Engine rpm/4 stroke/low power issues

[cannonball2]

The motor has the primary gearing inside, gear drive, you can remove the cover and count the gear teeth to get your primary, the secondary ratio is the relation between the engine sprockets, in your case 10/41 I believe or 4.1:1. Overall gearing is important. The lower #s 11-12 are high ratios the higer #s are lower ratios, confused now? lol

 

[GreedyRogue]

Actually I understand all of that just fine. What I don't understand is how you claim
"My primary ratio is 20t/80t=4. The secondary is 10t/44t"

As you said you are using a fixed gear bike, with a 44t rear. Assuming you have the standard 10t engine gear you would have a ratio of 4.4:1 Where you get your "primary" ratio is beyond me, let alone multiplying it by the "secondary" ratio to get a total ratio of 17.6:1. That's the part that is confusing me.

 

[cannonball2]

My engine is a 4 stroke Grubee, really doesnt matter. It has a tooth belt primary drive. 20t on the engine 80t in the driven pulley 4:1. The pulley drives a shaft with a 10t chain sprocket which drives a 44t wheel sprocket 4.4:1 These two mutliplied together give the overall ratio 17.6:1. Your engines primary ratio is hidden behind the clutch cover. It would tale a lot of power to turn a bike wheel with a 4:1 ratio.This has nothing to do with my bikes pedal ratio. Until we know what your primary reduction is we dont know what the overall is on your bike, but a 41t on the final is generally high.

 

[GreedyRogue]

Now that makes more sense, you actually have 4 "gears" your working with. Most people only have the 2 gears to work with, eg. engine to rear sprocket.

But getting back to my issue, the no power thing. Yesterdays top speed was 19.5. on the same road I am now pulling 21. I have not changed anything since yesterday. It's a little warmer today but more windy as well. I still have no top end power. Once I hit 3/4+ throttle that's it.

I went to the motorcycle shop today hoping to find a smaller main jet, but all they have is mikuni and keihin jets. Are dellorto the only ones that will work in these engines?

 

[camlifter]

on the right side of your engine behind the clutch cover there are 2 gears one on the crank and one on the clutch. iirc the ratio of a grubee is 5 to 1

 

[cannonball2]

on the right side of your engine behind the clutch cover there are 2 gears one on the crank and one on the clutch. iirc the ratio of a grubee is 5 to 1

Well if the Grubee is a 5:1 then the overall is 20.5:1 which should be pretty good.