Is the fuel turned on?
I just picked up a little 96 yamaha pw50 2 stroke dirt bike, and the thing doesnt want to start for some reason. Im a total 2 stroke noob , but so far ive figured out that it :
IS getting spark
has decent compression at spark plug hole
exhaust doesn't seem to be clogged
I took apart the carb (never took apart a carb before) and it looked pretty clean, and I could see through the little brass orifice that goes between the bowl and the top of the carb (is that the "jet"?)
there doesn't seem to be a whole lot of suction at the carb inlet, but maybe a 50cc 2 stoke doesn't make a whole lot of suction?
anybody out there have any ideas? could it be the reeds? do those go bad?
Thanks in advance for any advice.
Is the fuel turned on?
key turned on?
I'd laugh if that was the case, but Peter Kates will tell you i'm a victim of that one, too
yep, and there is fuel in the bowl.
oh ive learned the key trick the hard way many times, fortuantely this thing doesnt even have a key.
Did you replace the spark plug?
Just because it sparks, doesn't meen it's good with a 2-smoker
I did not, it does look kinda rough too. Im gonna get a new plug tommorow
Make sure the switch is in the "Start" Position. It retards the timing so the bike will start, but can't rev enough to engage clutch. It keeps kids from starting the bike with the throttle pinned and slamming into the nearest house/car/tree....If that's not it, call me.
If that doesn't do it - take the plug out and put about 1/4 teaspoon of gas down the hole. Put the plug back in and try to start it. If it runs for a few seconds the ignition and the internals of the engine are fine the problem is upstream of the cylinder.
Some of these little bikes have a washer in the exhaust that limits how fast they can go - these can get plugged and it won't run at all. Hope this helps.
Thanks for your help everyone
New plug, poured some fresh gas in the spark plug hole, kicked it over and... nothing, wont even sputter, spark plug came out wet with fuel. I did notice that in the START pos. it gets alot of spark, and in the RUN pos. its hardly gets any, and it doesn't seem very consistent. what exactly does a "top end" overhaul include?
When you kick it over - does air get puffed out of the exhaust?
A top end overhall on a 2 stroke is simple. But - those little 50's are usually tough. If it has compression the top end should be in good enough condition to run. Maybe not run great - but run.
I took apart the head, the rings seem to be intact, I see some scoring but for a 96 that probably hasn't been well maintained it didn't look too bad, but I have no reference as to what "good" looks like.
is it time for a new top end?
I do get some air out the exhaust, not a whole lot but i can feel it puffing out
holy crap! i almost lost my eyebrows, i took the exhaust off, put the head back on, dumped fuel in, put spark plug in, kicked it about 10 times and almost my damn head off.
The piston looks like it was siezed (they probably ran it on regular gas - not premix). At the very least your looking at a new piston, set of rings, wrist pin and bearing, circlips, head and base gaskets. Take the cylinder into the shop and see if they recomend a hone or overbore. Do yourself a favor before trying to get the circlips out - put a rag over the opening for the lower end...
Does the crank turn rotate smoothly through its motion?
Stroke it more than 2 times?
so it looks that bad huh?
its got an auto-lube pump thing on it, it looks like it injects oil in the carb from a pump thats mounted in the engine. so I think it can run regular pump gas?
The crank seems fine, no slop and smooth rotation.
It does look bad - but fixable - the galled material on the piston shows it was siezed. The pump may have stopped working. So, after you get it rebuilt, unhook the pump, plug the port on the carb and run premix. Check around and see if there is a block off plate to let you take the whole system out. 32:1 or so - the same mix used in your weed whacker will work fine. Just make sure your little one knows which can to fill up from.
The shop will be able to give you a better scope on boring vs. honing. a top end kit should run around $100 including the gaskets...
ah cool, I was wondering about premixing. so even though there is compression there's probably not enough to get it fired up?
I was looking at this if I can get it for less than 100$ i still havent figured out where the "top end bearing" goes
eBay Motors: Yamaha PW 50 PW50 cylinder & piston kit NEW (item 330165050654 end time Sep-14-07 17:52:52 PDT)
Right - you need a certain amount of compression to get it to fire up. while you have it apart check the mating surfaces for flatness (feeler gauge and a glass mirror work fine). Lay the mirror on the table and place thhe cylinder head on it. Go around it with a 0.010" or 0.015" feeler gauge and try to get it to slide between the mirror and the part.
Thats the wrist pin bearing. When you pop out a circlip it will let the wrist pin slide out. The bearing will be on the top end (small end) of the crank. Before you order - make sure what size you need (stock, +0.010, etc.) if they bore the cylinder you need to go with oversized parts.
Also - take a look in the crankcase to see if any bits and pieces fell down in there. The exhaust might be full of gas, tip it around and make sure it's clear.
lost the auction for the new piston kit. might as well go for the big bore kit, any idea how much is would cost to have a cylinder overbored?
Yes piston was seized but if kid not racer probably OK
Rings get trapped in grooves espescially by seizing stuff then near zero compression and of course little or no intake suction either clean and scuff up piston a little
carefully extract the piston rings and clean grooves so piston rings spring in and out.
reassemble and start..and ride. enjoy. worst case a puff of ether.
make premix like 50 to 1 for safety sake. when riding see if there is a lot more smoke when on the gas if is then pump probably OK.
the oil line feeding the pump makes a severe 90 degree turn and often cracks there ... trim and replace.
say something nice about Ronald Reagan 2 strokes know the lefty's killed them
I just found the crack in the pump line, I don't like that set up so I took the drive gear off the pump, need to find a good way to cap the feed line to the carb, removed the oil tank and lines, and clipped the throttle line going to the pump, and am just gonna run premix. Just got the big bore kit off ebay so hopefully the rebore will take out the scratches, maybe I shoulda tried re honing and working the rings before I ordered it, oh well.
Do new reeds make that much a difference in performance in these little guys?
The money you spent on the rebuild kit will ensure that it is fixed right. Sometimes you can get away with trying to free the rings up - there's a good chance it would come back to haunt you.
On a low performance engine like this one - if the reeds aren't cracked leave them alone. Was the governer ever removed? If not, the engine never even saw the revs. For the oil pump port on the carb - swing through an autoparts store and look for some vacuum port plugs, or take a piece of tubing, slide it over the port and fold it over on itself and tie it down as a temp fix.
The govenor is a washer in the exhaust port
remove and enjoy
my kid weighs 40 pounds and I think he can get up to 30+
so they can get hurt
I coasted him down hills and practiced braking before any powered runs
So far some spills no injuries including a dramatic hidh side with the dog where all 3 went ass over teakettle