Cutting out on 75% or more thottle

[Adammcf]

Ive done 100 miles now since putting the engine back together and still havent gone over 4k revs.
Now when I try and use anything more than 75% throttle the car cuts out for a second and the last time it happened there was a huge back fire from the exhaust. The car runs ok the rest of the time although the idle could be a little smoother.

Any ideas?!

[Ant]

Cam timing spot on ?
Any obvious air leaks ?
The poor idle could mean both, so get stuck in

Stay off the loud pedal too M8

[Adammcf]

When fitting the timing belt the TDC on the cam and bottom pulley were both lined up fine and even after about 4 manual turns of the crank it remained ok. Hopefully it hasnt moved somehow since then.

As for air leaks I cant hear anything and all the pipes seem ok.
Its a weird one.

[Toby_Unna]

damp dizzy cap?

that's caught me out before on bmws even when i could see no reason for it to have got condensation in it

can make all sorts of daft things happen including not liking too much throttle

all electrical connectors on properly?

[tourer-dan]

Check for air leaks by spraying carb cleaner around the inlet manifold joints and other air pipes. Check the metal breather pipe under the inlet manifold is correctly seated too. Did you remember to replace the o rings here?
My local specialist advised me to let my valve clearances out a bit as my engine was *too* quiet and the idle was a bit lumpy.

Why did you take the engine to bits in the first place? Is this an un-cured previous problem? Be careful of backfires as they can kill your AFM (apparently).
all the best
Dan

[Adammcf]

The old head went porous so had to change it all for a recon head.
The car idled exactly the same before the head went so maybe its a bad dizzy or rotor arm or a dodgy set of leads?
It might even be a dodge idle control valve perhaps?
Its the cutting out when getting near 75% throttle though that was worrying me a little.
Ive only done it a couple of times and it has only backfired one of those times so I'll make sure I use less than 50% throttle to be safe.
I'll give the dizzy a good clean out and see if it makes any difference.

[tourer-dan]

Don't worry about the idle control valve, as all it does, predictably, is control the idle.
Lumpy running can be compressions too, so check those.

[Adammcf]

I hope not, that will be the next problem and I'll end up having to rebuild the bottom end with new rings etc!
The idle isnt too bad to be honest, I think its the blow out in the centre section join that makes it sound worse.

[Adammcf]

Did another 60 miles tonight and the engine is getting stronger and stronger and the idle is getting better. Once I sort the little blow out in the centre section join I reckon it will get better still.
I didnt use any more than 2/3rds throttle tonight but already its feeling good and didnt hesitate once.
Fingers crossed once run in it will be fine.

[Gwynleym10]

You didn't have any water/oil/dirt in yourplugs/HT connections did you?

[Adammcf]

Nah they were all clean although they may have got dampish from sitting in the garage for the last 6 weeks.