Plug looks good but piston and exhaust port have excessive carbon build up?

[Simo63]

Try a decent oil like Motul 800 at 40 to 1, you'll have no carbon deposits. I don't see the point in using those old school outdated oils.

Interesting point of view John. 

My experience is that I've been using good old fashioned mineral based Castrol 2T in my VMX bikes at a very rich 20:1 since the 70's and never, ever had any problems with carbon build up.  A few months back now I pulled my 77 YZ250 and 77 YZ400 down and aside from a nice coating of oil over all the crank, piston etc and a very neat light brown burn patterns (a bit heavier in the lower revving 400), the internal workings were perfect. 

To be honest I couldn't be happier with this oil mix.  I know quite a few others that also run it without any problems.

Simo I work on bikes every day and from what I've seen inside engines those using quality modern synthetic oils at 40 or 50 to 1 are cleaner with less carbon, less oily deposits running out the exhaust and run cleaner and crisper than the others. The wear factor is also very good, a lot of these bikes do way more hours than we do.
Modern technology is a good thing and oils have come a long way..

Interesting John. I don't work on them every day but I just don't have a reason to change what has worked for me for 30 plus years.  I've never had any problems to be honest.

When I was road racing my RS125's back in the 80s and 90s I used A747 as it was a mineral based and synthetic blend but the engines were revving so much harder.  And I have friends in the go karting world that use it for the same reasons.

I don't know mate, something about old dogs and new tricks but do you honestly think I would notice the difference?  I ask that because I am the sort of person that doesn't like to change oils at all.  And by that I mean if an engine has been running on oil A then I just could not change to oil B.

Also my bikes are jetted pretty well on Castrol 2T at 20:1 mix and I don't have any issues (except my Evo but I'm blaming Carl for that  )

Anyway, I digress, this thread is about Kenneths carboning up problems not my resistance to any change     I'm always happy to listen and learn so maybe at Toowoomba we can discuss further?? That would be

[JohnnyO]

Fair enough Simo we all have our own experiences & opinions. Happy to discuss it any time..

[JohnnyO]

Just an observation on the topic, at the recent conondale classic there was nearly always someone on the start line beside me who's bike was running so rich they were constantly revving the ring out of it to try and clear it out for the start..

[80-85 husky]

face it guys, not a real lot of people can figure jetting and that magic art of tuning all that well and things stay standard...

I took up racing when a mate conned me into it. he was on his second PE 175. I bought a PE 250 X and quickly figured it wasn't right... Mr McHanic jetted and timed and exhausted the muffler and she was off like a shot!

My mate (who I thought had half a clue) was staggered at the difference and rushed off to get his bike done..he had been riding them stock out of the crate with just the exhaust washer removed and the airbox cover tossed... he had no idea what was available in those engines..so it doesn't suprize me at all when people are running what it has in it.

they are either to stubborn to fiddle or too lazy or lack confidence in their ability to sort things out. (face it , trying to shift a needle clip in the scrub is one of lifes high tension points...)

its like 2- oil...look at the harrow video and some of those old smokers are near on fire there is so much oil in the mix......and that xl 250 s

[Simo63]

Just an observation on the topic, at the recent conondale classic there was nearly always someone on the start line beside me who's bike was running so rich they were constantly revving the ring out of it to try and clear it out for the start..

Lol, that might have  been me on the Evo (YZ250H) .. but like I said, I'm blaming Carl for that.  It's a new Mikuni but I was trying bigger jets to overcome my detonation problem but I went too far 

[Kenneth S (222)]

Thanks guys for your comments,

John, to answer your question, I had a borrowed 38mm Mikuni in it as the guy who worked the engine had recommended the 38mm Mikuni to match his port job. I have now installed a brand new 38mm Mikuni so I'll have to start again. This thread has been good though, I always thought if the plug colour was right, then the jetting was the best it could be. There seems to be some good analysis I can work with. By the sounds of it the main is too big. Exciting really because it is going like a train now and if it has that much more horsepower and throttle response with the jetting sorted out, woo hoo!

Ken