now it idles great, accelerates great, and has good power throughout the rps...stoked!!!