qt50 issues

I got a 1980 qt50 a couple months ago, didn't run when I got it, so I drained the gas, cleaned the carb, new plugs, pretty thorough tuneup overall and got it running. It ran good, but I rode it the other day and at the end of the ride it didn't want to idle and was kind of gutless, and would not run without throttle. Now it won't start at all. I did the oil pump block off conversion and am mixing my gas at 40:1 with no problem until this. I have good spark and can smell gas on the plug. I noticed that the inside of my gas tank is fairly dirty, so I tied the oil tank in as reserve and tried running out of that and still nothing, it almost sounds like no spark, but the spark is great. Any advice would be appreciated, I'm a little stumped here.

Re: qt50 issues

I'd re-do the carb since you say the inside of the tank is a little dirty. Something could have plugged it up after you cleaned it the first time. Make sure to get the long pilot jet under the main jet out and cleaned/unplugged. Hope it comes out ok. Tiny screwdriver carefully.

Re: qt50 issues

^ After you re-clean carb, add an in-line filter. (paper)

Re: qt50 issues

Haven't cleaned the carb yet, went and got new fuel line, filter and shutoff today. Drained all fuel and will clean tank and carburetor tomorrow. I also ordered a new carb just in case. Hopefully I'll be back up and running soon

Re: qt50 issues

I definitely gotta help you. Get a very thin peice of welding wire or guitar string.

Sounds like the finicky bottom chamber jets are plugged. The ones in the float bowl are not always "cleaned" with carb cleaner spray can pressure or even cleaned through soaking.

These jets and the main jet, with the little tube next to it clog easily as well. You can also use a wire twist tie.

Take your time if you do this.

Be careful if you attempt to remove the jet in the little tube.

Youll need a really good jewelers screwdriver to get that one loose (edited)

Re: qt50 issues

Thanks for the help everyone, pulled carb apart this morning and it is definitely the little pilot jet, I totally missed it when I first cleaned the carb. I am going to get a screwdriver set for the jet now.

Re: qt50 issues

I got this good quality set that has 8, 2-3mm wide, 4 inch long rods that remove from the handle. Pretty sure it was intended for pc repair but one of them fits the pilot screw perfectly.

Be careful of the cheap jewelers screwdriver sets.

Ive had them break, midway through the jet removal on similar carburetors

Re: qt50 issues

Got it! I got a weld torch tip cleaning set to clean the jets out. Worked perfectly and she fired right up! Thanks everybody!

Re: qt50 issues

Hell yes! Get that hopper running and enjoy the 25 mph freedom!!!!!

Re: qt50 issues

Get a metal mesh cone type air filter and you might just to enjoy 28 mph freedom, maybe 30 ! All that extra for about $12. Flyin' down the highway !

Re: qt50 issues

Took it for a ride yesterday, short ride, 1/2 mile or so. Ran great. Started right up today, took off and it bogged down again just the same as it was doing before. At this point, I am going to do a full removal and very thorough tank cleaning for both tanks and wait for the new carb. I'm also wondering if my 2 stroke oil is an issue, I'm running a generic motorcycle oil, but am curious if switching to something better will help. Any other tips are welcome, thanks in advance.

Re: qt50 issues

Use synthetic 2 stroke oil for sure.

If you bought a clone carb, be warned. Some of them have the wrong size jets.

You probably need to do another cleaning to that carb.

Also, be sure itys not pulling in air at the intake.

Find an air filter that fits the carb.

Go for a mini bike or pit bike type. Original air filter is notorious for being faulty.

If you have an original petcock fuel valve, check that its filter isnt gummed up.

I broke mine off on purpose and i use an inline filter. (edited)

Re: qt50 issues

So to update, I have pulled the tank and upon further inspection realized it's fairly rusty inside with some sludge in the bottom. I rinsed with old gas 3 or 4 times, got most of the sludge and debris out, then soaked overnight with vinegar. Rinsed the vinegar out this morning and refilled it, have been vigorously shaking tank every couple hours, I have a small handful of nuts in it as well to hopefully break rust and or residue loose. I have also replaced the carb and have a new air filter on the way. Once I have the tank back on I am going to replace the fuel line and filter(again). I think it was a combination of the tank being dirty and some bad 2 stroke oil(it was black and smelled of ammonia, and once I dumped out the rest of the quart it had chunks at the bottom). I might finally get this thing going tomorrow.

Re: qt50 issues

Great progress!

Glad you got a bit dealt with.

Re: qt50 issues

Update 2

Tank is clean, all new lines and filter, petcock clean as well. New carb and air filter. Started up, idled ok, revved good for a minute, then was bogging down when given throttle and wouldn't idle. I am going to pull the new carb apart and inspect the pilot jet on it, I may drill it up bigger(thoughts?). I am a little confused at this point though.


Re: qt50 issues

My girlfriend discovered that her 84 QT50 was bogging today. It was all from the cable junction that the throttle cable comes from. I feel like it was restricting movement for the cable just enough, so it bogged.

I need to lube all of the cable points to be sure this will maintain proper working order.

I moved the junction to a loose area and wired it there.

It revs so well now.

Also, check the screw in parts at the top of the carb. Im not sure the exact specs on how those go in, but i have mine set right for her moped.

Hope this helps

Re: qt50 issues

Problem solved! It was the plate where the choke and throttle connect to the carb. I took a shortcut and ran the old plate on the new carb, that was a mistake. It wasn't exactly the same and wasn't sealing at all. Swapped the new one on today and it fired right up and with some minor carb adjustments it idles perfectly. Took it for a ten minute ride and it ran great!


Re: qt50 issues

Glad you had an easy fix with that.

Ive done that once or twice.

Dont forget to clean the brakes & hub! Hub rust/dirty or glazed pads are like oil at 10mph!

I found decent brakepads on eBay.

Happy riding, man!

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