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Running badly when revs are low

Kermit4

Enthusiast
Messages
31
Location
Algarve,Portugal
#1
Hi All,
The "new" R4 has been running great until yesterday when the engine would not run unless on full choke even when hot. Thought I would check the obvious causes and sure enough when I looked at the carb (Zenith model 28 IFP V05084) the tiny vacuum tube leading to the distributor had come loose at the carb end. Great thinks me and reattached it and checked the joints with the rubber pipes were all tight. Problem is the car runs exactly the same. Any suggestions as to why this is? Any ideas gratefully received.
 
Messages
198
#3
Hi Kermit

There would be a number of things to check which could be the cause, including the following: short hose back of base of carb with internal one way valve, if valve defunct, hose disconnected or hose perished, partially blocked jets, sucking in air ie carb base gaskets worn, worn manifold gasket, cracked manifold, manifold nuts loose, carb needs tuning ie adjust air mixture screw/idling screw, more involved complete carb strip down, clean, overhaul or carb internally worn.

Hope this helps.
 

Kermit4

Enthusiast
Messages
31
Location
Algarve,Portugal
#4
Cheers! I guessed there is too much air getting into the carb when the engine is warm. Will take a look at the things you suggest. Many thanks for quick response..
 

uaz04

Due Momianesi
Messages
91
Location
Istria, Croatia
#5
Smell petrol, or see leaking around carb? Maybe the float valve, usually gets replaced at every carb service.
 

mojobaby

Enthusiast
Messages
1,175
#6
Hello Kermit the way I see it, if you pull out your choke, you are cutting off excess air and thus enriching your mixture.
The fact that your car runs okay like this, means that it must be getting air from somewhere else, as jcarruthers suggests.

A few years ago I had similar symptoms and it turned out that the 2 nuts holding down the carb were loose. It happened suddenly, one day it ran perfectly and the next day I was pulling out the choke.
 

Kermit4

Enthusiast
Messages
31
Location
Algarve,Portugal
#7
Cheers. I had guessed much the same. checked my nuts (!) and all OK. Mine was the same; ran really well then suddenly won't run at low revs without choke. Ironically runs fine when gunning it on the road but fails miserably when revs are low or under load. Can't see any obvious leakage but will check again. The funny thing is it ran rough for a day then was OK now bad all the time. Oh well I guess it is find the leak time!. No petrol leak and the small pipe in the air intake is putting more fuel in when accelerator pushed to the floor.
 

Kermit4

Enthusiast
Messages
31
Location
Algarve,Portugal
#9
No. Any advice on what to check/do? Many thanks.
PS I am no mechanic so idiots guide helpful!
 

laxeian

Enthusiast
Messages
186
Location
Galicia
#11
You may have a Femsa distributor on yours which are slightley different, but work using the same principles as the above link, there is a very good video on forum that shows you how to check and adjust points, but typically I cant find it to post link!.
I’d check your HT leads aswell ( do this one at a time so you do not get positions confused) take each one off at plug end, look into the rubber, you want to see ‘clean ‘ metal in there, if its not it will be a blue colour, you can clean these back up with a light sandpaper/emery cloth, repeat distributor end, when you have pulled each off at distributor side look down the hole in distributor, again your looking for ‘clean’ metal.same process.
The distributor cap just unclips, look at the terminals on the underside, again your looking for clean contacts, the middle contact should be black/grey though, the rotor arm ( on the distributor body itself) should again have clean contacts, the top shoud show light scoring and colour from middle contact in cap ,the edge that come into contact with the four posts on underside of cap should be clean, your can pull the rotor off and just lightly scrape it on some smoothish concrete to ensure this.
Also worthwhile removing one of the easier to get to plugs ( back or front cylinder) and just checking to see if they are not fowled up and have a gap.
Cleaning should return it back to running properly, but ideally if you find any of the above you really want to be ordering and replacing problem areas to ensure reliability.
Just basic basics but hope it may help, sure theres a lot more that could be added.

EDIT:- in the ‘tech tips’ section at top of page there is a thread on how to change/adjust the points on a Femsa distributor.
 
Last edited:

Kermit4

Enthusiast
Messages
31
Location
Algarve,Portugal
#13
Ended up taking the R4 to local garage who stripped and cleaned the carb. Now runs great but a tad worried that the dirt is getting in from the fuel tank. So will run great until carb gets dirt in it again. I guess it is just a waiting game to see what happens. Thanks for all the advice on the forum. I think it is great that there are so many enthusiasts out there who are willing to help. Makes owning the R4 even better!!
 
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