Engine Trouble Won't rev high enough?

[p4cm4n]

so a few weeks ago I put together my build from some years ago.

Many thanks to SBP, specifically Jim for all his help. He personally emailed me with answers to all my dumb questions.

Now I think I have some engine problems.

My mixture is 40:1. My idle is what I consider perfect. My plug is a pretty close to perfect if not perfect color, after much fidgeting. My engine is a 66cc on a cruiser bike, 7 speed with a SBP shift kit. Now that I've adjusted and perfected things like my rear dérailleur and brakes and started moving, I can't get a decent speed.

I'm 230lbs give or take, I haven't been hauling a load behind me. Going from gear 1 on the bike, (don't have tooth specs with me now, can get them later) I hover about 18 miles an hour. Going up each individual gear, I only gain about 1-1.5 miles per hour, occasionally 2. By 7th gear, I top out at 29.

If I don't sit on the bike, prop it up, and use WOT to spin the tire, you can really feel that two stroke vibration on my pre-balanced crank. But while on it, very comfortable ride...no vibration really considering..just can't get any speed or anything.

Any ideas of things to look at?

 

[p4cm4n]

Oh yeah, to throw it in there, it's a b6hs plug with 93 octane fuel, gumout brand (sheetz) oil, a 2011 skyhawk, and the standard setup from SBP sprocket wise

 

[Deleted member 12676]

Have you
-replaced that s**tty stock air filter?
-used sandpaper on glass to plane flat your cylinder head to prevent power robbing leaks? (you can also use this method to increase cylinder compression which is a sure fire way of getting more power output. Just start out with a really rough sandpaper to take off a half millimeter from the mating surface.)
-put an iridium plug on it?
-used a rotary tool to increase intake port duration by raising the skirt?
-cleaned the contact area for the stator coils mounting screws which are the ground path for the spark? resistance there reduces spark power which reduces engine power.

 

[crassius]

at 230lb, that's all some folks get

with shift kit, many folks see a loss of speed due to extra turning weight in gear system

if the problem is elsewhere, think in these terms: if motor seems not to rev as high as you'd expect, then your high gear may be too high, try a smaller pedal crank gear - otherwise if engine is reving high enough, you may need a larger pedal crank gear

 

[Thanks]

jaguar :

You may have been one of the replies on a previous thread for me - specifically that I cannot get the body of the engine apart. I can get the top of the head off, that is all. Not the cylinder body. I have not done any shaving of size there, however it is flat (I have checked). I may do this.

The plug is a NGK b5 or b6hs. I think I have both. Haven't tried iridium. I'm going to do a plug chop today most likely and will try to get an iridium to replace after.

Haven't done anything with the skirt as I can't get inside the body safely.

The contact area for the stator is mostly clean, some of the magnet looks rusty though. Could this affect it? I tried to get a new coil but couldn't install for some reason as the wholes lined up in a slightly misaligned fashion which concerned me for clearance on all sides.

And thanks crassius seems I may be too fat I rode this a few years ago when I was about 180-190 and got a fair bit of speed out of it on the standard 44 tooth sprocket. Hoped the shift kit would extend that. Oh well.

 

[Thanks]

oh and I have a brand new dellorto clone with low profile air filter.