Engine dying at full throttle

[malcolm]

I've been fiddling with the R4 Gordini. Previously I had the thing running reasonably on the original distributor but it wouldn't run well around town and increasing throttle at high load would make make the engine slow down.

I decided it was probably worn ignition timing causing the problem so bought a shiny programmable distributor from 123-tune. The car is now a lot better around town, but starting is rubbish and the engine dies if I press the throttle too quickly.

Does that sound like too retarded to you too? Advancing does help but I'm nervous that I need to run over 40 degrees max advance to make it happier which seems way too much. There is no sign of pinking when I advance the ignition more than I'm happy with.

If the engine was too retarded it ought to work predictably just a bit slower. The engine shouldn't die. I'm wondering if I have a fuelling issue or a weak spark issue. I've changed the coil and plugs in the last week. Plugs were on the white side of normal.

Any thoughts anyone? I suppose I could bung the original distributor back on and record the advance curve with a strobe and use that as a starting point.

 

[angel]

Are you sure it's not related to the idle jets or accelerator pump circuit? Could it be that you have opened too much the butterflies in order to gain idle speed, making the progression circuit redundant?

It seems strange to me, too, that it dies from beeing too retarded, but you can give it a try, anyway. Is the 123 fully programmable? You can then give it as much idle / low rpm advance as it feels happy with, while keeping max advance on the safe side. If it has some preset curves (as I remember on 123 ignitions), you can choose a curve that is not steep and increase static advance.

 

[malcolm]

It might be a bit lean. I have a similar problem with the Renault 5 TX where it can die on the first choke but is fine on the second. I've bought a carb rebuild kit for the R5 which might help.

The internet suggests hemispherical combustion chambers need 40-44 degrees maximum advance, and also that engines running too lean need more advance than engines running correctly which might explain why the Gordini needs so much. I half remember a jet blowing out when I blew through the carb with an airline. I couldn't find it so put one in from a spare carb. I can recall not being sure if it was the right jet or in the right place so that could be worth some investigation. I have the Renault carb books now so can find out what it should be like.

 

[christoph]

Have you checked your acc pump jet ?Have had some timing advance issues having built up a 1289 ts with modded head Salv sacco cam and big weber 36 dcd the rolling road dyno to set up showed the original dizzy could not deal with advance reqirements at load and idle.
I have now gone Megajolt distributor less wasted spark fully programable to give the required advance curve will go back on the rollers when installed was 80bhp last run

 

[malcolm]

The accelerator pump works OK. I need that for starting.

I filled up with 95 octane to see if I got any pinking and have been out for another tuning run. I've increased the advance by 5 degrees above 1500rpm and ended up with a maximum advance somewhere around 45 degrees (including the static advance). That has fixed the hesitation problems on full throttle. Increasing the advance by 5 degrees caused slight pinking at about 2100rpm so I've backed that down a bit and have the same sharp ramp up from idle as the original distributor.

45 degrees seems like a huge amount of advance. But the car feels very similar to how it felt on the old distributor so chances are that's what it was like. I still ought to look at the carb.

 

[christoph]

Sounds good do a plug cut make sure your not lean on the second choke

 

[malcolm]

plug cut

I probably am a bit too lean. Plugs are a bit white but in perfect condition otherwise. What's a plug cut? I searched the internet and it gave me pictures of fish.

Edit: found it - plug chop:

When its hot and white, but looks pretty clean,
You're 'bout to blow your shit up; you're running lean.

Might be worth a look then. The photo is a plug removed a couple of days ago after maybe 20k miles. Looks fine there but is more white without the camera flash.

 

[Mausje75]

It`s to white ( lean ) and therefore to hot... can cause misfire

 

[malcolm]

I've got something embarrassing to report. The engine was dying because the choke linkage on the carb had become detached and the choke was closing on throttle. Big oops.

Will do some new tuning based on a more predictable engine response next weekend.

 

[Mausje75]

Sometimes this kind of things can happen..

But i would stil replace the sparkplugs and set the carb a little richer. Your engine is running a little to hot.

 

[malcolm]

Moved on a little further - Combustion is fastest at roughly the right fuel mix. Too lean or too rich slows the combustion speed and requires more advance.

The blindingly obvious way to check for too lean (apart from the white on the spark plugs) is to pull the choke out a bit and make it richer. Mine started pinking when I pulled the choke out. Faster combustion - so it was too lean.

I've retarded the ignition by 5 degrees pending pulling off the carburettor to work out why it is too lean. That'll have to wait a bit as the Renault 5 carb is also off for a rebuild at the moment to sort a lack of fuel on the first choke.

One thing I'm thinking is I have a tendency to blow out carbs with an air line to make sure all the jets are clean. The air control jets set into the top of the carburettor are very easy to blow out when you blow through with an air line. The smaller the air control jet the richer the mixture. Missing air control jets would result in a lean mix. Will need to check if any have blown out without my noticing.

 

[Mausje75]

Missing the air control jet, you would normaly have trouble to adjust your R4

 

[angel]

The real influence of the air corrector on air/fuel mixture happens at the top end of the rpm scale, on lower rpms it's really a matter of the main jet and emulsion tube.

 

[malcolm]

I think I've fixed it. The enrichment jet on the secondary choke was no longer in the carburettor top, but had fallen into the base and blocked the hole where the extra fuel should have come out.

Also the brass pipe at the bottom of the photo appears to vent the float chamber into the plastic intake duct on top of the carb. I've fitted a restrictor but am wondering if it should be blanked off completely. There is another vent for the float chamber at the top which closes on throttle.

It's now running happily at my more retarded setting.

 

[malcolm]

Years later I have the answer!

The problem with the original distributor was that the advance springs had become slack. It reached full centrifugal advance at much lower rpm than it should, so it had to be retarded to avoid pinking at that tricky 2000rpm region meaning advance at higher rpm wasn't enough.

The problem with the fully tunable 123 ignition was I had become confused about how the vacuum advance worked and cocked up the settings creating the same problem. The vacuum advance increases advance at low throttle but not at full throttle - it's a driveability and efficiency thing. The reason my engine was dying at full throttle is there wasn't enough advance left after I pressed the throttle to the floor and the vacuum kicked out.

Anyone else with the same problem running a worn out standard distributor might get around the problem by simply disconnecting the vacuum advance and increasing the static advance. That would give a map closer to the designed map than a worn distributor with the vacuum enabled. Worth a try if you have the trouble.

I'm having another burst of fiddling with the 123 tune distributor. It's getting very driveable now.

 

[Simon Sapsted]

Hi Malcolm,read the thread with great interest as I am planning similar build to yours with help from Mr Reno (Paul C)I have engine but no dizzy so was looking at a ign123 but could not find a local supplier that can supply with the long shaft the Gordini engine needs.Could you kindly supply me the details. Regards Simon.

 

[malcolm]

I bought mine from http://www.classicautoelec.com/allu...ectronique-programmable-renault-5-alpine.html

They make their own extension shaft. I thought they were also available from 123 tune these days.

 

[petak]

Malcolm....Is it really that good as you can read on net?

I have problem locating vacuum advance for my ducellier distributor and thinking of buying one 123 for my GTL.
Price is turn me down for getting one.

But if it is much better than ducellier dizzy than will find way to get one.

123 does not have vacuum, point, condenser......that can go wrong? Or i have missed something?

 

[malcolm]

The Ducellier advance unit was available from Renault 6 years ago. Might be worth trying them.

The 123 distributor is full of electrics so is unlikely to last as long as the mechanical original. It has a vacuum connection which presumably connects to an electrical sensor inside, but there is no condenser or points. I have fitted them to the R4 and the MG, though the ignition curves I have ended up with are similar to what the original curve would have been.