Going crazy, Jog won't get good compression.

[robotguy]

Hey guys... I'm losing it.

I got the new rings for my 89 jog in, installed them,
double and triple checked my work, and......
it's still getting only about 90psi compression out of the spark plug hole.
Exactly the same as before I did the ring job.

It's still running like hell as well.
It runs, but has very little power.
I also replaced the intake manifold boot because mine was cracked.

I just don't understand.

I replaced the cylinder gasket and dome gasket,
what else could be causing bad compression?
Could the crank seals cause loss in compression?
Bad reeds?

Is it possible that the cylinder has been worn to be too large,
thus creating a poor seal?
There are no scores or scarring of any kind on the cylinder or piston.

This is how I feel right now.
,.,.

Thanks for any help you can give on this bizarre problem.

[robotguy]

I did a test, and don't like the results.

I added a bit of oil to the cylinder to see if it would bring the compression back up
for a bit, just to see if the cylinder walls being worn is really my problem.
How about YEP!

Well, it ran just like it used to until the oil burned off.
That's why it would run awesome after I checked compression.
Cranking the engine while not running would flood the cylinder a bit, so I'd have really good compression
until it burnt off, then it ran bad again.

Looks like it's about time for the 70cc kit, unless someone here has a
stock 50cc cylinder in good condition.

Uggh.
Will I have to get a new carb for the 70cc kit, or will a 90 jet in the stock carb work ok?
I won't have a pipe....

[fastrazz89]

You could have blown crank seals. Have you honed out the cylinder at all? If you do hone it, you will need to run a larger piston.

[fastrazz89]

Ah you beat me to it! We posted at the same time lol

[robotguy]

I didn't hone it, I don't know how to hone a cylinder.
The walls of the cylinder look great, that's why I don't understand why I'm not getting good compression still.


Do you think it's a better bet to just get the 70cc kit, or
hone my cylinder and get a new oversized piston and rings?
I figure by the time I do all that, it's going to to be almost as much as a 70cc kit,
what do you think?

[fastrazz89]

Personally, I would go with a 70cc kit, because it has an ALUMINUM cylinder that is already ported and ready to go. You will gain more power with the 70cc kit also.

[robotguy]

Yeah, I bet you're right.
So could I use the stock carb, or does it need upgrading?
Does Provo scooter sell a 70cc kit for the vertical engine older zumas and
jogs?

[robotguy]

So I found 2, I could get a 70cc Polini kit with the cast iron for $180ish
or the Airsal aluminum race cylinder here at Provo for $139.
Is aluminum better overall?

I guess I'll probably need a bigger carb too,
as i DO NOT want to seize this up.

What carb would you recommend that will fit with the stock
intake? 19mm?

I'm still not going to get a pipe yet, because I want it to be quiet still.

[fastrazz89]

Aluminum is a much better choice- I'd do the aluminum kit from provo. If you keep the stock exhaust, you should be able to run the stock carb and airbox without any problems. Many people have run like this with a 70 kit and a stock airbox, stock carb, and stock exhaust with no problems.

[robotguy]

Awww man,
I like the sound of that!

This thing is plenty fast enough at 50cc
when it's running with good compression.

Looks like I'll be dropping another $150 into this baby.

[dwsracing]

Ya, then you can do any upgrades like carb, exhaust ect. if you want a little more out of it. Have fun
Dave

[robotguy]

I found out it's a glazed cylinder, that's why I have so little compression.
Glazed cylinder + new rings =low compression.

I'm going to deglaze it as soon as I have time, and the I should be running again. I'm surprised that no one here had
experienced something like this before.

I guess my old rings were so worn, that once I started running it again,
the oil just passed the rings and glazed the cylinder hard.

I'm very happy I'll be able to keep this stock.

[OveRReV]

it'a always mandatory to have the cylinder deglazed before installing new rings or new piston kit, with a glazed bore the new rings will have a hard time seating so compression will leak past the ring rapidly.

if you were to ask me i won't just settle for a ring change & change the piston too, a fresh piston gives a tighter clearance thus maximizing compression, if you can hear your old piston slapping even if it's hot it's time for a new one.

[robotguy]

Ok guys,
I've finally gotten it good.
I deglazed the cylinder , but it was still running poorly,
only running low speed, totally gutless.
The deglazing and new rings got the compression back to normal (120psi+)

Decided to check the stock exhaust, and it was very plugged up
from years of the previous owners crappy oil.

I unplugged it for now with a toilet snake, shook some stuff out
and she's running great again.
I'll bring it by a muffler shop for them to burn all the crap out sometime soon.

What does piston slap sound like?
Like a knocking sound? I do hear a little knocking a bit when I first start it, but only for
10 or 20 seconds, then it goes away.

I bet the main problem from the start was the stupid plugged muffler,
oh what a dope I am......