QT 50 First ride....

Hello everyone,

i finally did my first run on my QT 50. Its running pretty good. It does about 25-27 mph and up some pretty steep hills it does 20 and holds it. I did about 11 miles and it was a blast.

I have to appologize to someone who posted and who i responded to. It looks like it does have two speeds. I noticed it tonight. Espeically now that i changed out the tranny fluid.

Also someone mentioned about the hesitation on the top end. I still have it in mine despite my current carb adjustment. I have a feeling it is a rev limiter of some kind. when i hit a hill i can give it full throttle no problem and it doesn't bog as it slows a bit and has a load on it. it jsut accellerates, if it was a carb problem i would think it would be sputtering and coughing. And would loose the power up the hill when pulled all the way back. I'm going to keep playing with it and see. Anyone have any ideas? any other qt owners notice this?

I know if i adjust the carb anymore it'll have a hard time starting and won't run as smooth as it is now.

Re: QT 50 First ride....

Yeah i had the same problem and i also got sick of going 28mph so it's now bored 50 over with custom cold air intake tri zinger carb (60cc) and i am probably going to go with a cdi off of the tri zinger because it has no rev limiter the qt50 does,and a fabricated leo vince exhaust,but the ride on the stock qt50 is very comfortable hope you enjoy!

Re: QT 50 First ride....


i to just had my first ride on my qt50 this morning. in your post it says you replaced the tranny oil how much oil did you replace it with? i put i think 300 ml in mine when i replaced it last night is that enough?



Re: QT 50 First ride....

thats fine. Its a little more if you took the whole side cover off and replaced stuff. But a simple change is 300. Get a manual off of www.mopedriders.org. its under maintnance, its great to have. Its in .pdf format.

Re: QT 50 First ride....

ok, i have a QT50, that hesitation is probably the motor runnin rich and "4-stroking". The QT50's had a problem with there air boxes...they were to restrictive and the motor would starve for air. remive the air box and run it and see if it makes a difference.

no REV limiters either

Re: QT 50 First ride....

correction...they did have a rev limiter, but that was only in the start position on the key switch. after you switch to run, they dont have any limiter.

Re: QT 50 First ride....

I did another ride this morning. Had a blast as usual. I also went to a empty parking lot to try some adjustments on the carb. Tried lowering and highering the needle and it didn't do much. In one position it bogged at start off. Also played with the airsscrew. hat didn't do too much, but i found a position it run best on. So i put the needle back to the middle factory position. i removed the air filter and it didn't change. I think I'm going to assume its the gas flow. The petcock is clean but its got the stupid bowl on the bottom of it. It doesn't allow the fuel to just rush down. When i had my go kart gas tank on the ped to try it out it didn't seem to hesitate like this. I only did like one run because the control unit was messed up, so I'm not positive, but i think so. I don't know whey they didn't just make the shut off direct like most other bikes. It seems like it has to fill that bowl up then overlflow and run down the ful line. Just an idea for now. I'm going to take and strap my go-kart tank to the rear rack and see if it runs like it did that time i tested it. Just gotta get some longer line. I'll let you know. If thats the case i'm going to try a mod to the petcock. Hopefully this will help other owners having the same issue.


Re: QT 50 First ride....

its definitely not the petcock. The fuel is flowing good. I played around with the needle on the throttle tonight and it seemed to smooth some of it out. it still seems to four stroke a bit at full throttle but if i leave it a bit back from there it runs great. I lowered the needle one notch down and it seemed to improve take off as well as smooth out the top end. before it was fussy to get it to stop four stroking. now it runs steady as long as I don't pull it full back. next step is to take the air filter off and see if it stops for good. I took the air filter off on the stock needle setting ( in the middle) and it didn't do much. Maybe it'll work here since i leaned it out a bit by lowering the needle. I'll keep posting what i find out. Hope this is helping some of you QT owners that are having the same problem. if that doesn't work then i guess I'll try another jet down. Any one else got any suggestions? So far its been a very interesting learning experience.

if i get a new jet do i need to get a new needle?

Re: QT 50 First ride....

One of my qt's stoped 4-stroking and ran a lot better with a good carb cleaning, pre-mix instead of injection and opening up the airbox.

the other one still bogs a little at the top. these bikes are slow because of a lot of rich fuel and not much air.

It is amazing what the QT will use for fuel. I've used some nasty gas, some super rich gas and have purposely tried to foul the plus with too much oil. It smokes like crazy but doesn't foul. most of my other bikes would foul out within a few minutes of a yucky mix.

I scanned those two QT manuals. Hope they help. I heard there were some perf parts for them.

Re: QT electronics

the QT has one of the most horrible electrical systems you'll ever see on a moped. I swear there are Yugo's with more complex electrical systems.

I'm good with electrical and I pray my QT never has wiring problems.

Re: QT electronics

Its not too bad. I had a electrical problem on mine. The control unit was messing up. I was able to trace the wires easily by the schematic. Once you take a look its pretty much straight forward. Just at first glance its like. What the heck are all these wires. But it all makes sense once you follow it. If you only have a two position on off switch yours doesn't have a controler. But on mie it wouldn't let the ignition advance becasue it was screwed up. I'm runnign it jsut on the cdi and it seems to have fixed it. But i have a new controller coming this week i got off e-bay. I'm wondering if that might help wiht the stuttering at full speed. I remember at one point it stopped and i could have sworn it was when i had the control unit in and it was working on that rare ocassion. We'll see friday. SHould be here.

If i play wiht ym airbox and it does to better i might jsut drill come holes in it to increase airflow. Make sure its on the front so its at least still filtering.

Re: QT electronics

Another run tonight with the new setting on the needle ( one notch up from Center). seems to run pretty good. it still hesitates but not as bad. Only does it at full throttle not in between anywhere like it used to. I also tried taking the air filter off at this setting and it actually made it run worse. Lost a bit of power and bogged slightly. I think for now I'm going to leave it alone. I'm going to price the main jet and see how much it might be for a smaller one. if its cheap I'll get one. if not I'll wait. It was worht a shot but so far i got it running smoother but still have not resided the stuttering at WOT. it does full speed though. just if i try to go beyond that it won't let it go.

Re: QT electronics

If anybody ends up re-jetting their carbs, I'd love to know to what size. Mine has the exact same top end 4-stroking BS.


Re: QT electronics

I'm going to hold off with the jets for now. Seems like most everyone is having this issue. I really am wondering if its normal. I'm not sure if a yamaha dealer would know or not. But i did a plug chop tonight and it seems to be right on. Even if i do a chop when it hesitates. Its still nice and golden brown with a slight brown residie around the outside. No build up and no eating up of the plug or fouling. I put my needle back in the middle also. Going up hills it seems to lug a bit. On straights it seemed smoother by lowering the needle but on hills it lost it some. Other than that it runs great. I run it up to about 26-27 and leave it there. When i hit a hill and need it i can go full throttle and it doesn't 4 stroke that anymore. Not a huge hassle and since the plugs not showing much signs of fauling i'm not too much worried right now. I'll play with it some more when i get a chance. But I would be curious too if anyone ventures out to get a new jet.

Re: QT electronics

I say go for the jet! Last night I took the jet out and filled the intake side (not the needle seat side) with solder - well not so much filled it as put a nice puddle in the orifice which formed in to a little perfect cup via surface tension. Used a 30 watt soldering iron and soft electronics solder. I then proceded to literally poke a hole in the solder with a dental pick. The result? Top end smartened up for sure, but I think I went TOO far so I'll have to open it up even more. Very easy project. If you screw up and get solder all over everything, fear not... Just heat it up to the solder's melting point, put it in a pickle jar, cover the top and shake the hell out of it - no more solder, try again.

Honestly, I think I reduced the jet size no more than .010" which apparently was too much. In order to get it to run properly, I had to run it with the "choke" which isn't really a choke, wide open in order to get a little more fuel in there.

I will update everybody on the results as they become available.


Yay! I finally figured out a jet that makes the QT run right, and it's smaller. Not exactly smaller, but I soldered over the old jet, and made a new hole with a needle, then enlarged it with a piece of steel green floral wire. I'm not 100% sure of the size, nor can I measure it, but it's only a few percent smaller, and it frikkin' runs great. I have no idea how much faster I go either (speedo cable comes in tomorrow), but it completely eliminates the 4 stroking BS at high end, and people pass me last.

The current jet was a 70, I'd try a 75 or smaller.

There's the answer to everybody's QT problem.



Hello Andy,

thats awesome. COngrats. I was doing a search on some old threads and everyone has pretty much had this problem. One of the guys did just as you did but he left the wire in and soldered. I forget exactly what he used. But the solder wouldn't stock to it. once it was cold he pulled it out and it did the same thing. I'm tempted to try it but don't want to mess up the jet. I may do it anyway. I have sime really small drills here too. I can always do that then drill it too.

I guess the main reason for yamaha doing this was so that they could keep it below 30, right around 25. Keep us updated if you notice more changes or when you can get it to run off choke.

Awesome job


appology. I reread and see that you did get it running off choke with the larger hole with the green wire.


I was doing some thinking and some reasearch and i think i might give it a shot. The soldering that is. I took the jet off last night to take a look at it, the size of the hole that is. I'm going to measure it and see how big it is, then see how muhc smaller the wire i have will work. I'm going to do as you and try the needle hole and work from there. I'll let you know how it works for me. Its a nice day so if all goes well i should eb able to test it too. I have one of those twisties they use for the bread bags. Is that about the size hole yours is?


Eh, just about. I'll put a digital vernier to the wire and let you know.

I talked to a carb guy. Jet size goes by the actual numbered drill index size (#60,#70, #75, etc) and those are SMALL and hard to find outside a machine shop supply house. When you solder, clean the hell out of the jet first with a toothbrush and some alcohol. You may even want to give it a carburator cleaner bath. Amonia sometimes cleans brass well too. Make SURE you use a decent electronics grade flux (from Radio-Schmack) and use a soldering pen. Make sure the tip is nice and clean and conical in shape.

Forgive me if you're a confident soldering pro, because I'll explain this for a relative non-soldering person to understand.

1. Place the jet on a flat, heat resistant surface threaded side down, screw slot side up.

2. Apply a small amount of flux to the actual jet orifice area.

3. Clean the iron, dip the end of your sodler wire in some flux and then apply a small amount of solder to the iron tip so a pin-head sized blob of solder hangs from the tip of the iron when you hold it perfectly vertical.

4. Place the tip of the iron in to the orifice and apply a very small amount of pressure and hold it for.... say 10 seconds or so. The flux will smoke off and the sodler will flow in to a nice little dish.

5. Remove the iron and give the jet 30 seconds or so to AIR COOL. The jet is not going to be damaged by the minimal heat of the soldering. There's gonna be flux and other crud that needs to be cleaned away. Toothbrush and solvent to the rescue!

6. If you did it right, there should be a nice smooth little concave dish of solder where the jet used to be, and no leakage to the back side of the jet, where the needle seats. There might be flux though, so...TOOTHBRUSH!

7. Use something sharp like a needle to poke through the solder. Go slow. The solder is softer than the brass, so go slow and you won't damage the jet. You shouldn't need a drill for this. Enlarge to whatever size floats your boat.

8. Trial and error till it runs. Remember, gasoline is flammable, and although I've never seen or heard of it happening, a soldering iron could set it off.

If you screw it up, fear not! solder is very easy to remove. Just heat up the part, then whack it on a hard surface while the solder is liquid. Molten, scorching hot dangerous poisonous heavy metal solder flys everywhere and it's clean. Thats how I do it. The safe way would be to heat it up and put it in a pickle jar, cap it and shake.

Good luck to you.

Re: QT 50 First ride....

I posted another post on what i did. That is great discription. I did similar but i didn't just put a dab of solder. I used the iron to heat the whole jet. Then i added some flux to get it nice and clean and let the solder get sucked in the hole. While it was hot i inserted the wire.

But i love your steps. Very good step by step. It should help anyone that is going through the similar thing we are. If the rain lets up this weekend I'm going to have to go for a real ride with it. I did a ride up the street and it was nice to not have to let off the gas. This is pretty cool. I wonder what the 65 jet from yamaha measures. I looked on bikebandit.com and they offer two jets, a 75 and 65. We have the 70.

All i an say is WOOOO HOOO!!! LOL. Just gotta do that plug chop to see if i need to open it up or not.

Re: QT 50 First ride....

I was told that the jet numbers actually correspond to ANSI drill size numbers - the higher the number, the smaller the drill. See http://www.engineersedge.com/drill_sizes.htm - a 70 is the 0.028 - a 65 is larger at .035. I went smaller. also, had a friend clock me tonight with the new setup - 34 mph on a straight flat. I'm a bit big for the bike at 200 lbs, so it's doing well.... also, just blew the oil seal on the kick starter, so fun fun... any suggestions as to anythign else I should check while I'm in there?


Re: QT 50 First ride....

That sucks the oil seal blew out. How did that happen? did you fill the tranny too much? 34 mph is great. I'm getting about 27-28 on a flat and i am about 170. up hills it'll pull me at 20 mph, but steeper hilsl its 15. the jet seems to be running geat. I did a 30-40 miles ride today and i dida chop on it and it looks nice and golden brown.

I'd change your tranny oil if you aven't already. It only take 300 cc's, about 1/3 quart. Other than that not too much to do. I'd maybe lube some things. the bolt that runs throught the frame to hold the motor. Thats the pivot point for the suspension. It's gonna get some wear. if your shaft drive gear in back hasn't been lubed I'd do that too. Just take that plastic cover off in the back. Not too mucuh else. Just lube thigs as needed and ride. Check tire pressure once in awhile. the front is suppose to be 18 and rear 28. I think the fronts soft so you don't hit those bumps hard. i had them both at 32 psi and it was way too hard. when i read the sticker on the frame it said those two pressures. best of luck on the seal. shouldn't be too hard i hope.

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account