L28 + webers, nasty off-idle stumble

[Guest BrandenZ]

L28, DGV weber carbs, alison electronic ignition, new plugs + cap + wires + rotor.

 

When tipping in throttle, the motor chokes terribly. It's also boggy if tipping in more throttle from a part throttle condition. Outside of that it idles great and runs WOT like a champ. I had the same problem with an L24 motor (same ignition + dist too), so I'm almost positive it's a carb (air/fuel) issue.

 

Here's the puzzling thing.. I had vacuum leaks from the carbs to the manifold. Bad ones. Immediately I thought I found my problem. However, upon pulling the carbs, cleaning, and completely resealing them (0 vacuum leaks now), the stumble condition got worse. A lot worse.

 

Any ideas? Before I could idle the car at 1k by either advancing timing or adjusting the idle screw and it wouldn't stumble. Now it stumbles as high up as 1500rpms. :-/

[ZR8ED]

There are a couple of causes of off idle stumbling.

 

First what is your jetting combos particuarly your accel pump jets and idle jets?

 

1 Does it stumble if your very slowly increase the rpms?

2 Or does it stumble only if you quickly stab the throttle..(not nessessarily WOT)

 

1 small idle jets. good smooth idle doesn't mean you have the proper jets. The mixture screw can mask improper idle jets.

 

2 accel pum jets too small.

 

3 this assumes that they are properly sync'd, mechanically in sound working order.

 

Post more info if you need help.

 

Thanks,

Scott.

[SHO-Z]

I have had similar problems on my webers. I have fixed it by setting the idle screw ½ turn in and adjusting the idle speed with the idle enrichment screw. The webers have a transition jet that is covered by the throttle butterfly at idle. If you have the idle set so this jet is not covered it does not work properly and the engine will stumble off of idle.

[gramercyjam]

After making sure the carbs are good and clean and assembled correctly, I like to start the troubleshooting by making sure the float levels are correct. DCOE's are extremely sensitive to float level settings. I think I remember the "correct" setting is somewhere around 7.5 to 8mm. You can go up or down from that and it will affect idle and off idle response.

[briann510]

our 3.2 stroker with triples we had the same problem. cured it by increasing the accel pump jets quite a bit and leaning the mains from a couple steps. pretty much cured the off/low idle stumbles. the only time it does it now if the engine bay is really hot as in sitting after shutoff and restarting after heat soak under hood temps go way up. using a cowl hood and wrapping fuel lines helped alot with that issue.