Re: Yamaha QT 50 oddity

I rode to work this morning, with the fuel shut off valve only 3/4 open. No better... I thought that slowing down the fuel supply might help.... no dice...

I know what you mean about the float. But im not sure I can make it run lower... Its just sits on a bushing/axle looking thing, and I don't remember a 'stop' that opne could move around...

THe needle is sitting at the bottom of the slider now. I wonder if its making it all the way out of the jet? Is that what you mean by moving it up some?

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

If you re-read my last post you will see that if the needle clip is in the top slot, needle as low as possible, this is the leanest position.

Your float most likely adjusts like a car float. There is a tab on it that pushes on the float needle. Bending this tab adjusts the float height from the top surface of the carb. Measure the current float height if you decide to change it so you can go back.

If you pull your fuel line and turn the gas tap to 3/4, you will most likely see way more gas than your engine can use. The chances of controlling mixture this way are real close to zero.

Ron

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> If you re-read my last post you will see that if the needle

> clip is in the top slot, needle as low as possible, this is

> the leanest position.

>

I took it apart today, and carefully looked around... The needle doesn't seem movable (well it is, but it doesn't seem meant to be moved and left there) The spring for the throttle cable goes down into the slider, and rests on the needle.... so moving it up the slider, the spring would only push it down again...

> Your float most likely adjusts like a car float. There is a

> tab on it that pushes on the float needle. Bending this tab

> adjusts the float height from the top surface of the carb.

> Measure the current float height if you decide to change it

> so you can go back.

THe needle has a notch in theend of it, similar to a nail head. the 'head' sits in a slot on the float. The play in this slot, is what appears to stop the float. No metal stuff around, save for the little axle the float hinges on...

I adjusted the oil pump cable a hair past the mark the manual mentions. The pump will still pump oil, at idle and at WOT, im pretty sure... I don't think I'll keep it this way for long...

Im thinking about stopping by the Yamaha dealer tommorrow, too...

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

Obviously, I have not seen the inside of this carb and no one else seems inclined to jump in and straighten me out.

The needle in most carbs has grooves near the top with a clip in one of them, the clip is then held in place by the spring. If you do not have this and the relationship between the float and the float needle is not adjustable I guess the only choice you have is a smaller main jet.

It bothers me a bit that you have to fix a problem which did not used to exist by changing a part which should never wear. I suppose, if the slide needle never comes all the way out of the needle jet, then it could have worn, or the needle jet could have worn from the needle rubbing on it.

Ron

Re: Yamaha QT 50 oddity

Man long thread!

check this out:

http://mopedarmy.com/forums/discuss/1/13028/11497/

its another forum with a QT50 with similar trouble, though im getting about 26 out of it on a good day... but it still intermittantly looses power... Some dude on the above thread mentions the piston rings...

what intrigues me is that the mechanic at the Yamaha shop last night mentioned that one of the rings might have a problem, and it leaking periodically, and then loosing compression. That kinda makes sense, as I have been through everything else, and thats how the engine sounds. Its still firing when the loss of power occurs, and it kinda sounds as if it were loosing compression.

He says the head comes off, and then the block/cylinder slides off, leaving the piston and crank behind. I might try looking at that this weekend...

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

You have classic symptoms of running too rich but if you really want to check the rings, just pull the exhaust and look through the port. You can press on the rings slightly with something non metallic and check that they are not broken (will be loose) or stuck (will be tight). You can also check for carbon in the exhaust port.

Btw, did my last post tell you anything and can you tell me anything in response?

Ron.

Re: Yamaha QT 50 oddity

the needle doesn't look worn... I didn't look at the jet when it was apart... I will try to remember to check that when I attempt to get the head off. it can't hurt to clean that out can it?

You have also mentioned that I could check the rings through the exhaust... the intake is on the very top of the motor, and the exhaust on the very bottom... not the easiest to get at... I find it easier to pull the head, with the 4 stud bolts, than to take the battery off, the gas tank off, and then lean the bike upside down to get at the exhaust (really well; I did try once with the bike leaning over on its side, but it wasn't very fun... :)

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

Go for it.

Ron

Re: Yamaha QT 50 oddity

ROn,

Took the head and the block off the crankcase tonight...

Nothing bad to report, I mean I didn't find an obvious problem... I did get a better angle on the exhaust port,a nd was able to clean it better... Got more gung out of the corners....

the head was and the piston top were kinda crusty, so I cleaned those carefully with a small screw driver and a couple wire brushes.

The spark plug is clean as a whistle again. the new one was slightly black with soot before I made the first oil pump adjustment... Does that blow the theory of it running rich?

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

I don't have time to re-read all of these posts so let me try to summarize from memory and you can correct me.

You bought the ped, it had not been run for years but ran fine.

It began "4 cycling" (my terminolgy) at about 25 mph.

Removing the air cleaner and box did not help.

Turning off the gas at full speed caused the power to return just before it died.

Cleaning the carb did not help.

Decarbonizing the cylinder and exhaust port did not help.

Conclusion:

Your ped is running too rich.

Maybe the carb was partially plugged when you got it and running fresh gas through it cleaned it up some and you need a smaller main jet.

Maybe your needle and/or jet are worn.

Maybe there is fuel in the float, affecting your fuel level.

I am surprised that removing the air cleaner and air box does not help but I guess yours must be a really good design.

Review all of this then re-post.

Ron

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> I don't have time to re-read all of these posts so let me try

> to summarize from memory and you can correct me.

>

> You bought the ped, it had not been run for years but ran fine.

It did run fine, but Im not sure how long it sat... I could have been only a couple weeks, as the kid I bought it from was letting people try it ou while he was selling it... and I think a younger brother or neighbor was riding it too... so I can't sat say it sat for years, more like a few weeks, if anything... and its got just 2000 miles on it...

>

> It began "4 cycling" (my terminolgy) at about 25 mph.

it does indeed sound funny. A sudden lose of power is all I can say for sure. Ive never heard a true example of 4 cycling, so I can't say that for sure. A friend of mine also mentioned the word 4 cycling when he rode it the other day... so that might be the case...

>

> Removing the air cleaner and box did not help.

You know, I don;t think i have tried that since I adjusted the oil pump the first time.

>

> Turning off the gas at full speed caused the power to return

> just before it died.

Not power to return, just stopped loosing power long enough for the speed to build up...

>

> Cleaning the carb did not help.

correct.

>

> Decarbonizing the cylinder and exhaust port did not help.

nope... something did change though... its cutting out more often now.... and taking longer to recover.

>

> Conclusion:

>

> Your ped is running too rich.

I was thinking it might be running too lean, actually, after seeing the spark plug again.

>

> Maybe the carb was partially plugged when you got it and

> running fresh gas through it cleaned it up some and you need

> a smaller main jet.

>

> Maybe your needle and/or jet are worn.

>

> Maybe there is fuel in the float, affecting your fuel level.

THe last time i had the carb off, I poured some gas in a big bowl, and held the float under the gas for a few minutes... didn't seem to gather any gas inside it... and I didn't see bubbles of air escaping.

>

> I am surprised that removing the air cleaner and air box does

> not help but I guess yours must be a really good design.

I'll try this as soon as I get a chance, that and the exhaust pipe too... which hasn't been ruled out yet either...

>

> Review all of this then re-post.

>

> Ron

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

Without being picky here, this is a classic symptom of running too rich. If you are too lean, you should be able to speed up by operating the choke slightly/briefly.

>> Turning off the gas at full speed caused the power to return

>> just before it died.

>Not power to return, just stopped loosing power long enough for the speed to build up...

You have to shake the float to check for gas inside it. The chances of having a big enough leak to sink it or blow bubbles are slim.

>> Maybe there is fuel in the float, affecting your fuel level.

> THe last time i had the carb off, I poured some gas in a big bowl, and held the

> float under the gas for a few minutes... didn't seem to gather any gas inside it... > and I didn't see bubbles of air escaping.

What did the plug look like and did you check it after a high speed chop or after idling a while?

> I was thinking it might be running too lean, actually, after seeing the spark plug > again.

By the way, screwing around with the oil injection could cause severe engine damage, besides confusing the symptoms. You should set it exactly as the book says.

Ron

Re: Yamaha QT 50 oddity

Ron Brown wrote:

> You have to shake the float to check for gas inside it. The

> chances of having a big enough leak to sink it or blow

> bubbles are slim.

Didn't hear any gas in it, nor did i see any...

>

> What did the plug look like and did you check it after a high

> speed chop or after idling a while?

After running like it has for a week or so, its a very light tan color. almost a Khaki color.

> By the way, screwing around with the oil injection could

> cause severe engine damage, besides confusing the symptoms.

> You should set it exactly as the book says.

I just adjusted to to spec. It was out of line, and took care of ALOT of the same 'flooding out' kinda of sound the engine had... There are also a couple adjustments that need to be checked by someone with special tools... I might have the Yamaha shop look at that...

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

Re-read this question and answer it again.

Ron

>

> What did the plug look like and did you check it after a high

> speed chop or after idling a while?

After running like it has for a week or so, its a very light tan color. almost a Khaki color.

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> Re-read this question and answer it again.

>

> Ron

> >

> > What did the plug look like and did you check it after a high

> > speed chop or after idling a while?

>

Brown. the color is brown.

> After running like it has for a week or so, its a very light

> tan color. almost a Khaki color.

Re: Yamaha QT 50 oddity

I got a smaller main jet, and put that in today... Had to special order it, that why ive been so quiet this past week...

but the damn thing won't start at all... I put the old jet back in, and its not even fireing I don't think. I pulled the spark plugm and held it to the block, and I can't see a spark... I one little weak one, but that seemed to be it...

I got out a little multi meter, and the coil tests out of range for resistance. the primary is about .3 ohm (supposed to be 1.5), and the secondary tests at 10 Kohm.(supposed to be 6Kohm)

Worthy of a new coil? the Yamaha shop says they are only $35....

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

Your coil is most likely ok. Different meters give different readings and yours sounds close enough.

If you have points, make sure they are opening and closing and making good contact.

If not, check all the connections to the electroninic ignition module and ignition switch. Make sure the plug cap is good too. Especially look for something you may have disturbed while changing the jet.

Ron

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> Your coil is most likely ok. Different meters give different

> readings and yours sounds close enough.

I checked again i nthe evening, and in the darker light, I could see a good spark. But it still doesn't fire...

>

> If you have points, make sure they are opening and closing

> and making good contact.

>

> If not, check all the connections to the electroninic

> ignition module and ignition switch. Make sure the plug cap

> is good too. Especially look for something you may have

> disturbed while changing the jet.

There are no wires around the carb. and everything checks out... I pulled the gas line, and it spits out gas, just like it should...

it just refuses to fire... could the plug be somehow be getting Un grounded when in the head?

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

Does the plug get wet? If not, something is plugged in the carb. If wet, try a new plug.

There is no way for the plug not to be grounded when installed but it can leak to ground because of fouling.

Ron

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> Does the plug get wet? If not, something is plugged in the

> carb. If wet, try a new plug.

>

> There is no way for the plug not to be grounded when

> installed but it can leak to ground because of fouling.

>

> Ron

I while the new jetwas on special order, I had the carb just sitting there, on the bike, with the bowl off, under the front steps, but it never rained anyway... I wonder if a spider or something crawled in there, and died in a passage? I'm gonna check that, and pull the head and block off again...

Oh, the spark plug seems dry...

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

If the plug is dry, there is no reason to pull the cylinder until you are getting gas through the carb.

Ron

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> If the plug is dry, there is no reason to pull the cylinder

> until you are getting gas through the carb.

>

> Ron

You want to buy a used Yamaha QT 50?

I pulled the carb, and looked around, and it didn't seem plugged at all...

I put my thumb over the intake, and pulled the kickstart, and I could feel something, but I couldn't tell if it was suction or blowing... I grabbed a couple pieces for grass nearby, and held them infront of it, and they didn't blow out... so I assume that the intake is sucking, but not very hard...

Still not firing. The spark plug seems dry. the intake side of the carb is wet with gas. and there is a spark. WTF?!?! junk it?

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

I am not familiar enough with this bike to be specific but if you do not have the throttle open, you will get very little suction at the intake. If you have a reed valve, it could be bad. It is hard to imagine a cylinder/piston problem causing this without you noticing a complete lack of compression.

Ron

Re: Yamaha QT 50 oddity

thats the one ting I havne't checked... its a bitch to get to. the screws for the intake manifold are right up against the bottom of the frame, so I would have to drop the engine... Which I think I might just have to do... If it was cracked, that would also explain the iintermittance of the previous problems too, you think?

Ron Brown wrote:

>

> Bryan,

>

> I am not familiar enough with this bike to be specific but if

> you do not have the throttle open, you will get very little

> suction at the intake. If you have a reed valve, it could be

> bad. It is hard to imagine a cylinder/piston problem causing

> this without you noticing a complete lack of compression.

>

> Ron

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> I am not familiar enough with this bike to be specific but if

> you do not have the throttle open, you will get very little

> suction at the intake. If you have a reed valve, it could be

> bad. It is hard to imagine a cylinder/piston problem causing

> this without you noticing a complete lack of compression.

>

> Ron

reed valve is fine... its not so bad to take the engine off, but to get it on, alone WOW!! thats rough.... :)

I loossenedthe exhuast, and it started, but idled very rough. I pulled the pip off altogether and it runs like a top, with the smaller jet. Haven't tried with the larger one (orginal).

SO, is seems that a plugged pipe all along... The local Yamaha she wants $112 for a new one.... :( Im scoping out ebay now, and my uncle runs a kawasaki shop, I might ask him what he could do... OR I might try building a glasspack that I can swap out when it plugs again...

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

This sounds like a hell of a plug.

Try poking wires in both ends and see if you can pull anything out.

Ron

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> This sounds like a hell of a plug.

>

> Try poking wires in both ends and see if you can pull

> anything out.

>

> Ron

I did that, on the suggstion of my uncle that runs a cycle shop. THat ot a torch up both ends to try to burn anything out...

I used a wire coat hanger, and made a little loop at the end of it... to use like a pipe cleaner... and I pulled out some carbon, not a lot though... but the real thing was a glob of little inch worms the size of a cotton ball... Icky-poo!! Its runs pretty well now, but I lossened the exhaust and stuck a washer in betwee nthat the head, to let is vent some more, and it runs like a top!

Loud as hell, but I get 30mph on level gound, where as I started with 25 tops before...

thanks for all you help, but I think I back in the saddle now...

Re: Yamaha QT 50 oddity

Ron Brown wrote:

>

> Bryan,

>

> This sounds like a hell of a plug.

>

> Try poking wires in both ends and see if you can pull

> anything out.

>

> Ron

I did that, on the suggstion of my uncle that runs a cycle shop. THat ot a torch up both ends to try to burn anything out...

I used a wire coat hanger, and made a little loop at the end of it... to use like a pipe cleaner... and I pulled out some carbon, not a lot though... but the real thing was a glob of little inch worms the size of a cotton ball... Icky-poo!! Its runs pretty well now, but I lossened the exhaust and stuck a washer in betwee nthat and the head, to let is vent some more, and it runs like a top!

Loud as hell, but I get 30mph on level gound, where as I started with 25 tops before...

thanks for all you help, but I think I back in the saddle now...

Re: Yamaha QT 50 oddity

Ron Brown /

Bryan,

Outstanding!

Be a little carefull about running with leaky exhaust, this can lean you out enough to burn the piston. See if you can find some way to clean the exhaust.

I have never tried this, but in the olden days when men were men and no chemicals ever did any harm, the recommended way of cleany a 2 cycle exhaust was to pug one end and fill the pipe with caustic soda solution. I believe that is quick lime or unslaked lime. It gets really hot when you add water. Ask your uncle if he heard of it and happy pedding.

Ron

Re: Yamaha QT 50 oddity

An acetylene torch works great for burning out carbon in an expansion chamber

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