help with new BBk ---- please!

[sc00ter]

Oh boy, is the Nitro a 2 stroke or a 4 stroke? IF memory serves me right its a SYM built 4 stroke but I might be wrong. Old age does that. What was the compression before the BBK? What is compression after? That would be one of your base readings regardless of cc size. Always check compression first. If you went from a 50cc to a 100cc, you will need to change out the idle (pilot jet) and possibly move the needle slide position OR replace it with a different taper. Could be the transmission needs to be re-calibrated because the belt is pulling in to early also. Also not getting enough air? Is the plug wet right after stalling out? Is it really dark black (rich) or ashy white (lean)? Did you get a base reading of the operating temp before the bbk? Just asking because data points help diagnose problems too. I mostly do 2 strokes (use a full Vapor system for go-carts when tuning) but have done a 4 stroke Zuma 125 into a 165 no-name kit from Taiwan and that thing was super fast afterwards. Zuma motor ended up in a Ruckus build. Miss that motor.....

[micco]

Originally Posted by sc00ter

Oh boy, is the Nitro a 2 stroke or a 4 stroke? IF memory serves me right its a SYM built 4 stroke but I might be wrong. Old age does that. What was the compression before the BBK? What is compression after? That would be one of your base readings regardless of cc size. Always check compression first. If you went from a 50cc to a 100cc, you will need to change out the idle (pilot jet) and possibly move the needle slide position OR replace it with a different taper. Could be the transmission needs to be re-calibrated because the belt is pulling in to early also. Also not getting enough air? Is the plug wet right after stalling out? Is it really dark black (rich) or ashy white (lean)? Did you get a base reading of the operating temp before the bbk? Just asking because data points help diagnose problems too. I mostly do 2 strokes (use a full Vapor system for go-carts when tuning) but have done a 4 stroke Zuma 125 into a 165 no-name kit from Taiwan and that thing was super fast afterwards. Zuma motor ended up in a Ruckus build. Miss that motor.....

Thanks for the reply, i appreciate it.
Your memory is fine! yes a SYM build 4 stroke
Sadly i did not take any compression or temp reading - as i do not have the tools.

It does "feel" like its running hot. i checked the plug and its black, but its also from last year. I'll put a new one in a start it up and check it out tomorrow.
I was playing around with the mixture setting, but it had little to no affect.

Maybe i'll put the stock jet back in? None of them are marked, so i don't know the actual size of them.

I also confirmed the timing is bang on, and the rockers are at .004.
Also on the stand and rev'ing, it seems like its restricted. Previously i could go to 9k, now it struggles to get to 7k.

...should have went to a 80cc kit

[sc00ter]

Another thing I just thought of, and this is actually very important. Did you do a leak down test after it was re-assembled? If you are getting air in anywheres then setting the carb will be extra hard to dial in. Heres the crazy part. The new plug wont really read a accurate color (as far as rich or lean) until you get some WOT runs on it first. The Moped Army website has a pretty good plug reading guide for tuning. So if the scoot wont do WOT runs then you have to get the basics down first so you can do WOT runs. I dont think down jetting the main is a wise choice, and Im pretty sure you will have to up the pilot. Tuning is part science and part patience. Oh, and I hate those "No number" jets! We use the factory jets to the brand of carb we are working with. I still think the belt is pulling into the pulleys early, meaning re-tuning the trans to match the bigger motor is in order.