Help for a new guy? QT question

Recently was gifted a 1980 QT50, non-running for 20+ years. The usual story: Lot's of bad varnished gas. I cleaned the tank and replaced the carb with aftermarket. I put a Niche 60cc piston/head kit on it. Ran like a champ for break-in and about 30 minutes. Unfortunately I believe it is soft seizing. I was hoping not to get into the crank seals but that's where I'm at today. I replaced the left side under the stator easy enough but I wrecked a new seal installing on the right side. There is the bushing/collar on the shaft and one end is beveled. I believe the beveled end faces into the motor. The collar that I'm referring to is #6 on the attached drawing.

I couldn't get the new seal on to the collar when the collar was already on the shaft. Is there a special order of installation? For instance, should I put the seal into the case and then insert the collar into the seal? This could make sense since the beveled edge would be the leading edge. Or would this wind up pushing the seal in too far?

Finally, how do you guys know for certain when your oil pump is working? I have no problems with premixing but I need to research how to delete the pump.

Thanks,

yamaha-qt50g-19791980-usa-clutch_bigyau0833b-3_17ca.gif

Re: Help for a new guy? QT question

Put the seal in first, lube the collar and seal lip then gently push the collar in. If your oil pump has been bled just pull the oil line off the carb when it is running just long enough to see if oil is pulsing out of the open end .

Re: Help for a new guy? QT question

Thanks Bob!

Re: Help for a new guy? QT question

Did you upjet accordingly when you put the new kit on? If not that's gonna be more than a soft seize real quick...

You'll know you oil injection isn't a problem when you bypass it and premix...lol. I don't trust injection at all.

Re: Help for a new guy? QT question

Well.... I did not upjet and I'm at 70 on my chinese clone carb. When I say soft seize, I mean it starts okay with choke, warms up, runs very strong for about 3-5 minutes and then stalls. 30 seconds later it restarts but only good for about 1-2 minutes. I'm guessing that this is soft seizing. I have a 49cc head/cyl/piston ready to install and I think that I'm going this direction (stock), along with new crank seals, before I start modding. The only reason I didn't do the seals from the get-go is because the motor only has 700 miles on it. In fact, I haven't even considered the reed valves. What can I say, I'm from a four stroke world but I'm learning.

When you bypass oil injection, do you remove a gear to the pump? Or do you loop a hose?

Re: Help for a new guy? QT question

Jack Rutherford /

When you bypass oil injection, do you remove a gear to the pump? Or do you loop a hose?

Either.

Age is more detrimental than mileage especially with 39 year old seals.

Re: Help for a new guy? QT question

I don't know how well you can see this, but this is a picture of my piston through my exhaust port using a mirror.... I'm not seeing scratches, just some off color (golden). Keep in mind, the piston is only 15-20 minutes old (tops). This is also a fresh plug......not a precise "plug chop". Any observations?

IMG_2834.jpg
IMG_2836.jpg

Re: Help for a new guy? QT question

Which method do you prefer? Aren't the two hose ends different sizes?

Re: Help for a new guy? QT question

Jack Rutherford /

Yeah the oil inlet and outlet are two different sizes. If you can find the hose that will split the different in width between the two, go with that and fasten the loose end down with a zip tie or otherwise.

Just take the head off and while you are at it - the cylinder off the piston. I used to fret about taking the cylinder off after just putting it on but now I just yank the damn thing off and get after it. Then take a picture of your piston and the inside of your cylinder.

Re: Help for a new guy? QT question

Captain Janeway /

> Geoff L Wrote:

> -------------------------------------------------------

> Which method do you prefer? Aren't the two hose ends different sizes?

I run the hoses together because I've had one of those expansion plugs pop out causing immediate engine kill and walk of shame home

Re: Help for a new guy? QT question

ouch... I found a link to this block/plate. Do you think that this requires the whole pump to be pulled off the motor? Is that even possible?

http://www.fastfromthepast.com/dopbop-pw5c

I'd prefer this over a questionable fitting hose solution.

Re: Help for a new guy? QT question

Just my opinion thru experience on original QT50 oil injection system: It's a simple, well engineered dependable system. Two of my QTs have around 4000 miles on them with original injection system still functioning. Oil lines have been replaced during engine rebuilds and system was bled on start-up. It's what I'm sticking with.

Re: Help for a new guy? QT question

I can see two stroke oil at the carb so I'm sure that the pump is at least functioning. j

What makes the motor "four stroke"? Is that too much fuel/too rich of a mixture at that particular time?

My 60cc kit seems to start "four stroking" between 25 and 30 mph WOT. Wouldn't upjetting, a common practice for bigger piston sets, cause this issue?

Re: Help for a new guy? QT question

Jack, thank for this link. I noticed on an old post from you that you used Miniky (clone) carbs. Did you use one on a QT and did you upjet, when and why? Or better yet, do you remember where you got jets from? They look similar to the Mikuni VM12 "large round" jets.

Re: Help for a new guy? QT question

> Bob Naske Wrote:

> -------------------------------------------------------

> Just my opinion thru experience on original QT50 oil injection system:

> It's a simple, well engineered dependable system. Two of my QTs have

> around 4000 miles on them with original injection system still

> functioning. Oil lines have been replaced during engine rebuilds and

> system was bled on start-up. It's what I'm sticking with.

I have an express with 5300 miles and still running the injector just fine. The one thing to remember is that they will leak some oil into motor over long term, like several months or years. This will lead to difficult starting and heavy smoke when started again.

The other thing to watch on qt50 is the oil injection hose that connects to carb. It's under left plastic cover. If the bike is ever wrecked or knocked over on that side it can pull the hose loose or break off the brass nipple on carb. I've found that the express and yamahopper run best with injectors on non synthetic injector oil from the dealership.(edited)

Re: Help for a new guy? QT question

Thanks live evil. That makes sense. I think my injection is working. I've replaced the crank seals today and will take it for a ride tomorrow to see if any changes. If its still dying, I'll revert back to a new 49cc setup.

I'm looking all around the internet for decently priced round main jets. It seems that I could buy 10 sizes that I don't need for about $8 or I can buy one size that could possibly need for $8. By my math, to troubleshoot main jetting I'll be spending about $25-$32.

Re: Help for a new guy? QT question

> Geoff L Wrote:

> -------------------------------------------------------

> I'm looking all around the internet for decently priced round main jets.

> It seems that I could buy 10 sizes that I don't need for about $8 or I

> can buy one size that could possibly need for $8. By my math, to

> troubleshoot main jetting I'll be spending about $25-$32.

You likely already know this site : https://www.jetsrus.com/FAQs/FAQ_identify_that_jet.htm

Not cheap , but , definitely good .

Re: Help for a new guy? QT question

I found that site... but thanks anyway! It will be my likely route.

Re: Help for a new guy? QT question

Another question for the group: How can I rule out an electrical issue caused by temperature? This may not be a soft seize issue at all. The bike fires up and cruises great for five minutes or so and then starts the routine of dying out until it cools down. I'm a points and condenser guy so I immediately think about a failing condenser. This is a CDI, something somewhat foreign to me. I swapped out the CDI for a JOG CDI with no difference. I swapped out the ignition coil with no difference. I tried another carburetor with no difference. I replaced the crank seals.

Its either something that I don't understand regarding the 60cc kit or its ignition related (something that I suspect). The stator coils are low mileage (700 miles). Are these prone to failing under heat?

P.S. - I don't really think the motor is overheating. I only have a handheld lase and the max temp that I saw on the head was around 315 degrees. I've read on this site higher functioning temps.

Re: Help for a new guy? QT question

" The stator coils are low mileage (700 miles)." Are they Chinese knock-offs or OEM Yamaha???? I'd be suspect of inferior materials if they're not OEM.

Re: Help for a new guy? QT question

I honestly don't know. I would assume that they are OEM. They looked OEM and all else is stock on this QT (700 original miles on the bike itself)

Re: Help for a new guy? QT question

You know the old cliche...a picture is worth a thousand words.

Re: Help for a new guy? QT question

A picture of the stator charge coil? I'm 99.9% certain its the stock coil but I will take a picture of it and upload it. Sorry, I may have made this confusing, but I'm asking if there is history of QT50 charge coils going bad? And could a symptom be intermittent failure at certain temperatures?

Re: Help for a new guy? QT question

> Bob Naske Wrote:

> -------------------------------------------------------

> " The stator coils are low mileage (700 miles)." Are they Chinese

> knock-offs or OEM Yamaha???? I'd be suspect of inferior materials if

> they're not OEM.

Re: Help for a new guy? QT question

I was saying that the stator coils are low mileage - because I believe them to be original to the bike that has only 700 miles.

Re: Help for a new guy? QT question

Jack Rutherford /

test your spark and see how strong or weak it is - that may point to the charge coil. qt50s have a weak charge coil especially on the 79 model but it is a problem throughout the years. How does it rev up when you hit the throttle - strong or weak?

And might as well check connections throughout the system - plug boot to plug - tip of plug to connector inside boot - plug boot to ignition coil wire - orange coil wire to its connection - stator wire connection - and look for any missing wire insulation throughout.

Re: Help for a new guy? QT question

What Jack just said and look for rust- remove plastic cover that covers magneto and look around in there. You may have to remove flywheel to really see behind it . Sand the flywheel magnets if they're rusty and tips of all coils,

Re: Help for a new guy? QT question

Jack Rutherford /

video? Also I assume it ran fine before the 60cc kit was installed or what's the history here?

ok never mind on the history - non-running for decades.

check and make sure the gas cap vent is not plugged as well. Install clear fuel line so you can easily verify that the carb is always getting gas because it could be a fuel delivery issue instead.(edited)

Re: Help for a new guy? QT question

I was initially concerned with fuel delivery but have ruled it out. The gas tank had horrible varnish which I thoroughly cleand. I replaced the petcock.....twice. I replaced with the original carb with miniky clone (I didn't even bother with the original carb because of the varnish situation and couldn't find a complete rebuild kit at the time). In fact, I tried two different miniky VM12 clones. I've tried various inline fuel filters. I've even cut the screen off the petcock since I was using an inline filter.

My initial suspicion of fuel delivery was because the motor would stop after 3-5 minutes and when I would look down at the clear fuel line I could see a gigantic air bubble move up the line. Then the motor would start after 30-60 seconds, but only for a brief run (less than a minute). One time when it died i shut the petcock off and actually clamped the line above the carb. The float bowl was full of fuel....so I ruled out fuel starvation. FYI - I checked the float height by using eyeballing the clear drain line next to the bowl (while drain was open). Furthermore, had the same results with two clone carbs.

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