99cc predy cam mod

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young grease monkey

New Member
Sep 20, 2011
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Chicago
i'v had my engine apart for a while now and was turning the flywheel and looking at the cam timing. i noticed that halfway in the compression stroke, the exhaust opens about 1.5mm. this is to make it easy to turn over i think, but will hurt lower end power. i found the culprit!


it has a centrifugal activator that disengages it. it may help idle if i remove this because it will help low rpm power
 
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dmb

Active Member
Dec 4, 2010
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lakewood ca
the activator lifts the lifter to release compression in starting. removal will aid in a sore hand and no power gain.
 
wayne z

wayne z

Active Member
Dec 5, 2010
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louisiana
dmb said:
the activator lifts the lifter to release compression in starting. removal will aid in a sore hand and no power gain.
Click to expand...
That's right, the compression release de-activates after the engine reaches about 1000 rpm. Normal idle is about 1200-1800 rpm.

The engine will be hard to start and be prone to kickback and jerking the starter handle away from your grip, without it.
 
wayne z

wayne z

Active Member
Dec 5, 2010
1,743
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louisiana
Prolly could add weight to the weights, but for what reason? to idle lower? These are fan cooled, splash lubed single cylinder engines, and they don't lube, cool or run well at very low rpms.
I know that none of my engines spend much time at idle LOL
 
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young grease monkey

New Member
Sep 20, 2011
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Chicago
Ok, just an idea. The design on mine is different, looks like there are at least 2 different cams out there. Mine is all one piece and smaller. Oh, and an update on my bike; I noticed that part of the cylinder head is flat top and hits the piston when there is no gasket. I can get it machined down, I will probably take off .05 of the edge of the piston or head.
 
motorhedfred

motorhedfred

Member
Jul 31, 2009
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United States
young grease monkey said:
Ok, just an idea. The design on mine is different, looks like there are at least 2 different cams out there. Mine is all one piece and smaller. Oh, and an update on my bike; I noticed that part of the cylinder head is flat top and hits the piston when there is no gasket. I can get it machined down, I will probably take off .05 of the edge of the piston or head.
Click to expand...
Unless you're planning to run it without a head gasket, there's no need to have it machined. The gasket gives you the necessary clearance. You want a certain amount of "squish" between the bottom of the head and the top of the piston.

This makes it more efficient because it forces the air/fuel mixture that would normally be trapped in there as the piston reaches TDC to squirt out into the combustion chamber as the power stroke begins. The factory designed it that way.

If you want more compression, you can have the whole gasket surface milled down some. this is all covered in the AGK performance build up for the 99cc HF.

http://www.affordablegokarts.com/99cc-predator.php

BTW, where did you find the other cams you mentioned ? Is there another company out there making cams for the 99cc Predator that we haven't heard of ? Don't be holding out on us now....

MHF
 
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