Engine diagnosis

[tmoney12]

Hello everyone, I figured I would post this in the general forum because my engine issues could be common to most ski engines. A little background, I have been reviving a 1988 650sx from the dead. Engine mods include: shaved head, 38mm keihin carb and mathing manifold, K&N filter, aftermarket pipe and waterbox. After tearing the motor apart to clean and inspect I found the water in the engine cases. After flushing the bottom end, I found the rod bearing and crank looked really good. The Reed cages were corroded and needed to be replaced. I found some on flee bay and reassembled the engine. When cranking the engine I found I had a very weak spark. Again I found a cdi unit on ebay and now the spark is good. So here is my problem: The engine will only run at high RPM with tons of choke and for about 20 seconds. The smoke coming from the exhaust is crazy. I did put a bunch of 2 cycle oil in the bottom end after the flush but tried to drain as much as possible. I thought maybe the oil in the bottom end would be causing this, but I have ran it enough to burn that off I would think. I also noticed that when the engine starts to die an orange flame burns burns in the intake. Do you think this is a main seal problem, or a reed problem? I have gone through the carb and it is emaculate. Jetting is 155 main and stock pilot. Engine ran perfect with these settings 10 years ago when I put it up. Engine will not start unless choked and wont even come close to idle.

Any ideas on what could be my problem? Thanks for reading.

-Tmoney12

 

[stanton]

thats sketchy your crank was ok after sitting in water..but if u say so.
sounds like a massive air leak. im no mechanic tho.

 

[ger87410]

I'd guess you have more then 1 problem.

Start with a leak-down test. Probably also verify the timing.

 

[tmoney12]

Thanks for your responses. I did pull the flywheel and the stator looked great and tested good. I have never messed with the timing so I would think the timing should be good considering I replaced my cdi with one from the same model. The only thing I can of is crank seals or reeds but I am not sure.

 

[ger87410]

Thanks for your responses. I did pull the flywheel and the stator looked great and tested good. I have never messed with the timing so I would think the timing should be good considering I replaced my cdi with one from the same model. The only thing I can of is crank seals or reeds but I am not sure.

A leak-down test would answer that.

 

[tmoney12]

Well by the time I buy a leak down tester I could just by new crank seals and rule that out. Looks like that would be a good start. Does anybody know the symptoms of worn reeds? Would it be blow back through the carb? The orange flame in the intake leads me to suspect that.

 

[tor*p*do]

crank seals are not the only place a motor can leak
do a leak down test

 

[tmoney12]

I tore down the top end and replaced all the gaskets except the bottom end and crank seals. I put new head, base, exhaust, and reed/intake gaskets. Anybody know where to get a leak down tester for a good price?

 

[Kny21]

Doesn't that motor have the crankcase drain valve on it? Is it blocked off or still using that mechanism? If it's still there I'd bet $ it's causing most if not all your headaches.

 

[tmoney12]

I have the crankcase vent blocked off along with the oil injection pump removed.

 

[WaveDemon]

I tore down the top end and replaced all the gaskets except the bottom end and crank seals. I put new head, base, exhaust, and reed/intake gaskets. Anybody know where to get a leak down tester for a good price?

www.watcon.com

I don't see it on his site anymore. Email him, I bought mine there and it works great.

 

[Shifty]

A leakdown tester could be made up using some brass plumbing fittings available at ACE. It would cost around $18-20

Buy a 1/8" scrader valve (like from a bike tire), a 1/8" tee and a 1/8" barb (as picured)

Buy a pressure guage that reads from 0-30psi or so and put it all together on the brass tee. Then block off you exhaust manifold and intake manifold with gasket material sandwitched between your exhaust manifold/ headpipe and intake manifold/ carburetor.

Hook your new leakdown tester to the pulse fitting in the cases with some fuel line...... perform test at 8psi or so.

 

[tmoney12]

Thank you shifty! I appreciate the information.

 

[tmoney12]

Well i built a case pressure tester and found that my engine is holding 9psi just fine. I now believe that my carb is the culprit to my engine problems. I have a CDK II 38mm. Is there anything tricky I should know about rebuilding this carb? I have had it apart already and cleaned it up good. I am getting ready to buy a rebuild kit and do it right. Any suggestions on best place to get one? Thanks.

 

[craven]

to burn off oil in a crank case does take a long time, perhaps 10 to 20 min maybe even more.
if you need to choke it to get it to run then you are straved for fuel. Because you said the reeds were rusty, you should check the pulse line to the fuel pump and the fitting into the case. From there I would suck on the fuel pump line in the carb and check for leakage.
Orange flame in the carb would usually indicate bad timming or bad reeds. If you phyiscaly look at the reeds you should see the all the petals are contacting the reed cage(need to be out of the engine for this) I only mention timming because imagine the piston not covering the transfer port when it ignites, the spark could burn the fuel all the way back to the carb but that is just a theroy, I would think that it would run like cr@p if this was the problem.
I suspect fuel delivery. Good luck.

 

[Sospikey]

While at it; check the one way valve at the tank. They tend to die, leaving the tank un-pressurized. That would give similar sympthoms. If you rebuild the carb, get a new needle and seat as well.

 

[tmoney12]

I pulled the reed cages out and looked to see if the reeds were contacting the cage properly and they are. When I pulled the flywheel and stator to check the front seal for leaks, I installed the stater with a slightly retarded setting so that should hopefully help. I checked the one way check valve on the tank and found that it seems to be working normally. I am thinking my carb must be screwed up in some way. I will order a rebuild kit and check it again. Thanks everybody for your input.

-tmoney12

 

[craven]

I pulled the reed cages out and looked to see if the reeds were contacting the cage properly and they are. When I pulled the flywheel and stator to check the front seal for leaks, I installed the stater with a slightly retarded setting so that should hopefully help. I checked the one way check valve on the tank and found that it seems to be working normally. I am thinking my carb must be screwed up in some way. I will order a rebuild kit and check it again. Thanks everybody for your input.

-tmoney12

pulse line and fitting?

 

[tmoney12]

I pressure tested through the pulse line and that didnt leak. I then put my mouth on the pulse line fitting on the carb. The fuel pump would only allow a small amount of air in and out then would stop. I assume that is how the fuel pump is supposed to operate.

 

[tmoney12]

Well I finally got my ski running. I ended up purchasing a carb rebuild kit and what do you know it runs. I wanted to say thank you to everybody that posted on my thread and helping me track down the gremlin. Thanks again!!

-tmoney12