650/X-2 Looking for a little Help

[JC_1992]

I recently purchased a 1987 650sx that has been bone stock since it was new. I purchased it from a guy who had it sitting in his garage for 1 1/2 years without being started or anything. I cranked it and after about 10 seconds of cranking it caught and would consistently fire the back cylinder but the front was intermittent.

Now I have..
-removed all of the old gas
-put new gas and a good additive in
-removed the oil injection system and mixed a high quality TCW3 oil in the gas
-put two new NGK B7ES spark plugs in (gapped to spec).

Taking the front spark plug out it will run on the back cylinder like a champ. Both spark plugs are sparking in the same manner and color when grounded on the head. I did cut the spark plug wire and re-thread it into the boot to see if that was the culprit. I also cleaned inside both of the boots with electrical contact cleaner and Q-tips.

First I was thinking it was a carb issue, but then why would one cylinder be running good? Could it be the reeds are damaged to that cylinder? Or could it be that something in the CDI box is worn out and not providing a good spark under compression?

Thanks for reading and I look forward to some advice.
-James

 

[Vumad]

The spark plugs spark at the same time. That is to say, it doesn't matter if the boot is on the front or the back plug, they can be switched. So, if you switch the boots and the rear cylinder does the same thing, you can rule out spark as your issue with the front cylinder (although keep electrical in the back of your mind until you find a cause).

It's not the carb if you have a single carb. It could be a reed.

Much more likely, it's a bad front cylinder. You need to compression test it before you do anything else.

 

[JC_1992]

What is a good compression tester to buy? Or can I just grab anything and check the difference in the cylinders and tell if the front is bad based on that?

 

[Vumad]

I don't know a good one and yes that will work. You're not going to rebuild a ski cuz it says 140 instead of 150. But if the back is really 150, but it says 130 and the front is 90, you know you have a problem. YOu get to see how good the gauge is when you rebuild the motor.

 

[JC_1992]

I switched the plug wires and still only the back cylinder fires consistently. It starts right up blipping the throttle and both of the cylinders will go and then in less then 10 seconds the front cylinder drops and begins to smoke a lot.
My brother in-law has a compression tester so I will be checking that tomorrow or Tuesday night

 

[TheCoz43]

comp testers are like $10 at auto zone, it is worth it to have one before you ever go check out a ski!

 

[JC_1992]

Checked the compression today. The back cylinder was 145psi and the front was 135-138psi. Tried/checked them multiple times. So I am ruling out compression as the problem.

What should I check next? The front reed? Or...?

 

[JC_1992]

Anyone have any ideas?

 

[Vumad]

have you checked the reeds? Are you able to post a video of the running issues?

 

[JC_1992]

I have not checked the reeds. Do I just unbolt the intake manifold? What should I look for good and bad? Do you happen to know the torque spec when reinstalling the intake manifold?

I will try to get a video of it tomorrow.

 

[WFO Speedracer]

Look for a broken reed or a reed that does not sit flat against the cage, if it has stainless steel reeds in it ditch them regardless of what they look like and buy a good set of aftermarket reeds.

 

[JC_1992]

What kind/brand of reeds would you recommend if they are shot? Not looking for performance as of now. Just a good quality replacement.

 

[JC_1992]

Both sets of reeds looked very good. Cleaned them and put them back in. Took the carb apart and blew everything out with carb cleaner. The problem still persists.

 

[WFO Speedracer]

I didn't see it posted but did you in fact swap the two spark plug leads and see if it still ran on the same cylinder and did you check the comnpression?

 

[JC_1992]

Yes I swapped the spark plug wires and still only the back cylinder ran.
As far as compression the back cylinder is 145psi and the front is 135-138psi

My brother in-law suggested ohm'ing the CDI box. Does anyone have a good write up on how to do this or the specs as far as what the resistance of each should be?

 

[JC_1992]

Anyone with 650sx CDI box specs for resistance?

I took the head off and one side had a lot of corrosion and someone had tried to use gasket material to seal it. SO i bought a complete gasket kit and replaced every gasket on the intake side. Problem still persists.