QT 50 Running Problem...

Hello Everyone,

I was just given a 1982 Yamaha QT 50 Yamahopper. It was sitting in a garage for the past 15 years but is in pretty good shape. Rust in tank and on the chrome peices but only light. Can't wait to begin my restoration of it. Before I get to that point i need to get it running first. Other than that it has everything except the plastic covers for the electrical under the seat. I see a lot of people are missing that too.

It has spark, and has good compresssion. And it does run. after cleaning the carb. The only problem is it won't stay running. And the only way i can get ti to start is to hold my hand over the opening of the carb while kickig it and with the choke on. This suction allows it to suck more gas and will let it run. I can feel a lot of suction when its running so its got vacuum there. as long as i keep doing this every 30 seconds or so it'll keep running. I'm not quite sure what might be causing this issue. Seems to me like for some reason the carb might not want to suck the gas or somethings causing it not to suck the gas as much as it should. Could it be dirty or stuck reeds? I have yet to take that apart. I'm not running the gas in the tank becasue of the slight rust, I have a small plastic tank I'm using to test it for now. I was just curious to see if any of you might have any ideas. Any help or info would be greatly appreciated.

Rob

Re: QT 50 Running Problem...

Smitty Smith /

sounds to me like it just needs a good tune-up. If all of the circuits inside the carb aren't open and clean , then the carb won't work properly. It's possible, however unlikely, that the reeds may not be sealing off. New spark plug?

Re: QT 50 Running Problem...

Smitty... this is a common yamaha prob. You probably have rust in your tank... and that rust has gotten in the fitting where your gas line conects to the carb. Reamove the carb and clean that "nipple" with carb cleaner and an air compressor. After that, you will probably need to install an in-line fuel filter.

Re: QT 50 Running Problem...

Make a test tank from a plastic gas can hook a fuel line to it and run it to the carb. Try running the ped with this and see if it starts and runs better. If not the carb has dirt blocking the passages. When you put your hand over the carb it slows the air volume down so the gas it picks up is more equal to the proper air fuel ratio. with hand removed, the carb passages will not let enough fuel pass for the amount of air it is sucking. Temp trick is to get it running, rev it up and put hand over the carb like you are doing. The extra RPM creates a larger suction and it will pull some of the crude through the carb passages and it may run better for awhile. Best to take carb off and disassemble it, spray all the passages out with carb cleaner and the blow it out with compressed air.

Shake the bike and drain all the gas out of the tank. With it will come much of the rust. once empty, if the tank is removable take it off and put some small nuts and screws in there. Fill it with some mineral spirits and shake the hell out of it to loosen as much rust as possible then drain it. Take the nuts and bolts out. Clean the petcock out too.

Re: QT 50 Running Problem...

Thanks guys. I have tried the temp tank. Thats how i've been trying to run it. I didn't dare put gas in the tank with the rust. But i did reclean the carb again today at work. I cleaned it ok the other night. But i soaked the whole thing disassembled in some WD 40 and it cleaned it nice. I used the compressed air too. I have yet to install it. Before i do that i might take a look at the reeds but since it runs ok it might not be them. Once the bike was warm the other day it ran fine. I'll try a new plug too. The one in it looked fine but it wouldn't hurt. I tried adjusting the air screw too but it looks liek where it is works the best. Thanks again for the help. I'll let you know how it turns out.

Re: QT 50 Running Problem...

Smitty Smith /

Streetcruiser, were you not reading what he said the problem was, and what he has already done????????? I realize you've worked on a few 'peds, BUT, I was rebuilding 'peds while you were still kicking the slats out of your baby crib!!! I have been a small engine mechanic for about 30 years, and a moped machanic for about 17 years now.

Thanks--->Smitty@ SmC mopeds and Customs

Re: QT 50 Running Problem...

Looks like I might have found a problem slightly not sure how much this would affect it but i'm sure it will. It has the wrong plug. I think its got a lawnmower plug in it. CJ8. I've seen those plugs before. Its a champion. The NGK is a BP4HS and cross referecnced to a Champion is RL95YC. SO i think its way off. It probably runs too cool and can't burn the oil and gas. When i did get it started and got it warmed up it ran fine. By this time the ctlinder is nice and hot and can probably go from there. Just a rough guess. Smitty think this might be it? Fuel is flowing and carb seem to be fine. Looked into were the reeds are and its super clean in there. I bet when the plug fowled and they installed this one thats why it never ran good. The bike only has 400 miles on it so it can't be anything major. THanks again.

Rob

Re: QT 50 Running Problem...

Smitty Smith /

VERY possible, and a very fine deduction there Rob. Definitely replace that spark plug with the correct one or equivalent. I prefer NGK brand over Champion. Some other things you may want to just check is the tightness of the head bolts or nuts. to check for cylinder base leaks, and/or head gasket leaks, I spray soapy water on the cylinder while it's running, and if the engine faulters, then you have a leak. With only 400 miles on it, there shouldn't be anything major wrong, but I like to check these things anyway...you never know. Sounds like you're getting real close to having it ready to ride again, keep up the good work!!!

Re: QT 50 Running Problem...

Don Pflueger /

yea thats a major difference in plug types. the cj8 is a short plug and a lot colder heat range than the required rl95yc. the "yc" designation denotes an extended tip. so, the cj8 was firing up inside the threads for the spark plug hole, and not able to ignite the fuel properly since the ceramic could not reach the correct heat range required to fire the amount of fuel in that cylinder.

Re: QT 50 Running Problem...

Xyplestop Florbledo /

Oh yes, the "any plug that fits is the right plug" mentality. My Express had a similar issues.

In a dozen bikes and 50 cars, I've seen some amazingly inept mismatches.

Bought an RX-2 with lawnmower plugs in it once.........

Re: QT 50 Running Problem...

Don Pflueger /

having grown up in my dads auto repair shop, ive seen a lot of crazy things too.

Re: QT 50 Running Problem...

Thanks for all the info again guys. I got it running. It was defintely the spark plug. it was too short and it was firing inside the cylinder. All i needed to do was tune the carb once the plus was in. the shop manual was wrong on that too. its said 1 3/4 turns out but it was way less than that for it to run right.

Thanks again.

Re: QT 50 Running Problem...

Don Pflueger /

that 1 3/4 turns is just a point to get the engine started for the first time. its always richer than what your final adjustment will be. glad to hear you got it running.

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