cranks, idles, runs for a sec, dead.

Need help, at wits end. Here's the situation. 1983 Yamaha QT50 or yamahopper, ugly yellow color. Been sitting at Dad's house since 1985. I have a 1980 QT50 that I use for parts. Anyway, cleaned out the gas tank, new fuel line with filter, couldn't get all the crud out of the tank. Took the carb out and luckily it had oil in it so all the parts were still good and not trashed. Tore it all apart and cleaned it. The bowl and all the jets, and needle valves were in good shape. Popped the head off and cleaned top of piston, reassemble. Took the cover off and checked the capacitors and wirings, all in good shape. Took muffler off and cleaned it. Took the autolube pump out and cleaned it and bleed the air off when I put it all back together. Checked the wires coming off the stator and they all checked out with an ohm meter according to specs. I have the maintenance manual for it. Relubed all the cables and all working as they should.

Got it running the other day, ran fine. Don't have a battery for it and I'm using the original spark plug, get good spark from it and it's gapped right. Drained the transmission oil and put new 10W-30 in it, as per the book.

Here's the problem. It will crank up fine, idle and rev up, no problem, but after a few minutes, it will simply die. I checked the gas drain on the bottom of the carb, it has gas and I can see it in the filter, so I know its not starving for fuel. I know the oil pump works because of the exhaust color. I put a new air filter on it. I don't have a battery on it, but all the lights work fine when she's running. Before it dies, and your giving it gas, you can hear the carb moan, so it should still be getting gas in it.

What the hell is going on? Ideas, suggestions? Could it be the spark plug?

Re: cranks, idles, runs for a sec, dead.

Sticky float or float needle valve? Did you check the gas drain when it was running?

Run it and let it die. Turn off the fuel petcock immediately as soon as it dies, then check the drain and see if there is any gas in the bowl.

Re: cranks, idles, runs for a sec, dead.

Ron Brown /

Scott,

Also, pull the plug and check for spark immediately. How long does it take to start it again when it dies.

Ron

Re: cranks, idles, runs for a sec, dead.

Gas could still be starved, is the gas tank vent blocked? gas will still be in the line but it won't go anywhere. Or do these use a vented cap?

Time between

Usually it takes about 30secs to one minute before she'll fire up again. There is no vent on the tank as far as I can tell, so it should be in with the gas cap, which is pretty rusty. Could that be a contributor????

Re: Time between

It still sounds like 'starved for fuel"... pull the fuel line to the carb off... does it flow freely or not?

You can hear the carb 'moaning' ... so you know its getting gas ?

the carb moaning doesn't mean its getting gas

and ..... when you open the carb drain.. does it KEEP flowing ?... and KEEP flowing ?... (use a catch can)

If the float needle and float and petcock are working properly... it will keep flowing

(unless its a vacuum petcock)... in which case you will have to provide mouth suction to the vacuum line to let it flow

Re: Time between

Some ped gas caps have a small pin hole. If this hole is stopped up or rusted over your ped will start, run and then die.

Re: Time between

Thanks a bunch!!!!!! Problem is starting to make sense to me now. Got to be a fuel problem.

Re: Time between

does it have a battery thats dead? or does it not have a battery?? are the lights coming on when it runs?? its possible without a battery the regulator is overheating and causing a weak spark.... does it start right back up? like within a minute or 2 if so thats prolly not the problem......Rog

Re: Time between

It fires up between 30secs to one minute after she dies.

Re: Time between

Ron Brown /

Scott,

Read all these posts again.

Fred's looks good because it has a good chance of pointing at, or eliminating, the gas supply to the carb which is the subject of many of the other posts..

A plugged gas tank cap might cause a problem but as soon as you take the cap off and replace it, it will run a lot longer before it dies the first time. This makes this problem unlikely but Fred's test will show it.

Fred's test will also show a problem with the float and needle valve.

You may still have an ignition problem. If your ignition is electronic, it could be temparature sensitive, if points, you could have a bad capacitor.

Do Freds tes and if it points you to the problem, you are good to go. If it does not, check spark and repost.

Ron

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