+1 more about the carb...

my son still races mx on 2 strokes and i can tell ya a clean carb is super important

also make sure the air filter is clean

once running, spray carb cleaner or starting fluid around the intake,and the stator side of the case to see if crank seal is out

put in a new plug as well..

after that look into the timing or electrical system
 
Buy some injector cleaner and make a strong mix with clean non ethanol fuel put the whole carbie in for a couple day soak to start with, you might find it imagined up inside some of the passageways and jets also make sure the air filter is in good nick and clean, they don't like being lean, if it is getting to much air it can be as bad as not enough also a good idea is to build a fire out in the open and put exhaust system on in till it stops smoking a gently tap it to loosen the carbon in side, be g carefully as I have seen a system throw a flame about 6 foot once from a system that was long overdue for decoking, two strokes can be very fickle even little things effect them alway make sure you only use motorcycle grade two stroke oil as the lawn motor stuff is crap in a bike alway change the spark plug on a regular basis
 
Thanks for the help guys i will try a few of your tricks , i spoke to him about it and he is going to bring it over and i will have a good look at it. He tells me it has a leak around the head gasket and one head bolt is stripped , i might start with this first.
 
Thanks for the help guys i will try a few of your tricks , i spoke to him about it and he is going to bring it over and i will have a good look at it. He tells me it has a leak around the head gasket and one head bolt is stripped , i might start with this first.
I think you just found your biggest problem but the fore mentioned suggestions are also handy maintenance things overlooked by many, whilst I never raced I spent the first six years of my bike riding life screaming around on two stroke Dirt bikes and did all my own maintenance and hoting them up by port and polish plus a expansion chamber.
Once a year this included decoking the exhaust and you would be amazed at how much it improves the performance
 
I think you just found your biggest problem but the fore mentioned suggestions are also handy maintenance things overlooked by many, whilst I never raced I spent the first six years of my bike riding life screaming around on two stroke Dirt bikes and did all my own maintenance and hoting them up by port and polish plus a expansion chamber.
Once a year this included decoking the exhaust and you would be amazed at how much it improves the performance

I think while i have it stripped down i will do the carb and the exhaust for sure, thanks for the heads up.
 
Wish I lived closer I would show ya how to make the thing rev it's tits off by adding a booster port in the piston and open up the transfer ports in the barrel but you would also need to get a bigger carbie and expansion chamber .... Sorry I am foaming at the mouth again, I haven't changed much I am still like that .... Make a small change here that leads to a slightly bigger change there and before you know it you have created a monster .... But you have fun:D
 
As a former Suzuki mechanic, check the air filter and make sure it is not installed backwards. We had a similar problem on one and installed the new crank seals, micro tuned the ignition, and set everything in the carburetor. We then reversed the air filter so it didn't restrict the air flow and ya' know it, it was the best running bike!! Yours truly had the reddest face! I learned not to overlook the obvious LOL.
 
My 2c would be its loading up, I’d say clean or better change the plug & lean off on the fuel mix. Then if its still playing up maybe the jets are worn or the carb needs cleaning as mentioned. Recalling my youth the engines were bullet proof but you had to carry a plug spanner and a piece of 1200 sand paper on a decent ride.
 
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