PW 80

I have a PW 80 that will start with the choke on but revs up. If you take it off it acts like it is running out of gas and dies. I have cleaning jets and adjusted the floats with no change. I suspect a ignition side seal air leak. Any help would be appreciated.

Check the crank seals behind flywheel. Is the plug good. Air filter clean. Slide in correctly.

Intake or crank case leaks are a PITA to find, but if you don't, bad things happen.

Try spraying aerosol carb cleaner around every joint from the carb to the "manifold", then around the cylinder where the head gasket is as well as the base gasket. Listen for the engine speed to change, if it does, that's where there's a leak. These are all easier to fix than the intake side crank case seal. If it is the crank case seal, this can be removed and replaced without splitting the cases by drilling a very small hole in the seal, screw in a dry wall screw and use that like a handle to pull it out.

Also there's a rubber O-ring type thing where the carb joins the intake, make sure that didn't fall out when you replaced the carb. If you didn't remove it when you cleaned the carb, it could be damaged and should be replaced.

I end up pulling the flywheel Sunday afternoon and the seal was shredded. 

Edited by VinceDC

Well, that's certainly clear. As always, it never ceases to amaze me as to how poor the condition a PW80 will be in and still run. I'm really tempted to pour beer in the gas tank, I'd put the odds at 50/50 that it'll run.

OK guys I have a question. I just picked up a 94 pw80. Got it from a guy who said it ran great but had been in garage for 6 months. Anyhoo, started up and ran for a few seconds no problem. Got it home and it rode great for about half a block then died. Now it'll start with one kick after initial choke cold start process but will only run for about 2 to4 seconds then dies out. Seems fuel starved but it's getting gas. Carb has been apart so many times its like a 5 inute process for me now. If I shut off gas and remove plug and like kick start all the gas in the crank case out and then replace plug, turn on gas and then start it runs great for about 20 seconds and then dies. Spark looks good, compression test shows 125-130psi. Have not examined reed valve because ya damn near have to pull motor for that. Any suggestions anyone?

Did you try a new plug? Is th we oil pump working? 

Pop the fuel line from the carb off, put it in a suitable container. Turn the gas on. Is there a steady flow? Does it taper off and stop? If the latter, you have a clogged screen in the tank.

You said you've had the carb apart a dozen times, what did you do? Did you check the float height?


I'm concerned with this "kick all the gas out of the crank case" bit. Are you getting significant amounts of liquid fuel out the spark plug hole when you kick it?


What's your air filter and air box look like?

  • So I got a seal and put it in and now it won't start at all, I have spark . Compression is 110. Gas is getting to the carb. Jets are clear. Even with starting fluid no go. Air filter is clean. I have never had one stump me like this. I don't know what to do.

If it won't start with ether, there's only two possible causes: horrifically low compression (eliminated as a possibility) or lacking spark at anywhere near the correct time. Is there any chance you lost the woodruff key and have the flywheel on at the wrong position? When you say you have spark, you checked post-seal install, correct?

Thank you for the additional ideas. The spark was checked after installing the seal. I will check the flywheel. I am pretty sure the key is there. I will also recheck the compression. I have no history on this bike other than it sat for some time and a kid kept missing with it trying get it to run right. Not knowing about the seal. I also thought maybe a plugged up exhaust? It has a full FMF system. Besides the flywheel, is there any way for the spark timing be off?

Thank you

The PW80 is an incredibly tolerant bike. The flywheel could be the wrong flywheel, the stator plate could be misaligned (although this should be obvious with the flywheel off), the coil could be installed upside down it is symmetrical like the stator plate.


Exhaust could be plugged, unlikely with an aftermarket one, but possible. The factory one has a "box" near the stinger that I've never investigated. The FMF is pretty much a goofy looking piece of pipe, looks the same on the inside as the outside.

It appeared that I was first one in there since it was assembled new. No makers on screws and nuts. The bike itself appears to have pretty low hours and hasn't been messed with much.

Edited by VinceDC

Checked the flywheel and it was good, put it back together. Then it started?? I don't know why. So now I am just adjusting the carb. Is it normal for it to not have much low RPM power. It idles good and pulls strong from mid to top but is a little weak on the bottom. Of course this is with a 185lb rider at 6500ft.

Thank you

What main jet is in it ? We are at 7600 and I have  a 115 main. This weekend I removed the snorkel from air box backed the oil pump off a bit and dropped needle down one  step.  Now we have a great running machine it will wrap clean in all gears and pulls great in first.

If it won't idle I would lean toward pilot circuit being clogged or idle mixture is off.

Edited by dadat40

Unfortunately, I have no experience with a PW80 at high altitude. I'm at roughly 400 feet above sea level. You've cleaned the carb, right? Did you adjust the mixture screw? This will have quite an impact on the way the bike behaves at low throttle opening as well as at idle. The auto clutch doesn't fully engage till around 2200 RPM, everything from idle to that point the clutch is slipping so you will never get a feel for how the engine truely runs at low RPM.

In stock form, it's not going to behave anything like most 80cc smokers. It's engineered to produce a very flat power curve, run forever in the worst conditions and generally be ready to go anywhere with a 6-8 year old at the helm. You can change this of course, but don't expect too much out of the 4 hp it produces stock. It's actually more like 2.3 hp at the rear wheel according to my experiments.


I do recommend replacing the snorkle with a triangular shaped piece of sheet metal as one of the first hop-ups.

I did adjust the air fuel screw. It mainly does not want to pick up RPM quickly. If you open it up quickly it has a little delay for 2-3 seconds( almost a bog) before it starts to really move. It also has a hard time pulling 2nd gear if it is up hill. Just as a reminder this has the FMF system on it. It has an on the pipe feel to it at mid RPM. Once you in that it moves. My eyesight is not so good ,but I believe it has a 90 main. I will check again. May be a little lean. Might lower the clip on the needle. It does rev to the limiter. I am selling this bike I just want it to run as good as it can.

Whoa, like I said I have no experience with mile high elevation, but 90 main seems way too lean. What's the pilot? Stock is 17 or 20 (I don't remember) and 125 or 130 main (again, specifics escape me.)

You always want a bike that you plan to sell to run as well as it can. I like sellers who don't understand this, saves me tons of money. Two winters ago I bought a DR-Z125 that wouldn't start. The PO thought he was smart and pulled the guts out of the silencer. It was also January. The bike wouldn't start. I paid $600 for a $1,000 any day of the week bike because of his red neck engineering. Also he had it listed for several months so I'm betting other people walked away when it wouldn't start for them too. I cleaned the carb, put a stock silencer back on, bike fired up and ran great. Even has a title so I'm deluding myself to dual sport it right now, would be a fun 'round town mini-motard especially if I can find another DR200 motor to drop in it.


Buy a few jets from Niche Cycle on eBay if you don't have them, he sells them for $3 a piece, IIRC.

Edited by Smacaroni

The pilot is a 15 which is stock. The 2005 came with a 125 main. I will get my wife to see if she can read it. I may be wrong on the 90. With the FMF pipe at sea level or your alt. wouldn't the main tend to increase a little. Increased flow from the engine. In this case the intake has not been altered in any way. So I don't know that the exhaust is doing anything for the bike. As mentioned by dadat40 I think a 115 main should be close.

I had to look up the parts fiche, but mine too came as 15/125. The FMF pipe flows about the same as the stock pipe, but it also flows both ways, the stock pipe is designed to flow out only. You're probably aware that most 2-stroke pipes are designed to "suck" fresh fuel air mixture through the cylinder and ram it back in before the exhaust port closes. The stock pipe has a goofy funnel type thing in it which I suspect it's to be a one-way valve. For this reason, the FMF should perform a bit better than the stocker. But it's definitely nothing special, what little I do know about 2-stroke expansion chamber design, long head pipes (which applies to the PW80 FMF pretty pipe) produces best results at low RPM. Long relatively thin expansion chambers with shallow angles (again, FMF pretty pipe barely qualifies) produces a positive impact across the widest RPM range.
I personally don't think the FMF pipe is all that great, it could be a whole lot better, but it does look pretty.



Long straight head pipes are not for me. Giving up strong acceleration in the top part of the rpm range - which, to me, is the most enjoyable part of the 2T experience - for the sake of more mids and bottom end just isn't my idea of a good time, although I've tried really hard to like it for many months now. It seems like most modern pipe makers are in agreement with me on this one. I grafted a tapered (divergent) head section onto my 175's pipe, and the difference was night-and-day; like getting back a normal 2T powerband (hard pull to redline) instead of the original surge-and-die response - and in this case, I didn't lose any low end, just some of the mid hit, which mainly just resulted in wheelspin anyway. Vintage pipes seem far more likely to have long head pipes than those used on EVO or modern bikes.

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