Yamaha QT50 won't started

I've been working on restoring a 1980 Yamaha QT50 for the past few months. I can't get it to start for the life of me. I've rebuilt the carb with new jets and gasket. I have a new cdi coil. New spark plug that has a good constant spark. I've tested for compression and there's plenty of it. I've replaced the battery. The gas tank has been kreemed. Replaced the muffler. Replaced the throttle cable too.

I think the problem may be one of a few things. The oil does not appear to be getting to the carb. The oil line from the autolube pump to the carb is clean, when I open the throttle, the autolube pump is supposed to let oil into the oil line, but nothing comes out. I have plenty of fresh oil in the tank. Would this prevent it from starting?

Another issue is the muffler. Before I put it on I shook it and noticed a lot of stuff moving around inside. I'm going to heat it over a fire to burn off whatever's in there. I don't think the muffler's clogged though because when I kickstart it, smoke comes out.

Another issue could be that gas is not getting from the carb to the cylinder. When I put my hand over the opening of the carb while kickstarting it, there is suction. Also smoke comes out of the carb when I kickstart it.

I would really appreciate any suggestions. I've had this moped too long and had no success, so I'm about to give up and bring it into a shop.

Re: Yamaha QT50 won't started

Yo, I think that if you have spark and there is some suction at the carb, then what may be happening is the fuel is being interrupted between the carb and the piston. So, drop the engine down a little bit (I've got a QT50) as it might be a little tight for your hands. Take the carb off completely and remove CAREFULLY the intake manifold thingy that it hooks onto. Underneath you will see some thin metal reeds attached to a plate that exists between the carb and the piston chamber. Mine was completely fouled and caused untold confusion and frustration until I cleaned the sonofabitch out. That might make the difference.

P.S. How do you know that there is plenty of compression?

handymanmccoy@hotmail.com

Re: Yamaha QT50 won't started

Peter Frank /

Thanks for the reply. It makes sense that the intake manifold could be fouled up. The previous owner appears to have been running it without an air filter. I'll check it out tomorrow and let you know what I find.

I checked compression using a compression gauge.

Re: Yamaha QT50 won't started

That carb has a fuel bowl drain screw. You should see a tiny stream of fuel coming out when you loosen it. If it doesn't,there is a fuel restriction somewhere. Still it should fire on starting fluid. Check that the timing is right, spark occuring slightly before TDC when you turn it over the right direction. It should spark when the piston is about .1" BTDC.Also, a bad crank seal will NOT let enough vacuum be created to pull fuel into the cylinder. But that is a LONG SHOT.

don-ohio (:^)

Re: Yamaha QT50 won't started

Peter Frank /

I've checked the intake manifold, and it's clean and clear. I'll check the timing today once I get the bike put back together later today. If I do see that the timing is off, I don't know how to adjust it. The manual says that timing on this bike is non-adjustable.

I'm still suspicious of the autolube pump too. It's definitely not sending oil to the carburetor. Would this prevent it from starting?

Re: Yamaha QT50 won't started

It won't preventing it from starting but... it'll seize your piston if you run it with no oil.. disconnect the thing and premix your gas and oil!

Re: Yamaha QT50 won't started

ok. you said that smoke came out of the carb? that means timing is off. i have a '82 QT50 and i belive there is some kinda of adjustment for the timing. also, pull the plug out and make srure the bike isn't flooding. cleand your carb real good making sure your fuel float is operating properly.

Re: Yamaha QT50 won't started

PFrank,

If the plug's wet, take it out and kick start the scooter without the plug in it. It'll dry up. Put the plug back in and kick start.

I had a QT50 before, and they're really nice scooters. Watch out for the carb, though. They're a big pain in the ass when you get gunk in the carb. Even the teeniest bit.

Try this- spray some starting fluid in the intake hole of the carb. Kick start a few times. Did it start?

EK

Re: Yamaha QT50 won't started

yeah.. my QT50 is just starting to give me hell. the fuel float isnt operating properly :-(

Re: Yamaha QT50 won't started

I had a issue getting mine to start too. Are you turning the screw out 1 3/4 turns for the air mixture screw. Not the idle adjusting screw. below this there is a flush mount screw for air and fuel mixture. I had to back mine out about 3/4 turns to get it to start. If i set it like they tell you it won't work. So i screwed the screw all the way in and kicked, then turned the screw a little and kicked again. Eventually it finally started to get the gas and run. I fine tuned it from there. Try keeping your hand over the carb and kicking it until it pops. You said there's suction.

Re: Yamaha QT50 won't started

StreetCrusier14,

With these scooters, you are better off taking the carb off, clean it completely and make sure you put everything back together the way it was before- they're senstive.

Then slash your gas line and put in a lawnmower filter. That'll save a whole lot of headache. I had my QT50 running well for over a year since I did that.

Before then, without the lawnmower filter, I had to work on the carb like every 5-6 months and that was annoying.

Also, in addition, the petcock is supposed to have a fine screen between the petcock nut and the petcock itself. '88 models and older moped probably has screens that are totally gone by now. A sink screen would work well. Brass is a better metal screen and lasts a very very long time.

Extreme rust in the gas tank is my biggest complaint with the QT 50.

EK

Re: Yamaha QT50 won't started

Peter Frank /

The plug is wet when I take it out after trying to kick start. So I suspect the engine is flooding. I removed the carb and sprayed starter fluid in the intake and it started up. That makes me think there isn't a timing problem, there's a flooding problem.

What should I do? I've taken the carb apart a hundred times and it has always been clean and the float seems to be fine.

Re: Yamaha QT50 won't started

Peter Frank /

Problem solved yo. Clogged muffler. I had a muffler bbq and its all better. The autolube pump still doesn't work, I'm going to try "bleeding" it, whatever that means. If that doesn't work, I'll have to mix it myself. Does anyone know what the oil mixture should be?

Thanks,

PFrank

Re: Yamaha QT50 won't started

Hey Were did u get that bbg muffler email me at label_rider_247@hotmail.com i'm really lookin for my 1979 Yamaha QT50 hopper

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