Compression issues with 2003 Yamaha Zuma 50cc Scooter...

Just for the record, this is my first "project bike".

I knew it might have some issues when I bought it used, but I'm at my wits end with my local dealership...it feels like they seem more intent on mining my pockets than actually fixing the problem.

I might be being a little harsh, but just because I'm a woman does not mean I can't smell b.s. when it's launched my way and I'm now more intent on fixing this engine myself.

So far I've taken it in to the authorized dealer's repair shop for a new set of rings installed to the tune of $400.

3 months later the compression issues resurfaced, and whenever I try to talk to the mechanics up there they sap my confidence in them even further....just jargon and mixed messages and we keep going in circles without any clear "yeah, sure - bring it in and we'll fix her up for you no problem".

It's a little infuriating.


Here's the deal::

2003 Yamaha Zuma 50. Roughly 3300 miles on the engine.

Used two stroke 50cc - previous owner may have used ethanol gas, but I can't confirm this.

Bike has a hard start, and will not keep a steady idle. Usually dies if gas is let up on.

We've tried adjusting the oil/gas and air ratios to spec to no avail.


Right now I suspect it might need a carburetor cleaning, possibly the air filter as well, but I'd like some extra opinions on what I might need to look for once I tear this thing open.

If you need any more details, let me know....



Thanks in advance.

What are the compression readings in the cylinders? Do you know how to use a compression gauge? If so, do a "dry test" and then a "wet test" and give me both sets of readings.

Originally posted by GENERAL EYES
Just for the record, this is my first "project bike".

I knew it might have some issues when I bought it used, but I'm at my wits end with my local dealership...it feels like they seem more intent on mining my pockets than actually fixing the problem.

I might be being a little harsh, but just because I'm a woman does not mean I can't smell b.s. when it's launched my way and I'm now more intent on fixing this engine myself.

So far I've taken it in to the authorized dealer's repair shop for a new set of rings installed to the tune of $400.

3 months later the compression issues resurfaced, and whenever I try to talk to the mechanics up there they sap my confidence in them even further....just jargon and mixed messages and we keep going in circles without any clear "yeah, sure - bring it in and we'll fix her up for you no problem".

It's a little infuriating.


Here's the deal::

2003 Yamaha Zuma 50. Roughly 3300 miles on the engine.

Used two stroke 50cc - previous owner may have used ethanol gas, but I can't confirm this.

Bike has a hard start, and will not keep a steady idle. Usually dies if gas is let up on.

We've tried adjusting the oil/gas and air ratios to spec to no avail.


Right now I suspect it might need a carburetor cleaning, possibly the air filter as well, but I'd like some extra opinions on what I might need to look for once I tear this thing open.

If you need any more details, let me know....



Thanks in advance.

Have you checked for a vacuum leak? How did the plugs look when you first redeveloped the problem? Dark and wet? Dark and dry/ powdery? White? Brown?

When it wants to die, have you tried manually choking the carb? To see if it is actually running too lean?

reply to post by DarthMuerte


We're sans garage at the moment, and on a very limited budget (can't afford diagnostic devices).

We're working with a service manual, wrenches and elbow grease at the moment.

You can get a compression gauge for less than $20. You can probably borrow one at autozone or whatever your equivalent is.

What about the plugs? If you don't know, get a fresh set and go run the engine for a few miles then pull them out and see what color they are. What about your exhaust? Black smoke? Bluish smoke?

Originally posted by DarthMuerte
Have you checked for a vacuum leak? How did the plugs look when you first redeveloped the problem? Dark and wet? Dark and dry/ powdery? White? Brown?

When it wants to die, have you tried manually choking the carb? To see if it is actually running too lean?

Vacuum leak, no idea. I assumed the dealership would have done that when I took it in initially.

If memory serves, the plug was new, and looked as fresh as when it was first installed.

Haven't tried manual choke yet....

reply to post by DarthMuerte


Exhaust, when running, is slightly blue.

Originally posted by DarthMuerte
You can get a compression gauge for less than $20.

Thank you! Will do so at first opportunity.

Originally posted by GENERAL EYES
reply to post by DarthMuerte

 

Exhaust, when running, is slightly blue.

With a 2 cycle motor, slightly blue is ok. You are burning a fuel oil mix. What does the spark plug look like now?

A quick way to check for a vacuum leak is to let it idle and then CAREFULLY spray some carb cleaner around the base of the carb(stay away from the throat) and then around the heads and any other vacuum hoses you might have. If the idle surges, you have a leak. Note where you are spraying when the surge occurs(there may be a slight delay) be slow and methodical and VERY CAREFUL to avoid hot surfaces.

reply to post by DarthMuerte




Roger that.

reply to post by DarthMuerte


Hmmmm. I'm not sure how many 50cc motorbike engines were multi-cylinder?

What are the compression readings in the cylinders?

Maybe it's two yard blower motors bolted together? A V-TWIG

reply to post by GENERAL EYES

Used two stroke 50cc - previous owner may have used ethanol gas, but I can't confirm this.

Bike has a hard start, and will not keep a steady idle. Usually dies if gas is let up on.

We've tried adjusting the oil/gas and air ratios to spec to no avail.

Ahhh the lovely 2stroke motor.
My suggestions are pretty simple, seeing as it's only 50cc's and that's small.
Anytime you run a two-stroke motor, the exhaust will have a blueish tinge.
That's the oil/gas mixture burning, no big deal.
But it should only be a slight smoke, not lasting...and if you had new rings installed, not much at all.
My problem is that you spent $400 at a dealer when you could've found a used motor for that much!

If you have a service manual, great but a Clymer or Hynes will be best.
Ok so this is what I'd do...
Idle is controlled by a screw and a combo of the throttle passages in the carb.
Since I am not familiar with that particular engine, I would do the basics.
Tear the carb apart and clean/thoroughly check all passages and possibly install a rebuild-kit.
A clogged port or needle that isnt sitting properly will cause problems...
Check the intake boot for cracks and replace if found.
They are cheap, and if you can name the carb and it's size...easy to find parts.
By name I mean....Mikuni 28mm...etc.


Next best thing....youtube.
I get alot of info on motors I am unfamiliar with from there.
Tear downs....rebuild....etc.



Goodluck.

Originally posted by RocketMan0266
reply to post by DarthMuerte

 

Hmmmm. I'm not sure how many 50cc motorbike engines were multi-cylinder?

What are the compression readings in the cylinders?

Maybe it's two yard blower motors bolted together? A V-TWIG

Thanks for the awe inspiring contribution of your obviously voluminous knowledge about engines.
The information I gave and questions I asked relate to all internal combustion engines. With your obviously high level of knowledge and skill, surely you must know that it is an engine, NOT a motor.

reply to post by havok
You know, Youtube is probably a great idea. I never thought of that.

they are taking you at this stealership stop going there call around or even place an ad for a good mechanic.

it sounds like they didnt hone the cylinder and just replaced the rings, now the rings have been worn by the grooved cylinder and youre new rings are now with your old rings SHOT to hell,

wish I could help I do this stuff for a living and wouldnt have charged half of what they charged you. the rings probly cost 30$ and their days worth of work was not worth 400$ take it back to them tell them they need to fix it right and you are NOT paying them for their screw up...

if they dont want to fix it I would seriously take them to small claims court these sheisters make a living of doing crappy work and need to be punished for their thievery.


if you can take the cylinder off and take some pics of the cylinder wall piston and rings I can tell you exactly whats wrong.

what color is the spark plug?

to add ethanol gas should not wear a motor out that fast that sounds like a shovel load full of it. I hate shady mechanics sorry youhave to deal with them.

UPDATE

First of all, thanks to everyone for your suggestions and diagnostic advice.
I really appreciate it.

Last night a friend I haven't seen in ages listened to my tale of lament and pointed me in the direction of someone who is probably the only honest mechanic in town - he does free diagnostics and backs up his word with his work.

I'll most likely be taking it down to him at first opportunity, and if he's as honest as they come, I'll be more than happy to give him my business.

*fingers crossed*