Low compression By kymcove21 (Read 1,776 times)

[kymcove21]

Hello all.

My 2009 kymco sento 50 has been a bundle of joy for me. Recently I changed the transmission fluid and overfilled WAY OVER what is reccomended. I then took out the carbon deposits with seafoam. Then opened up the carb to inspect jets. Once reassembled, it started and idled fine per usual. Once I tried to go however, the engine lacked power. I rode it about 8 miles and noticed this lack of acceleration, top speed and overall performance. Brought it to local shop and they said the compression is low. They adjusted the valves and it was able to achieve ~15mph which was better than when I brought it in. They still said that the compression was low after adjustment and it felt that way. What can I do to make this scooter sound and perform like she once did? Bore kit? All new gaskets? Rollers? I need someone to tell me what is wrong. Thanks!

[Bashan]

The transmission fluid would not affect the compression. Did you drain down to the proper level?

What do you mean you removed the carbon with Seafoam? How did you do that and is it back to a standard gas in the tank or is it loaded with Seafoam?

To trash your compression the rings would have to be damaged, and or the valve seals, and or the valves misadjusted or damaged. I can't imagine you did that with anything you described.

If you have a boatload of Seafoam in your gas drain the tank and put your normal gas in there. Check your valve gaps, there's tutorials in the Library.

Buy or borrow a compression tester (auto parts store) and test the pressure, there's a tutorial in the Library. Don't trust a shop.

Rollers are CVT, they won't change a compression problem IF that's what's wrong. Don't start changing gaskets and rings until we're sure what's wrong. Slow down, take a breath, don't panic, this can be worked out.

[kymcove21]

Thanks for answering so quick! I ran the engine till hot, then removed plug, put in about 2 cap fulls put plug back on, waited 15min then revved until smoke was no more. I did decrease the amount of trans fluid after riding the 8 miles on the overfilled transmission to no avail. I then checked plug, bone dry. The air filter was also bone dry and didn't smell of the trans fluid. However, this am I found a leak of some oil coming from a bolt on the left of the engine id code. It is black oil and the bolt is fairly large. It just is NOT accelerating and achieving top speed anymore and this all happened after the changes I made. ALLLLSSSOOO if it matters, when i entered the seafoam and tried to start after 15 min, it wouldn't kick over as if something was blocking it. I opened the plug up, tried again and got some backlash of seafoam out of the hole. I really want my baby running again. Also, does anyone know what kind of engine this thing has? people say GY6 but the engine code doesn't match up with the traditional GY6. Thanks!

[Alleyoop]

What is the number stamped on the case by the SIDESTAND: ALSO SEE THAT SCREW all the way on the RIGHT IS THAT WHERE it is LEAKING OIL?
Alleyoop

[kymcove21]

I honestly am not sitting in front of it, but I did this investigation and my number that is 1p39qmb ends in an E, I remember that and it began with an S. I just have no idea now where I can find parts for this scooter. Also, yes that is where the oil was leaking. That bolt is like black from all the oil.

[Alleyoop]

That is another OIL DRAIN PLUG, so tighten it up it may be missing the copper gasket.

So you have the the 1P39QMB motor not a problem, It may have a little bigger piston but not necessarly it could be just your 139QMB motor won't know unless you take the head off and measure the piston.
But parts are very common for those motors so not a problem.
Alleyoop

[Bashan]

So you poured Seafoam into the plug hole and then cranked it? Is that correct? I'd like to see what Alley thinks and maybe Jack if he's not busy. You could have wiped the lubricant off of the rings and trashed them. What do you think Alley? I'll call Jack and see what he says but I think this may be your problem if that's what happened. Who told you to do that? Rich

[kymcove21]

I read it on a website that went over it step by step to remove carbon from the engine, BASHAN. in regards to ALLEYOOP, I dont have a copper washer or seal for that. Also ALLEYOOP, my engine doesnt have that 139 code on it, it has different numbers and letters. I need a tutorial on how to replace the rings if this seems to be the issue... Thanks and keep up the suggestions on this post please!

[Alleyoop]

I know it does not have the 139QMB code It has the 1P39QMB as you said and I am telling you it is not a problem for parts very common 4 stroke motor just as the 139QMB. Your 1P39 motor MAY have a little bigger piston 41.4 if not the 39mm that is all.
Alleyoop

[kymcove21]

It has neither. My code starts with an S and ends with an E. There is an 8 as well in the code. I found a site that sells oem parts, now just which ones do I need lol. I am so glad people actually know what to do with this issue on scootdoc!!!!!

[Alleyoop]

The letters do not mean squat, it is what is after the first letters and the last letter.
Just post what the heck it is stamped on the case.

And here is your scoot.
www.motorscooterguide.net/Kymco/Sento-50/Sento-50.html

[Bashan]

You have to run a compression test in my opinion. The symptoms are consistent with that. But you won't know for sure without the test. If it is low compression there is an additional test but let's get that far first. I'm sorry, but I just do not trust shops to do these things. I know shops I would not even think twice if they said it was low compression. But some others I just would want to do my own confirmation. It's like some car repair shops....you know what I mean. Maybe you know these guys, I don't know, I'm just a suspicious type. Rich

[Alleyoop]

So what is the motor type?

[Bashan]

Yes, and take a pic of the engine code so we can stop the confusion.

[kymcove21]

I am running a compression test with haqndheld later and will also post pic of engine number. The engine has the same specs as the Kymco Agility if that helps.