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Weber 40 dcoe transition hole rpms?


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Anybody know what rpm I should be passing through the transition holes on my weber 40 dcoes? I have a stumble mid range and I expect it could be a transition hole issue. Not sure if there is something stuck in there causing a blip. It happens when I accelerate through the gear and also if I'm cruising on the why. Does that sound lime a potential transition hole issue? I've check just about every other thing on this car and it's driving me nuts.

This car was running great and then this stumble appeared after some spirited driving.


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because it's load dependent. Actually, throttle position dependant.

If you're under significant load,

they can be exposed at just above idle.

If you're upshifting, they're closed even the motor may be at 5k.

All that said, the easy way to diagnose 'em is to change the progression

jets. If you go richer with no change, then go leaner. If that doesn't

make a difference,

fix your ignition.

Then look for air leaks at the gaskets.

That's been my experience.


"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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AND THE BEST explaination for you is found in

the Tuning and Parts Manual available from PIERCE MANIFOLDS.

This booklet explains how each circuit operates, when, and

what parts effect change. A complete listing with part numbers

for ordering are also contained. You need to sit and read through

this guide and fully understand each stage of the DCOE.

And when you think you know which new jet

or digit you need? PIERCE has them all.

And before you make any changes to the carbs,

you must have the ignition timed properly - then

leave it alone during any carb setting changes.






'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

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