77 Marathon still no power

dobey · 04-20-2010, 04:03 PM

I have rebuilt the top end, the carb is perfectly cleaned, installed a new comet clutch (drive) and the thing still wont rev. It starts fine in forward and reverse and putts around at lawn mower speeds on the flat but wont rev high enough to get the driven clutch more than 1/3 engaged.

I described it to a local cart repair guy and he suspects the crank seals, do you guys have any other ideas? I see the drive clutch side crank seal on buggies unlimited but not the other side.

DOOmsman · 04-20-2010, 04:38 PM

If you need seals one of our sponsors can help.
What is the compression like?

mb523 · 04-23-2010, 01:16 AM

Hey dobey!

When you rebuilt the top end, did you by any chance take note on which way you installed the piston? Most new pistons have a marking and arrow to show which way the piston goes. It has something to do with the port on one side. It will still run if it is in backwards, just not very well.

An easy way to check if it is in backwards is to remove the exhaust header pipe and look into the exhaust port. While rotating the engine (spark plug disconnected or removed to prevent fire) you should NOT be able to see a port on the piston. That port on the piston should face away from the exhaust port.

Let us know what you find and goodluck.

crash12888 · 04-23-2010, 09:08 AM

How does it run with the belt off?
Does it rev up then?

04-20-2010, 04:03 PM	#1
dobey Not Yet Wild Join Date: Sep 2009 Posts: 8	77 Marathon still no power I have rebuilt the top end, the carb is perfectly cleaned, installed a new comet clutch (drive) and the thing still wont rev. It starts fine in forward and reverse and putts around at lawn mower speeds on the flat but wont rev high enough to get the driven clutch more than 1/3 engaged. I described it to a local cart repair guy and he suspects the crank seals, do you guys have any other ideas? I see the drive clutch side crank seal on buggies unlimited but not the other side.
dobey Not Yet Wild Join Date: Sep 2009 Posts: 8

04-20-2010, 04:38 PM	#2
DOOmsman Gone Wild Join Date: Jul 2008 Location: Reddick IL Posts: 11,220	Re: 77 Marathon still no power If you need seals one of our sponsors can help. What is the compression like?

04-23-2010, 01:16 AM	#3
mb523 Peanut Join Date: Feb 2007 Location: Western Massachusetts Posts: 656	Re: 77 Marathon still no power Hey dobey! When you rebuilt the top end, did you by any chance take note on which way you installed the piston? Most new pistons have a marking and arrow to show which way the piston goes. It has something to do with the port on one side. It will still run if it is in backwards, just not very well. An easy way to check if it is in backwards is to remove the exhaust header pipe and look into the exhaust port. While rotating the engine (spark plug disconnected or removed to prevent fire) you should NOT be able to see a port on the piston. That port on the piston should face away from the exhaust port. Let us know what you find and goodluck.

04-23-2010, 09:08 AM	#4
crash12888 Gone Crazy Join Date: Jan 2007 Location: Chesterfield, Va Posts: 6,021	Re: 77 Marathon still no power How does it run with the belt off? Does it rev up then?

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