Any 2 stroke gurus??

T

timtune

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Full Disclosure - This regards my sled. Specifically a 1980 Kawasaki Invader liquid cooled 440

Was running fine and then it blew an exhaust gasket. Ever since the new gasket it hasn't ran right. It has no power under load. On a stand it runs like a champ. With the track on the ground it just bogs out. Good blue spark in each hole.

Used a propane torch full blast no flame at the one accessible end seal and it did nothing to the rpms. Compression test shows ~120PSI each side**. Pulled the carbs, again, they look factory virgin fresh inside. I'll blast them with cleaner and comp air just for grins but I don't expect any change.

Thoughts??

** Am I correct in thinking good compression is no indicator of good bottom end seals?
 
A compression test won't tell you much about the bottom end seals, just turning over the motor at least. Just use the old practice of running it and brushing something over the seals (as much as you can get to) that will bubble or get sucked in if there's a leak. You can also try spraying ether or another fuel source over the lower end seals, and see if the engine runs up a bit. Since you have compression and spark, I'd bet on that or on the carbs.

Have had some good times on the old Invaders. Once those things came out (like my 1974 Chapparal 440) with liquid cooling and slider suspension, the industry had to admit that it needed refinement. Though my 1978 El Tigre 5000 was quicker on trail acceleration and also had slider suspension, though it wasn't nearly as plush as the Invader's. My uncle and two of my cousins had them, and one is left in the hands of my cousin, his only issue with it has been finding new tracks for it over the years.
 
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Shaman said:
A compression test won't tell you much about the bottom end seals, just turning over the motor at least. Just use the old practice of running it and brushing something over the seals (as much as you can get to) that will bubble or get sucked in if there's a leak. Since you have compression and spark, I'd bet on that or on the carbs.

Have had some good times on the old Invaders. Once those things came out (like my 1974 Chapparal 440) with liquid cooling and slider suspension, the industry had to admit that it needed refinement. Though my 1978 El Tigre 5000 was quicker on trail acceleration and also had slider suspension, though it wasn't nearly as plush as the Invader's. My uncle and two of my cousins had them, and one is left in the hands of my cousin, his only issue with it has been finding new tracks for it over the years.
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I'll add clutch/chain/track to your list of potential issues. If it's not behaving, the symptoms match. When running it in the air, are you spinning the track? Are the clutches moving properly? Can you use the brake to add some load and watch the clutches while it's in the air?
 
GreyGhost said:
When running it in the air, are you spinning the track?
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Has to be, if the clutch is working even a little, it should spin the track with any throttle. But he didn't 100% specify, so fair question.
GreyGhost said:
Are the clutches moving properly? Can you use the brake to add some load and watch the clutches while it's in the air?
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It shouldn't matter, if the clutch has spun back to its low speed position, the belt should be low in the PTO clutch, high in the secondary and final gearing should be aggressive as a result - you can easily see this just by observing the height of the belt in the two CVT clutches. Thinking back to my old snowmobile days (haven't done it in decades now), it IS possible that if the clutch springs aren't pushing the PTO or secondary clutch properly and your gearing will make the engine bog, as the CVT clutches are biased to high speed and not acceleration. That's usually on the secondary clutch, if memory serves, but it can also happen to the primary if the weights are too heavy or the spring is too soft and it engages at too low an RPM for the engine to have enough available power to move the sled easily.

It's a pretty common issue on older sleds where the springs lose their strength. I remember wrestling with it back 'in the day'. The good news is that it isn't all that difficult or expensive to change the springs out for either stock ones or something slightly tuned for either more speed or more acceleration (can't have both).
 
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Shaman said:
But he didn't 100% specify, so fair question.
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Kind of did. "on a stand it runs like a champ" Yes with the track in the air it spools up great.

I havn't done anything to the clutch. I really think it motor related. I wanna say carbs but they look good.
 
timtune said:
Kind of did. "on a stand it runs like a champ" Yes with the track in the air it spools up great.

I havn't done anything to the clutch. I really think it motor related. I wanna say carbs but they look good.
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Runs like a champ was slightly ambiguous as it may not have been above idle or belt may have been off. As it's a quick and easy test, I'd try using the brake in the air to load the motor while watching the clutches. You may be correct and it's an engine issue but if I can rule out a lot of other components, that helps to ensure time and money aren't wasted going down the wrong path.
 
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