300ex smokin like a freight train

[bone705]

a local guy asked me to freshin up his 300 for him. It smoked like nobodys business so i figured the rings were cooked. when i got into it the rings looked fine and even the cylinder still had the crosshatches. i went ahead and replaced the rings and vavle seals. i put it back together and it still funnels out of the exhaust. its not so bad at start up but once you get going it starts smokin bad. i tried cleaning all the oil out of the exhaust and no results. anyone have any ideas?

[beak7707]

It is a serious smoker, I helped him work on it. It was put together correctly, we placed the rings right and it was rehoned. I have no clue why it smokes sooo bad, anybody out there have any info. This thing is a junker, the cases are cracked and what not, but the top end looked pretty good in it.

[Aceman]

Not overfilled with oil? Piston is within specs? Valve guides not excessively worn? Ring end gaps staggered around piston? If everything checks out, maybe it just has some oil in the pipe like Bone said. One thing to try would be to get the quad warm so it starts smoking again, shut it off and remove the pipe. Start it again and see if it still smokes, if it doesn't then you know the exhaust must have some oil in it that starts burning when the pipe heats up. If it turns out the oil is burning out of the pipe I would just ride it around for an hour or two and see if you can burn it off.

[85atc350x]

I had the exact same problem with my 350x. I had a local machine shop bore my cylinder .020 over and I put it back together with the new piston and rings. The engine smoked like a freight train for 2 weeks until I decided it wasn't a matter of the rings seating or having oil in my silencer. I took the cylinder off again and used a inside diameter cylinder micometer only to find the a**hole bored it .007 too big. The only option I had was to get a .040 piston and have it bored to .040 over. Needless to say the buthead that did the first job for me didn't get my business this time. I've had no problems with smoke since then. What I'm getting at is did you use a micrometer to check the cylinder size??

[bone705]

well i rode it a couple miles up adn down the road and its pretty much smoke free. she still has some puffs every once in awhile but i think shes fixed.

[beak7707]

Thats good to hear, I hope it is fixed. 85atc350x we didnt have the cyinder bored it is still on stock bore. But yes it was taken to a cycle shoped and checked, it was right on so the rings were just replaced.

[bone705]

i opend the lid on the gas tank to check the gas and saw a bunch of rust in there. so i had to take the tank back off and i cleaned it out and put some fresh gas in there.

[beak7707]

Run that thing off a cliff... Did you clean the carb out? I am sure the jets are pluged up.

[bone705]

took the carb apart yesterday and everything looked fine.

[beak7707]

So its not smoking now? Does it still feel under powered?

[bone705]

it stopped smokin for a quite a while and right when i loaded it up it spit out a couple puffs. for the power, like you said its a stock 300:rolleyes: it feels about right. ticks pretty loud. wouldnt you say that has to do with the wear of the cam?

[beak7707]

Yeah I can adj the valves again, I have my feeler gauges.

[Scott-300ex]

same thing is goin on with my brother 'n laws 4x4 suzuki 250, it smoked like hell, then he rebuilt the motor and it still smoked like hell, new rings, piston, honed, i don't know about valve seals but im sure they were new, and he tuned it up the best he could, and carb rebuild kit, it still smoked, so i told him to let me look at it, i was ganna move the needle in the carb, well today i went over there to check out his new trailer and and he said his friend found a carb from a 500 and he rejeted it and him and the previous owner said its got way more power now than ever but still smokes, so i'll tell him about the oil in the pipe and stuff, but it sucks cuz he just rebuilt the thing to stop it from smokin and it still smokes

any ideas?

[Plante400]

since we are dealing with smoke

i have a question

when i first start my bike up it will smoke a light black.

is this because my varb needs cleaning or i need to run better gas?

440 11:1 no other mods

and again it Only smokes when i first warm it up but it smokes Alot

[EX_Junkie]

Plante400 mine does the same thing. I'm assuming it may be because i have it jetted a little rich intentionaly. Been doing it for about a year. SHouldn't cause any problems. I've never fouled a plug or anything do to it.

[Scott-300ex]

Originally posted by Plante400
since we are dealing with smoke

i have a question

when i first start my bike up it will smoke a light black.

is this because my varb needs cleaning or i need to run better gas?

440 11:1 no other mods

and again it Only smokes when i first warm it up but it smokes Alot

might be your valve seals, once they get warm they expand and close off oil goin into the cylinder

also, if it smokes a bit, it is just cleaning out the cylinder from what was left in there and stuff, like carbon

[Aceman]

It sounds like your pilot circuit is jetted pretty rich. I wouldn't worry about it if it doesn't foul the plug and your quad starts alright.

[Out_Sider]

my 300 had the same problem.. turned out to be slightly bent valves

[beak7707]

I think it just needed to burn all the oil out of the head and pipe. After we rode it a couple heat cycles it let up quite a bit. I think once it got it all burnt out and the rings seated it cleared up. Hopefully its good to go now.

[Plante400]

thanks Alot guys, for the info.. that makes me feel alot better.. i always thought it was excess from the last time i was on it.

im glad i wont have a problem but it sucks making a big cloud of smoke haha


but the last time i rode it smoked Very little on start up so that was sweet..


well thanks again guys