Turbo seems to be lacking fuel when comes on boost
Turbo Mini Forums

I am at a lost end here.

I had my engine running perfectly last year at about 7psi. It is a gt17 1293 engine with a fairly common spec of bits. You can see the details in my build thread.
Engine came out to fit a new floor and while out I fitted a new forge actuator to up the boost as the standard one was limiting to 7psi for some reason.
Everything appears to be fitted and plumbed in exactly the same as before but it isn't all working properly.

When you try to apply full throttle it just bogs and jumps around. If you ease the throttle you can just about get round this spot and get decent boost when it goes mad (as in up to 19psi if I want.)

I took it to john sleaths yesterday and we couldn't get it running. I thought it was just a needle issue but he believed it was not getting the fuel so a carb issue.

The fpr is increasing pressure as it should but I haven't had it to bits to check it's ok as john said it seemed to be working fine.
I rebuilt the carb today found no blockages or anything unusual - still the same issue when driven.

This is occurring as soon as it tries to boost at around 2500-3000rpm.

John disconnected the boost pipe to check and it still did it at about 4k rpm when running in n/a.

I have attached a link to the video on YouTube I took while it was on the rollers.

https://youtu.be/16zSkDaIJqY

Any ideas would be appreciated.

Thanks

carb ? dashpot ok ? springs ? oil ?

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

All fine rebuilt carb today still the same same with or without dashpot oil and with the spring that was in it or with a green spring

What pump, fuel filter and regulator? Can you measure the fuel pressure?
Did the rolling-road track AFR ?
Does it rev out when not under load?

Edited by PhilR on 18th Jul, 2015.

Revs out fine when not under load. Was a bit of old fuel but fully topped up with v power before rolling road.
It's a copy of the Bosch 044 I think. Afr's were ok I believe.
Fuel pressure was tracked too that increased up with the start of boost then obviously just dropped with everything else.
Just a standard fpr. Was something like 6.5psi then rising. Would only boost about 3psi max before it cut.
No smoke or anything from exhaust.
Ran an extremely rich needle and it still did the same at exactly the same point

it held 6.5psi fuel pressure without boost ?

Sounds like a lot.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

I'm sure that's what the computer said rising to about 10-12 psi I think when the boost tried to come in.
I might be wrong but think that's what it was.

Forget the FPR it has no effect on the fuelling. It's only there to keep the float bowl topped up.

In the video it just seems to hard stop. What ignition system are you using?

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

Edited by stevieturbo on 18th Jul, 2015.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

I know it is going lean because the afr show it goes way lean at the point it jumps about in the video.
The ignition is megajolt and runs fine you can see it follow on the megajolt it jumps back down on the values and then tries to build again but can't.
The spring I took out before I went and replaced with a green spring but sleath reckoned the original had a better feel so swapped it back. It does look a bit fucked though see the photo here

"In short" Make sure you've Not got a low figure soft cut rpm setting in the megajolt software. . . . And search the T piece trick and implement That on the Carb.

Edited by BENROSS on 19th Jul, 2015.

That spring looks knackered. It could be binding.

Rpm cut is at 6500 it is obviously happening before that as it will Rev out to that with no load

Is there any reason why the car ran perfectly before without the t piece trick and would need it now?

On 19th Jul, 2015 bakker110 said:
I know it is going lean because the afr show it goes way lean at the point it jumps about in the video.
The ignition is megajolt and runs fine you can see it follow on the megajolt it jumps back down on the values and then tries to build again but can't.
The spring I took out before I went and replaced with a green spring but sleath reckoned the original had a better feel so swapped it back. It does look a bit fucked though see the photo here

Edited by stevieturbo on 19th Jul, 2015.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

It had 20w50 oil in to start - same problem
Then proper su carb oil exactly same
Afr were off exhaust probe on the rolling road and on gauge when I've checked.

With the megajolt you watch it go up with the Revs and load and then when you can see the car jerking the green advance value that follows it around dropped a row on the vertical scale (as in down in load not down on the table) then it makes a sort of anti clockwise recovery and kept doing it.

I'll try it again with a different spring but can't imagine it makes a difference as it didn't before.

swapped the plugs? checked the gaps?

plugs can be a PITA, if you have two that are going down at the same time, they could knock the spark out on the other two due to being wasted spark, unlikly, but one to rule out,

also, is it leaning out then cutting out? as this does point to fuel... or is it cutting and leaning at the same time? as that points to the spark.

Yes i moved to the darkside

Instagram @jdm_brett

Have you checked the trigger wheel is in the correct place and the MAP sensor is working correctly and has no leaks in the pipe.

Are you using an EDIS? If so, try another one.

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

Ok I'll try the t piece thing is it just a tee between the plenum and the take off the carb just in front of the fuel supply then into the fpr as usual?

Trigger wheel is fine never been touched. Carb was rebuilt so nothing is blocked.
Edis is working. As said it is drive able around this point but if you want it by using full throttle you can't.
It's not cutting out it just leans right out then tries again like it ends up kangarooing down the road.

Ok for the record I have done the t piece trick first time it seemed to piss fuel everywhere out the plenum which I didn't think was good messed with fuel pressure regulator a bit as it was really bad on idle although I have no gauge to check it seemed ok.
The fist video is pre t piece trick

https://youtu.be/9qZSHQjvtfM

This video is a little drive after. Well it is much smoother and doesn't jump around but it still goes really lean at the low revs when you floor it.

https://youtu.be/_oSsK4whdo4

By the way I was meant to add

Do you think it is fixed and the rest is left in the needle?

Bump anybody got any thoughts on the latest? I just don't want to go back to the rollers and waste my time and theirs if it is more than just needle fuelling still.

Some thoughts. 1500 rpm full throttle is not a part of the map I would normally be on, but for mapping purposes it needs sorting. I would think the main problem is the needle needing to be whittled down a bit, however it might be worth trying some automatic transmission oil in the dashpot, as it's lower viscosity, but doesn't change much with temperature. Should allow the needle to lift a little faster.

'Where does the engine go?'