New PW50 Dad needs advice

[TCpapa]

I recently bought two used PW50s. One is 02 and the other 03. They were in a little rough shape but we have cleaned them up. The 03 is now running great. It pings like crazy but has plenty of power for our 6 yr old. The 02 also pings and has been more trouble. At first it wouldn't start at all. I have taken the carb apart 4 times already and it will run now but will not idle. I cleaned the pilot jet several times and if the idle is high it revs up and engages the clutch. once it drops below that point is slowly drops rpm and then just dies if you don't pump the gas.

Today I took the cylinder head off and it had tons of carbon deposits. I also decarbonized the pipe a bit. It will now come so close to holding the idle. Would the piston slap cause it to refuse to idle? It has less power than the 02.

Thanks for any help. I don't mind taking these apart now. They are pretty simple machines.

T

 

[gibson1959]

if it is reving high on its own check for air leaks, it will cause it to run lean hence the high idle. the cheapest way to check is to use a lighter and go around the engine but i would stay away from carb. u will know then if u have an airleak. it is worth a shot before taking anything apart again

 

[QKENUF4U]

the cheapest way to check is to use a lighter and go around the engine but i would stay away from carb.

WHAT !!!!! :yikes:

i agree that you may have a air leak/vacumn leak. i would idle it up a bit more till it will idle and then take carb cleaner and spray one spot at a time. if it dies on you then you have found a leak

 

[bhamner]

If the piston is slapping that badly, then you would think that the rings are shot. Have you done a compression test? How does it run when riding? Have any power (comparitively speaking)?

 

[TCpapa]

I don't have a compression tester yet so I am not sure how much it is getting. It still has enough power to get the kids moving around pretty good. Son 35 lbs moves fast. Son 80 lbs moves. Dad 180 lbs. moves slow.

After taking it apart enough times it is running good at medium to full throttle. It just has a hard time at no throttle. I have cleaned the pilot jet several times and it was pretty bad to start with.

How can I tell if the rings are shot? I assume the play between the cylinder and piston is a bad sign. Can I replace the rings or will it need a new piston etc.?

Thanks for all the help. I think it is getting close.

 

[TCpapa]

Today my 5 yr old and I went riding around the yard. We have a few hills but it is mostly flat and grassy. I got the older bike warmed up with a new plug and it runs good but has no power. If I can get going down hill even a little it will wind up and go but even with me off the bike can't pull itself up a slight incline. Not even close to a hill.

It still has some trouble idling. If the rpms drop just a little it will die if you don't pump the throttle. If the idle is a little high it keeps picking up rpm while on the stand but I guess that is to be expected. I tested for air leaks but didn't find anything. I checked the plug after riding for a while and it looks good. It is tan but only on one side.

I still haven't had a chance to check the compression. If it needs work on the top end, what are the options? How do you know if you just need new rings or a new piston, bore, etc.?
It's fun just to watch the little one zip around on his pw50. He thinks he's about 16 and is starting to get pretty confident.

Thanks for any advice.

 

[frankiewhipit]

with the cylinder removed, bring it & the piston to a machine shop & ask them to measure the diameter of them. as per my experience with pw 50's if it's slapping/pinging it probably needs to be bored & a new piston installed. also on e bay someone sells a power up kit for them, it consists of a set of reeds,main jet, air box vent, air filter & exhaust mod instructions, that combined with some looser clutch springs really wake the pw up :cool:

 

[TCpapa]

Thanks Frankiewhipit.
The **** powerup kit looks good. I will have to think about that one.

For now I was able to do a compression test on both bikes. With the engine cold and the throttle wide open I got about 90lbs on the bike which runs pretty good and about 80-85 lbs on the bike that runs ok, lacks power and won't idle. I am wondering if the idle problem is with the pilot jet. I have taken it apart and cleaned it will and blown it out with compressed air. It was getting better and maybe needs deep cleaning. Should I take the jet out and soak it in something? How long?

Do the compression numbers seem a little low and what would be the next step?

Thanks for everyone's help. They may not be screamers but they are fun.

 

[wanaride]

You have probably already checked this, but did you remove the exhaust restrictor "washer" from the exhaust pipe?

 

[TCpapa]

You have probably already checked this, but did you remove the exhaust restrictor "washer" from the exhaust pipe?

I did check it. I took the pipe off to clean out the carbon and it had already been removed. The head and pipe had quite a bit of buildup. Once that was clean it helped a little bit.

Thanks for everyone's help. My little guy and gal are looking forward to these bikes.

 

[Baker1]

TCpapa - here's a coupla more thoughts for you...

I've cured "no idle" bikes by adding the throttle-play adjustment process to the combo of idle speed and air screw setting on the carb. In other words, the bike wouldn't idle right until I took all the slack out of the throttle cable and THEN set the idle/air screw combo properly.

I had one jr bike recently (can't remember which) that transformed from a sputtering no-idle disaster to a perfect bike by moving the e-clip on the main needle 1 notch. I don't remember offhand if PW50's have multiple notches on the main needle, but check that out. We had chased our tails on that bike for days, so grabbing straws, we started dinking with the e-clip. We sort of intentionally moved the clip to a notch leaner even though we knew that wouldn't help anything on the idle circuit. WOW - that little bike took off!

A run-away idle problem almost has to be an air leak somewhere. Sometimes they are a nightmare to find. I prefer starter fluid to the options described above. Use very localized tiny bursts of spray anywhere there might be an air leak between the carb and the bottom of the head. If the bike revs up suddenly, you found your leak. Some air leaks can only be found by taking stuff apart until you find a failed gasket.

No power is either a fueling issue (too rich, too lean, dirty carb, dirty air filter, float level set wrong, wrong main jet or pilot jet, or an air leak);
...or a worn top end - needs new piston/rings or complete new cylinder head assy or bore and plate head and go oversize on piston/rings.

Good luck!

 

[TCpapa]

Thanks Baker!

It does have notches on the main needle. I messed with it a bit a while back but I did it at the same time as a few other things and don't know if it helped or not. I then put it back to where it was to begin with. I'll try it again. I was also going to take the pilot jet out and soak it for a while in carb cleaner. It looks clean but maybe it needs just a little more.

I think it may need a new top end. I don't have any experience with these and I'm learning as I go. I know there is alot of play in the cylinder. I took the head off to clean the carbon and the piston could be moved back and forth in the cylinder. I doubt it has been bored over stock but want to check the cylinder before I get a new piston set. I couldn't feel a ridge at the top of the cylinder so it may not be too far out.

I was also going to get a new main jet (65 or 67.5) and see if that helps. I am at 4,500 ft elevation and both bikes seem really rich.

 

[TCpapa]

I spent some time tonight with both bikes. Changed oil on both and went through the carb completely (again) on the 2002 and moved the clip on the need on the 2003. They were bogging pretty bad when giving throttle from idle. It seemed to help.

The 03 is running like a champ. A new plug gave it a little more kick for the little ones. The 02 seems to run ok in most throttle positions except for idle. I don't think there is anything blocking the pilot jet. The petcock is clean and it has fresh gas. It can almost hold the idle and it lacks power compared to the 03. It has a hard time getting moving in short grass.

I assume it needs top end work. I'm not sure if I should get a standard or overbore piston. I suppose I'll need to pull the cylinder and measure that.

Thanks for listening. Let me know if you have any suggestions.

 

[Baker1]

I'm also at 4500'. I usually do well going down 1 size on the main. I never change the pilot jet.

As you probably know, moving the clip "higher" on the needle = leaner on the main circuit. A "lowered" needle buries the taper lower in the main jet, therefore must travel farther up out of the main jet to reach the main fueling profile. Enough fuel is going by the main at low throttle for it to make a difference when you move the clip leaner. I've had bikes that were very happy with the clip in the leanest position.

Take the head to the local bike shop, have them take a quick look at it. They can sometimes tell if the nicasil coating is shot just by looking. If you replace piston/rings/pin/clips only, it'll be around $65. If you need a new cyclinder, add $225 or so. Or find a local re-plate shop. Unscratched cyclinders can be re-plated for $125ish.

www.mrcycles.com will sell you oem cyclinders and pistons and parts for less than you'll pay for aftermarket parts. My preference is oem for anything except serious competition.

Good luck!

 

[frankiewhipit]

I spent some time tonight with both bikes. Changed oil on both and went through the carb completely (again) on the 2002 and moved the clip on the need on the 2003. They were bogging pretty bad when giving throttle from idle. It seemed to help.

The 03 is running like a champ. A new plug gave it a little more kick for the little ones. The 02 seems to run ok in most throttle positions except for idle. I don't think there is anything blocking the pilot jet. The petcock is clean and it has fresh gas. It can almost hold the idle and it lacks power compared to the 03. It has a hard time getting moving in short grass.

I assume it needs top end work. I'm not sure if I should get a standard or overbore piston. I suppose I'll need to pull the cylinder and measure that.

Thanks for listening. Let me know if you have any suggestions.

yes, check the cylinder before you buy a top end, also maybe try switching the carburators

 

[TCpapa]

It took me a while but I got the cylinder to the machine shop today. It didn't look terrible but we are going to clean it up and get a new piston kit. That will take care of one bike. Now on to the other one. It is running well but slaps and pings. I haven't taken it apart yet but was wondering if its possible to pull the cylinder and just put new rings on it to get a little more life out of it. I don't want to throw a lot of dough at both bikes. We are thinking of selling one and getting a larger bike for the other kids.

When I took the other bike apart the rings were pretty worn down but the piston was in good shape.

Thanks for everyones help.

 

[Jasle]

the PW does not have nikasil coating in it. Straight cast iron cylinder. you can bore and go bigger quite cheap.

They typically will score around the exhaust port because mud builds up there and they get little if no cooling and the hot exhaust goes out there. You can probably put new rings in it but if the grooves are bad enoudh to feel with your fingernail you might as well do it right the first time so you not there in a few weeks doing it again. A new cylinder is under $150ish cheaper yet to bore it. Not the most expensive bike to buy parts for.

 

[TCpapa]

It's been a little while but we had some work done and now I have more questions. I had the pw50 cylinder bored .020 over and put in a wiseco piston. It went quite well. The only trick was the circlips. My fingertips will recover soon.

Once it was back together it fired right up and has a new life. It starts in about half a kick and runs great until it warms up. After about 5-10 minutes it will just die with or without throttle. It starts right back up but then will die again in a minute or two.

Does anyone have a hunch as to the cause? It has the stock jet and fresh gas and plug. It runs absolutely great while cold.

Thanks everyone.

 

[theroyz71]

May need bigger jet to compensate for overbore. Try a 72.5 main.

 

[pink63impala]

maybe try to swap the carbs and see if the bad running bike runs better, that may narrow down the cause to the carb or what not

 

[wyatt]

this could be a longshot but the silencer could be restricted.
Check for carbon buildup inside.

 

[TCpapa]

Thanks for the advice. I haven't taken the pipe off recently. I'll have to check it. I took it out today and adjusted the carb before we set off. I bled the oil pump and turned the air screw in about a full turn. It must have been running just a little too lean and was heating up and stalling. We rode all over today and it didn't stall once. Finally. Now it makes the other bike seem so sad. I'll have to fix it up although I am thinking of selling it and just keeping the one good one and looking for a xr/cr 50 or something larger for my other kids. I seem to have one in every size bike. Too much dough. We've been looking for used bikes locally. Maybe the fall/winter we'll be able to find some good deals.