2010 115hp 2stroke, Idle not smooth, hard to plain

[rafaelnfernandes]

Hi guys,

You were awesomely helpful on the other posts so I'm back with more question. Since the subject is not related, I'm opening up a new thread, I did the search, but did not find something quite like my problem...

So, last time I put the boat on the water, the Yam started fine, as it normally does. BUT Iddle wasn't smooth as usual... It wouldn't die, just vary the rpm a little bit (as if it was going to die, but come back to normal, very quick, like 1second).

Cold or warm, it's doing the same, even after minutes at WOT, if I went back to idle, same thing...

The second problem is... sometimes, specially if its the first run of the day (or after a few hours of being shutdown), it starts fine, but as I put throttle to get the boat to plain, it looses power... It revs up ok in idle, but under load, it struggles to pass the 2200 2400 rpm barrier to get to plain...

I'm was running on a fresh new tank of gas. The engine has only 71 hours on it... but the previous run was maybe 2 months ago.

So, dealing with this problem, I tried a few things and found out that:
if I tried to plain a few times, after 3 to 5 attempts it will do.
When it looses power, RPM drops, and I have to throttle back, or it will die
After it passes the 2800 rpm mark, it runs just fine, like nothing ever happened
To overcome the problem, I put it in gear, throttle up to around 1500 rpm, use the choke (briefly pushing in the ignition key on the remote), and add throttle, it revs up just fine.

First thing I thought was fuel starvation, but I kind of ruled that out, as it runs just fine at anything above 2800 rpm.

The spark plugs look just fine.

I thought of the dirt in the carburetor, but in my past experience (with smaller 2stroke motors), when this happened, it would be a pain to get them to start and they would have problems getting to WOT rpm, none of this are happening this time.

This problems seems to be getting worse. It present it self once a few trips ago, maybe twice more recently, but became usual in this last trip.

Any suggestions? I'm no mechanic but whatever you guys say I will pass along the the mechanic that helps me out.
(I'm too far in the country side of Brazil, no Yam dealers of specialized mechanics around)

Thanks a lot, and I'm sorry for the long post, I just tried to give as much information as I could about the problem.

[99yam40]

If choke helps, it is a fuel problem.

Clean carbs and adjust as the service manual calls for
test fuel pump pressure and vacuum
Check for leaking fuel pump
check for air leaking into fuel delivery system

[rafaelnfernandes]

Thanks for the reply 99yam40.

I will give it a shot with my mechanic.

Do you know where I can get the service manual? (digital format would be highly appreciated) I tried yamahapub.com but they dont ship overseas... o the other online stores I only found "generic" service manual, not from YAM.

My motor is a 2010 115hp 2 stroke v4.

I thought about running a full tank of "gas with additives" (they sell this at the pump here, for a few cents more, supposedly it has cleaning additives on it), do you think it worth the try? in that case does it make any difference to burn through it at WOT or lower RPM, maybe varying RPMs?!

Thanks,

Rafael

[99yam40]

look up the manual # you need and do web search to see what you can find.

if the motor is running lean on one or more cylinders you can toast pistons and cylinders running it and hoping it will get better

[rafaelnfernandes]

look up the manual # you need and do web search to see what you can find.

if the motor is running lean on one or more cylinders you can toast pistons and cylinders running it and hoping it will get better

I tried doing that, but I could only find a few pages... and the companies trying to sell their own manuals manual online, they include this # on their "sample" pdf.. so, mostly of what i could find online were this pdfs...

About running lean, I didn't think of that... in the past I only used small motors, so any cylinder running lean would be an obvious loss of power...

Thanks for the reply... I will have the carburetor checked in the next few weeks and post the results here.