5 GT Turbo Renault 18 turbo carburetor problems

[andyturbo2]

Hi all

After picking some brains

I have got the car running now, it has a 270degree cam, slightly oversize inlet valves. Starts well, idles from cold pulls well etc but when it gets warmed up the revs falter and it stalls.

Have an afr meter installed and when it's cold on idle it's around 14.7. When you drive it it's around 11 to 13 ( just running it in 3000 RPM rev limit, 0.5 BAR Boost limit)

I have smoked checked the xar, inlet Manifold, brake servo and associated pipework for air leaks and all is sound.

When the car stalls the afr heads from 14 towards 17 and then 20 before the engine stops.

The idle air control screw has little or no effect on idle

It's like there is an air leak but I'm damned if I can find it

Anyone had a similar problem before??

Cheers Andy

 

[Brigsy]

Clean the idle jet, and go from there

 

[andyturbo2]

Clean the idle jet, and go from there

Done that

Been doing some more investigation and tuning today, the stalling now seems to be confined to when you brake, having tested various other theories I'm left with the only obvious cause being that the fuel is moving away from the jet under braking, if I coast to a halt whilst pressing the brakes the idle stays steady. If I then brake the engine stutters and stalls.
There doesn't appear to be any adjustment for float level

Any suggestions?

 

[Brigsy]

Id say its not related to that from experience as the fuel pressure reg will keep the float chamber full. Servo would only cause an issue if its leaking and you would notice issues with the servo assistance, worth checking though if the diaphragm is not right then might be causing an issue.

Its hard to diagnose without looking but to me it sounds like the mixture is weak for some reason, air leak or whatever. Id poke a small drill through the idle jet, check the o ring is in good condition and fix the mixture screw as it should be working. Set hot idle mixture and rpm with lights on to 14afr and go from there.

 

[andyturbo2]

Id say its not related to that from experience as the fuel pressure reg will keep the float chamber full. Servo would only cause an issue if its leaking and you would notice issues with the servo assistance, worth checking though if the diaphragm is not right then might be causing an issue.

Its hard to diagnose without looking but to me it sounds like the mixture is weak for some reason, air leak or whatever. Id poke a small drill through the idle jet, check the o ring is in good condition and fix the mixture screw as it should be working. Set hot idle mixture and rpm with lights on to 14afr and go from there

I have used a smoke test machine to check the servo and the carburettor for air leaks, all ok. I have also checked that the fuel pressure regulator responds to boost and that it is supplying suitable pressure off boost which it is. I have checked the idle jet and that is clear, will check the orifice in the carb and t
he idle jet air corrector to make sue they are clean, the idle jet fitted has 41 stamped on it which i assume means 0.41mm has anyone ever fitted a larger one ?

Will do some more tests tomorrow

Andy

 

[mick]

Hi all

After picking some brains

I have got the car running now, it has a 270degree cam, slightly oversize inlet valves. Starts well, idles from cold pulls well etc but when it gets warmed up the revs falter and it stalls.

Have an afr meter installed and when it's cold on idle it's around 14.7. When you drive it it's around 11 to 13 ( just running it in 3000 RPM rev limit, 0.5 BAR Boost limit)

I have smoked checked the xar, inlet Manifold, brake servo and associated pipework for air leaks and all is sound.

When the car stalls the afr heads from 14 towards 17 and then 20 before the engine stops.

The idle air control screw has little or no effect on idle

It's like there is an air leak but I'm damned if I can find it

Anyone had a similar problem before??

Cheers Andy

Did you increase the idle jet size?
Try a 50