Hif44 Mixture Screw
Turbo Mini Forums

The engine is back in the mini now and its changing gear fine.

I have taken it for a drive twice now, and after about 30 seconds to a minute it becomes very jumpy and will not pull in low down gear, (barely pulling in first) making strange noises etc but no backfiring.

Its running a megajolt and we have checked we are getting a spark and all seems to be fine.

This is what is a little confusing, my first thought was electrical but all seems to be ok on that side of things.

I think i may just try to weaken the mixture a touch at a time and see whether it helps.

The problem here is that when being rolling roaded, with the old head (pretty much a standard mg metro head) the fueling was set with a needle which was pretty much a standard needle to get it about right, (this was done at slarks) now i have fitted a much better head, much larger valves etc so I would have thought it would need more fuel not less?

Can anyone shed some light?

Does this mean that it is overfuelling?

Can i just turn the mixture screw half a turn and try again to see if it is any better?

Thanks

Jon

the mixture screw will only effect idle.

to effect mixture during running, the needle profile and spring should be looked at. all else equal that is.
open to correction though.

if the megajolt is ok and the map ok on the rollers when it ran fine, with the other head
richen the mixture a full turn in see what happens
is the plugs sooted ? or white ?
you will be able to get the mixture somewhere near using the screw, it does affect this throughout the rev range under load, but highly tuned motors requires the needle profile altering, most .... but not all !

I have turned it, i.e. making it more rich and it seems to run (a little) better. Prob about 1/2 a turn.

I am also running a BDL needle, i think this will make it run far too lean.

I do have another needle which is BBW, do you think sticking this in will richen it up.

What I am trying to do is run for a coupe hundred miles and then take and get fully set up on the rolling roaded.

The plugs were slightly sooted, but after running I would say they are turning slightly grey, does this mean anything?

Thanks

Jon

if you have just swaped the head and all was well before with the megajolt on the problem will lie with the mixture

we are talking here a turbo engine?
if so you want a BDD needle in and adjust the mixture to get the right co

i would get to a RR sesion ASAP john
what cam have you in ?

Hi

The BDL needle seemed to be running it too lean, the plugs were turning a white colour.

I have put a BBW needle in and they are now Brown, so a good sign.

The car does however shudder, seems to run ok at idle but shudders quite severely under acceleration.

Could this be valve clearances?

What I am trying to achieve is to just get the car running well enough to complete a 100 or so miles before i get it rolling roaded.

Thanks

Jon

Has anybody got a wideband nearby to check it's fuelling ok whilst you run it in? It will put your mind at rest that's it not fuelling incorrectly if so you could find the problem before the rollers.

Have you checked the gap on your plugs Jon?

If something is worth doing, it's worth doing half of.

i would suggest thicker oil in the dash pot, after a plug gap check, if the plug gaps are right try closing them up a bit if it improves the coil may be dying

it also sounds like it could be leaning out way to fast thicker oil will give more fuel under acceleration

Yes i moved to the darkside

Instagram @jdm_brett

Good call Brett.

If something is worth doing, it's worth doing half of.