I have a 1986 ex France Telecom R4. Had it for 15 yrs, and it now has 150km on the clock. It recently started playing up for the first time. Seems to drop a cylinder or 2, bad vibration when idling, but works fine once one is bundling along nicely.... I,ve changed plugs, plug leads, distributor head and rotor, all to no avail. Checked compression, thats fine too. I think it must be the carb, about which i am fairly clueless. Mine is a Zenith 921F, and it doesn't feature in the Haynes manual, as probably was only fitted for sales in France. i have a feeling i need to play with the mixture scres, but I have no idea which one it is.... Can anyone help. By the by, I'm in France
- Thread starter malcolm.s
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Steve Hennessey
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I am not familiar with the carb fitted, but I suspect that you may have leaking carb base gaskets or manifold gasket. Have you replaced the points as well?
I haven't replaced the points, but they were checked in the local garage, and apparently they are fine.
I'll try to check the two gaskets. Is there a method of doing this before replacing them? For checking a blowing gasket I'd use soapy water, but can't think how to check a 'sucking' one....
I'll try to check the two gaskets. Is there a method of doing this before replacing them? For checking a blowing gasket I'd use soapy water, but can't think how to check a 'sucking' one....
In the Haynes manual, on the exploded diagrams for Zenith and Solex carbs, they refer to 'Idle Adjustment Screw' and 'Volume Control Screw'. Are these the same things, and are they both for contolling the mixture? I'm a little confused because the manual refers to the 'Mixture Screw', but its not shown under that name in any of the diagrams.
Steve Hennessey
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To check the gaskets, have the engine running at idle speed and either dribble oil or squirt WD40 around the gasket areas. If the gasket is faulty it will suck in the fluid and you may hear the engine falter of see a puff of white smoke from the exhaust.
All carbs have a fast idle screw that controls the butterfly - in to increase the idle speed and out to decrease.
Hidden away somewhere you will see a mixture screw set into the base of the carb. It will either be seen on the outside or within a hole. If it is the latter a small electricians screwdriver will be needed to adjust it. You need to turn it either way until the engine achieves the maximum revs. I use a rev counter to do this but it can be done by ear.
I forgot to ask before, but how did you check the compressions?
All carbs have a fast idle screw that controls the butterfly - in to increase the idle speed and out to decrease.
Hidden away somewhere you will see a mixture screw set into the base of the carb. It will either be seen on the outside or within a hole. If it is the latter a small electricians screwdriver will be needed to adjust it. You need to turn it either way until the engine achieves the maximum revs. I use a rev counter to do this but it can be done by ear.
I forgot to ask before, but how did you check the compressions?
I checked the compression with a guage. They were all 11-12 bar, which is ok, I think?
I tried the WD-40 around the bottom gasket, and nothing obvious happened. Certainly no change in running or white smoke..
I cannot find the idling screw! I presume there must be one? Driving me bonkers! I will persist.....
I tried the WD-40 around the bottom gasket, and nothing obvious happened. Certainly no change in running or white smoke..
I cannot find the idling screw! I presume there must be one? Driving me bonkers! I will persist.....
Steve Hennessey
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Sorry, don't relate to bars (unless they serve beer!) as I'm used to pounds per square inch. However, if they are all similar then it's a good sign.
When checking the compression did you remove all plugs before testing and made sure that the accelerator pedal is held open? Did you dribble oil around the manifold gasket as well?
The idling screw is there somewhere, but I doubt if it's the cause of your problem. Have you ever cleaned out the carb?
When checking the compression did you remove all plugs before testing and made sure that the accelerator pedal is held open? Did you dribble oil around the manifold gasket as well?
The idling screw is there somewhere, but I doubt if it's the cause of your problem. Have you ever cleaned out the carb?
I think thats about 120 psi or so.
Yes, i removed all the plugs for the compression check, but didn't test the manifold gasket.
I found the mixture screw! As you said it may be, it was recessed. I unscrewed it and the engine ran a bit faster, but I seemed to come to the end of the thread after abt half a turn, and anyway, you're right, it hasn't solved the problem, to my disappointment. I think I'll have to change the gasket. Can I use that stuff from a tube, or will I have to find a proprietary one?
I have never cleaned out the carb, and wonder if I am capable of it! I'm always terrified a spring is going to jump out from Gawd knows where. I've consulted Mr Haynes, and his description doesn't fill me with confidence, as my type of carb isn't featured. Oh, and I see he says not to use liquid gasket.
Yes, i removed all the plugs for the compression check, but didn't test the manifold gasket.
I found the mixture screw! As you said it may be, it was recessed. I unscrewed it and the engine ran a bit faster, but I seemed to come to the end of the thread after abt half a turn, and anyway, you're right, it hasn't solved the problem, to my disappointment. I think I'll have to change the gasket. Can I use that stuff from a tube, or will I have to find a proprietary one?
I have never cleaned out the carb, and wonder if I am capable of it! I'm always terrified a spring is going to jump out from Gawd knows where. I've consulted Mr Haynes, and his description doesn't fill me with confidence, as my type of carb isn't featured. Oh, and I see he says not to use liquid gasket.
Steve Hennessey
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120 psi is good. Looks as if you'll have to replace the manifold gasket but do the test first just to reassure yourself that the gasket is the problem.
You'll have to remove the carb when you change the gasket so you may as well overhaul it at the same time. Buy a new top carb gasket, base gaskets, a needle valve jet and an accelerator pump diaphragm/plunger (depends what's fitted) and an 'o' ring for the mixture screw from your local Renault garage. Don't be frightened of it - just work methodically and with absolute cleanliness. If you have compressed air available, all the better. Wash the carb in cellulose thinners and blow everything clean. Assemble with the new parts. The manifold gasket is easy to do but you'll need a 6mm allen socket for the lower nuts. Soak the front exhaust flange nuts with WD40 before attempting to loosen them. When replacing the manifold, tighten from the middle outwards.
Then you can adjust the mixture and fast idle screws. The whole job should take you about 2.5 hours.
You'll have to remove the carb when you change the gasket so you may as well overhaul it at the same time. Buy a new top carb gasket, base gaskets, a needle valve jet and an accelerator pump diaphragm/plunger (depends what's fitted) and an 'o' ring for the mixture screw from your local Renault garage. Don't be frightened of it - just work methodically and with absolute cleanliness. If you have compressed air available, all the better. Wash the carb in cellulose thinners and blow everything clean. Assemble with the new parts. The manifold gasket is easy to do but you'll need a 6mm allen socket for the lower nuts. Soak the front exhaust flange nuts with WD40 before attempting to loosen them. When replacing the manifold, tighten from the middle outwards.
Then you can adjust the mixture and fast idle screws. The whole job should take you about 2.5 hours.
Righto. I'll have a bash at all that tomorrow----if I can find the spares from my local Renault garagiste. This is a very rural area, and often the garages have untold treasures in dusty old back rooms. The old mechanics are usually pleased to help with this sort of car, ie one that isn't full of electronics. Be interesting to see whether I can get hold of the bits you kindly mention... I'll let you know!
Well, its definitely the Inlet manifold gasket! I sprayed WD40 onto it, and it suddenly ran smoothly for a few seconds, and, Lo, there was white smoke. perhaps I should call it Ratzinger. Anyway, looks like I have no choice but to change the gasket.
I tested the nuts holding the manifold, and three were immovable with reasonable force, but the third one was not exactly loose, but turned fairly easily. I turned it maybe a full turn, then stopped, as it didn't get any harder, and i fear either the nut or the bolt is stripped. If so, I guess its into a garage that can do a helicoil, (?) I'm back to England tomorrow for a bit, so I'll order all the parts and have them ready for my return.
I tested the nuts holding the manifold, and three were immovable with reasonable force, but the third one was not exactly loose, but turned fairly easily. I turned it maybe a full turn, then stopped, as it didn't get any harder, and i fear either the nut or the bolt is stripped. If so, I guess its into a garage that can do a helicoil, (?) I'm back to England tomorrow for a bit, so I'll order all the parts and have them ready for my return.
Steve Hennessey
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Good, so now you know the problem. The manifold is held on with studs and nuts so you won't need a helicoil. If there is a stripped thread on one of the studs but the nut won't come off then remove all other nuts and gently pull the manifold towards you while turning the offending nut. It will come off eventually. Do soak the nuts with WD40 or penetrating oil the day before you do the job. If one of the studs needs replacing then remove it from the head with grips or a stud extractor.
But what happens if the stud, being made of steel, has stripped the thread in the block, which I presume is aluminium?
I have to drive abt 100km in the car tomorrow. Is there any point in cleaning around the outside of the gaskets and temporarily lining with silicon or liquid gasket? Actually very difficult to get at because the manifold bracing piece gets in the way.
Am I actively harming the car by driving it in this condition?
I have to drive abt 100km in the car tomorrow. Is there any point in cleaning around the outside of the gaskets and temporarily lining with silicon or liquid gasket? Actually very difficult to get at because the manifold bracing piece gets in the way.
Am I actively harming the car by driving it in this condition?
Steve Hennessey
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If the stud has stripped the thread in the cylinder head then it would need helicoiling but you won't know that until you attempt to take the manifold off. If you do have a stripped thread then you may have to remove the head in order for it to be helicoiled. However, it is very unlikely that this has happened.
You can't use silicon sealer because of the heat in that area.
Because the gasket has gone where it has, the two middle cylinders will be getting a very weak mixture so it may harm the exhaust valves on a long journey which then causes an even bigger problem. I would not use the car myself until the gasket is done, but it's up to you if you want to risk it.
You can't use silicon sealer because of the heat in that area.
Because the gasket has gone where it has, the two middle cylinders will be getting a very weak mixture so it may harm the exhaust valves on a long journey which then causes an even bigger problem. I would not use the car myself until the gasket is done, but it's up to you if you want to risk it.
Steve. Not sure if i am in trouble or not.! I have removed the carb etc., I have also removed three of the nuts holding on the manifold, but the right hand one is turning the whole stud in the block. Presume this means either the stud is threaded, or the stud has threaded the inside of the block.... Anything I can do abt it?
malcolm
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The stud is threaded at both ends, and will unscrew at the end that offers least resistance. Often the nut stays on and the stud unscrews itself from the head. Best to keep on unscrewing it. It'll probably come out cleanly, and all you'll need to do is remove the nut and screw the stud back into the head once the manifold is off.
I'm such a twat! I thought the screws on the stud were opposing! Didn't realise they went the same way, and it came out beautifully with no damage. Darkness fell when I got it all to pieces, so I have to go to bed trying to remember the order I took it to bits!
Couple of points: Theres a lot of burnt oil difficult to remove around the inlets and outlets. Thought I might try to scrape it off with sharp edges of chestnut wood. Won't come off with petrol on a rag.
I only have 2 brass nuts. Should I really not put it together with those and 2 steel ones?
I have not dismantled the carb as have not been able to find the 'kit' for my Zenith 321, and don't even have new bottom gaskets for it. The old ones seem in good nick, can I risk just putting the carb back on with the old gaskets?
I am a very timid mechanic, and can't tell you how much fun it has been to get this far. Certainly cd not have done it without your expert help!!
Couple of points: Theres a lot of burnt oil difficult to remove around the inlets and outlets. Thought I might try to scrape it off with sharp edges of chestnut wood. Won't come off with petrol on a rag.
I only have 2 brass nuts. Should I really not put it together with those and 2 steel ones?
I have not dismantled the carb as have not been able to find the 'kit' for my Zenith 321, and don't even have new bottom gaskets for it. The old ones seem in good nick, can I risk just putting the carb back on with the old gaskets?
I am a very timid mechanic, and can't tell you how much fun it has been to get this far. Certainly cd not have done it without your expert help!!
Steve Hennessey
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Malcolm,
The burnt oil etc will come off with either cellulose thinners or paint stripper. If it's really carbonised then use the latter.
On my R4 all the manifold nuts are steel although I can't see there's a problem using brass ones. I would use brass ones on the exhaust flange always.
Just remember that all gasket surfaces must be clean. I hope you are using a new manifold gasket! With the carb base gaskets use a thin smear of gasket sealer such as hylomar.
The burnt oil etc will come off with either cellulose thinners or paint stripper. If it's really carbonised then use the latter.
On my R4 all the manifold nuts are steel although I can't see there's a problem using brass ones. I would use brass ones on the exhaust flange always.
Just remember that all gasket surfaces must be clean. I hope you are using a new manifold gasket! With the carb base gaskets use a thin smear of gasket sealer such as hylomar.