Stalling after boost when throttle lifted - Help
Turbo Mini Forums

Howdy,

So I noticed that when I warm her up, she runs great.
Say I am at the lights and nail it in first, get on boost, then hit the anchors and clutch she stalls. Doesnt matter what gear really, but say you are cruising along, nail it, boost up, then hit the clutch and brakes and stop it either wants to stall or does stall...

Any ideas?

Peter

1132cc Turbo ~120 bananas ATW - Fun Fun Fun

it sound like its linked to you head gasket problem. both linked to not running right.

You mean the tune or something else?
Only blows headgaskets at 15psi but this happens even at 8psi

Could too rich a mix cause this?

Peter

1132cc Turbo ~120 bananas ATW - Fun Fun Fun

May be telling my grandmother to suck eggs,but check that the SU piston(are you on a Carb?) is not sticking.If it sticks,the engine rocking as it stalls usually vibrates it down.It may only happen after WOT.

Edited by Brett on 14th Aug, 2008.

Yes i moved to the darkside

Instagram @jdm_brett

Carb was rebuilt - and cleaned. Hmmm, piston was a little sticky.

Thanks, ill check it out!!

Peter

1132cc Turbo ~120 bananas ATW - Fun Fun Fun

You seem to be saying this happens when you brake..Do you have a brake servo? if yes then the vacuum lines to it or the non return valve??

website:- http://www.terryhunt.co.uk

Hi Turbo Tel, no brake servo mate...

Its odd, it doesnt do it absolutely everytime, seems to get better after driving a long time on and off throttle (ie in traffic) and only when I nail it, then basically pull her up and dont touch the throttle again...

1132cc Turbo ~120 bananas ATW - Fun Fun Fun

maybe your slow idle is slightly to low or the fueling is not quite right at idle id guess its slghtly lean

Just thought also does ur vacuum advance work maybe its stopped pulling in the timing

Yes i moved to the darkside

Instagram @jdm_brett

your mixture is too lean at idle or low revs or the carb piston is sticking/or returning too quickly (spring too heavy) either way there isn't enough fuel by the sounds of it. Do you have a float chamber extension on your carb? If not get one - this will make sure you always have sufficent fuel in the carb. Most likely you have a sticky needle valve in the float chamber - the hasty braking will cause it to shut, killing the petrol supply - so check this out first. After that it's a trip to the rolling road to make sure your needle/spring is right. Good luck. Philtune.

had a similar problem on a 200sx. turns out the dump vavle was shit! let to much air in and cos the same probs as you have

Yes i moved to the darkside

Instagram @jdm_brett

dont have the car any more, but once the dv was removed it was fine.

i wouldnt bother with a float chamber extension. dont know anyone who's needed one.

mine seems to be fine without it.

i would go with a sticky DV to be honest

My mini has been doing exactly the same thing too. Removed the dump valve and carried on stalling at low revs after i nailed it. Can just manage to hold it if i blip the throttle but then takes an age to start again once it has stalled...

Re float chamber extension - all racers use them (maybe no use on a road car?) but don't forget most Turbo'd A-Series dont have a swirl pot so fuel is fizzing, and coupled with the huge heat build up you get massive evaporation if you are running on the lean side. The extension means there is more fuel to heat i.e. bigger heat sink. Without knowing the specifics of Pristic's set up, it is very difficult to know exactly what is causing his problems. But he needs to check his mixture/fuel delivery. Philtune.

Cant honestly say I'm convinced on the need for float extensions for most road applications.. I'm running a T piece fuel return (possibly lots of airation) and its nearly always in the mid 90's here, yet no boiling fuel!!

However agree on the fuel delivery theory's,
Could you regulator be the problem? if you nail it and the fuel pressure is not rising enough the level in the float chamber would be lower than it should until the boost drops and the pump can catch up.

Same thing if the lines are restricted in any way, or the float valve is gunged up. It would be Ok until you start using a lot of fuel (nailing it!) then the level would drop a bit and that may be what you are seeing..

However, I would have thought you be seeing this in the AFR's under boost especially if you hold the boost for a while??


Terry

website:- http://www.terryhunt.co.uk

Just checked out your last few posts, seem to have had problems with vacuum leaks etc, sure they are all fixed??

Also whats a Pulsar dizzy? does it have vac advance?

Terry

website:- http://www.terryhunt.co.uk

The ambient temperature in USA or UK is not significant. The fact that the float chamber is directly above the turbo is the problem - local temperature!!!!! If the fuel gets too hot it then evaporates the moment it exits from the jet into a hot carb mouth. If there is insuffieint fuel at that point as well, then hey presto no fuel into the head and the loud pedal has no affect. Might be worth investigating the regulator as suggested. If you haven't got a fuel pressure guage this may not be easy. But essentially you need to make sure you always have at least 4 or 5 psi of fuel pressure delivered to the carb above the boost pressure - then you won't run out! Don't forget to check the needle valve as a number of us have suggested. Philtune

Ambient temps not a factor? Interesting..

All I am trying to say is that before you waste your cash on a float extension look elsewhere, there are plenty of people that do not use them and do not see any problems.

My carb does not get very hot even after a full boost drive because of the air flowing around and through it. When it does get really hot is after its sat for a while and the hot turbo and manifold gets a chance to heat it up.

Maybe you could fabricate some kind of heat shield for the carb? it will reduce any possible heat problems and prove a point. Just a piece of alloy with maybe some sticky heatshield cloth will reduce radiant heat and be a far cheaper alternative.

website:- http://www.terryhunt.co.uk

Thanks!!

A few answers to your questions and comments.
1. Float is not getting too hot, Turbo sits over clutch housing not behind motor.
2. 4-5psi constant fuel pressuse and running a Malpassi Rising rate reg...
3. Forget the pulsar dizzy thing, its gone, running Megajolt V4 now. (FYI Pulsar dizzy is a Modified curve off a Nissan Pulsar with a mini drive dog on it. Quite a few guys with N/A motors running pulsar setup down here.
4. Vac leaks all fixed - was a crappy BOV which I replaced with a turbosmart type 2 vee port.
5. A/F readings are steady on boost and all sorted after rebuilding the carby.

Might be a sticky float or piston/needle.

Noticed it happens more when its cold weather and motor not fully warmed up, I dont nail it when its not warmed up obviously.

Its really cold here at the moment (well, for Aus anyway)


No.1Racer, mine will stall and I can hold it if I blip the throttle too, but if it does stall completely I can start again no problemo... sometimes get a backfire through the carb, but I think its just excess fuel.

Overall, she is running on the rich side now...


Peter

1132cc Turbo ~120 bananas ATW - Fun Fun Fun

All of what you have just said convinces me that the SU piston is sticking a little open when you lift off.Have you had a look yet ?.Although all SU experts issue dire warnings about cleaning piston or the inside of the vacuum chamber I have always given them a quick rub with metal polish.

when I lift the piston up all the way and drop it, it comes down ok and at the very end seems to 'stick' a little before dropping all the way. Like it 'catches' a little.

What do the others reckon? Clean the piston and vacuum chamber? It was cleaned with carby cleaner only, no rubbing at all.

Pete

1132cc Turbo ~120 bananas ATW - Fun Fun Fun

Does it do this with the chamber and piston off the body of the carb, ie eliminating anything sticking on the needle?
If so and it only "catches" at the bottom, it sounds like there's a little distortion, or a high spot, at the bottom of the vacuum chamber.
I would use something like "engineers blue" to try and find where the contact is occuring and use some "agressive" cleaning just in that location.

Schrödinger's cat - so which one am I ???

Sounds to me like you have found the problem.Now just do what Rod says and your troubles should be over.