Leaning off problems while boosting with T piece trick in at vmax rolling road with Stuart
Turbo Mini Forums

Hi All,

Bit of history. I had the car MOT'd at SRE and Neil attempted to set the car up however I had an issue with the clutch slipping so I had to come away and sort that which I did. It turned out the lugs on the back plate needed machining.

Slight problem today. I have run the engine in now and spent the day with Stuart at vmax scart (as he is nearer to me) to set it up on his rolling road.

I knew the car had a bit of a fuelling issue under load and thought that this would be rectified once set up.

However once there and on the rollers the carb seemed to be misbehaving with leaning out. After a lot of head scratching and trying different things we tried the t piece trick to no avail.

Only thing for it was to strip the carb. Stuart cracked on with other work while I used his tools (thanks Stu!) and got the carb on the bench.

Stuart could not see anything thing untoward but changed the float valve and checked it all over. I put the car back together and connected everything with the t piece trick. Back on the rolling road the car was fixed, 130bhp at the flywheel happy days.

Then Stuart put the pipework back (taking the t piece off and blanking the lean off pipe and would you believe the car started to lean off again under boost so we put it back again but the problem remained.

Throughout the day Stuart modified the standard BDD needle and in the carb is now two springs one green and one yellow.

It holds to 12.2 air fuel ratio then leans off so much that the engine cuts out.

Any thoughts would be great; the only thing we can think of is trying a different carb and changing all the pipe work.

Fpr knackered? Pump failing? Clogged filters?

Sorry what’s fpr?
We checked the fuel pressure under boost and it increased with the boost so no problems there. The filter does need changing Stuart said as it is the glass type and not recommended and a little dirty.

Im also running this coil, http://www.minispares.com/product/Classic/.../coil.aspx|Back to search
Is this the correct one? Im not running mega jolt.

Fuel pressure regulator. What about when it was leaning off? You've checked the carb so start working backwards, remove the filter and see what it does, then check fpr, fuel lines etc.
The coil is fine, that won't be contributing to the leaning off.

Have you got the restrictor in the plenum?

Is the part lean-off pipe free of even a small split?

I'm not sure how two springs will help. It'll hide an issue and bugger your fuelling, actually making it leaner under steady load, but will make it richer under transient loads.

I'd go back to a standard spring.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Of course sorry its been a long a day.

Good news regarding the coil then.

The fuel pressure was fine when it was leaning out.

I wish i had taken the fuel filter out when i was there now. The pipes we changed with new ones that Stu had in the workshop.

I guess i am going to struggle to know if i have sorted the issue with out actually being there on the rolling road. Last thing i want to do is damage the pistons and melt them!

Plug gaps ?

"So wat we gonna do tonight Brain?"
"Same thing we do evernight Pinky!"
"Try to take over the world!"

The part lean off pipe is fine all new.

The spring business im afraid to say is over my head. I'm no expert in this field and have no option but rely on help from you guys and Stuart.

The restrictor in the plenum, I know there is a pressure spring valve in there which has been removed. Is this what you mean Wil?

Could this be a problem concerning the bi metal jet holder?

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=311

Hi Sprocket,

That makes an interesting read, its a shame that the pictures are no longer on the thread though.

Not sure if that would cause the issue i have or not.

If you are relying on the AFR gauge to tell you that it is running lean then it can mislead.

Two years ago I had the same or similar probs and it was the plugs fading. Uncle Robert patiently explained to me that the Lambda sensor is an oxygen sensor and if the plugs are not working properly there will be more free O2 in the exhaust. The engine falters and will eventually cut out because the plugs are U/S. In my case it was because I used the wrong plugs (stupid boy) but even the right plugs can give up sometimes.

I hope it is that simple for you, but at least its no big deal just to change the plugs to find out.

Hi Tadge,

Im not sure if it is just AFR guage that Stuart uses to check the running but my guess is his guages should be ok as he uses them all the time to set cars up.

Might be worth swapping the plugs and checking gaps though.

Thanks

I think you misunderstand what Tadge is saying. It is not the gauge that is at fault, just the limitations of it's operation. Like any measuring tool, you need to understand what it's limitations are to be able to use it properly. Stuart is only likely to be using an Oxygen to monitoring AFR.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Sorry yes your right, i read that wrong and understand where Tadge is coming from.
What plugs do you guys run and i'll get some and swap them out?

hmm a lean out on boost to the point where it cuts out??
without blowing the engine up??

this sounds like the float bowl is emptying for what ever reason

and i run NGK BPR6ES plugs mine, engine is fine with these up to 22/23psi and more with water/meth

Edited by Brett on 11th May, 2013.

Yes i moved to the darkside

Instagram @jdm_brett

I should confess properly. I used some "soft" Champion plugs to run the engine in and, stupidly, forgot to change them.

In an attempt to find the problem I enlarged the fuel tank outlet, changed pump, filter carb and FPR all to no avail, I then drove it to Dundee and back (900 miles) and to Rotterdam and back (another 900 miles) all staying off boost as it would not take it, of course.

All because the plugs were fading because they were the wrong type, which Robert spotted in about 10 seconds.

I,m not suggesting that the plugs in your car or anyone elses are the wrong ones, just that if they start to fail they can produce the symptoms that we are discussing, and this can be very puzzling, given that it shows up as lean mixture.

There is no harm being done to the engine as it is not running lean and that same engine has gone on to do about another 8000 miles, including achieving my ambition at Avon - 15.9/91.

Sorry to go on about it but it did occur to me that it would take no time to see if it was an answer for you.

BTW, those two trips I mentioned averaged over 40mpg - just shows what throttle restraint can do !.

Hi Brett,


Well it’s not actually to the point that the engine cuts out. Its starts bogging down and leaning off. Stuart said it would melt the standard pistons in seconds if he took it any further.

Going back to the springs in the carb, I think the reason we ended up with two in there was because when we were trying different things, with one spring Stuart ran the car up with the dash pot plunger out and when the engine started to lean off the piston in the carb rose to the top of the carb he asked me to gently press down on the piston and the engine picked up again.

Although it’s rather a pain in the arse and an expensive one it’s a massive learning curve.

Thanks Tadge,

I will check the plugs this morning and see what they are. Pretty sure they are the ones the standard metro turbo uses.

I see your down South, are you doing the London to Brighton run next Month

Dont just check that they are the right type, which they probably are - fit new ones in case they are failing.

Stuart was quite right that IF the car was running that lean it WOULD melt a piston, my point is that my car had all the same symptoms but was NOT running lean.

Another confession - I dont drive a mini.

My car is a 1959 Austin, rear wheel drive model A35 - most people consider that I am totally off my trolley turboing such an ancient piece of automotive history, designed in the middle of the last century, but I do like to be different.

Next project is a clone of the car on a van version of the same, presently rather stalled awaiting paint.

Tadge, sure will!

That sounds awesome, have you got a pictures?!

The search button is your friend, as they so often say on here.

I,m not trying to sound clever as I,m not and have demonstrated this in this thread,(and elsewhere on the forum !) nor am I suggesting that this is the only possible answer to your problem. but I thought it was worth considering.

I have relied for some years on the goodwill and knowledge of others on here,who have supplied any knowledge that I may have on turbo A series.- and they have been very patient with me !

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Where are you at 1275min I am over in Brookwood just past Woking.

I have started posting on Instagram also my name on there is turbomk1golf

Nothing is impossible it just costs more and takes longer.

Not far madmk1 I'm in Frimley.

Shit the bed your not!! T@z is over there as well.

I have started posting on Instagram also my name on there is turbomk1golf

Nothing is impossible it just costs more and takes longer.