Smoking Yamaha moto 250

[Gwbarm]

I have been looking for one havent found one yet. Plenty you can buy but no free ones.

[Need-help-with-quads]

Ok the Cdi is Mitsubishi so it should be oem

[Gwbarm]

Thats good i would think that is not your problem.

[Gwbarm]

I did find this one a little newer but may help.

 

d68a92.pdf

 

[Need-help-with-quads]

 

 

[Need-help-with-quads]

So basically what is happening now that I’ve driven it around a little bit and gotten to test some things Is I’ll drive in first, it doesn’t go any faster then I kick it to second and it goes just a tiny bit faster and then I kick it to third and it stays the same but then fourth it slows down and then in fifth it hardly moves at all and that whole time it sounds like crap

[Gwbarm]

Thats bad loosing power in every gear, i think you need an engine rebuild.

[Need-help-with-quads]

Are you thinking just top end?

Or should I look into the bottom end and check that as well while im at it

[Need-help-with-quads]

Because when I bought it the crankcase vent hose was gone and I don’t know how much dirt if any got into the crankcase

[Gwbarm]

I am thinking top end rings valves reworked. Unless you heard knocking noises and it shifts good i wouldnt suspect a bottom end problem. As far as the vent hose being off i would drain the oil put in new run it a little bit then change it again. If the oil looks milky do it again.

[Mech]

If it's got 150Lb of compression like you say, it should run ok.

[Need-help-with-quads]

Oh and where would I find a new vent hose?

Also your saying get piston rings and check valve clearances?

And new valve seals?

[Gwbarm]

I agree 150 PSI  is plenty to run on i was just basing my opinion on the smoking and what i saw in the video, never seen a carb or vent problems cause that much power loss so quickly. I have seen it from a plugged exhaust. Could be wrong but it is definately loosing power.

[Mech]

Yeah a blocked exhaust will cause power loss alright.

[Need-help-with-quads]

Ok I’ll switch it to a different one because the one on there I got from an old parts quad but I’ll switch it back to the one that was there before and see what happens

[Gwbarm]

You could check the exhaust, wrap a rag around the inlet and blow some air in there and see if it flows smoothly.

[Mech]

Yeah, or just take it off and go for a quick fang..  Well that's what I'd do.

[Need-help-with-quads]

Ok so I finally got time to take the exhaust off and when I did the thing ripped and it went fast now so thank you I have yet to drive it more with a proper exhaust to see how it runs with everything put together so I’ll let you know

Oh yea and it quit smoking

[Mech]

The old exhaust is probably full of burnt up oil crud. caustic soda softens it and then a bash or ten loosens it and a hose gets a lot out. Or, if you have oxy-acetylene, and like to annoy the neighbors you can burn it out most spectacularly by putting a flame to the front end till it's starting to glow a bit of carbon, then turn the acetylene off. It turns into a rocket..  With a lot of smoke.

It makes the pipe red hot though and pretty much either burns it out right then or rusts it out withing a few months.. But it is fun.

It even sounds like a rocket..

[Need-help-with-quads]

Alright so i put I different exhaust on and it works better than the other one, but it idles perfectly and will idle all day but then I take it down the road and after about 2 minutes it pooped on me, so I pushed it back about a 1/4 mile and then I jumped it and it started right back up. Do you know what is happening now?

[Mech]

Either a shortage of fuel from the tap, or some electrical component is getting hot and temporarily closing down.

If the tap's not letting out enough fuel to keep up with the requirement when the throttle's open, or the float needle's partly blocked causing the same problem, then it can take quite a distance before the shortfall shows up. If you turn the tap on and open the carb drain screw it should be obvious if it's not maintaining flow. Make sure you watch it for long enough for the bowl to empty and then see what the flow's like.

The electrical's a bit harder to diagnose but if you have a timing light you could drive down the road watching that to see if the spark fails after a while, or take a spark-plug with you and quickly connect it to the lead and check for spark when it stops running.

[Need-help-with-quads]

Ok I just tried again this time with a charged battery and I think it could be a shortage of fuel because after it bogged and sputtered for a while it died and then I cracked it and it started back up and idles perfectly, is the tap the fuel petcock?

Oh the petcock filter could be clogged I’ll check that as well

[Need-help-with-quads]

Also forgot to mention that put a bunch of seafoam in it and it was at 150 for compression and after the seafoam cleaned out all the carbon it’s down to 90 pounds of compression idk if that matters though

[Mech]

Yup, the petcock is the fuel tap.

[Need-help-with-quads]

Alright yea I’ll try looking if it’s clogged any

[Mech]

I'd check the flow through the carb too..

[Gwbarm]

Yeah the seafoam cleaned out all the oil carbon and everything, try putting some oil back in the cylinder and check the compression again see if it goes up, if it does its definately the rings , you might also check the valve clearance and see if it has changed since using the sea foam. 

[Need-help-with-quads]

Just realized that when I tested compression the second time I didn’t have the throttle open so I’ll test it again and get back to you

[Mech]

Haha. Yeah good. I was wondering why you weren't having starting troubles at 90lbs. Hopefully it will come up a lot. If it doesn't, try as Gw says and put about a teaspoon of engine oil down the plug hole then do a compression test. The compression will come up by a lot if it's rings, and hardly change if it's valves.

If you do a compression test without the oil, then watching the needle as you do the compression test is also a good idea. You should crank it over about six compressions and watch to see if it's at full/maximum compression on the second compression, or whether it gets a little higher each compression till it maxes out. That's a sign of bad rings.

[Need-help-with-quads]

Ok so I messed with it and found out that it chugs oil and when I tested compression without oil at wide open it was back at 150 and then put oil in the cylinder and it went up to about 185

And now for some reason it doesn’t want to idle now that I filled it up with oil, and im getting blow by. So I’m thinking way too much oil is getting in the cylinder so that’s why it making it run bad?