300/440/550 New/Hi/WTF?

[DMan II-40]

First of all I'm new here. Saying hello for the first time. I'm also new to skis, and plan to learn about them. I'm more of a car guy but I have always wanted a ski so figured what the hell.

So I bought a 1986 JS 300 (yes I know most don't approve) that wasnt running. It has spark and compression. I blocked off the oil pump system, replaced the gas, and got a new battery.

Just tried to start it for the first time and it was turning over but no go. After about 3-4 attempts I put a little gas in the carb. Started cranking it then BOOM! The rubber exhaust pieces that were connected blew apart and my ears are still ringing. I'm guessing this means the exhaust is plugged up or something and also the carb probably wasn't getting gas (that fuel filter thing wasn't full yet I realized so that could be the problem.

If you guys want pictures let me know. I appreciate any help. Also please don't suggest a new motor as I want to learn, and getting the 300 to work the the first step to me understanding standing these machines better.

 

[DMan II-40]

Took off the exhaust and doesn't look like it is plugged up but I'm cleaning it off anyway. Thought it could have been the waterbox but that seems to be passing air.

Could have just been a back fire or something. I'll have to finish cleaning off this stuff put it back and try it again.

Any thoughts?

 

[Wave Chaser]

Its possible you put to much gas down the carb. The unburned gas ran thru the engine into the exhaust and then lit off. Basically a backfire and yes its loud and will blow crap apart.

If the engine cranks and has compression you should be able to get it running with a little work.

good luck

 

[DMan II-40]

Ahh, I see. Yeah I need to learn more about carbs. Everything I know about cars is fuel injection, so this is all new to me and interesting as well. Thank you

 

[jetski9010]

Yea sounds like you just dumped too much fuel in there and it went in your exhaust and backfired. If your cranking it over again and it wont start pull the plugs out to see if they are wet with fuel or if there dry? If there dry then you can start looking into carb problems.

 

[DMan II-40]

Is there a fuel pump? (haven't got my book in the mail yet) Because when I turn on fuel I don't hear anything. And the sediment tank never got full (not sure if it should). Unless I get good answers from you guys I probably will just wait for my book to get here so I can read it.

 

[jetski9010]

Yes the fuel pump is the round thing on the side of the carb. Try to prime your system to get the sediment tank and fuel system full. Take off the return like that goes back to the tank off the carb and blow in it. If air leaks out the vent or other places on your gas tank plug them up for now so its air tight. This should push fuel into the inlet side. Keep blowing till your see fuel coming out the side of the carb where you took the line off. After it is primed then try to start it.

 

[DMan II-40]

Yes the fuel pump is the round thing on the side of the carb. Try to prime your system to get the sediment tank and fuel system full. Take off the return like that goes back to the tank off the carb and blow in it. If air leaks out the vent or other places on your gas tank plug them up for now so its air tight. This should push fuel into the inlet side. Keep blowing till your see fuel coming out the side of the carb where you took the line off. After it is primed then try to start it.

Ok so I took off the return line at the carb, plugged my tank up and blew into it. Nothing happened. So I figured I would try a compressor and all that did was make the tank expand a little bit. Now that I think about it I bet I need more gas in the tank. I only put one gallon so the pressure was just going into the lines instead of pushing the fuel. Correct?

Can't believe I'm having so much trouble just trying to prime the system, lol.

 

[jetski9010]

try taking the line off that goes in to the carb and when you blow into the return line watch and see if fuel comes out the line that you took off that goes into the carb. If thats the case something in your carb is wrong. It could be cloged or it could have a diagram in the wrong way.

 

[DMan II-40]

try taking the line off that goes in to the carb and when you blow into the return line watch and see if fuel comes out the line that you took off that goes into the carb. If thats the case something in your carb is wrong. It could be cloged or it could have a diagram in the wrong way.

So I just switched the lines on the tank because I only had about a gallon of gas in there the main pick up line was to short to get gas. So I put the main fuel line on the reserves stick and it primed fine.

Now I tried to start it and there is fuel, but all I am getting is a back fire ever so often, but no start. Any idea?

 

[madscientist]

humor me and disconnect the exhaust hose from the water box ( muffler) then try to start it.

 

[DMan II-40]

haha no thx. I like hearing

 

[madscientist]

i have a reason for this, not to play a joke. realistically you asked for help, but if you avoid this offer you may kick yourself down the road for not trying it. small animals will nest or roost in long exposed outlets of watercraft

 

[DMan II-40]

I took off the waterbox before and blew in it and air passed through it fine. I could feel the backfires coming through the exhaust exit.

 

[jetski9010]

So I just switched the lines on the tank because I only had about a gallon of gas in there the main pick up line was to short to get gas. So I put the main fuel line on the reserves stick and it primed fine.

Now I tried to start it and there is fuel, but all I am getting is a back fire ever so often, but no start. Any idea?

It might be a timing issuie. Your going to have to pull your flywheel and check if your flywheel key has sheared. Anything think you want to check while your flywheel is off is if the stator bolts somehow backed out and cause the stator the turn all the way to the end of the slots messing up the timing.

 

[DMan II-40]

So I took off the flywheel cover and it looks like the flywheel bolt in the center is all ed up. Never seen one before since as I said I'm new, but it is all oval shaped and doesn't seem to be any surface to put a ratchet on there.

 

[DMan II-40]

bumping my old thread as I still never got the ski to start. I did get the flywheel off and it seemed ok. I put in a new key and made sure the stator was dead on. Again same thing.

 

[DMan II-40]

Compression test got an average of 112 psi. With oil I got 140 psi. Someone said compression should be at least 119psi on the js300 so I guess I'm a little low. Is it ok to just get new rings and use old piston if its ok. If that is the problem, since I don't have a dramatic drop in compression I'm assuming that the cylinder wall is ok. Maybe just get new rings, and a hone?

 

[gtgoat]

I read through this thread and I'm not sure what you are trying to do... just get it running? You have to be more systematic when you are checking motors out. First check the basics; fuel, spark, compression. It sounds like you have enough compression (I wouldn't take this motor apart to hone it b/c you could spend the money on a used 440 or 550 engine that will bolt right up with the 440/550 engine tray).
Did you pull the spark plug out, keep the wire on, leave it grounded, and see if it is sparking consistently? If that checks out take the carb off. Take the 6 screws out of the bottom and carefully (very carefully) open it up. if you're not careful you'll be buying a carb rebuild kit (you can reuse it on the 440/550 motor you'll want to put in in the future). Old fuel dries up and leaves white powder (nothing happens if you sniff it). Check out all the gaskets, diaphrams, and brass in the carb. Spray it with carb cleaner and blow compressed air through the passage ways.
Clean the old fuel out of your tank too. Now see what happens.

 

[N2 H2O]

Be careful. Some carb cleaner will deteriorate the rubber gaskets in the carb. If oil in the cylinder bumps up compression, it is most likely your rings. Just new rings should be fine since your compression isn't absolutely terrible. If it didn't start with gas down the carb, you most likely have weak or no spark, so I would check that.