Hesitation on Sudden Throttle

[malcolm]

Worth an ask to see if anyone else has any ideas. The Gordini has the Renault 5 Alpine engine with a Weber carb.

Been fiddling over the last few weeks. The ignition timing was much improved by fiddling with the advance curve http://www.renault4.co.uk/tech-pinking.htm

Fitted a new throttle cable at the weekend and made sure I could get full throttle - might not have been getting it previously.

Since all that I've found if I floor the throttle suddenly the engine dies for a second before doing it's thing.

I've checked the throttle pump and it's working perfectly. Ignition timing is set as advanced as it can sensibly be without pinking. Vacuum advance works (and has some adjustment to alter it's limits that I haven't fiddled with). Points were new about 2000 miles ago and haven't been cleaned but seemed good after 500 miles.

Only thing I've found is the dwell angle had drifted to 50 degrees so I altered it to about 58 degrees tonight.

Might be a blockage in one of the jets - idle jet seemed to become blocked this afternoon so I've hosed them all out with an air line tonight. Got a filter on there and everything seemed clean, but definitely one blocked jet this evening.

I shall report back on how it goes tomorrow, but really asking in case this seems an obvious symptom of some malaise that might make it awkward to do 1500 miles over the next 2 weeks.

 

[barnfind]

Try This!!

Frustrating.
We used to get this a lot on our Beetles and it was usually down to an excessively weak mixture caused by air leaks on the induction side, or the vac advance (if there was one) wasn't responding sufficiently rapidly.

You seem, to have tried the most obvious things, so I would look into these two areas.

Try squirting WD40 or a starter fluid around the various flange joints on the manifold (and the butterfly spindles) while the engine is idling. Any increase in RPM suggests an air leak which you might be able to correct with a quick nip on a spanner. or might need a gasket job. Obviously if it shows a leak on a butterfly spindle then that is more serious and needs a new set of bushes.

On the distributor, try sucking the vac tube and check that the points plate in the distributor moves properly.

 

[reggie]

Put the air filter back on to test, it is easier to suck air than fuel, so it will,

 

[Steve Hennessey]

Malcolm, did you fit a new accelerator pump diaphragm at all? Apart from everything else mentioned, if the pump diaphragm has any weakness in it, it will produce those symptoms.

 

[malcolm]

Seems to be ignition related. I reckon the timing drifted a bit/ points closed up. I advanced the timing on the way home from work and it helped a lot (though that's messed up idle again).

It's always seemed very sensitive to timing. I'm starting to think it's the rotor arm not aligning with the cap. Been sold bits from the wrong distributor type maybe. I think the R4 Ducellier bits are the same so I'll try those tomorrow.

Will also look at Derek's car to make sure I've got all the vacuum hoses in the right place. Pump is on original seals but squirts nicely even on very slow throttle movement so I reckon that's good.

EDIT - Hmmmm - just been out to change the distributor cap for an old one from a R4. Seems to have helped a lot.

 

[iMacThere4iAm]

Hi Malcolm, did you & Clementine ever figure this one out? I've been having the same problem lately. When I press the accelerator, I get almost a braking effect for half a second, then it picks up. If I do this when standing still, the engine stalls unless I press the throttle very gently.

It seemed to start after I opened Felicia's carb, cleaned it, and replaced the gaskets. This makes me think the carb is the problem, but I can't be certain.
It seems to get worse with a hot engine. Closing the choke seems to help a bit.
I did previously have a huge air leak, but that is now fixed. I suspect it's not related to the hesitation problem.
It's a GTL with the Zenith 28 IF carburettor.

 

[malcolm]

The ignition timing was out.

If you've had the carb apart have you refitted the vacuum advance to the carb and is it working?

Otherwise I'd set points gap and timing as a starting point.

 

[iMacThere4iAm]

I've checked my timing is good. The vacuum advance unit on the distributor works - I have tested it by sucking on the tube. However, the timing doesn't change at all when I reconnect the tube. Is that normal? I'm not certain that the carb is properly sucking a vacuum in the tube - does that make sense? This has been bothering me for a while and I'm pretty much out of ideas.

 

[malcolm]

With the GTL carb the ignition normally advances a lot when you plug the vacuum pipe in to the distributor. possibly the vacuum port in the carb is blocked?

If you have no vacuum advance it'll feel a bit stuttery at town speeds too.

 

[iMacThere4iAm]

My problem turned out to be crud in the idle jet. Probably dislodged from elsewhere in the carb and stuck there while I was cleaning it (such irony). I blew it out and Felicia sounds sweeter than ever

 

[mike4gtl]

Hesitation, Deviation, Repetition. You have 60 seconds on the subject of post colonial Africa.