Weber 34 ICH

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Weber 34 ICH

Post by [email protected] »

anyone got any experience with these? It’s all set correctly (good idle speed, good emissions) but at random points it won’t idle (just drops to nothing when the clutch goes in) without choke and runs like a bag of spanner’s at low throttle. Having checked the carb during one of its intermittent fails there is a constant trickle of fuel coming from the upper accelerator “boost” jet which appears to causing flooding and the stall. During normal running this additional fuel isn’t happening. Something is getting stuck or needs adjustment. Anyone got any ideas? It’s brand new, only done a couple of hundred miles so I doubt it’s worn and it’s fed from a new tank through a new filter so nothing should be blocked.
STEVEW
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Re: Weber 34 ICH

Post by STEVEW »

Hi there.

The carb may be "brand new" but has it been sat on a shelf for a long time?

When the engine is running and starts "overfuelling" try gently tapping the side of the carb to see if that solves it.
A simple test/fix which costs nothing. :D
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Re: Weber 34 ICH

Post by [email protected] »

Fine suggestion I’ll give that a bash, I don’t know when I will next get it out (winter will soon stop play) but that will just tell me something is sticking, sadly, not what. It’s making me not want to drive it much, it becomes a proper little mare to driver when it throws a wobbler! :crying:
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D366Y
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Re: Weber 34 ICH

Post by D366Y »

I ran one of these for several years without any issues - but I was using it as a daily!
It may be brand new but that doesn't mean it's not faulty - Steve's check would be my first point of call, possibly could be a faulty jet if it's constantly letting fuel by when it shoudlnt?

Cheers
Danny
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Bug
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Re: Weber 34 ICH

Post by Bug »

D366Y wrote: Tue Nov 16, 2021 11:45 am I ran one of these for several years without any issues - but I was using it as a daily!
It may be brand new but that doesn't mean it's not faulty - Steve's check would be my first point of call, possibly could be a faulty jet if it's constantly letting fuel by when it shoudlnt?

Cheers
Danny
The jet is basically just a calibrated hole, so the only way it can have an issue is if it's blocked.
If this is, as suggested, the accelerator pump jet that's dribbling then it could be that the pump is sticking slightly in.
On the inner side, next to the cam cover, is a square fitting with a lever in the middle which is actuated when the throttle opens.
Inside the square bit there is a diaphragm. The gap behind this fills up with fuel and when you accelerate, the lever pushes the diaphragm which squirts that fuel in through the accelerator jet. This fills the slight gap in fuel delivery caused by the wider throttle opening and subsequent drop in pressure differential across the main jet, until it can catch up.
When you release the throttle the lever should move back, allowing the spring behind the diaphragm to push it back. The chamber then fills with fuel again, ready for the next throttle opening.
If you have fuel dribbling from that accelerator jet then I would initially be looking at the lever that pushes the diaphragm in. If this is not fully moving out then it is enabling fuel to continually run to the accelerator jet, partially flooding the carb.
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Re: Weber 34 ICH

Post by [email protected] »

That’s what looks to be happening (the pump thing Bug mentions not the Jet) But the lever seems to be fully out when I’ve looked at it in fault condition. Indeed last time it corrected I turned it off for a few minutes to move the cars around so I could get it on the drive and it was fine. But a stop previously for as long or longer, hadn’t made a difference. I may have to look into fiddling with that unit. Quite why after a couple hundred miles it’s thrown a wobbler is a mystery. Perhaps if I try disconnecting the actuator rod and see if it still occurs?
Bug
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Re: Weber 34 ICH

Post by Bug »

[email protected] wrote: Thu Nov 18, 2021 6:47 pm That’s what looks to be happening (the pump thing Bug mentions not the Jet) But the lever seems to be fully out when I’ve looked at it in fault condition. Indeed last time it corrected I turned it off for a few minutes to move the cars around so I could get it on the drive and it was fine. But a stop previously for as long or longer, hadn’t made a difference. I may have to look into fiddling with that unit. Quite why after a couple hundred miles it’s thrown a wobbler is a mystery. Perhaps if I try disconnecting the actuator rod and see if it still occurs?
Can't think of any other way for fuel to get to the accelerator jet.
Have you tried opening the throttle by hand while you look down the barrel, just to see if that is the correct jet? You should see a squirt as you open it up, then it should stop. I cannot remember now, but I'm wondering if there's a simple valve (ball bearing and spring) between the accelerator pump and the jet. The pressure when the diaphragm moves would open it, but maybe it's not seating again sometimes?
I'm sure the 32/36 has such a ball sitting under the Y-shaped accelerator jets, which just works under gravity, dropping back to seal the system after the squirt has occurred. Can you take the jet out and see what's under it?
Or.............. he says, running out of straws to grasp at.................... perhaps there's a tiny bit of grit in the accelerator jet. So when you pump it, the pressure builds up but can't get through straight away, so slowly dribbles out afterwards.
Bug
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Re: Weber 34 ICH

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