No start checklist

[adam79]

Im on my way to a friend's house to take a look at his late 80's little yamaha 50cc dirtbike. He says its 4 stroke. Apparently it was running fine a year ago, he left it for a few months, and now he cant get it to start, which is what Im going to try to help with. I believe the starter is working fine.

So, I am looking for advice on what sort of a check list I should follow. First I was going to check and see if the petcocks work and if it is getting gas. Then I was going to test for spark. Then I was going to spray some starting fluid inside the combustion chamber and attemp to start. If none of that works, I'm planning on taking of the carb(s?) and cleaning. If the throttle is set to high, and it is sucking in to much air during start up, couldnt that also be a problem? Sadly I dont have a mercury or vacuum synch gage.

Does anyone have any suggestions? Thanks.

[oseaghdha]

compression
sparks
fuel

[adam79]

ok, it is getting fuel, and it looks like the choke had been left on. There is no spark. Brand new spark plug, still no spark. It is a kick start, so I dont know if makes a difference. What is funny though is that out of the 25 times I held tested the new plug, it worked 1 time, and it shocked me. Why would it get spark only 1 time? Where could the problem be?

[Rasputin]

Could be that you need to unscrew the plug cap and cut off a 1/4 inch of plug wire and reinstall the plug cap. Possibly you twisting it around while checking for spark made the connection just long enough to raise a few of your hairs. Does it have a battery? If so is it charged up? Other than that I dont know much about em, cept I think they were 2 strokes

[adam79]

I will try that. All I know about the bike is that it is a 1986 yamaha 50, and it has no battery.

[egsols]

Yamaha 50cc dirt bike....is it a PW50....if it is I think its a two stroke, so it will need a mix before starting!

[adam79]

yes, it is an 86 PW50. I got it started, and running. the choke bobber mechanism inside the carb was stuck, so the choke was stuck in 'off' position. The choke cable is also over extended I think, so even after I somewhat freed the bobber, the choke still doesnt work. So, I must spray starting fluid inside the chamber a few times to get it running. I dont know if it's the cold weather, but the bike's exhaust is pretty white, even after warm up. The bike also sputters at high RPM (which it didnt do when I first got it running).

The new spark plug is fouled, so this I believe is the cause of the sputter, and because the plug is fouled I think it is running to rich. That can be fixed with a turn of air mixture screw, but what puzzles me is why does the bike pour out white smoke if it is running rich? I wonder if the oil pump is getting oil to the carb for mixing. The guy at the Yamaha store said that could be the cause. He also said that the oil I should be using is yamalube 2S. Will a cheaper oil do? What kind? He said that the yamalube was designed for the oil injection system in the carb.

[prometheus578]

Two types of two-stroke oil.
Mix type, and the type for injection. Make sure that you're using the injection type.
Yeah, white smoke means too much oil in the fuel mixture, but could also indicate something else.
Now, the way a 2 stroke works... the movement of the piston in the case/cylinder is what draws in the fuel. As the piston move upward on the compression stroke, the vacuum this causes in the case is what draws in the next charge o' fuel, etc.
Now then... If all things are perfect, such as the fuel mixture and you're still having a large white cloud from the exhaust, you may have a seal leak.
As I said... for 2 strokes to function, the piston causes a vacuum in the crank case area.
Now... at the ends of the crankcase, you have roller bearings that the crank rides on. There are also seals on the ends of the crankshaft.
If one of these seals goes bad.... that crank vacuum... sucks the oil from the transmission into the crank area past the bad seal, and hence, oils up the fuel mixture.
How common is this with your model bike, I don't know.
I worked at a shop that sold those cheap bikes from Taiwan... every new bike that I took out from the crate, the first thing I had to do was remove the cover and the clutch pack and replace that crankshaft/tranmission area seal.
Something to consider.
No way to really check it without disassembly, though.. other than the presence of a lot of smoke.

[adam79]

if the seals are bad, but the owner doesnt want to invest the money, will to much oil in the mixture result in negative consequences over time? Does it foul plugs the same as a rich mixture?

[prometheus578]

well, I suppose it could slowly suck all the tranny fluid out of the thing... provided that the spark plugs don't get oil fouled first.
Negative consequences also could be the neighbors complaining about the white cloud.

[prometheus578]

Then again... thinkin' about it...
All that smoke could be from oily fuel residue burnin' in the exhaust system from when you were fightin' and fartin' tryin' to get the thing runnin'.

[egsols]

Like Prom said, two types of oil. I know it sounds self serving from the dealer but I would use the Yamalube. I went over the bars on a YZ125 many moons ago because the owner wanted to save a couple of bucks by using cheap oil. end result... motor seized in top gear.

Also, I've found with two strokes, is some types of plugs (i.e manufacturers) foul very quickly. Try to use the plug that Yamaha reccomends. I had a RD125 that would foul a champion in a day while ngk's lasted weeks.

I don't know if I would use starting fluid to help start it. Its pretty hard on those little two strokes. Just my 2 cents worth.

BTW how's the compression?

[adam79]

I believe the compression was somewhere between 120-130psi. I dont think the bike will ever start normally until I replace the choke mechanism that was frozen inside the carb, and the choke cable. At least not now, in the winter. But, yeah, thanks for the tip on the starting fluid. Is that because it is not mixed with oil?

[egsols]

It is my understanding that starting fluid was meant more for diesels where the motors are built stronger and combustion is based on heat and compression, that is an explosion, whereas the gas motors are based on the fuel burning, under compression and with a spark to ignite them.

I just worry that with the high volatility of the starting fluids, in the small displacement motors, it may place too much stress on them.

I started many a diesel with ether but always used it very sparingly and only squirted it once the motor was turning over.

If it was running fine before he parked it, it is most likely just gummed up, I wouldn't start trying to adjust the carb, just give it fresh fuel, add some seafoam and see if that helps loosen things up.

[adam79]

Does that mean that starting fluid is more combustible and abrasive than gasoline?

Cleaning the carb was the first thing I did, then I tuned it. Once the bike is started and running, it works great. But....getting it starter is the problem, especially in this cold washington weather. The choke needs to be dealt with before I can go any further.