Is 40km/h with a 36t sprocket normal?

[cyclepro101]

I have a Z80 (66cc) on a mountain bike. I have upgraded to a 0.76mm main jet, cut off the internal pipe on the muffler cover and screwed in a 3/4" socket with a 3/4" extention pipe and I have a few extra holes drilled in the back of the carb cover. I have also reamed out the intake side of the carb a little and had a bit of a go at opening up the muffler flange where it bolts onto the cylinder. I also have a new NGK spark plug cap and wire and use a NGK B**6** plug. I have also put on a 36 tooth sprocket.
Now is 40km/h about what this thing should do flat out? Maybe if I was going down a hill or let it ring out a bit longer I could get 45km/h but I thought it would go a bit faster than this. It pulls pretty good but just wont seen to rev way way way out. It pulls pretty good to about 38km/h then goes back to chugging a bit. I have also only done 350km/s about 3 tanks. Will it loosen up a bit more?

Steve

[Cabinfever1977]

40kph is 24mph. i can get my bike all stock with a 44t upto 32mph on flat ground and i can do 24mph up a hill. so what ever you did didnt help you any. that 36t spocket should get you up to 35-40mph on a 26" bike. unless you have a smaller bike,what size bike are we talking about?
and no, what ever its running at now is probally what it will do,if that.

[cyclepro101]

Thanks, Thats what I feared. It has std. 26" wheels. Anything I should do or check to get some speed out of this thing?

Steve

[Cabinfever1977]

what gas/oil ratio are you using?
and maybe you need to move the c-clip on the carb slide.
what speed did it do before changing the sprocket and modifing the other stuff?
a picture of the bike will help a lot.

[joe-craft]

one of your problems would be your jet size, i tried to change my jet size now its just flooding my enigne and not getting any power, so you should either fix your jet put it back to 70 and try it then.

[Bikeguy Joe]

Sounds like you are overly rich and the engine is four cycling at WOT.

[Cabinfever1977]

maybe you should get a new engine and leave it stock and then use your 36t sprocket and you should be able to do 35-40mph+

zoombicycles has engine kits for $109.95 and includes free shipping

[cyclepro101]

I question some of the speeds guys on here tsay they are getting. Using this Kart Sprocket Calculator Sprocket Calculator
With 26" wheels and a 10 tooth on front and a 44 or 36 on the rear I am getting correct speeds at 6000 rpm.
Also I did go back to the std jet and it was crap. Starving for fuel at WOT.
Also I will take a photo and post later.
I still say at 300km's its probably not fully run in yet. As the instructions say not to go over 20km/h for the first 500km's.

Steve

[cyclepro101]

OK, here she is. I esspecially like how I made the rear disk brake work. I needed to pack out the disk and file off some of the caliper to get it away from the chain. Also have a very strong connection to the frame now. The new sprocket has made it very smooth and I have also glued a foam mouse pad over the clutch cover and stuffed some cork in the fins and that has made it very very quiet.

[Rockenstein]

My bike with a wheel circumference of 2081 mm will hit 45 km/h on flat ground without issue...will cruise at 35 km/h until the fuel supply runs out without missing a beat. Are you sure your speedo is reading correctly? I use an Echo cycle computer and verified it's speed accuracy with one of those road side speed trap signs that was set up near me. The Echo cycle computer allows you to enter the exact numbers for the circumference of the tires I'm using, does your computer\speedometer allow you to do this?

For reference I've got 449 km worth of running on the engine, run a 32:1 mix, engine is unmodified sans the centrifugal clutch, carb needle clip is in the top notch, muffler is lightly packed with 2 stroke muffler wadding, I use an NGK B9HS gaped at .020 and I'm running a 44 tooth gear.


PS: Really liking that disc brake setup, good job man!