Crank case seals ......

[westy66]

Hi Chaps,

I still have had some problems with my 92 Mk2 being slow to drop the revs (not a problem at rest when blipping the throttle, but it appears after riding it for a distance on full'ish throttle - say a mile or 2). The bike had been stood for a long period (at least a year in a shed) when I got it so I got round to thinking maybe some of the rubbers have perished due to age and inactivity.

Thinking it was sucking air from somewhere (as these forums confirm), I have changed the reed block rubber, gasket and cleaned and put the carb back to stock settings, but it still hasn't made a difference to the revs dropping, however it does start now (which it wouldn't do when I got it).

One of the local TRF boys who has raced a lot of 2 stroke motocross suggested the crank seals maybe on their way out as the symptons (poor starting, revs slow to drop after riding) sound very much like his bikes with blown crank seals have in the past. It does seem logical as if they are sucking air it would accumulate in the crankcase and as it burns off the revs would drop accordingly.

I am going to take off the flywheel cover and see if any oil is leaking from behind the flywheel which would confirm it. Pleasingly it doesn't seem to be burning gearbox oil. Are there any other quick checks I can do?

So 3 questions really:

1. Has anyone else come across the symptons of knackered crank case seals - if so what are they?

2. Can I do it without stripping the engine - maybe the nice engineers at Honda are clever enough to have designed it that way?

3. Am I looking in the wrong area altogether and could it be starved of fuel from something like the float height being wrong and it only shows up when on main jet for a sustained period? (or it this a red herring?).

Thanks in advance - Westy

[knackeredMk1]

Before you get into splitting the crankcases -

It sounds like you are running a bit lean. Have you tried replacing the pilot jet Possibly with one a size larger. Pilot jet problems are quite common on CRMs and it maybe that your pilot jrt is just a bit clogged after laying up.

[marve114]

i get this with my mk2 some times i put it done to tescos fuel

i notice it most when i stop at lights and the tick over just hangs up a bit but does eventually come down
my bike is pretty stock apart from a full dep system

[westy66]

Interesting, mine is stock apart from a DEP pipe!

I wish I could find someone with a standard Mk2 carb spare, I'd drop that on it and see what happens.

hmmmmm ..... off to the for sale / wanted board I think



So, if it is crank seals I've got to split the engine then?

[knackeredMk1]

Yes. - You have to split them.

[fallenmikethebike]

Go with NKMK1 advice first off.perhaps wind in the mixture screw a tad .
what plug you running with?
take the slide body out and check around the bottom for roughness, especially at the point where the tickover screw makes contact with bevelled cut away, it may be heat is making it hang up just a fraction.