Posts
36
Joined
10/16/2016
Location
AU
Hi, I've received some great help on here previously for this old PW50 I'm trying to get working properly again and have a new problem with it.
I had most of the bike pulled apart to replace both crank seals so maybe I've put something back incorrectly.
After I warm it up it will idle in the "start" position with no problem but as soon as I switch to "run" it seems like it's running at full throttle or close to it. If I move it back to "start" it will settle down straight away and do the same thing when I go back to "run".
Not sure if it's related or not but there is also some fuel leaking from the carburettor. Not enough to have a constant drip but I notice it when I wipe my finger around it or leave it for an extended time.
Before I replaced the crank seals it used to rev by itself but it was much more erratic than this. I'm not sure but I don't remember the start/run position having any impact on it. The excessive smoke has cleared up now too, so I think both seals are OK.
I think the slide (?) is installed correctly? Turning the handlebars side to side doesn't pull it up at all.
The float needle has a very faint ring around it about 1/3 of the way down from the tip. You can barely see it in person, surprised it somewhat shows up in this photo. The rubber feels quite hard, is that how it should be?
Should that be replaced? If this was letting in excess fuel, could that explain the fuel leaking or is that something else? Also, would the extra fuel cause the bike to rev by itself or would it more likely bog it down?
The only other part in the carb that I can see has damage is this following piece. I can't find it on any parts diagrams so I don't think it's possible to order a new one.
It goes through the hole at the top in that last photo down to the opening at the bottom/side of the bowl. That is the "before" photo, it was the only one I had showing that.
Is the fuel leaking and the bike revving itself possibly related or more likely to be separate issues?
Any ideas for what I should be looking at?
I had been looking at buying a new float needle and bowl gasket but for the same price I can get one of those Miniky copy carbs off ebay. Some people have issues with them but I would be spending the same amount on two parts that I don't even know whether they will fix my problems.
Sorry for the long post, appreciate any ideas people have.
Thanks
I had most of the bike pulled apart to replace both crank seals so maybe I've put something back incorrectly.
After I warm it up it will idle in the "start" position with no problem but as soon as I switch to "run" it seems like it's running at full throttle or close to it. If I move it back to "start" it will settle down straight away and do the same thing when I go back to "run".
Not sure if it's related or not but there is also some fuel leaking from the carburettor. Not enough to have a constant drip but I notice it when I wipe my finger around it or leave it for an extended time.
Before I replaced the crank seals it used to rev by itself but it was much more erratic than this. I'm not sure but I don't remember the start/run position having any impact on it. The excessive smoke has cleared up now too, so I think both seals are OK.
I think the slide (?) is installed correctly? Turning the handlebars side to side doesn't pull it up at all.
The float needle has a very faint ring around it about 1/3 of the way down from the tip. You can barely see it in person, surprised it somewhat shows up in this photo. The rubber feels quite hard, is that how it should be?
Should that be replaced? If this was letting in excess fuel, could that explain the fuel leaking or is that something else? Also, would the extra fuel cause the bike to rev by itself or would it more likely bog it down?
The only other part in the carb that I can see has damage is this following piece. I can't find it on any parts diagrams so I don't think it's possible to order a new one.
It goes through the hole at the top in that last photo down to the opening at the bottom/side of the bowl. That is the "before" photo, it was the only one I had showing that.
Is the fuel leaking and the bike revving itself possibly related or more likely to be separate issues?
Any ideas for what I should be looking at?
I had been looking at buying a new float needle and bowl gasket but for the same price I can get one of those Miniky copy carbs off ebay. Some people have issues with them but I would be spending the same amount on two parts that I don't even know whether they will fix my problems.
Sorry for the long post, appreciate any ideas people have.
Thanks
If you are still using the oil injection , the throttle cable has a little junction box where it splits into two cables. One for the throttle, the other for the oil pump. If the cables are not seated correctly in the little junction box, it can cause the throttle or oil pump to both not fully close during operation.
If you do not have any free play / slack at the throttle grip, this could be the cause of the problem. Also make sure if the cables are seated, that the throttle cable free play adjusters are not adjusted to far out, which would cause the same problem.
Kind of a pain to pop the box apart, but it can be done. Your first pic looks like the slide is not quite fully closed. Should be just a slight trace of a gap at the back of the carb when slide is fully closed. Check the box, and cable routing.
The bowl gasket looks a bit varnished / hardened. I have a few new ones here, but it would probably cost a million dollars to ship it to you.
There is no float height adjustment on the PW carbs. With the bowl off, hook a piece of fuel line to the fuel inlet, and blow through the line by mouth, while lifting the float up to the fully closed position. If it is sealing, the air flow will stop as the float is lifted to the fully closed position.
There is an air screw adjustment on the PW, but they do not have such an effect on things as to cause the condition you are experiencing.
If you were in the states, I believe I have some old PW carb parts that do not mean much to me. Just the shipping would far outweigh their worth ,though.
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I put the bike back together yesterday and after it warmed up it would idle in "run" with no problems. I'm thinking the carb adjustments were way off. I had already played around with it and pulled it apart so couldn't check afterwards.
I checked the float needle like you suggested and it sealed off good. I'll grab a new gasket next time I order parts from the dealer. I'm not sure if that brass tube is supposed to be removable because I can't even order a new one. I'll just leave that as it is.
Unfortunately the bike was once again hard to start. This was with a brand new NGK spark plug installed. It was also quite smokey again which I don't think was the case when I had the idle issues.
The oil injection is still on the bike but it's not being used. I still need to block that off properly too. I'm going to try some new fuel at 32:1 and see how that goes.
I have mentioned in a previous thread that this bike has the tinny rattle sort of noise that is somewhat common on these bikes. I haven't opened it up to have a look yet but does a new piston/rings usually fix that or does it need a new cylinder too? Should that issue be resolved ASAP or is it OK to run it as it is? I suppose that could contribute to the difficult starting, any chance it would lead to more smoke too?
If shipping was reasonable there are probably many little parts I would buy off you, depending what you have laying around. Once it's running right then I will worry about making it look a little nicer etc.
Thanks
A small compression test gauge will tell you more of the top end condition. The best stock numbers I have seen are about 125-130 psi for a PW. Low compression can also cause hard starting. Most will not run under 75-80 psi.
Piston rattle is common on them. With the pipe off, look up into the exhaust port with a light. Those bikes run hot, and a seizure on the exhaust side is not uncommon. Look for scuffing on the piston, and rings pinned down in the grooves.
Only a good, straight bore, proper piston clearance will take the rattle away, for a while. Just the nature of air cooled two strokes to make some chatter after a bit of run time. If it has decent compression, starts easy enough, and runs good, don't let a little rattle spoil your fun.
You may get by with a new piston and ring set, if the bore is still close to specs. I spent around $190 for an OEM Yamaha cylinder & top end kit for one bike. Then took a chance on the ebay China kit for another. The ebay kits worked fine for me. I have bought a few of them.
Still have the OEM kit sitting new ,in the box. For the money, and what the bikes are, you could buy 3-4 ebay kits for the price of an OEM kit.
Try a good oil at 40-50:1. There are some low smoke formulas out there.
When I had it pulled apart I looked at the exhaust port and there was two small bits of carbon in there but I left it until I take the cylinder off so I didn't push any inside or scratch the piston. I don't think there was enough to make any difference. The restrictor has been removed and I could not see any build up on that end of the exhaust. There was some build up down the other end where the expansion chamber and silencer join. I scraped out what I could and then gave the expansion chamber a light tap all around and shook out some more. Without having any experience with a new/clean one, it did feel heavier than I thought it should be. Probably still more in there.
I don't have a compression gauge but should be able to find one to borrow.
As you know, an OEM piston costs more than a whole top end ebay kit does, so I will just be getting ebay parts if/when I get that far. This bike is pretty rough so isn't worth the OEM cost. If I go up to the 60cc kit do I need to change jets or anything else on the bike? The studs/nuts on there now are rusted so I'm hoping they come off easily.
I had just been testing it on some lawnmower fuel I had which is 25:1 mixed premium/95. I will give it a fresh tank of regular/standard and see how it goes. There are no kids riding it (only "big kids") so would 40:1 be the best for that as it won't be putting around at low throttle at all?
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