engine stumble lower rpm
Senior User
Joined: Feb 2002
Posts: 465
Likes: 0
engine stumble lower rpm
I got a 390 with a holley 4v
it stumbles around 1000-1500 range
if I put my foot into it.I think
either the secondarys open up to
early and choke it, or it runs lean
until the secondarys open since thats
where my power seems to be. Am
I on the right track to go after the
carb?
Fe power
it stumbles around 1000-1500 range
if I put my foot into it.I think
either the secondarys open up to
early and choke it, or it runs lean
until the secondarys open since thats
where my power seems to be. Am
I on the right track to go after the
carb?
Fe power
Post Fiend
Joined: Feb 2001
Posts: 6,624
Likes: 8
From: Missouri
engine stumble lower rpm
Most of the time when you are having trouble with the engine "falling on its face" at right off idle it is either a lack of ignition timing advance or not a big enough accelerator pump. You aren't going to even make the secondary's think about kicking in at 1500 rpm and below so you can rule that out. Try advancing your timing to about 12BTC and try it again.
Laughing Gas
Joined: Jul 1999
Posts: 1,048
Likes: 22
From: Lacey, WA
engine stumble lower rpm
Hi,
Ratsmoker is right on target. Something else to consider: Make sure the Accl pump linkage is adjusted correctly. The Holley web site tells how if your not sure. Also you may consider changing the Accl pump nozzle size. By reducing the nozzle you make for a longer shoot duration. This keeping the mixture richer longer.
Hope this helps.
Lee
Ratsmoker is right on target. Something else to consider: Make sure the Accl pump linkage is adjusted correctly. The Holley web site tells how if your not sure. Also you may consider changing the Accl pump nozzle size. By reducing the nozzle you make for a longer shoot duration. This keeping the mixture richer longer.
Hope this helps.
Lee
Post Fiend
Joined: Feb 2001
Posts: 6,624
Likes: 8
From: Missouri
engine stumble lower rpm
The fuel bowls hold enough fuel that it would not be possible to cause this problem. Fuel starvation problems will show their face at high rpms way before they effect idle.
Post Fiend
Joined: Sep 2000
Posts: 8,238
Likes: 3
From: Oregon
engine stumble lower rpm
Which Holley do you have? I ask because the 750s have too big of a center squirter for most of our trucks. I've known many guys who have this problem out of the box. The center squirter dictates only duration, while the cam dictates volume. Often times, we need to lengthen the duration of the shot to compensate while our engines get our heavy trucks up and going. This is done by putting in a smaller squirter, not a larger one as is conventionally thought. Adjust the timing to 12btdc as Rat mentioned, if that doesn't work try putting in a #25 center squirter and see what happens. I've had three different guys try that and it fixed their stumble.
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Senior User
Joined: Feb 2002
Posts: 465
Likes: 0
engine stumble lower rpm
Good advice on the linkige Lee, I cracked the
hood pulled the cleaner, then wound the nut up
good and far so the pump lever goes better,and
so does my truck
. never mind the last question.
I will still do the advance to get even more go.
I did that on my truck with a 390 2v, also
very good advice.
hood pulled the cleaner, then wound the nut up
good and far so the pump lever goes better,and
so does my truck
. never mind the last question.I will still do the advance to get even more go.
I did that on my truck with a 390 2v, also
very good advice.
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Junior User
Joined: Jul 2002
Posts: 59
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engine stumble lower rpm
I have recently rebuilt it, and I still can't shake the stumble. It is more noticeable if I slowly depress the pedal rather than "goose it". It's also noticeable on turns. If I accelerate after a tight turn (90 deg) it has to "catch up". Thanks for your help!
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