engine stumbles when I floor it
Thread Starter
Drifting
Joined: May 2001
Posts: 1,329
Likes: 12
engine stumbles when I floor it
Hey guys.. I rebuilt the engine in my frame-off and the only change was a switch from the q-jet carb to a holley DP 650. I didn't change anything on the carb but if I open the throttle real fast the engine bogs for a fraction of a sec and starts reving. If I take a bit more time to open the throttle (still fast but not instant) , it'll rev just fine. I'm guessing my idle is spurting too much fuel.. is this right?
Race Director
Joined: Mar 1999
Posts: 10,258
Likes: 1
From: Calif.
Originally Posted by Pacin'California
I'm thinking this might have something to do with the accelerator pump giving you too much of a shot...
-Steve
-Steve
Or the squirter(s) are too small. Or too large.
Or the float level is too low. Or too high.
Advanced
Joined: Jun 2004
Posts: 63
Likes: 0
From: North Canton Ohio
Accelerator pump discharge nozzles sound like they are too small. The shooter is fairly easy to change (shouldn't even need to pull the carb). I would purchase a slightly larger one or purchase small diameter wire gage drill bits and a pin vice and gradually increase the size until the stumble goes away.
Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Originally Posted by stingr69
Check the accelerator pump linkage for slack. If there is any slack this will cause a hesitation you describe.
-Mark.
-Mark.
Assuming that the problem is due to the carb change, I'd suspect a sudden lean condition caused by not enough fuel to match the increases airflow. You didn't say under what conditions this is occuring. If it's while your blipping the trottle at idle, it's very likely an accellerator pump delay. If you're mashing the throttle in gear at low rpm, it could be just the nature of a mechanical secondary carb having the secondaries opened too soon.
Instructor
Joined: Jul 2004
Posts: 210
Likes: 0
From: Missouri
I'm having somewhat the same problem with my 650 dbl pumper. I just rebuilt it which helped tons but there is still a super slight stumble in mine on a quick mash to the floor. I'm going to check the accelerator pump to see if there is any slack there.
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Instructor
Joined: Jun 2004
Posts: 233
Likes: 0
From: algonac michigan
Originally Posted by BatManFire
I'm having somewhat the same problem with my 650 dbl pumper. I just rebuilt it which helped tons but there is still a super slight stumble in mine on a quick mash to the floor. I'm going to check the accelerator pump to see if there is any slack there.
double pumpers have 2 shots.....bog is usually too much fuel
