Clearing cylinder carbon.

[Hitman]

My bike has been running way too rich for about 6 months now. Just got it tuned professionally and it was 3 to 4 turns out, it wasnt me that did the first tuning. Anyway now the compression is down, its probably carbon in valves. I had the top end done about 6 months ago so its reasonable fresh carbon. Is there any way to get rid of it? Ive got some Moreys upper cylinder lube thats surposed to do the job. But i was thinking a tank of some avgas + 91 combo?

[GSVR]

Lack of compression can only be due to 2 things : valves or rings.

As you have only had the top end done about 6 months ago then the bottom end must be letting gas escape.

If your talking 1989 250 what mileage has it done. Does it smoke?

Carbon buildup is generally due to oil getting sucked in through the inlet valve guides or past piston rings. You will notice smoke especailly when starting a bike after it has sat for a while (got cold) after a reasonably long ride (the engine has fully warmed up).

250s get ridden hard and after 15 years you would expect them to be getting tired. Rebuilding is ok if you into it but the money you spend would probably buy a later model bike.

Just my opinion but hope it helps.

[Lou Girardin]

Excess carbon raises compression. Are the readings even between cyls? Run a comp test again and then squirt a small amount of oil down the plug holes and turn it over a few times. Test again, if the comps are higher you have ring leakage.

[Motu]

A head job will often kill the rings,specialy if it's a bit tired anyway,a ring job will kill the bottom end....it's the way of a worn motor.Be a bit carefull doing what Lou says,it's an old trick,but your cyls are very small,so only use a small amount of oil - the compression will be higher anyway because you've reduced the clearance volume.

You wanna get rid of the carbon?? 5000rpm and dribble or squirt water into the carbs,best carbon cleaning agent you can buy....

[Ixion]

A head job will often kill the rings,specialy if it's a bit tired anyway,a ring job will kill the bottom end....it's the way of a worn motor.Be a bit carefull doing what Lou says,it's an old trick,but your cyls are very small,so only use a small amount of oil - the compression will be higher anyway because you've reduced the clearance volume.

You wanna get rid of the carbon?? 5000rpm and dribble or squirt water into the carbs,best carbon cleaning agent you can buy....

One used to be able to buy water injector kits to do that. I never used one myself but I knew someone who did and swore by them . I also noticed on various occasions when dealing with a car with a leaking head gasket , that the cylinder that water had been leaking into was always very nice and clean compared with the others. In fact it was a bit of a give away if the leak was internal and small enough to be hard to find.

[Lou Girardin]

One used to be able to buy water injector kits to do that. I never used one myself but I knew someone who did and swore by them . I also noticed on various occasions when dealing with a car with a leaking head gasket , that the cylinder that water had been leaking into was always very nice and clean compared with the others. In fact it was a bit of a give away if the leak was internal and small enough to be hard to find.

That was a side benefit of the water/methanol injection on my MX5. That and being able to run 8 degrees more advance without using an intercooler.

[WINJA]

A head job will often kill the rings,specialy if it's a bit tired anyway,a ring job will kill the bottom end....it's the way of a worn motor.Be a bit carefull doing what Lou says,it's an old trick,but your cyls are very small,so only use a small amount of oil - the compression will be higher anyway because you've reduced the clearance volume.

You wanna get rid of the carbon?? 5000rpm and dribble or squirt water into the carbs,best carbon cleaning agent you can buy....

ALONG THESE LINES I SAW A YAMALUBE PRODUCT THAT YOU SPRAY INTO THE CARBS WHILE ITS RUNNING TO DECARBON, IF YAMALUBE CAN STOP A YAMAHA BLOWING UP IT MUST BE GOOD

[speedpro]

One easy thing I did was get an old spark plug, whack the middle out and weld on a fitting for an air line. I then screwed it in and connected an air line. Turn the motor to a point where both valves are closed. Hold the crank in this position. Increase the air pressure slowly and listen to where the air is leaking from. Valve leaks are easy. If it's leaking past the rings you'll hear it easily down the camchain tunnel, been there, done that, heard it leaking from everywhere.