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Subject: "Yamaha QT50 Problem"    
Conferences > International Moped BBS > Topic #1223
Reading Topic #1223

illinilee
unregistered user
Sep-29-05, 02:09 PM (EDT)
 
"Yamaha QT50 Problem"
 
   I have a QT50 (w/1120 miles) that I just got running. It starts and runs well up to about 20-22 mph then seems as thought the spark is retarded, like a govenor. I have read it should run 30-32 and it seems like it could except for this issue. I have done the following:

Rebuilt the carb.
Replaced the plug.
Replaced the battery.

Maybe the battery is bad and not providing enough current to run it past that speed? Either that or my next step is the replace the coil, but it starts and runs so well up to 20-22mph I don't think the coil is bad.

I would appreciate any help.

Lee


 

 
Quick 350
Member since Mar-2-05
77 posts
Sep-29-05, 03:09 PM (EDT)
 
1. "RE: Yamaha QT50 Problem"
In response to message #0
 
   Is the motor winding out at that speed or does it seem to just put a long?

If it's just putting you might need to raze the needle jet a notch or two.

sounds to me like it’s a fuel delivery problem.

Recheck all your carb adjustments again and see what you come up with.

Mike


 
illinilee
unregistered user
Sep-29-05, 04:05 PM (EDT)
 
2. "RE: Yamaha QT50 Problem"
In response to message #1
 
   It will not wind out to redline. It just seems to get 3/4 there and can't exceed it.

Lee


 
Quick 350
Member since Mar-2-05
77 posts
Sep-29-05, 07:51 PM (EDT)
 
3. "RE: Yamaha QT50 Problem"
In response to message #2
 
   If your compression is good then it's a fuel problem.

Check you carb out and see where the needle jet is.

If it's in the center move it up a notch and see what that does.

Good Luck!

Mike


 
illinilee
Member since Sep-29-05
1 posts
Sep-29-05, 09:38 PM (EDT)
 
4. "RE: Yamaha QT50 Problem"
In response to message #1
 
  
Mike:

I pulled and cleaned the jet, adjusted the needle and rodded the exhaust pipe. It got up to 27mph. I found later that the airbox was not connected to the carb. boot. That airbox is very restrictive. I wont go without but may modify it for better air flow. Should the carb be rejetted if I mod. the airbox?

I want to get it to 30-35mph.

It's too cold to do anymore testing tonight.

TIA

Lee


 
Quick 350
Member since Mar-2-05
77 posts
Sep-30-05, 08:01 AM (EDT)
 
5. "RE: Yamaha QT50 Problem"
In response to message #4
 
   I don't believe that you will need to rejet.

A friend of mine has one of those Go-Ped HI-PO filters on his QT50 and it runs great.

His bike does a good 30mph at times but he also weighs about 110 lbs.

These bike aren't know for speed.

Good luck!

And remember it doesn't hurt to try different thing out.

Mike


 
tom
unregistered user
Oct-16-05, 10:55 PM (EDT)
 
7. "RE: Yamaha QT50 Problem"
In response to message #4
 
   i own a yamaha qt50, it runs fine! every time i go on it tho it always wants to get more out of it, giving little jerks, like it wants to go faster! does any one know how to make my qt go just that bit more it is trying to do??????? any help would be great!


 
terico
unregistered user
Oct-14-05, 04:59 PM (EDT)
 
6. "RE: Yamaha QT50 Problem"
In response to message #0
 
   My wife has a 1982 model with only 300 miles on it and from new it gasped and misfired around 26 mph, only reaching 30 over a cliff edge. I tried everything, or so I thought, except raising the needle. I have not looked at it for 4 years or more but I don't recall any more than a single notch in the needle? I reckon Yamaha may have boobed with the standard ignition timing settings, but I never spent enough time on it. May do next summer!


 
veedubtub
unregistered user
Oct-20-05, 07:28 PM (EDT)
 
8. "RE: Yamaha QT50 Problem"
In response to message #0
 
   your coil could be going bad or a ground wire to the engine need to be redone.


 
alphacat
unregistered user
Jun-05-06, 05:14 PM (EDT)
 
9. "RE: Yamaha QT50 Problem"
In response to message #0
 
   Suggest you also check the continuity of the spark plug wire.
If it has too much resistance, it will not provide sufficient spark to ignite the fuel at higher RPMs.


 
GEAR OIL
unregistered user
Jun-17-06, 02:24 PM (EDT)
 
11. "RE: Yamaha QT50 Problem"
In response to message #9
 
   HI ALL.... DOES ANY-ONE KNOW WHAT KIND OF GEAR OIL A QT50 USES IN THE SHAFT DRIVE? MINE IS LOW AND I DON'T KNOW WHAT KIND AND WIEGHT TO USE PLEASE HELP!


 
mark
unregistered user
Jun-29-06, 02:21 PM (EDT)
 
16. "RE: Yamaha QT50 Problem"
In response to message #11
 
   yes..the gearbox needs to be drained, and flushed...just tip it slightly when you are flushing it...the drain bolt is on the bottom left..it takes NON detergent sae 30 i recommend changing it every 6 months if you do any kind of riding...Mark


 
Jerry
unregistered user
Jun-05-06, 08:29 PM (EDT)
 
10. "RE: Yamaha QT50 Problem"
In response to message #0
 
   Hi Lee. I have a qt 50 that only runs 15 mphs. Mine sounds like it wants to go faster, but its like the cluch is slipping. And like yours it kind of acts like its got a govenor on it. Did you get yours fixed, if so, what was the problem? Thanks Jerry


 
82QT50
unregistered user
Jun-22-06, 09:33 AM (EDT)
 
12. "RE: Yamaha QT50 Problem"
In response to message #10
 
   Yes, I am a die-hard QT50 fan. It is the only moped I have ever owned, that my father bought for me when I was around 10. I still to this day ride it to work and use it on a mostly daily basis as it is my most important and reliable source of transportation. A QT50 is hands down indestructible. Mine (and my buddies) has been through hell and back.. several times, then drug back down again for a final blow...being ridden as a dirtbike for a year.. and she still purrs.
anyways, the most common problem with qt50's with the "restricted problem" is in fact a combination of simple things.
the stock main jet is a 65.0 this "floods" out the motor at high speeds under a heavy load. getting a 70.0 or 75 jet will be a great investment. Also, the air boxes are very restrictive. You either need to drill holes in the back cover, or buy a K&N or UNI pod air filter for full breathing. Another very common problem is the exhaust pipe gets full of muck, as does the exhaust port in the cylinder. What needs to be done is to take off the pipe (pretty straight forward process, but watch for stripping the bolts!) then stuff a potato or onion in the end and fill it up with kerosene. Let it sit this way for a few days, then drain it out and squirt hose water down it full force to rinse it. Then while the pipe is off, check your exhaust port.. either lay the bike on its side or lay on your back. shine a light in the hole and check the shape. It should not be round but have a triangle with its top cut off look.

___
/___\

something like that
just make sure theres no crud blocking up the works, and carefully scrape it out if there is. careful not to damage the rings. When done squirt wd-40 in there and crank it over a few times then wipe a cloth or clean rag around the edges of the port to get the extra crap.
Bolt your pipe back on, then take off the carb. can be done with a philips and a regular screwdriver clean out every passage with compressed air. If you dont have an air compressor.. spend 5 bucks on a can of air at your local store electronics section. Put in your new Jet then strap it back on. this will not take long.. its a very simple carburetor! before plugging the fuel line back into the carb, check too see how fast its coming out of the petcock. if its pretty slow.. it will actually cause your motor to "quit" and run out of gas on a very hard pull. You may need to switch it to reserve position for a quick fix, or clean the petcock out. just make sure it flows nice from the hose. next, it is VERY important to drain your OLD 2 stroke oil and run high quality synthetic oil such as Yamahalube or anything else that will NOT clog the port and pipe again. this is VERY important. then, just throw on your new K&N filter then fire it up. guaranteed to be a new machine and will pull away from your buddies.


 
Jerry
unregistered user
Jun-27-06, 02:08 PM (EDT)
 
13. "RE: Yamaha QT50 Problem"
In response to message #12
 
   Hey where can you buy a 70 or 75 jet? Thanks Jerry


 
Yamahaman
unregistered user
Jun-28-06, 07:10 PM (EDT)
 
14. "RE: Yamaha QT50 Problem"
In response to message #12
 
   I also have a QT5. When I get on the gas and get to about 25-27mph. the engine quits, then resumes power, then quits, then resumes power. Sounds like you already answered that question. Where do you get the new jet? Where can I get the K&N for this bike?

More problems.

I have no front or rear brakes. The shoes are probably gone. Is this a huge job to change them? where do I get parts?

Thanks


 
donp
Member since Sep-8-02
995 posts
Jun-28-06, 08:13 PM (EDT)
Click to send message via ICQ  
15. "RE: Yamaha QT50 Problem"
In response to message #14
 
   go to www.partsfish.com. you can get the parts you need there.

donp

Mow-Ped
lawn mowers-bicycles-mopeds
sales and service
1695 Sunview dr
Lyndhurst, Ohio 44124


 
Yamahaman
unregistered user
Jun-30-06, 01:59 PM (EDT)
 
17. "RE: Yamaha QT50 Problem"
In response to message #12
 
   Once you add a K&N style filter, how do the plastic side covers clip onto the bike (the ones that cover the carb and the other thing on the other side of the bike. Mine appear to use notches in the air box. I assume I am completely getting rid of the airbox and replacing it with the universal cylindical K&N


Thanks


 
82QT50
unregistered user
Jul-06-06, 03:59 AM (EDT)
 
18. "RE: Yamaha QT50 Problem"
In response to message #17
 
   Hey guys, sorry about not getting back to you all in time.
the first thing you all should do is try this simple thing first.

Dont RUN the moped like this forever of course, but for a test, take off the airbox completely. then also remove the black rubber/plastic peace on the end of the carburetor where the airbox slides onto. Now try running it up the road. If this fixes your problem, then all you need is to buy a K&N or UNI. if not.. your pipe is clogged more then likely.
its weird, but for some reason, the little black piece on the end of the carb actually restricts the air in just the right amount to make some qt50's bog like you are talking about. give it a shot.
oh and also, heres the air filters.

UNI-http://www.mfgsupply.com/m/c/UP4125ST.html?id=yMnLmdHr
K&N-http://www.n2performance.com/customer/product.php?productid=KNERU-0060

P.S - yes, the pretty side cover wont fit with any of the clamp on filters. ohh well!


 
fixer
Member since Jul-10-06
2 posts
Jul-18-06, 09:59 AM (EDT)
 
22. "RE: Yamaha QT50 Problem"
In response to message #18
 
   Well I ordered the KNERU-0060 K&N Air Filter for my 83 QT50. WRONG SIZE! The internal diameter where it attaches to the carburettor is way too big. I tried wrapping electrical tape around the carb but the carb would just "spit" the filter right off when I tried to tighten the clamp. I cut off the end of the O.E. black boot that goes between the air box and the carb and put it on the carb but had no success getting this K&N to stay in place. I finally super glued the aforementioned piece of boot to the orifice of the K&N filter(after thoroughly cleaning both parts) and that worked. Hey 82QT50: did you actually INSTALL one of the filters to which you refer????


 
donp
Member since Sep-8-02
995 posts
Jul-07-06, 07:40 AM (EDT)
Click to send message via ICQ  
20. "RE: Yamaha QT50 Problem"
In response to message #12
 
   "the stock main jet is a 65.0 this "floods" out the motor at high speeds under a heavy load. getting a 70.0 or 75 jet will be a great investment"


uuuuummmmmmm, this sentence makes no sense.
if the stock jet floods out the engine at high speed, why would you go bigger? if it does flood the engine, going bigger would only flood it more. stock jets are not designed to flood anything. if your engine is flooding at any time, you have other problems such as;
improper float height
sticky float hinge pin
worn needle and seat
dirt in needle and seat
leaky float
plugged exhaust port
plugged exhaust
bad spark plug
improper spark timing
the things i listed will cause flooding, but a stock jet is not designed to flood at high rpm. no manufacturer would design anything to work like that.

donp

Mow-Ped
lawn mowers-bicycles-mopeds
sales and service
1695 Sunview dr
Lyndhurst, Ohio 44124


 
fixer
Member since Jul-10-06
2 posts
Jul-10-06, 03:05 PM (EDT)
 
21. "RE: Yamaha QT50 Problem"
In response to message #20
 
   The stock jet in a QT50 is a 70, not a 65. And, no, they aren't set up to "flood" at top speed but that doesn't mean they are jetted for optimum performance. The manufacturer would rather be a little rich at the top end rather than be lean and end up with fried pistons under warranty.
The best way to find out what is going on with the mixture at the top end is by doing a "plug chop". With a brand new spark plug and the bike fully warmed up get it on a straightaway where you will be unimpeded for at least a half a mile. Hold it wide open for the half mile then kill the engine while going along.When you come to a stop, pull the plug and check the color. A nice milk chocolate brown is just right. White is, of course, too lean. And dark is too rich. If too rich change to a 65 jet. If too lean, try the 75.


 
g2daillie
unregistered user
Jul-06-06, 05:18 PM (EDT)
 
19. "RE: Yamaha QT50 Problem"
In response to message #0
 
   Hey look on the carb there will be a screw with a spring around it start the engine while the moped is on the kick stand don’t give it any gas if the tire moves your (idling speed) gas settings are to rich turn it, I cant remember if I turned mine to the left or to the right any way you turn it and when the tire slows down then apply the rear brakes then let go if the tire still moves turn it slower till the motor sounds right and the tire just stops


 
liftfan
Member since Aug-9-06
1 posts
Sep-09-06, 03:55 PM (EDT)
 
23. "RE: Yamaha QT50 Problem"
In response to message #19
 
   Somewhere in this BBS I read that somone have a used QT50
CDI for sale at $20.00.

Could that person contact me or anyone with a 1981 QT50
CDI unit for sale.

thanks

LIFTFAN.

Liftfan


 
donp
Member since Sep-8-02
995 posts
Sep-10-06, 08:55 AM (EDT)
Click to send message via ICQ  
24. "RE: Yamaha QT50 Problem"
In response to message #23
 
   go to www.partsfish.com, and sign up to be a member. you can get it new there.

donp

Mow-Ped
lawn mowers-bicycles-mopeds
sales and service
1695 Sunview dr
Lyndhurst, Ohio 44124


 

 

 


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