139QMB with 100cc kit is going kinda slow

[rperezeg6]

Hey everyone,

I have a 50cc 139QMB with a 100cc Big Block Kit. I feel like its lagging pretty bad. I have a top speed of 43mph on a straight road. I feel this is kinda slow for a 100cc scooter. Anyone have any suggestions as to why its going so slow?
I am not over weight or anything, I am physically fit. 
I have tried a few things so far though. I have installed a larger carburetor with a #90 main jet. I have opened the carburetor to move the inside pin up and down to try different positions. I just feel there is something wrong. I expected to get at least 50mph out of it.

I also have added
7g sliders weights,
performance exhaust.

Anyone have any thoughts as to what i am doing wrong? is my main jet still too small? Do i need heavier weights? do i need to change my springs?
Any suggestions will be great to hear.

Thanks everyone!!!!
 

[jmkjr72]

Are the carb and jet the same brand
Just because a jet fit in doesn't make it right the numbers very from brand to brand
That is also assuming you have a 4 stroke carb and not a 2 stroke carb the bodies will be the same but all the internals are diffrent

So start with the basics are you using the right plug for the carb and head and the valves are properly adjusted as well as everything in time

There are several adjustments on carbs the
piglet jet and air fuel screw are for idle to 1/4 throttle
The needle which can be changed and adjust is for the widest range of throttle from 1/4 to 3/4
And the main jet for 3/4 to wot

Are you sure you don't have a rev limited cdi

[rperezeg6]

I bought a entire big block kit. The carburetor came with the kit so i'm pretty sure its a 4 stroke. The 90 jet came with the new carburetor. I also bought a new CDI and coil/wire so it doesn't have a rev limit anymore and the spark should be pretty good. I forgot to mention that earlier.
What do you mean by the right plug for the carburetor though?
But now that you mentioned the valves. I remember reading that I should adjust the valves again a little while after installing. I remember it was definitely running faster before when I had first installed the kit. I'll open that up and recheck the valves. but could that cause such a drastic power loss?
Thanks!!!

[rperezeg6]

before i open it up, what size gap would you recommend for the valves/rocker arms?
thanks again

[jmkjr72]

I mentioned for the head and kit. Higher compresion requires a colder plug also some heads require a diffrent length or projector or non projector plug

[rperezeg6]

I just checked the valves. they seem to be ok. they were at .005 which is what I had originally set them to. I also added a 110 jet on the carburetor to see if that helps but now it just sputters really badly when I accelerate and bogs down.
any thoughts? :/

[Rebel]

I suggest one change at a time so you can evaluation what it did to the performance. How many miles are on the big bore kit. Have you checked timing marks?

[rperezeg6]

About 2,000 miles probably.
It idles well and with the 90 jet I had on originally it rode very smooth and accelerated well, it just never went past 43mph. so I don't think timing is the problem but I can take another look at it.
Any other thoughts?

[jmkjr72]

See I don't know jetting for 4 strokes but with a 2 stroke if you rode 2000 miles jetted lean you would have wore the thing out

I would run a compression test as a big part of the cooling on these bikes is the incoming charge of fuel and air

But I would read up on jetting as it sounds like you may have a jetting issue

[Rebel]

Yeah, compression test is in order.

[rperezeg6]

I'll pick up a tester. What PSI should I be reading. I am not sure what normal is for 100cc's.

[Rebel]

I am not sure what a 100cc big bore kit should be. Usually the kits sold as a 100 are actually not that big, probably a 80cc in reality or even a 75.

Man concern is if it holds compression, if it does not you may have a burnt valve.

[rperezeg6]

Seems like I have plenty of compression.
I think I'll take out the cam and redo the timing.
I ordered a main jet kit with various jets, maybe the #110 is too much for it.
Any other thoughts besides that? :/

[jmkjr72]

With 2 strokes that's a huge jump in jet sizes
Sa we stay with the stock 14 mm carb on a zuma we add a sport bore kit and mild street pipe we go up 2 sizes in jet from an 80 to an 84
Even with the after market carbs was may go from a 90 to a 95 unless it's a really wild build or a moded air box