PW 50 wont start!

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9/4/2013 4:52 PM

I have an 05 pw 50 that i bought used for my three yr old son. It was always a little hard to start ( 10-15 kicks when not warm). It gradually got to the point where it took me 30-40 kicks, till not starting at all. I have cleaned the carb numerous times (including replacing the pilot jet which i had been told was hard to tell if it was fully unclogged). I've rebuilt the top end, and checked the reeds. I pulled the exhaust off to make sure it was not clogged. The bike has spark, and gas through the carb but will not start. However, if i pour gas into the sparkplug hole or spray starting fluid the bike will fire right up but will only run for a few moments until the fuel is burned up. I've tried everything I can think of and my lil boy is gettin pretty tired of waiting!! Hoping for some help guys.


9/4/2013 8:09 PM
Edited Date/Time: 9/4/2013 8:13 PM

You are not getting fuel the carb! You may be getting fuel to the carb, but if it will start with starter fluid and not without it you still have a fuel supply problem.


9/5/2013 4:53 AM

Paw Paw 271 wrote:

You are not getting fuel the carb! You may be getting fuel to the carb, but if it will start with starter fluid and not ...more

I kind of thought that, but ive had the carb off and cleaned and checked all jets. The float is good, and the needle and seat seal properly. I blew out all the holes and tubes. I have reset the air screw and idle screw to factory specs. If I lean the bike over gas will run out the overflow tube. What am I missing?


9/5/2013 10:50 AM

You may not be getting fuel flow through the low speed circuit of the carb. It can be a plugged carb passage, plugged center orfice of the pilot jet or plugged main needle passage. Low vacuum of the engine will also cause this. This can be from low compression.

Have you done a compression test? Putting starter fluid in the cylinder and it runs some times indicates low compression as starter fluid will fire under lower compression than gas.

Also a weak spark can cause it to be hard to start. Check to make sure your are getting a good blue spark at the plug. A yellow spark will ignite starter fluid, but not gas. If the spark is yellow in color, clean all the coil connections and the plug cap. You can also do an ohms test of the coil on the primary and secondary sides. I don't have the exact specs for that bike, but the primary side should be above 20 ohms and the secondary should be below 16 ohms.


9/5/2013 6:51 PM

Paw Paw 271 wrote:

You may not be getting fuel flow through the low speed circuit of the carb. It can be a plugged carb passage, plugged center ...more

Ive checked all the carb passages and orfices and did a compression test. They all look good. My spark appears to be really strong (vibrant blue). Not sure how to go about the low vacuum or the ohms test (getting out of my knowledge level). Thanks for all your help so far and i would greatly appreciate any additional advice you have for me.


9/5/2013 7:00 PM
Edited Date/Time: 9/5/2013 7:06 PM

PW's are very low compression engines on their best day. A good stocker will only pump about 115-120 on a gauge. Anything lower than 80-85 and they will be hard to start.

Make sure the head is sealing good at the gasket. Spray some soapy water around the head gasket area as you kick the engine over. Make sure there are no bubbles squeezing out.

Another area on those little bikes to check is the ignition side crank seal. They sometimes will actually work their way out of the cases, and the bike will never run until you pull the flywheel and stator plate, and replace the seal. It is a small seal, and they are very easily distorted over time.

If the seal is out of it, no matter how fresh the top end is, all of your compression /cranking pressure is lost through the crank seal. I would bet this may be your problem.

I smear a little Yamabond on the outer edge of the seal, where it comes in contact with the cases to help it stay put.

You can also disconnect the white connector from the start / run switch behind the number plate to make sure the switch is not going bad. Leave the single black wire connected. It will still operate as a kill switch, but you will no longer need to place it on Start to get it to run. Just click it to Run. Careful though, as it will be ready to take off as soon as the throttle is opened, as this bypasses the little control module under the seat that retards the spark on the Start setting.


9/5/2013 7:11 PM

project racer wrote:

PW's are very low compression engines on their best day. A good stocker will only pump about 115-120 on a gauge. Anything ...more

I hope to get time over the weekend to take a look at some of these issues. Thanks for your help.


9/5/2013 7:41 PM

Let us know how it goes. I have owned several of those thing over the years. Still have the nice '06 hanging around. Maybe 5 hours on it.Photo





9/5/2013 7:49 PM

If you have the good spark, you don't need the resistance check of the coil. That's just if the spark was weak. If compression is good, your ok there. Low compression won't be able to suck the gas mixture in. You definitely have a fuel delivery problem. Some thing is wrong in the carb. After you kick it the many times, do you smell gas? Is the plug wet, or dry? If it's dry, there's no gas getting through. There has to be some blockage of the passages in the carb. You're getting gas to the carb, but not to the venturi of the carb, where it can be sucked into the motor. Check that area closely. One other thing that may sound stupid, is are you sure there's no water in the gas? Maybe in the tank? A little drop of water in the carb can drive you nuts. Water could have got in the tank, and as you add new gas, it's still there and gets to the carb. I bet you can get a new carb for that bike for less than a hundred bucks. We all like to figure out what's wrong, but sometimes you have to use the shotgun solution. Hope this helps.


9/5/2013 8:32 PM

mx5471 wrote:

If you have the good spark, you don't need the resistance check of the coil. That's just if the spark was weak. If compression ...more

I will drain the tank and put fresh gas in. The plug is dry so its not getting gas. I've cleaned many different carbs over the years but not sure if I really know how they work or the flow of gas through them ( something I need to better educate myself on). I do however have one on the way which I purchased used off ebay. I really appreciate your time and help. All of you guys have been great. Hope to have a productive weekend. Thanks again.


9/5/2013 9:26 PM

OK. Try the new one and see what happens. Hopefully it'll start up and run. If it does, great. But when you tune it, don't forget the jet needle. I had a guy that got a new carb for a 65, and it ran, but not good in the upper ranges. He tried everything but forgot about the needle. I took the needle out of the old carb and put it in the new on, and problem solved. Good luck.


9/6/2013 1:34 AM
Edited Date/Time: 9/6/2013 5:51 AM

I had this problem, there is a removable fuel filter, I think it's in the tap or the fuel line itself, i cant quite remember it was a while ago that I fixed it. Soon as I cleaned it out bike ran perfect. I just had a quick check, the filter is in the fuel tap, pull it off and check it out my bet is its blocked. It's a small nylon filter in the inlet of the fuel tap, dig it out, clean it up or throw it away and your problem should be solved.


9/6/2013 8:46 PM
Edited Date/Time: 9/6/2013 8:47 PM

Keep in mind that if there is insufficient vacuum to draw fuel through the passages of the carb, a new carb leaves you in the same position as the old one.

Do the free ,cheap stuff first. Pull the fuel line from the carb, and turn the petcock on. If gas flows, scratch a clogged petcock.

Loosen the little drain screw on the bowl of the carb. If fuel flows out of the drain hose, it is filling the bowl.

It should fire with a clean carb , fuel in the bowl, and a reasonable compression reading.

If it is not getting the plug wet after several kicks, low vacuum would be suspect. It relates to a well sealed engine. If the crank seal is out of it, or worn out, It will never draw enough fuel through the carb to run on its own ,as any crank case pressure is lost right out of the seal.

The crank case /cylinder is where sealing is critical to hold a vacuum, and keep cranking pressure /compression within an operable range.

A crank seal is about $4. I have had this happen on PW's , Suzuki JR 50's -LT 50 quads, and Eton models.


9/7/2013 5:08 AM

project racer wrote:

Keep in mind that if there is insufficient vacuum to draw fuel through the passages of the carb, a new carb leaves you in the ...more

Well, I cleaned the petcock ( which didnt appear to be overly dirty). I drained the tank to make sure no water in the gas. And still nothing. The new carb hasnt got here yet but I'm suspecting that I could have a vacuum problem. Little by little I'm scratching things off the lists of possible suspects and I'm learning alot along the way. Thanks again to all of you.


9/7/2013 7:16 AM

You seem to be ignoring Project Racer's suggestion on the crank seal. I also was thinking crank seal when I first read your post. Simple and cheap to fix if this is the problem.


9/7/2013 8:08 AM
Edited Date/Time: 9/7/2013 8:13 AM

Not trying to be a smart ass here, but in purchasing many PW's, some of them as out right junkers, replacing top ends and crank seals were the areas where attention was most needed to be brought back to life.

Other than a bowl gasket or pilot jet, have never had to replace a complete carburetor or any ignition parts on any of them.

Bought the old white 87 pictured above for $100, someone had tried to pry the cylinder off and broke the RH case half.

Replacing the case half on that one was the most engine work I ever had to do on one of those little bikes.

It fired off and ran well with the old carb that came with the bike, once the cases were back together, new top end , crank seals, and a good cleaning of the carb.


9/7/2013 9:35 AM
Edited Date/Time: 9/7/2013 9:39 AM

project racer wrote:

Not trying to be a smart ass here, but in purchasing many PW's, some of them as out right junkers, replacing top ends and ...more

Ok, just got the new carb on and ............NOTHING! I wasnt ignoring the crank seal, just was trying the other possibilities that I had a little previous knowledge of. So now that I'm ready to try the crank seal, where do i begin? Do i need to remove the whole engine from the frame? Is it the seal that splits the cases? Is there any info you can give me to guide me in the right direction with the least amount of chance of me scewing something up. I'm definitely in foreign territory as far as bike repair goes for me, but very interested in listening and learning. Once again thanks to all you guys! I also looked back at your previous post and you said seal was on stator side. I pulled up a parts diagram and the only seal I could see looked like it was on the clutch side. Am I totally confused or looking at something wrong?


9/7/2013 2:12 PM
Edited Date/Time: 9/7/2013 2:28 PM

Bummer on the carb.

You only have to pull the flywheel and stator plate to access the seal.

Remove the little plastic cover that is held on by three little screws. This is on the LH side of the bike as you sit on it.

You will see the flywheel staring at you. You will need to remove the nut on the end of the crank in the center of the flywheel.

The flywheel will want to turn as you try to remove the nut. Hold it with your hand , give your ratchet a few bumps with your other hand. The nut will come loose. Or if you have an air ratchet or little butterfly ratchet,this will make removing the nut easier.

DO NOT, use a hand impact that you strike with a hammer to remove the nut.

Then , you are going to need the correct flywheel puller. Again, do not pry or beat on the flywheel to try and get it off.

If you have a local shop close by, they should have a puller, or can pull it for a small fee. Don't lose the flywheel key when you pull things apart.

Once the flywheel is off, you need to use an impact screw driver to loosen the stator screws. Get a tight fitting bit, as the screws will round the Phillips slots easily. Give the impact a fairly good rap with a hammer, and loosen the screws.

Pull the stator plate out of the case cavity. The seal is right there centered over the crank end. Before you go any further, look for any signs of oil / premix in the cases and around the seal. If there are signs of this, the seal is leaking.

Get an angled pick, and carefully remove to old seal. Try not to knick the crank end. The seal is not in there that tight on those bikes.

Clean things up, get a new seal, oil the inside edges of the new seal, and carefully slide the seal over the crank. Do not nick the seal as it goes over the crank. A little Yamabond or Loctite on the outer edge of the seal where it touches the cases will keep it from moving.

Replace the stator plate, tighten the screws, slide the key way into the crank slot, and carefully slide the flywheel back on.

Torque the crank nut down, give it a few kicks ,and see what happens.

It is a simple job. The correct puller is a must, though.


9/7/2013 2:16 PM


9/7/2013 3:59 PM

Thanks for your very descriptive instructions. Looking at the parts diagram is there a chance that the right side seal could be bad also or is that a whole other situation, and your pretty confident that the stator side is the issue? Thanks again


9/7/2013 4:48 PM

Both seals should be replaced.


9/7/2013 5:10 PM
Edited Date/Time: 9/7/2013 5:33 PM

You could replace both seals, but if it were me, I would do the stator side seal first, put it together ,and see what happened. The motor has to come out of the frame for replacement of the primary side seal. And on a PW, that means the whole bike has to come apart.

The primary side seal stays pretty well lubricated from the gearbox oil, and does not suffer the effects of engine heat as much as the stator side seal. Even in some of the bone yard PW's I've had, I replaced one primary side crank seal ,and that was only because the cases were being replaced.

Make it easy on yourself, put a stator side seal in it, and go from there. If the primary side needs replacing, you have not lost anything by doing the stator side seal.

If it fires up and runs with a stator side seal, call it good, and let the kid ride it.

For what it's worth, I have seen many PW's that would not run due to a bad stator side crank seal. I can not recall ever seeing one not run due to a bad primary side seal. Not saying it could not be possible, but the critical, most commonly replaced seal on those is the stator side.

I have pulled the covers on more than one PW, only to see the seal totally out of it's boss / holder in the cases, sitting out on the crank end. That is where a little Loctite or Yamabond on the outer edge of the new seal is helpful in keeping the seal in place.

These are not F1,NHRA, or 250F engines here. It's a moped engine.


9/7/2013 5:39 PM

I have a seal and a puller on the way and I'll go from there. I will keep you guys updated because yaw are my life line at this point! Thanks again.


9/7/2013 7:11 PM

Yo project racer! Dumb question maybe, but what strength Yamabond do I need to use? And same question for Loctite as I will get the easiest one to obtain for me. Just want to be sure I'm doing things correctly. Thanks


9/7/2013 8:30 PM
Edited Date/Time: 9/7/2013 8:31 PM

I believe you will need "Yama Bond #4, it is nothing close to any Loctite that I know of. And you get it at most any Yamaha Parts Department.


9/8/2013 6:40 AM
Edited Date/Time: 9/8/2013 6:43 AM

Yes, as X says, it is the #4. Last time I bought a tube, I think they had discontinued some of the other #'s , and only offered the #4. Just a light smear around the outer edge of the seal is all you need. Maybe the total of three match head sized dots, then spread it around the edge.

Don't push the seal in too far. Flush with the cases or a tick more. They will go in deeper, however. You can usually press them in with your fingers- thumb. Try to get it in as straight as possible.

Make sure the key is removed from the crank before you install the seal.


9/8/2013 8:13 AM

You have put in a new sparkplug havent you?


9/8/2013 1:52 PM

Ok thanks. I"m waiting on parts now. To be continued.........


9/11/2013 2:22 PM

Ok, i got the flywheel puller today and pulled the flywheel off. ( Although I did have to use quite a bit more pressure than what i was expecting , but it finally popped and I slid it the rest of the way off the shaft. At this point project racer told me to remove the stator plate, but the stator wires are connected to the stator and run up thru the case. I did manage enough slack to get the stator plate off the crank shaft but its still kinda of in the way. My first question is, is there a simple way of disconnecting the stator plate and removing it or should i just try my best to work around it? Also, you stated that at this point where i can see the seal I should be able to tell if its leaking. I'm not sure, its some dried dirt and dust settled around, and some oily residue around the seal and shaft but it appears to me that it could be grease? I'm definitely no mechanic but I was hoping to see a much more obvious leakage problem. The seal also doesn't appear to have worked its way out either. Its still recessed back .02 or so from the turned down portion of the case that it sits in. Where do I go from here? Thanks again guys


9/11/2013 3:47 PM

Project racer is the expert on these little bikes. He'll answer back, and you can follow his advice. I never worked on a pw50, but have wrenched for 13 years on a lot of other bikes. I suspect the oily residue and dirt you see is the result of the seal leaking. Any dirt that gets in there will stick to the oily area, which wouldn't be there if the seal wasn't leaking.