Engine won't rev all the way while riding

Soflowrider

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hello new to the forum. Just installed my 66cc motor on my bike and started riding. I installed a tach so I could keep an eye on my RPMs while riding, I have since noticed that while the motor is engaged and at WOT I am only getting 2700rpms but when I have the clutch engaged the motor revs up to 5000 RPMs. I do have some upgrades to my motor, high compression head, expansion chamber, 30 tooth sprocket and dellorto carb with a #65 jet. The engine had this problem before I added the chamber, sprocket and the carb. My engine kit came with a high compression head which I swapped with the stock one before ever starting the engine. My top speed is only 33. Mph I figure I should be moving with this parts. Also the engine does excelerte past 2700 RPMs when going down hill but then settles back down to 2700. Any one have any ideas on what it may be? (One pic is of current condition other is of the high compression head)
 

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unless your weight is less than about 50 lbs, I'd guess your sprocket is too small - try a 41t or 44t to get a baseline of how the motor pulls
 
2700 rpm with a 30 tooth would be something like 16 miles per hour. how sure are you that your tach is reading right?
 
2700 rpm with a 30 tooth would be something like 16 miles per hour. how sure are you that your tach is reading right?


Not to sure followed the instructions to get it set for single piston 2 stroke. But have nothing to base it off of. I have similar tach on a 4-stroke long tail mud motor and it's dead accurate. But it doesn't sound like its reached its full potential at 2700.
 
i dont trust them cheap nasty tachs... reading anywhere from 5k to 16k when everything sounds right.

try to locate it as far away from the CDI as possible and use a resistor type plug, cuts down on EMI which makes the digital internals go ballistic.

do you really need one? they dont help you go faster!
 
i dont trust them cheap nasty tachs... reading anywhere from 5k to 16k when everything sounds right.

try to locate it as far away from the CDI as possible and use a resistor type plug, cuts down on EMI which makes the digital internals go ballistic.

do you really need one? they dont help you go faster!


No I don't really need it, but it still doesn't change the fact that my engine is not making full power under a load.
 
Not sure exactly your high compression head plays in this, but your 30T sprocket makes a BIG A gear. And your 65 jet is gonna be leaning things out at WOT. Doubtful you have enough power to turn that cog. Greedy for speed...
 
Not sure exactly your high compression head plays in this, but your 30T sprocket makes a BIG A gear. And your 65 jet is gonna be leaning things out at WOT. Doubtful you have enough power to turn that cog. Greedy for speed...

Just a little greedy! What jet would you recommend using? I was going to put back the 44t sprocket and see if any speeds increased. And I read somewhere that the metal gaskets that come with the kit are a one time deal wasn't sure if maybe was losing compression from an air leak of so sort.
 
65 works for me. I don't think that is the problem. Shorten that gear already. 39, 40, 41 if you need speed.
 
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