help with new BBk ---- please!

[micco]

Hi everyone,

Looking to the experts on this...

I have a 2009 tomos nitro 50 and just installed a 100cc kit...
What i've done...
- 100cc installed
- #90 main jet swapped - came with kit
- all stock airbox and exhaust

Scoot starts up, but under load it just bogs down, 2 min into the drive it just stalls out, has no power, etc

any thoughts or next steps?

I'm thinking too lean or rich...

cheers

[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.

[micco]

ok, i'll put the old jet back on and the old plug, and try it again.

I did some more reading and thinking i might have to adjust the needle.
From my understanding the needle control 1/4-3/4 throttle, and main jet the upper portion, pilot the lower.

I did spray some down kleen-flo starter around the intake and did not get any engine racing. So i'd assume there are no vacuum leaks etc.
The kits cylinder head removes the EGR system, however if i block the port on the intake it doesn't run/start well, so i left it all hooked up.

Not sure what you mean by tuning the tranny - but the kit did come with 8g weights...

[sc00ter]

No, use the jet that came with the kit. A 90 Main sounds about right. Your leak check solution is a good alternative, so if no weird rpm changes means all should be good. Now tuning the tranny sounds naughty, but its not. The 8 gram rollers also sounds about right. Seems the bbkit supplier provided the correct ball park items to help tune it in. Cant do the motor without doing the transmission. Rollers alone may do the trick. Now getting into clutch springs and a torque spring is a whole different tuning experience. I forgot who had a great how-to on transmission tuning. Provo scooter? Scoot Tuning? Will try to remember and post it.

[micco]

ok update....
i looked at the needle...and sure enough mine uses washers as the adjustment, rather then the retaining clip.
So i removed 1 washer, took it for a run and still bogged.
Looked at the plug and it was dark, so i removed the air box cover and went for another ride.
Night and day difference, didn't bog down and was able to get over 40kmph.

So my next purchase will be a performance air filter - any suggestions?

I did noticed a rattle sounds coming from the engine, almost like from the rockers/chain area - thoughts?

[sc00ter]

Does the intake snorkel have a rubber baffle reducer inside of it? If so, remove it and see what happens. Our sock Zuma 2 stroke airboxes have one and once removed we can run pretty much any set up with no issues. Also, once you remove the rubber baffle inside the snorkel (if it has one) OR get a fancy looking pod filter you will have to WATCH YOUR PLUG! Better yet pick up a cheap plug seat temp gauge (Trail Tech makes a nice one) and find out what max temp range your kit (or stock motor set up) normally runs in and MONITOR it till you get it all dialed in. On the noise. I know I picked up a bit of noise on my 125cc 4 stroke build just from installing the bigger top end. That being said, make sure the cam chain tensioner is working properly. The Zuma 125 tensioner was very finicky going back together, and didnt hold good tension until re-installed a second time (seating issue with the spring).

[micco]

good call on all those points - esp the tensioner.
I'll look into the temp monitor

[sc00ter]

Its hard to help people over the internet, and all this info is out there already, so I try to point people in the direction of the stuff that is not always covered. A Trail Tach/Temp combo is one of the best and affordable items a tuner can get. Also, a good compression gauge. We make our own leak-down testers as those are a must have when going big. At least you are working with a quality scooter. Just curious, what brand of bbk did you get and from who? I got a no-name bobo kit from Race Concepts out of Taiwan for my old Zuma 125 and had nothing but great luck with it.

[micco]

update:
Didn't see any restriction pieces in the air box, scoot likes it with the cover off, so looking for direct air cone style.

The EGR hoses are still hooked up, when i plug the one to the intake it stalls out.

Overall seems a 'little' peppier then at 50cc...but not much - sadly i expected more. Still limits at 60kmph (7500rpm), so i think something else is at play.
- checked the CDI, it looks to be a yellow DC fired, and says performance on it - so Im assuming its not rev limited
- i didn't see any washer in the CVT when i checked last year
- still stock rollers, as i don't have a tool to get at it, but i would expect just a slow accel...?

Any other thoughts?

The kit i got was some cheapo from ebay -
here is the link

My old 2001 BWS still destroys this thing on take off and top speed - hind sight, i should have kept that instead and lived with the 2-stoke exhaust smell when i got to work :P

[sc00ter]

I feel ya on the 2 stroke exhaust smell. My wife calls them "Stinky wheels!". You may need to see if they sell a upgear kit for the final drive. 01 BWS, a Zuma to us Yanks! That was the French made one. I freakin' LOVE Zuma's. I have a 70cc full Athena motor from a 09 Zuma that I think will drop into my Adly RT50. This Athena motor will hit 70mph top end and rips off the line. Oh, sorry. If you do a aftermarket variator you may pick up a bit more top end, but it still comes down to the final drive ratio that dictates top end. Plus, you need power to push those upgears, and you have a bbk in place already. Get it all ironed out as far as the motor first, then start considering your next option/upgrade(s).

[micco]

ok so you "saying" i should throw in the 8g rollers, and try again?

[sc00ter]

Experiment! Lighter rollers will make it accelerate faster but if to light will not fully engage the top end, heavier rollers will engage the top end but may be sluggish off the line. It's a balancing act that when done right will reward you with a fun riding experience. Now, to light rollers will not engage (compress) the torque spring and to heavy will cause the torque spring to compress too early making it bog off the line. Note that all bogs are NOT always transmission related as a poorly tuned carb can cause the same symptoms as a poorly tuned transmission and vise versa. I chased my tail in circles trying to tune out a bog in my transmission on mid range roll-on only to find out the float spring in my carb was messed up. That was FUN to figure out! I have it lazy now because if I suspect a carb issue, I just swap a known running carb off a friends scooter and go for a ride. Have also swapped out transmissions before since we all run pretty much the same set-ups now. You just need to find a good balancing point with gram weight. We use tuning rollers for setting up. Not uncommon for us to swap out rollers and sometimes springs up to 10 different times before finding the best setting! Impact gun off, torque wrench back on over and over and over and over..... And its still HOT when doing it! Worth it in the long run.

[sc00ter]

Almost forgot. You mentioned the EGR system. Please note IF it plugs into the exhaust for final waste removal, and you muffler has a catalytic converter in it (usually obvious from having weird heat shielding plates on the exhaust) DO NOT bypass it. Bypassing it will NOT give you more power! The Cat needs air to fully work, and that is what the piping provides. If bypassed the Cat will actually RESTRICT flow and act like the exhaust is clogged, making top end mushy and weak. Some EGR valves just dump back into the airbox. I have also seen some that dump into a "catch hose" that needs to be drained every now and then. Just know what you have first if you plan on bypassing it.