Too rich

[nickharman]

I find I now have to run with the choke out to run at all, even well warmed up.

Ive had the air cleaner off to observe how much I can open the choke butterfly to let more air in before she stalls and it's not much at all. It's almost closed

At the same time she dislikes clutch down when I stop for lights etc and will stall.

I've checked the jets and all seem clear, float chamber working normally. The gasket is torn between the float chamber and the void next door but I don't think that would be a problem?

It's a Zenith 28IF carb on a 1987 R4

I have never adjusted the volume control screw. Should I?

Thx

N

 

[malcolm]

Normally if you need to use the choke to keep the car running when warm it's going to be a blocked main jet. I don't remember if the photo is a Solex or a Zenith but in either case the main jet sits at the bottom of the float chamber.

I think it's a Zenith. I had to pull the carburettor off for access to mine. There is a brass plug in the float chamber that needs to be unscrewed to access the main jet. Once the plug is removed the jet comes off with a screwdriver and it's not a bad idea to drill it out with a 1mm drill bit while it's out to better run on modern fuels. For the Solex the plug is more accessible and the carb doesn't need to come out.

The mixture screw is more for idle and just off idle. I normally have them 1.5 turns out from fully in.

 

[nickharman]

Yes that's my carb in photo

Ive had the jet out and it's clear, I guess I best look again, what I can't do is drill it!

n

 

[nickharman]

Not getting very far, had the carb off again and checked the main jet. All good

Still stalling when stopping at junctions etc.

 

[Andy McGhee]

Nick
I'm not sure whether you've already done this, but it'd be worth double checking that the jet with the blue arrow is clear - they often get gummed up. I've found a piece of soft electrical wire works well.
The filter under the 'doorbell' often gets blocked too - worth a few squirts with carb cleaner.
Good luck!
Ditto for idling jet (the hole in the bottom often gets blocked)

 

[nickharman]

View attachment 31613
Nick
I'm not sure whether you've already done this, but it'd be worth double checking that the jet with the blue arrow is clear - they often get gummed up. I've found a piece of soft electrical wire works well.
The filter under the 'doorbell' often gets blocked too - worth a few squirts with carb cleaner.
Good luck!

Thanks

I was thinking of checking that, it's the idle jet of course, mind you that would not explain the need to run rich would it?

I see a complete overhaul kit for this carb is about 30euros, I may get one

 

[jcarruthers2]

Hi Nick

I was just wondering if you have checked the breather hose which runs from the back of the base of the carb/manifold to the T piece on the rocker cover. If this hose has come adrift/split or the internal one way restrictor valve is faulty/missing, it would cause similar issues.

 

[Andy McGhee]

Thanks

I was thinking of checking that, it's the idle jet of course, mind you that would not explain the need to run rich would it?

I see a complete overhaul kit for this carb is about 30euros, I may get one

Edit to my post re idling jet!

 

[nickharman]

Sorry is the. blue the idling jet?

 

[Andy McGhee]

Sorry is the. blue the idling jet?

In the second picture, yes.
I had a similar problem with my TL - the long tube in the first picture turned out to be blocked. The Autobooks manual calls it an 'enrichment device'.

 

[nickharman]

ok thanks Ill run some wire down it, doubt it will help the need for richness though,

The second picture is not the Zenith 28IF though

n

 

[Eccles60]

Assuming it's running way too weak (and thus needing the choke) I would suspect an air leak somewhere, either the breather (as suggested) or the carb or manifold gaskets.

 

[malcolm]

Assuming it's running way too weak (and thus needing the choke) I would suspect an air leak somewhere, either the breather (as suggested) or the carb or manifold gaskets.

That's a really good point. The other not obvious thing for air leaks is the breather hose to the bottom of the carb came from the factory blocked with a plastic piece with a 1mm hole in the middle. I normally block that hose completely.

 

[mr-reno-139]

Hi everybody not been on this forum much for a while on the top of the carburettor there is a metal domed cap which has a mesh filter underneath there is a tiny rivet holding it on which will need carefully drilling out when this is completely blocked it stops any air getting into the float chamber meaning you need to pull the choke out to compensate

 

[orsome]

i've lost my dome 12 yrs ago

 

[jcarruthers2]

Hi

My dome was missing too. I found a copper end cap in the plumbing section at B&Q which was a perfect fit. All that was required was to drill a small hole in the top to secure it in place.