78 Intruder losing a cylinder under load?

[MBCanuck]

I've all but revived my Dad's 78 Intruder but it just won't cooperate with me.  I'm just planning on using it for the odd short fishing trip where the truck won't go and pulling kids around the yard. Yesterday it seemed to be running fine, today I threw the kids in the toboggan because the weather was nice only to find I'd lost all my top end.  The sled still starts fine and it will sit and idle perfectly but it won't build any revs.  Take off and it seems to drop a cylinder.  After short limping loop I pulled the plugs and one was hotter than the other.  I'm guessing it's a clogged main but thought I'd ask the crowd with some experience if anyone had any other ideas. 
FYI, (if the picture worked) the wind shield is a cut down Safari wind shield I got for nothing. I'm at that age where comfort trumps style.   

[gixxer6]

I always start at the simplest thing first.  Try a new set of spark plugs.  If that doesn't help, try switching the spark plug wires and see if the same plug is still warmer than the other. 

[kawhead]

dirty  carbs/bad o ring on nozzle.....i'll beat jim to....crank seals.

[jimvw57]

Dang it!! getting slow in my old age..

[MBCanuck]

Thanks for the input!  The crank seals have not been done, but I've checked them as best I can and think they are ok.  The other indicator is that it was running good two days ago and then changed all of a sudden.  I only had a few minutes tonight but I found the spring in the plug cap missing on one side, lo and behold the cool cylinder.  I'll get a new cap tomorrow and see if that's it.  Hopefully.  That'd be a pleasant discovery. 
Does this sound like a failing coil to anyone?  When I stopped the cool cylinder plug was wet, so I suspect an electrical issue.  I won't worry too much until I get a new cap.
Thanks!

[MBCanuck]

Oh, and at the risk of sounding uneducated, what 'nozzle'? 

[mswyka]

Yes, if it is not an electrical breakdown I would also vote for a bad o-ring - the one on the bottom tip of the needle jet.

[MBCanuck]

That's easy enough to check.  Thanks again!

[kawhead]

needle jet o ring is correct, thanks mark.  plug wire ends is a good start....but....when we test c case pressure the motor is cold....crank's not spinning...as we ride the motor gets up to operating temp, and that old stiff rubber seal now becomes .........crap. just imo....

[MBCanuck]

I finally got my plug caps replaced.  Sled ran perfect, for a bit, thought I had lucked out.  20 degrees colder this weekend than last so basically it just took longer to fail.  Last week was -1*C and it started acting up right away.  This week -20 and it ran good for 5-10 minutes, then the same issue.  Lost the mag side cylinder as soon as it got to operating temperature.  Pulled up to the shop and it sat and idled nicely, again.  Crank seal or coil?  Any guesses?

[Lloyd (ljm)]

  "lost mag side cylinder"  What exactly do you mean? and how do you know?

 Does it lose spark? or is it not getting fuel?

 Other simple cheap things to check. Make sure all your electrical connections are good, double check all the grounds.

 Being as both plugs fire at the same time, Other than the plugs, caps and wires it should be an all or nothing deal.

  Have you changed the plugs?

 I had a Drifter do the same thing. I chased it for a year. Plugs sparked when cold but when it got warm one would not spark. changed that plug, issue went away.

 Lloyd

[gixxer6]

Have you tried switching the plug wires???  This would tell you if it was the coil or not...

[MBCanuck]

When I said 'lost mag side cylinder" I just meant that it's that side that consistently stops firing when the machine warms up.  I know it's that side because when it happens the clutch side plug is always hot and the mag side isn't.  I've swapped the plugs to rule that out, but can't swap the wires as the close side to the coil is too short to reach the far side. 

[Lloyd (ljm)]

Have you checked for actual spark when you loose power?

 If that cylinder is getting too little or too much fuel the spark plug will be cooler than the other one.

[Interceptor398]

I will add this, have you checked the gas tank for water on the bottom?  I've had this same type of thing happen a few times and tracked it back to water in the gas.  I no long dump the entire gas can into the tank.  The last quart or so I pour into a clear jar to check for water.  Almost every time there is some. In the Kawasaki owners manual for the LTD it says "Each time the fuel tank is filled , gasoline antifreeze must be added to remove accumulated moisture within the fuel system.  Moisture contained in the fuel system components could result in engine malfunction or internal damage."  It mentions "Heet" as a good choice.  I often wonder how much of the trouble we try to help with comes back to plain old water in the gas??  If the sled was running good for a couple time and then not so good I think it bounced around enough to suck some water into the fuel system??