Fz on steroids by Race Concepts

^^^ agreed. But the fact still remains that a CV carb will give more precise fueling. The biggest disadvantage of the CV is the butterfly valve which causes some amount of flow disruption. For all out performance, yes, a flat slide carb is best. I noted that you have said in you have a TM28 carb. I have one on my RXZ 135 & believe me it is ballistic in response. I really think you should give the TM a shot.

I feel that the TM28 will be too small for my 200cc engine. I had a 28mm round slide and was getting a lot of condensation on the body, The carb was very cold to the touch and restricting the airflow.
Compared to my 33mm PWK it is absolutely tiny, Almost toy like.
To retro fit it I would need to reduce the ID of the rubber elbow that joins the carb to the intake runner as it has been bored out/port matched to suit the 33mm.
I was thinking about putting it on my wifes Vespa LX150 as a replacement for the CV carb, Only thing is the wife has banned me from ever playing with it after I accidently burnt it down when the tampered fuel ate through the rubber hoses and diaphram in the fuel lines, causing the carb to flood, Trying to clear the carb resulting in a backfire, fuel caught on fire.....Quick "Vietnamese" read cheap respray + repair and it was "ok" again. I then took it and got a full ground up bare metal rebuild/spray in custom dark blue with a lot of metallic flakes.

If you want precise fuel delivery then EFI will always beat carb.
A carb is at best a compromise of a number of variable.

Fz on steroids by Race Concepts

^^^ a 28mm flat slide will flow 30% more air flow than a comparative round slide carb. Therefore it is equivalent to a 36mm round slide carb . The other plus of this type of carb is that while it flows more than a similar size round slide, due to the smaller venturi (compared to a 36mm) the velocity of air is greater which allows for a strong 'signal' which results in superb throttle response. I know that the TM has a very short throttle body and requires redesigned inlet manifold. I had to get one specially designed for my bike.

Anyway, I know that a FI will give more precise fueling, but we were talking about carbs out here.

Hi Guys ,

Kindly advice , how did you installed your new carbs ?
What did you do with the TPS ?

For my case is still have a stock CDI , but im planning to replace my stock carb with a Keihin 30mm round slide
My issue is the TPS part .....
Im worried that Without the TPS there will an issue with the CDI timing .

Please help me with this , any work around ?

Thanks in advance ....

You will have to block the TPS sensor to maximum if you install a (round or flat) slide carburetor. However, do not (simple logic!) expect the best adjustment of the CDI timing by suppressing the TPS: it has been designed to work function of this information, not on the info that the throttle is wide open all the time.
Right after I had the 200cc. kit installed (that was actually a misunderstanding with the mechanic who did the job: I only asked him to close the engine in order to protect it from the dust until I would gt the head work done) , the bike was not usable so much is was knocking. The new 29mm. CV carb had been installed, but there was to connection on it for the TPS sensor. I got one "made", and the bike, although still having exaggerated compression ratio, was then possible to ride....with extreme care! This just shows you how sensitive this is.

I am curious to try Mik's TM 28mm. although so long I am very satisfied with the way the bike behaves with the (modified) 29mm. CV. Just to see, and then maybe...???

One must effectively consider that there are "some" reasons why nearly ALL Japanese (= high end) bikes are fitted with Constant Velocity carbs instead of direct action ones. Not only is it less sensitive to air temperature and pressure variations, but it also gives a more gradual response than a direct action one, which are better fitted on, for example, trail bikes that need instant full response, while city of road drive does not...unless one likes to ride like a teenager on his moped zooming and zig-zagging through the traffic! I shall add that, on a "big" bike (ours are not "big"), a too quick response will make you instantly sit on the road, not on the bike! My first big bike, a 750 Honda "Four" had been prepared for endurance races by a very experienced pilot. It still had it's four CV carbs!

Hi Luc ,

Thanks for the advise , it take note of that , how about your CDI , do you have it replaced with an RCDI , does it still need the TPS data ?



Hi Luc ,

If you block the TPS sensor at its maximum position and have it fixed on that position , then the CDI will think the carb is on a wide open throttle so , it will be advancing the ignition timing even at low RPM am i right ?

I have another CDI, from Singapore, and that not only "looks" of top quality, can select though nine different setups from city to racing but that, being specially made for Yamaha FZ 16, effectively has a connection for the TPS.

Then, you are right (excepted that - I think - it will be retarding the ingnition in order to avoid engine knocking - not sure!!!!), and a dedicated CDI, programmed/ mapped in such a way that it does not need the TPS information, should effectively be fitted whenever one installs a slide carb instead of a "butterfly" one, hence cannot give this information. This is why, although wanting to try one of these "race carbs", just in case I find it gives a significant performance increase, as far as comfort and health of my engine is concerned, I may still stick to a CV carb with throttle position sensor.

Could someone throw some light on how one locks the TPS at WOT?
Guidelines would really help.

To get an increased top end, u obviously need extra revving. The high lift cam gives u extra power with a very slightly reduced low end torque.

This is my rather crude method of locking the TPS.
I connected the TPS and rotated the inner section until the engine light on the instrument cluster turned red and backed it off until the light went out. Marked it via scratching the outer body so the triangular inner section will align with the marks.
If you know what the resistance is at WOT then you can use that to determine the 100% throttle position and drill that position.
Got the smallest drill bit I can find and drilled halfway into the TPS. You can see my first attempt at drilling through and I drilled too high, The brass outer ring doesn't rotate, the inner piece/sleeve does, so drilled halfway (through the brass and plastic inner) Pushed a hairclip through to hold it in a "open throttle" position, then drilled the opposite side.
Push the hairpin or wire through completely (bend it over like a cotter pin if you wish and reconnect the TPS.
Now my TPS is locked.


I had tried "jumping" the connections on the wiring harness side to trick the CDI but that never worked, My check engine light stayed on.
The throttle has become slightly more "crisp" and although its not exactly waking the sleeping dragon type of mod it still is worth while.