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Discussion Starter · #1 ·
Hi All, I have a problem that I can't figure out on my Weber.

The rear carb is fine but on the front carb I am only getting fuel out of one of the accelerator pump jets. I have had it apart and cleaned the jet but the fuel doesn't seem to be getting to the jet in the first place.

When I hand pump the carb, fuel flows towards one of the jets but the other side is dry. There must be a blockage somewhere but can't work out where. Does anyone have any thoughts on this?

Thanks
 

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AO Detailing COTY Winner 2018
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Pump jets

I think I'd...

(1) swap over the accelerator pump jets between the 'good' and 'bad' halves of the carb, operate the throttle arm and see if previously 'bad' half of the carb is now ok. If so, then it's definitely a blocked/faulty pump jet - if not, then it definitely isn't
(2) remove carb from car, remove accelerator pump from base of carb (four screws), remove one of the pump jets from the top of the carb. Put an airline onto the port where the (now removed) pump jet was, blow air (or carb cleaner aerosol) and check that it comes out underneath the carb, where the accelerator pump mounts are.
(3) Replace pump jet, remove the other one, and repeat.
(4) if air does not flow, then you've found the blocked drillway.

One other possibility: the stroke of the accelerator pump is adjustable and - if set much too short - then the pump may not be able to deliver enough fuel to purge both drillways and to supply both jets. Start with the stroke set fairly long, and see if things improve...
 

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Discussion Starter · #3 ·
I think I'd...

(1) swap over the accelerator pump jets between the 'good' and 'bad' halves of the carb, operate the throttle arm and see if previously 'bad' half of the carb is now ok. If so, then it's definitely a blocked/faulty pump jet - if not, then it definitely isn't
(2) remove carb from car, remove accelerator pump from base of carb (four screws), remove one of the pump jets from the top of the carb. Put an airline onto the port where the (now removed) pump jet was, blow air (or carb cleaner aerosol) and check that it comes out underneath the carb, where the accelerator pump mounts are.
(3) Replace pump jet, remove the other one, and repeat.
(4) if air does not flow, then you've found the blocked drillway.

One other possibility: the stroke of the accelerator pump is adjustable and - if set much too short - then the pump may not be able to deliver enough fuel to purge both drillways and to supply both jets. Start with the stroke set fairly long, and see if things improve...
Thanks, I'll give that a go. I haven't taken the plate underneath off yet so I'll see what I find.
 

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AO Detailing COTY Winner 2018
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Thanks, I'll give that a go. I haven't taken the plate underneath off yet so I'll see what I find.
Take care when you remove the accelerator pump cover from the underside of the carb:
1. The pump chamber will be full of fuel (so disconnect battery first, and keep away from hot engines)
2. Be patient/gentle removing the cover so as not to damage the gasket.
3. Wear eye protection.

Good luck, and let us know what you discover...
 

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The first thing you need to tell us is the model of your Weber carbs. On the top of your carbs, there's a stamping 40DCOExxx. The figures after the 40DCOE are the "Tipo" or model number.
If your carbs are the older type, then the posts above will not help you, as they don't have an accelerator pump on the base of the carb. The later ones did, similar to a Dellorto.
The accelerator pump mechanism on earlier carbs is under the top cover.
It consists of an accelerator pump piston and spring, and a crude ball bearing valve that passes fuel to the pump jet.
It will be either a blocked pump jet, a stuck ball valve (very common in cars that have been stood), or a blocked channel in that circuit.
Steve
 
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