Yamaha Champ/QT50 non running update

josh /

Jul 03, 2001 01:24AM

Its me again with the Yamaha Champ (very similar to the QT50 except with "automatic" choke). On my last update I was still at the point of complete bafflement because I have compression (finger test), new fuel flowinf freely into and out of carb (pleas no one tell me to check carb or read Freds list), clean air filter also tried no air filter, and I have spark (blueish purple, would not call it fat but its there) but I DO NOT HAVE A RUNNING ENGINE!!! Let me repeat before everyone tells me to read Freds checklist (however helpful it may be) IT IS NOT THE CARBURETOR! It is also not points because it is CDI controlled.

The newest problem I have is that I have stripped the threads of the head so the regular spark plugs do not grip tight enough for compression. So I have tried a couple that are not the correct plug but are longer and grip the last threads and it is air tight and is NOT hitting the cylinder. My question is if these plugs are not the exact replacement will the engine not do a thing? As I said they are longer and are closer to the cylinder. I purchased a helicoil and tap repair but CANNOT get it in straight w/o Fing it up! But yet and still, it should at least cough or sputter or something shouldnt it. I mean even before this stripped threads deal I got nothing! It makes no sense! I even pulled off the carb and attempted spraying both starting fluid as well as gas/oil mix directly into the intake wich at one time early in my adventure would cause it to sputter and run until it was burned up, now NOTHING. This alone eliminates the carb as well as any vaccum problem that could be created with the automatic choking mechanisms. WHAT THE HELL !!?? Nothing has worked and I see no end and am VERY frustrated!

Re: Yamaha Champ/QT50 non running update

Fred /

Jul 03, 2001 02:25AM

Your post is well thought out.. and covers almost everything.

And you have stuck to it toughly and thought carefully about how your engine works... I am impressed.

You have a tough one there.

You really ought to fix the head first.

If I came to your house... this is what I would do.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

First I would take off the head and cylinder and take a good look at the piston and

cylinder bore to see if they are damaged.

If they were... they have to be fixed.

If they were good.. I would make sure that any decompression device was sealing properly when not being used

Then I would fix the spark plug threads.

If they can't be fixed easily and you still want to test it...

Then I would buy a new NGK B7ES motorcycle plug because I know a good ignition will fire it.

I would put that in and have you kick it while I listened for leakage at the spark plug.

If I could hear it leak I would stop till the threads were fixed.

But... if you are truly getting NO compression leakage with your funky plug threads.. then that plug will fire if your ignition is good.

Then I would probably drain the carb and disconnect the fuel line (to make sure it was not getting too much gas) and spray a little gas or starting fluid straight into the carb throat.

At that time I would have covered the compression and fuel... and if there was a problem then it would be ignition.

If it did not fire and run for a few seconds on the squirt of gas... then I would closely examine the spark plug boot and the spark plug lead to make sure they were'nt frayed or broken... then I would check all electrical connections going to the coil from the CDI.

If you find no troubles there.. then I would do a crude test for overall spark voltage .... see if the wire to the plug will shock you real good by removing the plug and putting it into the wire and hold it with your hand while touching the motor with your other hand while somebody kicks it over.. it should send a good spark up your arm.

If it doesn't.... there is a real good chance that your CDI has gone bad.

Re: Yamaha Champ/QT50 non running update

don-ohio /

Jul 03, 2001 08:57AM

Hi,Josh! I couldn't add much except maybe to look for a loose ground or connection to the coil or cdi and to ask if your battery is charged up(if it has one?) BYE!

Re: Yamaha Champ/QT50 non running update

josh /

Jul 03, 2001 12:30PM

Thank you very much for the informative reply. I have had the head off before and have seen the piston in the cylinder and it doesnt appear to have any physical damage, but I am not that familiar with the internals of the engine and this is all kind of a learning experience that I hope will help me with future troubleshooting. What kind of damage and or operation am I looking for with the cylinder bore as well as the decompression valve components. I have no idea of what a decompression valve is! If I were to remove the piston from the cylinder for cleaning and inspection I would need new rings and the such correct? The old ones cannot be reused? Upon inspection of the cylinder I see just some carbon on the piston itself and the cylinder walls do not look overly gouged or heavily scratched. By the way this motor only has about 4,800 miles on it and the carb is in excellent condition. As I said before it does have automatic choke with I beleive a BVS valve and one other piece I dont recall the name of, is it possible these are not working properly? But from what basic things I do know, if the components in the cylinder were working correctly and I have a spark it should fire correct? This is why I removed the carb and sprayed directly into the intake.

When I originally heard what I beleived was air leaking near the head, I sprayed soapy water all around the head gasket and spark plug threads, and that i when I saw the bubbles around the plug. Now with the longer (Champion) plug in there, there is a spark and there is no air leak that I see or hear, but still nothing. Yes I know I should get the threads fixed so i can get the corect NGK plug in there, and I have tried but like I said I am having trouble getting tap straight and dont want to screw it up even more. I do get a blue spark and it will zap me, and I cleaned and sanded all grounds and connections, but is it still possible the CDI is not correct, or is it something that either works or doesnt?

Please give me a bit more help on what to look for the motor internals if you can. And thanks again.

Re: Yamaha Champ/QT50 non running update

Fred /

Jul 03, 2001 04:41PM

What kind of damage and or operation am I looking for with the cylinder bore?

Heavy scratching and scuffing or gouging on the piston skirt and cyl bore.

as well as the decompression valve components. I have no idea of what a decompression valve is!

Your bike may not even have one... it is usually next to the spark plug on the head... it is a little valve and it is there to make starting easier.

If I were to remove the piston from the cylinder for cleaning and inspection I would need new rings and the such correct? The old ones cannot be reused?

If the cyl bore and piston is in good shape then the rings should be OK.

But they can also be stuck in their grooves on the piston and letting the compression escape into the crankcase.. they should move freely on the piston.

If they are stuck in their grooves then you should very carefully remove them after soaking the piston in solvent of some kind.. then clean the ring grooves.

Rings break very easily.

Upon inspection of the cylinder I see just some carbon on the piston itself and the cylinder walls do not look overly gouged or heavily scratched.

Carbon on the piston top won't hurt anything.

By the way this motor only has about 4,800 miles on it and the carb is in excellent condition. As I said before it does have automatic choke with I beleive a BVS valve and one other piece I dont recall the name of, is it possible these are not working properly?

4800 miles is more than most peds have on them.

I don't like the automatic choke deal... if the choke is stuck "ON" you will foul plugs all the time.. but it should still at least start with a fresh plug.

I don't know what a "BVS" valve is.

But from what basic things I do know, if the components in the cylinder were working correctly and I have a spark it should fire correct? This is why I removed the carb and sprayed directly into the intake.

Thats right.. if you have compression and spark then a shot of gas or starting fluid should get it to fire and run for a few seconds.

When I originally heard what I beleived was air leaking near the head, I sprayed soapy water all around the head gasket and spark plug threads, and that i when I saw the bubbles around the plug. Now with the longer (Champion) plug in there, there is a spark and there is no air leak that I see or hear, but still nothing.

Well if you are still using the soapy water and still don't hear or see any bubbles.. then I have to say that it will fire and run for a while.. (IF THE PLUG IS A GOOD ONE!)

By "good one" I mean fresh (not used.. or wet.. once a plug has "fouled" .. it is no good) and of the type that will fire on an old moped CDI... that is why I said to use a NGK B7ES.... I KNOW that it will fire on that ignition if the ignition is good.

I don't know what your Champion was intended for.

Yes I know I should get the threads fixed so i can get the corect NGK plug in there, and I have tried but like I said I am having trouble getting tap straight and dont want to screw it up even more.

Take the head to a local Auto parts store that does "machine work" (or motorcycle shop, or lawnmower shop) and ask if they will do it... they will prob charge $10 if you already have the kit.

I do get a blue spark and it will zap me, and I cleaned and sanded all grounds and connections, but is it still possible the CDI is not correct, or is it something that either works or doesnt?

How badly will it "zap" you? It should give your body a big convulsion and send a jolt about all the way up to your shoulder.

And yes... the CDI could be bad... but if it sends a jolt all the way up your arm then it is OK.

Please give me a bit more help on what to look for the motor internals if you can.

I already did above..taking a top end apart on a moped is about a 10 minute job... it is easy... so just do it... the only things to be careful of are covered in my guide... make sure the base gasket isn't torn... make(carefully!) or buy a new one.

Rings in correct position

circlips seated all the way

base gasket in good shape

Isn't "Scooter Therapy" in Milwaukee WI ??

Maybe they are close enough to fix/check this bike if you can't ?

I didn't know what a Champ was ... But I saw one on ebay last night.

Re: Yamaha Champ/QT50 non running update

Reeperette /

Jul 04, 2001 06:03AM

Not sure exactly where Scooter Therapy is...I DO know there are a coupla decent shops in Madison, WI...and that might be one of em.

At this point I would definately call in professional assistance.

-Ree

Re: Yamaha Champ/QT50 non running update

scott (WI) /

Jul 07, 2001 02:00PM

The champ does not have a compression release. Is the exhaust pipe plugged? Had a Express that started after I took off the muffler.

MOPED ARMY

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