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Renault 5 1.4 C2J - Wandering Revs

JamesAkers

Enthusiast
Messages
5
Location
Manchester
Hi all

I'm seeking help to identify the cause and solution to wandering revs on a 1.4 Renault 5.
With the choke on the engine starts after a few turns and rev speed can be adjusted by moving the choke lever. The revs continually fluctuate, moving up and down at idle. When driving the car the engine regularly surges and jerks forward.

The engine is a 1.4 C2J with a Weber 32 DRT 15/101.

So far I have worked through the following:
  • Rebuilt and cleaned the Weber 32 DRT (previously the second venturi butterfly would jam open)
  • Full oil and oil filter change
  • Replaced fuel lines and fuel filter
  • Replaced fuel pump
  • Replaced spark plugs
  • Replaced distributor cap (Beru VK359)
  • Full coolant change (previously the expansion bottle was bone dry and the pipe to radiator blocked)
After all of the above the wandering revs is still present. I've checked for air leaks across the manifold and carb and cannot seem to find any.

Questions:
  • Could engine compression cause this behaviour?
  • Is it a timing issue?
  • There is a suggestion that this is not the original carb. Is a Weber 32 DRT 15/101 correct for a C2J. What should the jet sizes be?
Hope you can help, any suggestions welcome!
 

Baron von Zach

Enthusiast
Messages
41
Location
Stockport
Has all this work been done because of the hunting tickover?
Or was it running fine before?
 

JamesAkers

Enthusiast
Messages
5
Location
Manchester
Has all this work been done because of the hunting tickover?
Or was it running fine before?

It was hunting before.

I started with the carb rebuild as it was getting stuck at high speed and hoped it would also cure the rev issue as well. I thought it might be a fueling issue hence the pump swap and then onto the distributor cap (which had corroded terminals). The wandering revs have remained (frustratingly!).
 

JamesAkers

Enthusiast
Messages
5
Location
Manchester
Thanks for the reply. I've had a look this morning and there is fuel dripping down onto the butterfly flap. When opening the throttle I could see the idle mixture screw poking through. I backed it right off (removing the 90° adapter to move it fully) and it doesn't seem to make any difference.

The mixture screw has no affect on the idle speed at all which is strange and the revs still wander.
 

Baron von Zach

Enthusiast
Messages
41
Location
Stockport
The mixture screw does indeed have no, or very little effect on the idle speed. It regulates the idle mixture.

For every application, a carby has a 'zero' spec. It's a basic adjustment to work from.
The specification tells you a specific amount the butterflies should be open and the number of turns the mixture screw should be out from fully seated. This should be in your workshop manual, or maybe someone on here knows the spec for a 1.4 C2J with a Weber 32 DRT.

In 90% of the cases the engine runs fine with this adjustment.
If not, then adjustments should only be made with a gas analyser up the exhaust.
 

Richard Williams

Enthusiast
Messages
110

JamesAkers

Enthusiast
Messages
5
Location
Manchester
The mixture screw does indeed have no, or very little effect on the idle speed. It regulates the idle mixture.

Yes, but adjusting it makes no difference to the mixture. I would expect to hear a difference to the engine moving between lean/rich mix when turning it in and out. Everything has already been set to original specs as part of the rebuild.
 

JamesAkers

Enthusiast
Messages
5
Location
Manchester
I have swapped the carb out with another Weber 32 DRT I had for parts. The same problem persists so am wondering where to look next.

If it is not the carb, air leaks in the inlet manifold, or the fuel pump, what could be causing the revs to jump about?
 

Richard Williams

Enthusiast
Messages
110
If of interest, I found the smallest , thinnest piece of organic matter sitting within the idling jet I would estimate that this would have caused an uneven flow. carefully removed under magnification resulted in a return to normal idling performance. Some may know this but one needs to take one's' examination of these things to a forensic level to detect such small objects.
 

Andrew4Renaults

Enthusiast
Messages
532
On a related matter, I find that many garages are unwilling (=unable) to change pollen filters on modern cars. I appreciate they're often tucked away in the footwell and tricky to get at without a degree in proctology, but nevertheless, I've found species of bugs, insects and other organic detritus in many a pollen filter, some of which I feel certain were on the "endangered species" list......
 

Mike Cordeiro

Enthusiast
Messages
44
Location
Algarve/Portugal
Hi James, on the video, the instrument cluster with rev counter, is it from an renault 11 ?
 

Andrew4Renaults

Enthusiast
Messages
532
I've watched the videos you posted at the beginning of this thread and the engine seems fine, although the revs seem odd, as it ought to idle at about 700-800 R.P.M. I wonder if you have checked the condenser, as the jerking and uneven running you describe can be caused by the condenser failing. By the way, in my days as a mechanic I came across quite a few Renault 5s with sticking venturi, so it's not uncommon! Are you SURE the carburettor's correctly set up?
 

angel

Enthusiast
Messages
2,168
Location
Athens, Greece
The throttle stop screw may have been turned too much inwards, so that engine is idling on the progression circuit, not idle circuit. Or butterfly / carb body worn around the spindle, causing too much air to be sucked in.
Check also that second butterfly is closing fully.
 
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