Bit of an air leak

[twistednuts]

Think ive got an air leak somewhere, bit of slight revving going on after throttle shut off, and general funny firing noises. Plug is lovely and brown though.

Im going to try raising needle to see if it corrects it for the time being. Is it worth altering oil pump to allow a tad more oil in so i dont go oil lean - or will one notch make that much diff?

[knackeredMk1]

Increasing the oil into the cylinder will lean the burn because there will be more hydrocarbon in the charge. Depends on the quality of oil used. Fully synthetic will make almost no difference but cheapo mineral will have a significant effect.

[helisupp]

The needle obviously did not lower itself, so why adjust it to cover up a defect elsewhere.

Is airscrew adjusted correctly when hot.

[twistednuts]

I'll have a gander at the air screw. Thought that only did first quarter of revs though?

Irony has now set in - I have time to play and mess with it, but its peshin down!!

[fallenmikethebike]

Make sure the throttle is closing smoothly and fully, frayed cable, throttle housing biding?
Can you hear it bottom out in the carb?
Mike

[helisupp]

You said "after throttle shut off" which is less than 1/4 throttle. Its nothing to do with revs.........

Somethings changed to make it do it as airscrews are not adjusted on a regular basis.

I would say too much fuel, so check your needle and jet for groove or wear, to rev it needs fuel and it seems to be getting too much

[knackeredMk1]

To be devil's advocate. The 'running on' could well be due to running lean and slight overheating. I have known this condition to occur when the weather has taken a turn to being colder or when a slight air leak has started.

You might be able to 'band aid' it with the air screw or by raising the needle BUT this is only temporary and you need to sort it FAST before it gets bigger.

[fallenmikethebike]

There is the trick for testing the inlet manifold by spraying with WD40 type oil, and see if that cures it temporarily.
Mike

[twistednuts]

Yeah heli, i get your point about the air screw. I'll check it out.

The reason i mentioned raising the needle was to confirm too much air, i kinda reasoned if this ironed out the revs it would point to an air leak. If it makes it worse it points to too much fuel.

Yeah mike, was gonna do that too. Just waitin for the rain to stop!!

Its only a temp thing to find the fault.

It deffo sounds lean when it does it - its the same as when petrol goes onto reserve.
I dont think its an over heat thing knacked, it does it with a cold engine. Does get worse after a good blast though.

[fallenmikethebike]

What condition is the filter in?
It needs to be sorted sooner rather than later, you'll end up with the dreaded death rattle of the engine due to run away RPM's otherwise.
Mike

[knackeredMk1]

When an engine runs lean it by definition runs hotter. This is what gives the auto ignition and allows the engine to run on.

When it is bad the engine will continue to run without a spark but when only a little it will make the engine 'hang on' to revs when the throttle is closed.

[twistednuts]

Ok knacked, it is only very slight though - it doesnt run on for long, a split second.

Air filter is like new, clean and well oiled.

Gonna needle it and report back...

[twistednuts]

Oh bugger, think ive made a schoolboy error. Checked air screw an its nearly 2 turns out

Not sure how sensitive that little screw is, but hopin its done the trick. Not had chance to check yet