Rough Running/ won't idle
Turbo Mini Forums

Morning folks- apologies for the long post!

Kind of following on from my question last week about where you should connect the Megajolt MAP line to…..

I've been building a Metro Turbo engine (albeit in a MG Midget) over the winter and the time came to try and start it at the weekend :)

So built up oil pressure etc, put the plugs back in and reconnected the Megajolt coilpack & crank sensor. Started first time! YIPEE I ran it for 20mins to bed in the cam & followers etc. while it was warming up I was checking for leaks, oil pressure good (60psi @ 2000rpm) no overheating, sounded a bit rough- I just put that down to carb needing adjusted and there was a slight hint of the exhaust blowing somewhere, turbo, downpipe elbow or downpipe I think. All good I thought!

But when I came to turn down the idle speed it wouldn't idle and was running like a bag of sh*t!
The Megajolt seems to be keeping it running but like I say revs are all over the place.

Everything is either new or rebuilt, carb, cylinder head, turbo, etc. etc.

Engine/ car spec as follows:

1293cc with 10cc omega cast pistons
Piper phase 2 cam (timed in at 108 deg)
Megajolt ignition- Loaded with std Metro turbo Map and connected to inlet manifold where the brake servo bolt is (along with a boost gauge)
Metro Turbo head with 26 or 28cc chambers- can't quite remember off the top of my head, new valves springs etc & converted to unleaded
std T3 turbo & cast manifold as per metro turbo
std Metro turbo carb fitted with a BDD needle, part throttle lean off blocked off, carb vent port blocked, oil in dashpot
Std Metro Turbo fuel pump & regulator, supply & return fuel lines 8mm

This is where things change slightly....

I had the inlet manifold modified- faces that bolt to the cylinder head were skimmed at a very slight angle, so it would allow the carb dashpot to clear the underside of the bonnet- MG Midget has a really low bonnet & I didn't want a bonnet bluge/ scoop!

Also I am in the process of getting the plenum chamber modified, again to clear the bonnet.

I should point out at this point, due to my shear lack of patients, while I was running the car and all the various tests/ checks I’ve done over the weekend the plenum was not fitted- I was going on the assumption that the turbo carb would act like a NA carb at idle/ low revs i.e. until the turbo came on boost.
But I could be wrong!??

The Megajolt had been fitted to the car last year while it was still the std NA MG Midget 1275 engine as was working perfectly.

I have checked the following:

Sensor position for Megajolt, static timing if you like, so that was a tooth out- NOW SORTED, sensor 90 after missing tooth on crankshaft pulley
Megajolt plugged into laptop and working properly
Valve clearances
I've still to do a compression check but that is my first move tonight.

So after my essay!

My thoughts are:

Head gasket blown- will be confirmed with compression check tonight
Metro turbo engine will not run properly at idle/ low revs with plenum off?
Leaking manifold gasket- this is my favourite, bearing in mind the slight exhaust blowing I’d heard & that the inlet manifold has been skimmed slightly!

Any other suggestions, thoughts, comments???

Again sorry for the long post but thought I’d give as much info up front as I can!

I reckon your bang on. Leaky manifold gasket.

With the inlet skimmed, the flanges will now be thinner than the exhaust flanges and won't clamp properly.

Also if the inlet is skimmed at an angle, the bolts/washers will be tightening against an angled face.

In the 13's at last!.. Just

I concur, manifold gasket/mounting

The carb will work without the plenum no problem. But for final calibration of the idle fuelling best that it's all connected up as it's to be.

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

cheers for the replies so far.

I should have said I did make up "special" washers to try and take into account the different angle of the inlet manifold to exhaust manifold but I am starting to feel they are not spot on..... :(

I might take the head off and put on a new manifold gasket but bolt the manifolds to the head before i refit the head with a new gasket to???

The other thing to consider is that the manifold is pretty tight on the exhaust as it is. So the two manifolds may be fouling leaving the flange and head not mated.

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

Wil

I had wandered how close the manifolds got, hence my thought of removing the head and refitting the manifolds to the head while off the car.

Ok did comp check, 190psi across all 4 cylinders give or take a couple of psi.

.........

MASSIVE manifold gasket leak! Doh!

As Wil suggested inlet manifold hitting exhaust, so out with the Di-grinder.

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that is quite some leak.. good skills

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Yes i moved to the darkside

Instagram @jdm_brett

Just about done, waiting for a new Payne head gasket and hopefully all will be sorted.

Can’t actually believe it ran like that either!

Oh well one for experience I suppose.

All sorted, MASSIVE improvement just need my plenum back, connect up the intercooler and do the final adjustments.

Cheers for the help and advice guys.

Good stuff, glad you have tracked down the problem.