80cc stock engine top speed problem

[Sully10101]

I bought my engine kit from ebay and with all stock parts, hits 40 mph and I've bought my son 4 engines and none of them come close to mine. I can't seem to fine the same engine again since the guy that sold it to me at the time only had a few kits. Why is mine so much faster and I weigh 100 lbs. more. The bikes are identical as well as the 36 tooth sprocket on the back. What could possibly be the difference?

 

[crassius]

ebay is a bit of a crap shoot - some sellers there have very old model motors, while some get newer models - the fast one may be a newer 40mm stroke motor

 

[Tyler6357]

Ha! Even if you had purchased 2 from that same guy they probably wouldn't be the same. It's probably that one has better compression than the others. Chinese quality control is very poor.

 

[Sully10101]

Thank you for your reply. It's been driving me crazy for months. So, what can I look for to make sure I'm getting the newer faster motor? Any certain brand or model or horsepower?

 

[Sully10101]

I have noticed it has very good compression. I even wondered if mine was just a freak accident. lol

 

[Tyler6357]

I have noticed it has very good compression. I even wondered if mine was just a freak accident. lol

The same thing happened to me, I have 2 bikes, one of the engines just runs better than the other. I tried testing my compression a few months ago and made a thread about it. ---> https://motoredbikes.com/threads/compression-test.52855/

 

[Sully10101]

I've been researching and racking my brain on this. I'm going to try a high compression head and see if that makes a difference. I mean, I know it will but, just how much.

 

[Sully10101]

I can't imagine putting a high compression head on my engine if I'm already going 40mph with a stock motor and parts.

 

[Tyler6357]

I've been researching and racking my brain on this. I'm going to try a high compression head and see if that makes a difference. I mean, I know it will but, just how much.

Well, a high compression head will do 2 things, (1) make the engine run cooler, the large fins and size of the head really helps dissipate the heat very well, and (2) increase compression, however, if you get a 6cc head you must have a squish gap of no more than .06" for it to have any effect, better would be a squish gap of .025"-.035" is optimum.

 

[Sully10101]

Wow! I did not know that. I assume that is listed in the specs for the head?