stuttering engine on gas

Post by **robintb** » 04 Dec 2006, 14:38

Anybody know what might cause this -

Engine runs fine from cold on gas, heats up to about 85-90 degrees C, then starts stuttering, no full power with throttle open when accelerating - fine when in fourth and crusing but just loses power under acceleration. Its like its missing a few strokes of the engine. Lumpy I guess might also describe it, it kind of intermittently pulls back then slowly pulls forward.

It doesn't happen on petrol.

Weird. Anybody got any ideas? Something to do with the vacuum advance on the dizzy?

2.0 Aircooled with electronic ignition.

cheers

Post by **Dubstar** » 04 Dec 2006, 21:59

The vaporisor could be icing up? Pull over and take a look at it when it's doing it. Happened occasionally on my old Audi 80 and the vaporiser would just be covered in frost.

Post by **kevtherev** » 04 Dec 2006, 22:47

true could be the vapouriser

I'm also thinking it could be weak..have you tried turning both the screws out a quarter

Post by **speleobod** » 05 Dec 2006, 18:42

All that can go wrong if engine is working fine on petrol is electric..... a useful tip from Steve Shaw.

Look in the WIKI on spark plugs, get single point and a range cooler and gap less than for petrol usually about 0.5 mil.

If you have played with the brass nut on the vapourizer then you will need to reset it as per instructions from Gasure. The main 'big' valve can be set by your local garage to a CO2 spec relevant to your engine and again advised by Steve from gasure.

Our 2L Aircooled now starts even in the cold and runs like a dream on new plugs after exhibiting exactly the symptoms you have now.

Post by **robintb** » 07 Dec 2006, 11:50

thanks all for info.

the thing is this all started happening after getting the proper electronic ignition dizzy put in. It wasn't doing it on the old 009 but just started really badly. So now it starts brilliantly. The plugs are clean ( they are the standard plugs for this engine as specified for petrol though) and new, all the electrics pretty much has been replaced with new or good second hand (dizzy, rotor arm, plugs leds, coil, hall unit, dizzy cap).

The gas was set up by Pete from Gasure upon putting the new dizzy in - I have tried adjusting the mixture (large inline screw) as well as the idle screw on vaporiser, but the problem doesn't go away.

I have started noticing its not as powerful on petrol as well as it used to be.

Could the hall unit be not amplifying the spark enough and how does the vacuum advance work with twin standard carbs - should it affect both carbs, as it looks like it is only connected up to the left?

cheers

Post by **HarryMann** » 07 Dec 2006, 23:37

vacuum advance work with twin standard carbs - should it affect both carbs

Its not the dizzi that affects the carbs, its the vaccuum from the carbs or (carb) that affects the dizzi.. so one does OK if they are balanced reasonably at idle..

Have you tried reducing the plug gaps as suggested above?

Post by **HarryMann** » 08 Dec 2006, 01:51

t kind of intermittently pulls back then slowly pulls forward.

That is often a sign of weakness to the point of poor combustion. Usually a blocked accelerator pump or emulsion tube in a carb... can you try richening it just a bit, see if it improves matters?

If not, or even also, check this out...

As far as sparks are concerned it is possibly now too retarded, a weak mixture requires a bit longer to burn... does it backfire or pop back through exhaust at all?

When you accelerate, if the vac advance/retard is working properly, the ignition will retard, possibly giving the symptons above. To test, disconnect the vac advance, don't cane the hell out of it, and not for long, but just see if that improves matters, listen for pinking and back off, then re-connext it immediately and.... >>

...suspect the timing is set wrong, but really the whole advance curve should be checked out properly... I don't know if you have vac advance as well as retard. To test I'd either do the above trick, or probably disregard any timing methods and set it up by trial and error, starting by advancing it just a bit to see... but if you haven't any experience doing this (about 2~3 degrees at a time) then get someone else to do it - but don't automatically trust a strobe or a static setting - they can depend on whether and how well the vac adv/retard system is working. Listen out for pinking when doing this by trial and error and lift off immediately (engine lid off of course).