New Stress Releif......need carb guru


Tree Hugger
Mar 6, 2005
Oxford, Connecticut
Last night I was bored, and said "It would be nice to be riding around on a scooter". I had remembered by brothers friend had one about a year ago, so I gave him a buzz. A hour later I am bringing home a MINT condition 1981 Yamaha QT50 Scooter for $75.

So I get it running last night then encountered a problem on my maiden voyage home at 12 o'clock. It starts to cut out but I get it home.

Today I have been tinkering with it, I have found that it will run mint for about 10 minutes, then start cutting out. I have the air screw adjusted to factory specs, and the clip in the middle of the needle valve. It's almost like it acting like is not getting fuel, or too much air or something. I don't really know, I'm not good with carbs. Any advice on what I can do to trouble shoot this? If it sits for a bit it will then run fine, then do the same after 10 minutes. I tried taking off the gas cap because I thought maybe it's not venting, but didn't change much. And I did take apart the carb and clean it, but's is still a brand new OEM carb.

I am itching to it the open road. :P

(I will post pics, camera is charging, it's a funny site)
Taking the gas cap off took me as far as my troubleshooting knowledge goes. Has it been sitting long? Water in the gas? Try some HEET.
Get it running, spray the carb , fuel lines, etc. with carb cleaner. If any change happens you have an air leak.
It may be 'mint' but rubber seals and hoses crack over time. That would be the first step.
You can also use compressed air if you wish.

Let us know what happens.
If no joy from that, check the float bowl for sediment. Because you cleaned the carb already, if their is sludge, it will show up there.
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  • #10
Looks like your on it Frans. Blew compressed air on the carb and she died, over and over. It looks like where the boot from the carb to the air cleaner connects, the circle it presses into has alot of slack between it and the rubber boot. I am thinking I should probably make an aluminum plate to rivet to the front to make the hole smaller and have a tighter fit. It's funny because I took it 3 miles around the block then all of a sudden it'll die. Then start.
Down home remedy:

Black electrical tape, ooooor order up some parts.
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  • #12
I'm still confused though. Why would it continuously run excellent for 3-4 miles, then cut out? These 3-4 miles are at WOT too. I am going to replace the ingnition coil assembly also, the sparks seems pretty weak.
A plugged fuel filter perhaps? Does it even have a fuel filter?

Never mind, if the fuel filter was clogged then it wouldn't run excellently for 3-4 miles. :(
I'd say that rubber thingy is making a decent seal when its cold, but then it gets hot and softens up. That's when the seal gives out and you're sucking air. :big-tongue3:
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  • #15
The fuel delivery system is running as it should. Cleaned petcock, drained fuel again, sprayed carb out again, changed fuel filter, removed fuel filter and ran a straight line. I'm going to order some parts, see what happens.

ummm... fuel filter maybe, check float level. sometimes floats have tiny holes too. or float valve itself, or it might be electrical - once something gets hot

its pimp though, i roll an xr50
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  • #21
I used to have a 00' XR50, and a 05' XR70. I got tired of them, and considering everytime I rode on the road I'd have to keep lookout for cops. Didn't stop us most of the time though.

The new one is strictly a street cruiser, chick magnet. 8)
you're gonna have to beat'em off with a stick -

I would probably opt for a more bass boat like color - more bling - chrome, and a some kind of horn that lets people know you mean business.
I would try the tape before ordering $200 in parts, unless the $200 in parts includes alot of the aformentioned chrome.:D
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  • #24
Haha, no chrome. The airbox parts are only like $40. A battery, some electrical parts, and a few odds and ends makes up that bill.