Arctic Cat Prowler Sachs 50 Loses Power When Warm

[ArcticMinibike]

I have a Prowler with a 47CC Sachs AMAX 2 cycle engine. I am in the process of restoring but the last time it ran many years ago, it would lose power once it warmed up.

Anyone have any suggestions?

A small engine tech suggested that the muffler might be plugged but if so, it is only partially plugged since I remember feeling exhaust venting from the back. If the exhaust needs to be cleaned, he said they used to use a torch to burn it out but gave no details on how to do that. Can I do it with a propane or MAPP torch? I'm assuming I'd remove the insert from the back of the muffler, heat it up, and knock it with a wooden handle or block. Anyone ever cleaned one? If so, how?

This tech also thought maybe one of the crankcase seals was bad and not allowing the case to "pressurize". I didn't know the case should build any pressure. Is he crazy for suggesting that would cause a loss of power, whether it is warm or not? I never had any fluid leakage from this engine but some of the case gaskets were in pieces 30 years ago when I last had it apart and I had no replacements. This time around I will be ordering a complete gasket and seal kit. I can't see how that would affect power other than the head and reed valve gaskets. Mine are in good shape.

BTW - the reed valve looks to be in excellent condition but I don't know how to test it.

Any other ideas on why it might lose power after it warms up?

 

[Rigaman]

Thats a pretty odd symptom. If it has power while cold, it should have power while warm. I will ask a couple buddies of mine that have Arctic Cats with Sachs engines. Someone must know.

 

[MB165]

Ensure the condenser, point gap/ timing is good, piston, ring and bore condition too. If it were my engine Id replace the condenser with a newly manufactured one, even if the origional tests good.
The exhaust can be heated to burn out any accumulated carbon ( ive used a oxy/ acet. torch with rose bud tip on some MX bikes), but be careful isnt your pipe chromed? Do it outside it will get VERY smokey. I guess a propane torch would work but its gonna take a while.
Good call to reseal it.....
The crankcase (not the gearbox) operates in vacum and pressure, depends on which way the piston is going. It is important there are no air leaks. If the crank seals or any gaskets were leaking youd have hard or no starting, erratic idle and possible seizure.

 

[Neck]

OK when your saying "loses power" are we talking bogs? Like MoeMoeMoe when you twist the throttle? How is your compression? The rings may have gone South.

 

[ArcticMinibike]

Finally got the compression tested. Cold maxed out at 140psi after a few pulls. Not sure what is considered normal for this engine but I'm assuming that's pretty good. I did replace the reed valve gaskets prior to testing. I also took the head off and dressed the mating surfaces between the cylinder and head. No gasket there so I wanted to make sure they were clean and flat.

Unfortunately I couldn't check the compression hot. I'm in the middle of my rebuild of the carb along with a number of other things. If it still has issues once I get everything back together I'll look at the condenser, the timing, and gaskets.

So what should the compression range be on this engine anyway??? I saw someone asked a while back for this same engine and he never got an answer. Just curious.

 

[ArcticMinibike]

I also picked up a NOS muffler cheap enough that it wasn't worth cleaning the old one. That might help as well as the old one was dripping with oil and deposits. Probably never been cleaned.