Cylinder upgrade

[scott7]

Hey guys, I'm putting in a 47mm bore kit. Other than that everything is stock except for 6gram sliders which I put in stock variator.
my scooter is a 49cc Tao Tao 139qmb gy6. I took carb off and drilled out bolts so I could get floor bowl apart. 
I was thinking of putting 90 jet in the stock carb and then taking out the air restrictors out of the the air box, what do you all think?
is there more I should do or have to do? Thanks

[90GTVert]

Sounds like a pretty good plan to me. You should do more tuning to the carb, rather than just putting a main jet in and calling it done IMO. Find what works best. Same for the CVT, unless you're happy with how it works on the first try.

[scott7]

Thanks ,90GTVert ,yea I was thinking of starting with a 90 jet then working down from there, will I have to mess with idle screw , if so I'll probably have to drill that out to get to it .i think it's caped off. I haven't messed with cvt much except replacing them. What would you suggest ?
What speeds can I expect from upgrade , hoping for 40 to 45 mph

[90GTVert]

I'd get the idle mixture screw in an adjustable state if it were mine. If it's got a needle that's not adjustable, I'd prob buy a whole new carb, but you can always try it out first. It may work great for you as-is.

Tuning for the right rollers is basically just replacing them repeatedly and analyzing the results of each change. Then you decide what to go with based on what works best. If you have a tach or simply feel that it needs to rev more or less, then you just swap lighter (more RPM) or heavier (less RPM) weights in to get where you want to be. You can even stuff weights with aluminum foil to add a little to them, though you need a scale with at least 0.1g resolution so you can keep them all even.

Your expectations are reasonable.

[greggkinney]

chances are that when you pullthe plug thats over the fuel screw that its going to be a half moon shaped screw not slotted . the moon shape sticks out its not recessed. i took the cap from an old school clear bic stick pen and heated it with a lighter (make sure its not flaming) and stuck it over the moon shape and let it cool to make me a tool to turn it. best to buy a tunable carb but make sure you dont downsize. alot of the newer tao taos have pd19j carbs not 18s. good luck and enjoy!

[scott7]

Thanks for the info you all . Well I put the big bore kit on earlier today. It came in the mail and I installed it. Lots more power ,but doesn't go over 35 mph had some head wind though.
If I tucked down I could get about 37mph. I'm not satisfied with that cause I can tell I have a lot more power. Lots more power on take off. Gets up to 35 pretty fast compared to what it use to. That's with a 90 jet and took out both air restrictions from the air box. Also has 6gram sliders in variator. I'm noticing a lot of pinging which it has always done just more now. Using 93 octane, it got dark on me so I haven't been able to check spark plug to see how it's burning , I did put air restrictor back in nozzle tube to see what change that would do, it bogged it just a little so I took it back out, it idles perfect, so what do you all think, so far.

[90GTVert]

Don't be too discouraged with that speed, as it may pick up once you do some carb and CVT tuning. You can loose multiple MPH if either is off by much.

Pinging may be that the compression is too high or the timing is too far advanced. If it happens to be lean, it will usually make it worse, but in this case I'm suspecting compression is high. You didn't mention a head, so I'm assuming you are using the stock cylinder head. That should work, but you may need to find out where compression is to see if it needs to be changed or install a thicker or extra base gasket to drop compression. Some modify the combustion chamber for a little more volume. You definitely don't want it to have detonation all of the time. I'd first go up to a 95 jet. If that didn't help or made it worse, then I'd try an 85 and continue dropping down till performance fell off. Take notes. Do runs in the same spot in a short period of time, and note results each way. Note any data you can. RPM, MPH, CHT, observation... whatever is available to you. You'll find a good jet that way. Same basic thing for the roller selection.

[scott7]

Thanks , I'll check compression later today and start changing jets, yes it is a stock head, I didn't know I could double bass gaskets, but would that be enough increase ?
And would I have to use new head gasket if I have to pull it back apart ?
What about buying octane to add to fuel ,will that work to stop pinging ?
Will heavy rollers in variator increase top end speed or stronger spring in clutch?
Sorry for all the questions ,just want to learn

[scott7]

Oh also the head gasket that came with the cylinder looked thicker that the thin metal ones I've seen before if that makes a difference

[90GTVert]

I've reused metal gaskets. Never had the other style, but I wouldn't expect it to be reusable. Depends on condition. Technically should be replaced. At this point, we aren't ever certain that compression is the issue though.

Adding octane booster or using racing fuel isn't a great solution. Cost prohibitive and inconvenient. Getting the compression to an acceptable level or dialing back ignition timing till it stops knocking would be more practical. Personally, I'd go with straightening out compression first and retard timing more only if necessary. That is as long as there's no aftermarket CDI or pickup mod. In that case, I'd prob swap back to stop and see if the condition improved.

CVT tuning may or may not improve speed. Depends how it's doing now. Heavy rollers don't always equal more speed. The goal is for the CVT to keep the engine near it's peak power for best performance. If you can do that, you'll get as much as you can out of it without additional mods.

[greggkinney]

ebay and amazon have inductive tachometers for $10-12, id suggest getting one. sometimes with these motors its hard to determine rpm's by ear. chances are that those 6g rollers might be slowing you down. speed seem to be more dependant on rpm's than it is roller weight. but rpm's are based on roller weight if that makes scene. hang in there, youll get it

[scott7]

Thanks for the info you all ,
Ok update- got home looked at spark plug, very small amount of black not much though, I put 94 jet in and it didn't run as good,kinda like a hesitation when taking off and like slipping at midrange if that makes any sense.then I went to 85 jet did not run very good either. Looked like it was running lean, so I went to 88 jet, ran pretty good but hesitated a little . So I went back to 90 jet. Seems to run best . This is all by feel though ,no tack no speedometer nothing but feel lol
88spark plug looked good 90 looks a little more darker, if I can get picture uploaded I'll post them.
Anyway seems to run best with 90 jet.
Compression test came to 160 lbs second test came to 150lb not sure the rings are seated all the way yet

Any advice is welcome and thanks

[scott7]

Ok so is there an after market cdi that will retard timing or do I need to enlarge screw holes in the pickup to achieve it ?

[90GTVert]

I don't know of any that will definitely retard the timing. I'd just elongate the holes on the pickup mount. If you need more than a couple degrees of retard, you probably need to dial the physical setup in better or something else is wrong.

[scott7]

Ok that's what I'll do plus I'm gonna put a stock variator on just to see what happens, I believe it has 8.5 rollers in it, I'll keep everyone posted on what happens ,thanks