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[10R_fettler]

[Wheeltrax]

Hi Rich, Have you checked the condition of the carb to engine rubber?
If it was split, for instance, it can seriously f##k up fuel delivery.
Im no mechanic but it might be worth checking it out.
Also, have you checked the compression?
2 strokes have a habit of eating pistons, rings, bores.

[tingy]

does the exhaust have a baffle in it? i had similer on my DT50 and the baffle was massively clogged up

also are you running it on premix or does it have its own 2 stroke oil pump?

cant say for definate on yours but when RD crank case oil seals are gone it will spit large amounts of oil out the exhaust so when it is running give it a rev with your hand behind the exhaust and see if loads of oil spits out

2 strokes are very simple so even if you need to take the engine out to check everything inside is ok it shouldnt be a massive task

[10R_fettler]

Hi Rich, Have you checked the condition of the carb to engine rubber?
If it was split, for instance, it can seriously f##k up fuel delivery.
Im no mechanic but it might be worth checking it out.
Also, have you checked the compression?
2 strokes have a habit of eating pistons, rings, bores.

Thats a good point about the inlet manifold rubber but its in perfect condition. I am wondering about the piston rings, as I havent had a compression test done. The piston crown looks normal (as far as I can see down the spark plug hole).

[10R_fettler]

does the exhaust have a baffle in it? i had similer on my DT50 and the baffle was massively clogged up

also are you running it on premix or does it have its own 2 stroke oil pump?

cant say for definate on yours but when RD crank case oil seals are gone it will spit large amounts of oil out the exhaust so when it is running give it a rev with your hand behind the exhaust and see if loads of oil spits out

2 strokes are very simple so even if you need to take the engine out to check everything inside is ok it shouldnt be a massive task

The inside of the exhaust is very oily but it doesnt spit oil out when running. Trials bikes use premix (about 70:1 or 80:1 ratio) and I'm using the correct oil. I dont know weather it's premixed petrol or gearbox oil that's fouling the plug. It will be very easy to do the rings and also quite easy on this model to do the crank case oil seals. I can check for vertical play on the big end if I do the rings i reckon and it wouldnt harm to do them anyway. Just not sure what try first as I cant help wondering about the spark.

[NinjaTim]

The weak spark could definately point towards the stator plate and is worth checking out first, I had a Honda CR125 mx bike that behaved very similar and replacing the stator plate cured it.

Everyone here has come up with viable explanations and it is also worth pursuing anything that points toward an air leak problem, ie crank case seals as you suggest, you sound as if you have a good understanding of how a 2 stroke works with what you have already tried so personaly I would be looking at the stator and anything that is interfering with the needed crankcase pressure, oh and do a compression test so you can rule out piston rings.

The exhaust is going to be oily with any 2 stroke thats not running correctly, its possible that a clogged silencer packing could interfere with the back pressure so that could be looked at but I would defenately be looking at the cause of a weak spark.

[Andy J]

is the carb float height correct, thus all the bowl fuel is used before it reills, I've seen it many times, albeit your problem seems to be at both ends of the revs  .

[10R_fettler]

I think the float is working properly Andy. To be honest it looks like no-one has ever touched the carb and it wasnt very dirty. I forgot to mention that - sorry.

Thanks for helping guys, I appreciate it. I'll test the stator now as i've just searched google and found the the readings it should produce on a multimeter.

This is something I haven't done before and all the tutorials show it being carried out with the stator removed form the bike or whatever, but..can I test it without removing the flywheel by just tracing the wire out of it up to the connectors under the tank? 

[NinjaTim]

I am not sure, I sent mine off to www.westcountrywindings.co.uk and they tested and confirmed it was fried, was a long time ago (13yrs or so) but I remember them being very helpfull

[Andy J]

it's the height of the float that's important as if it's too low at high revs you can drain the bowl before it can refil. Also check the valve under the float as the slightest bit of dirt or jel formed in that channel can cause problems

[r1ninja]

Have you checked that you have compression and  the reed petals aren't chipped or cracked

[HoodyZX10r]

Hi mate had a similar experience many moons ago with a stroker, stator side crank shaft seal was drawing in air. Died as you picked the revs up. Once it started to go it deteriated quickly and was very hard to start, would barely run. However i can't remember the piston being oily, but maybe its the clutch side seal gone aswell but then they tend to smoke! If your pulling the flywheel and the stator you should be able to have a look at the general condition of the seal? Has it been stood a while?

 hoody 

[ZX10R-RACER]

a lot of guess work going on here ..
these have a weak spark anyway its not like a really old bike where u see a big fat blue spark.
if the plug is oiling up either your mix is way to rich or u have a crank seal leaking , nothing else it can be.
If it had an air leak it would keep reving on its own and/or run lean.
I take it this is pre-mix? if so what oil u using and how u mixing it?
I ask this as i deal with modern 2 stroke mx bikes for a living and everyday i get some describe the same problem and 9 times out of 10 its an incorrect oil/fuel mix thats to rich and it just keeps oiling the plug.

[10R_fettler]

well, i've been so busy lately that I havent been on the forum for a while or even had tim to investigate the stator but here's an update:

I found the fuel tank cap breather hose to be blocked and hoped that might have been the silly problem but it wasn't. At the same time I put another brand new plug in and fresh fuel.

Racebikbitz: I use Ipone semi-synthetic 2 stroke premix oil at a ratio of 80:1 (a lot less oil rich than a motox bike, but it's what my sherco owners manual states). So I normally add 62ml of oil to a 5l can of super unleaded and shake it up for a minute or two. The reason I use semi-synthetic is that I think it burns better at lower revs than fully synthetic and results in a cleaner running trials bike. On my old priller rs250 i'd use fully synthetic, which is better on higher revving 2 strokes. Would you say that's right?

Anyway, I'll find some time to take the bike to bits and I'll do the crank case seals and rings while i'm on with it.

Ive given you all a BHP for your help...Thanks everyone!

[Wheeltrax]

M8, if youre delving into the engine it might be worth a full strip down and rebuild.
Peace of mind alone it would be worth it. You can bet that some other prob will arise soon if you get this current one sorted.
2 stroke need much more tlc than 4 strokes so do a rebuild and start with a clean slate.
Another plus is youll know the bike much better and be able to pin point issues much easier.