Smoking Yamaha moto 250

[Need-help-with-quads]

So my moto 4 is smoking white smoke and when I go to first gear and get about half throttle there’s no power and it sounds like it’s bogging

[Gwbarm]

White smoke is generally a sign of water leaking into the combustion chamber, but i dont think yours is water cooled. A matt black plug is usually a sign of a rich carb mixture and oil burning is shiny black, but you might have a combination of both going on and the plug looks matt black. I think i would first go through the carb is it aftermarket or OEM if its aftermarket i would not even rebuilt it , either get OEM(best solution but expensive) or get a new aftermarket one. You also might get away with just a cleaning you can try that first and see if anything improves.

[Need-help-with-quads]

I’ve got an oem mikuni carb I just cleaned it really good all the jest are clear float is set correct and I just tuned it so I don’t think it’s carb but I mean I could be wrong 

[Mech]

White smoke, if it's from engine oil is oil that's being evaporated but not burnt. It's common if a turbo fails for it to chuck oil into the exhaust manifold where it gets evaporated and makes distinctly white rather than blue smoke, and lots of it. In your case NH it might be a worn out valve guide, or just a valve guide needing replacing, or, a valve guide that's loose in the head.

Another thing that I've seen make amazing amounts of white smoke(from a lawnmomer) was when someone had accidentally put chain-bar oil in the sump by mistake. That thing filled my yard with smoke you could hardly even see through.. And no, I didn't put the oil in it. I figured it was the wrong oil though because it smelt wrong, and when I asked the owner.. They'd just had it serviced at the chainsaw shop..  Haha.. too funny.

[Gwbarm]

Thinking back i have had this happen to me twice before, and both times Marvel Mystery oil was involved, the first was a 60s honda motorcycle engine got it pistons were stuck let it soak in Marvel for a while freed up the piston got it started and pouring white smoke, at the time i decided it was either rings still stuck and worn and  aluminum piston hitting bore or the Marvel Mystery oil burning off causing the smoke, still not sure which. 

The second time it happened was on a fresh rebuild so i know that was not from stuck rings, i didnt have any assembly lube so i put it together with Marvel Mystery oil, after starting tons of white smoke for a while, then i determined that the Mystery oil was not letting the rings seat properly, too thin and slick, after running for a while everything was good. Never used it on a rebuild again. Still use it to unstick piston though.

May not really apply to your problem but not knowing the history of your engine just thought i would through that in.

[Need-help-with-quads]

So I’ve got to replace the valve guides? Would that fix the loss of power at half throttle in gear? And for some reason it revs just fine in neutral but then in gear it bogs down at half throttle

[Need-help-with-quads]

 

 

[Need-help-with-quads]

Also for the oil I just changed it, the guy had way to much in it so I drained it and put 10w-40 wet clutch compatible in it

[Mech]

The bad running and the smoke are almost certainly two separate problems.

If the smoke is a valve seal etc leaking it will most likely be the exhaust one if it's the evaporation scenario. If it's the inlet, the oil will get burnt and it smells like burnt oil, Evaporated oil smells different, more like oil.

For the bad running, the carb would be the number one suspect, and easy to check. I'd clean it and check the slide needle's position. The running from about 1/4 throttle up is controlled by the slide needle and the emulsifier tube. You need to take the emulsifier tube out and clean it carefully, especially the tiny holes up it's side.

[Gwbarm]

I was thinking it sounds carb related or fuel delivery also. May check petcock and clean filter screen and make sure you are getting an adequate fuel supply, if you didnt do it when you cleaned the carb pull out the emulsion tube and make sure the little holes are open, also there is a small jet down in a hole thats easy to miss.

[Mech]

It's easy to muddle the spacers and/or washers around the clip on the needle slide on some carbs. Some have spacers above and below the clip. Some of the plastic spacers are quite thick and make a big difference to the running.

[Need-help-with-quads]

Ok quick question, would that affect only in gear? Because it revs all the way up just fine in neutral, it only does that when it’s in gear

[Gwbarm]

When in gear it puts an extra load on the engine, pulling its weight and your weight around.

[Mech]

It's not strictly putting it in gear that's making it miss.. It's putting a load on the engine that's making the miss I'd think.

[Need-help-with-quads]

Ok so you guys think it’s misfiring? Also I just did a compression test on it and it has 150 pound of compression, also when I hit full throttle it has power again so it’s like it’s only doing that at half throttle but I guess when I hit full throttle it still doesn’t run the best

[Mech]

#9 #11

[Gwbarm]

I rewatched your video I think its fuel related its not wanting to take gas either not enough or its getting too much, it seems to settle back down when you let off the gas, hard to tell without seeing what the exhaust looks like.

[Need-help-with-quads]

Ok I’ll mess with the carb today after church and get back to you guys

[Mech]

Just take the top cover off, in place, and check and/or change the needle position. That's easy. If changing the needle makes a difference, then move it some more till it's in the best position for running between 1/4 and 7/8 throttle.

If that doesn't/can't make it run right, then take the carb off and strip, clean, inspect and adjust it.

[Need-help-with-quads]

Ok so what I did is I took my good carb off of my red moto 4 and put it in this one and it’s still did it

Oh and I put the carb from the issue quad and put it in my good quad and the good quad ran perfectly fine, also the needle adjustments are the same for my good one and the bad one

[Gwbarm]

Interesting no change. What are you running for a CDI my other suspect would be the timing isnt being advanced enough to keep up. 

[Need-help-with-quads]

I honestly have no idea how would I find that out?

[Need-help-with-quads]

Also I just found out it’s either a 1990 or 91 the thing doesn’t have a pull start so that’s how I determined that but yea I’m sure if that makes a difference

[Gwbarm]

I was avoiding going there hoping it was a carb issue. You have checked that out by putting a known working carb on with no change. You have checked the compression and it was good so the valves should be OK, although i would check the valve clearances to make sure they are in spec. Generally i dont suspect the CDI until it does not spark at all, and it may not be the CDI, but that does control the advancement of the timing to some degree. The service manual does lay out steps involved to determine a malfunctioning CDI, which involves checking stator resistances, pick up coil resistance and primary and secondary coil resistance, along with check power in and ground to the CDI so you could check all these things and see if they are up to specs. Sometimes you can have a weak ground so check all those connections good. Do you have a service manual? If not i will see if i can locate one.

[Mech]

Check the charging system is charging, and regulating..

Just slap a volt gauge across the battery terminals and see it's 12.6 at rest, about 13.6 after it's started, and gets up near but no higher than about 14.7 with a few revs. Then turn the headlights on and it should be able to maintain about 13.7 volts.

If you have a timing light put that on and check the spark isn't disappearing when the trouble starts.

[Mech]

It would be a good idea to check the stator readings as well, and check the connector looks original.. If the stator or cdi has been changed with the wrong part or incorrectly it could run like this.

[Gwbarm]

I think the original coil and CDI was Mitsubishi so you could check to see if its aftermarket.

[Mech]

I remembered in the night reading about someone who had a similar problem, except a bit worse in that the bike would barely move, and it was because there was a safety feature whereby the bike's revs were limited if the park-brake was on. He disconnected the brake switch(which was defective) and it went again. I can't remember if it was a yamaha or a kawasaki now though..  haha.

Worth a look, or read in the owners manual.

[Need-help-with-quads]

No I do not have a service manual if you could find one that would be fantastic and I will try and look into that stuff tomorrow if I have time

But also if I hit full throttle it revs up it’s only at half throttle area where is sounds like it bogs and has a rough time so I don’t think it’s the brake thing but it’s worth a shot anyway I guess

[Need-help-with-quads]

Also I do not have a service manual

I mean owners manual