@all here is a link for sprocket ratio
Motorcycle Sprocket Ratio Calculator

Yeah, I did experiment with 15/34 once & the pick up went damn bad. I mean, the top speed on every gear with 15/34 combo will take lot of time to match with 16/34. However, I haven't had the chance to test on 5th. The pick up was so sluggish too.

Sprocketting as on RX100 15front 39rear
final drive ratio for rx 100= 39/15=2.6

Hence if front sprocket size is increased to 16 Ratio will be 39/16 =2.437 If Rear sprocket size is decreased to 37T Ra tio will be 37/15=2.46

If rear sprocket size is increased will result in increased pick up but lower top end.
If rear sprocket size is decreased will result in sluggish acceleration and increased top end.
If front sprocket size is increased will result in sluggish acceleration and increased top end.
If front sprocket size is decreased result in increased pick up but lower top end.

The experience on TM28 & my learnings on them are worth while for another thread because it dates back to even the pre-rebuild era . I'm keeping it here so that all my experiences are collected under a single thread.

Somewhere during Aug/Sep 2009 when I'd changed the existing (cheated) cylinder to a stock one from YMIS. I was happy for the new one but at the same time, had to do a run in for 1000 Kms. Trust me, I feel stupid on this one because, I now know how easy the work is & at that point in time, I'd got the job done through a mechanic. Thank God, that guy didn't steal the cylinder

So during the run in period, I observed the vehicle to be too tight & being in run-in I never paid much attention on the smoothness. All my aim was to complete the 1000 Kms run-in ASAP.

After the deadline of 1000 Kms was over, I got it serviced from the same mech. He said, the vehicle is kept slightly rich & I still remember the words he said, "Rich na, actualla rich illa, aana richa irukku". Damn!!! confusing statement & this happened sometimes during Nov 2009 on a Sunday afternoon. Next day when I ride to office, I noticed something really strange which I never knew will haunt me for several months...

Ok

Ok, when the carbs are in perfect shape, will do the work out again. It only a matter for 15-20 mts changing. I mean, 15-34 right?

^^^ is exactly what I meant!!! See mine is stock barrel bought in 2009 Aug/Sep & has clocked about 22000 (13.5K + 8.5K) & about a month ago it still showed about 128psi in compression meter. This is why I said, LONGER engine life. But again, each his own.

From my thorough understanding, the front sprocks has to be as big as possible & the rear sprocks has to be as small as possible. But with this combo, the pick up is bound to affect on a huge scale (not 15/34 I mean, but generally). Anyway, I'll complete the carbs & then try out, I still have 15/16 sprocks & 39/34/38 sprock sets with me

I thought I was the only one poor in mathematics and calculating ratios.....Thanks for giving me company.

4 Speeds cannot go beyond 100-105KMPH true speed.

Are you sure? Apply the sprocket logic and think again on what you have typed.

To each his own. Out of 9 barrels, current one running on the bike is a ported and piped 165cc big bore. I get 33KMPL in bangalore traffic and expect it to run 20,000KMs before needing a rebore. I'd say if you're gonna get your barrel ported, get it done right.

That's a 14Bhp isn't it? I guess, a 12 Bhp could do anywhere between 115-120 Kmph on true speed isn't it?

Yeah, I did experiment with 15/34 once & the pick up went damn bad. I mean, the top speed on every gear with 15/34 combo will take lot of time to match with 16/34. However, I haven't had the chance to test on 5th. The pick up was so sluggish too.

WTH ? 280???

Well, my thought on modifying is, just keep the ride as close to stock as much as possible to retain for a longer life. If one needs to increase speed, pick up etc, then go for a newer one, unless they know what they're doing on the ride. Eg. simple mods like RDD CDI, magneto, upjet etc are fine, but mods like porting, increasing compression ratio etc will certainly bring down the engine life which is what I don't prefer.

I managed to do 126KMPH true speed on a stock 5 speed 3 years ago with just the right jets and a foam pod with the stock carb. Only thing changed was sprockets, 15/34.

In my case the carb was the very last thing i swapped. Only because my pipe needed 280 main jet to be run on the stock carb, which created a whole lot of other issues and thus had to change to a PWK28.

Tks. But you see, nothing in this world, atleast to me, comes simple, easy, trouble free. There're still 1 or 2 parts missing inside the carb & 1 or 2 to be changed :doh: I'm still fighting on it!!!

Whaaat ? Really? Yes, it should be possible.

Good to see you have got the stock carb.

Get a UNI filter and bigger jets. You will go much faster than what you will ever do with the TM28.

^^ run it.. remember the conversation about oil pumping when you close the throttle.

Oh!!! Sriram...not yet there buddy; I've still have got way to go, but not long enough

PS - I'm contemplating to run with side oil tank!!! C'mon bricks & batters pls

You are most welcome Aargee

^ Glad to know that your bike runs smooth with 4 speed carb. You might have felt top end compromised a bit, that could be because of TM28 used to run before. Happy riding!

Big day guys!!! Plonked a OE carb, never ever I've felt the engine so smooth. The top end seems to have come down a bit. A lot tuning on carb to be done, will do over the weekend. My Thanks to Gabriel_John & RameshMadhavan to have helped me source an used OE 135 carb. Thanks guys.