Alternative Carbs...

[keean]

I am interested in changing the carbs on the RS... The Mikuni carbs on the RS (TMS34) have a large number of different jets, and those servo air tubes... looking at more recent carb designs there seems to be a notable absence of such features... A lot of recent racing carbs favor a simple approach (just pilot and mains with an accellerator pump for example)... The latest greatest carb appears to be the Keihin PWM carb. This has a pilot/slow circuit, main and needle jets...

Has anyone tried the Keihin PWMs - will they provide as accurate fueling accross the range with less jets (no powerjet for example), and without the complex air servo stuff... Is the air-servo stuff necessary (other 2-stokes don't have it)?

(Micah - didn't you test an aftermarket carb? Did you do before and after dyno runs?)

[wsmc667]

I blocked off the air bypass valves and see no difference. Then again, I never operate the RS250 between 2000 and 9000 rpm.

[madcatDK]

To wsmc667.


Did you blok both air circuts?, or just the low rpm one?

[wsmc667]

There's a low rpm one? Heehehe, yeah, I blocked both, so I could remove those 3 silly arsed control boxes. Makes the Pit a little more simple. I also trash canned the double hoses that loop from the intake manifolds.
Chris

[Stu Jones]

On a standard bike the air solenoids don't do a massive amount. If you run the kit SAPC control box from Suzuki though the main air solenoids have a big influence on the jetting, I would recomend only disconecting the pilot ones.

[keean]

But what about replacing the carbs with Keihin PWMs - designed specifically for 125cc desiplacement cylinders (x2 for 250s) - You will obvoisly loose the servo add ons...

If you remove the servo system from the Mikuni TMS's they will obviously not perform as well as it would with them, but I am interested in completely replacing the intake system.

[madcatDK]

STU:

I dont have a kit sapc box yet, so how much difference will it make if I block of both air tubes on the carbs. Have you any experince with remowing the throttle sensor( for runnig two cables to the carbs).


Jesper

[wsmc667]

Originally posted by madcatDK
I dont have a kit sapc box yet, so how much difference will it make if I block of both air tubes on the carbs.

The RS250 which made the most power on the Dyno at willow springs (64.9 hp at 2500 feet elevation) had the air solenoids removed as well as the additional air tubes from the manifolds and otherwise was almost stock. The cylinders were shaved down a little to get the squish near .057". That bike had Arrow pipes and two sizes smaller main jets.

I also have SAPC box that I'm not using. Probably won't bother to try it out and will sell it instead.

Chris

[madcatDK]

Is that a kit sapc?, if so how much do you want and what will it cost to send it to Denmark?

[clarkie49]

Originally posted by wsmc667
The RS250 which made the most power on the Dyno at willow springs (64.9 hp at 2500 feet elevation) had the air solenoids removed as well as the additional air tubes from the manifolds and otherwise was almost stock. The cylinders were shaved down a little to get the squish near .057". That bike had Arrow pipes and two sizes smaller main jets Chris

wow, my cup legal bike made 66hp on pump at willow back in 2000

i still dont get why people arent making 70hp with a little more compression (0.6mm squish) and good fuel.

i might have to tear apart our stock shop RS250

[Micah / AF1 Racing]

You will get it soon Clarkie, my new heads should be back this next week....2 degree squish, 9cc total volume, .7mm squish...should be cool to see how it does.

As for carbs I am trying out a set of PSI big air carbs...they look really cool but who knows how they will run.



Notice the killer triangular bore...supposed to give good small carb like throttle response with the top end airflow of a 38mm unit.

[clarkie49]

thats some pretty colored carbs you got there

[Micah / AF1 Racing]

Yep, that is what I was thinking too when they came in...still have not tried them...but if I do not expect too much I will not be let down....they are the bling-iest ever though....too bad they are hidden under the tank and plastic.

[keean]

A lot of people think the Keihin PWM is the best 2-stroke racing carb available today... It would be interesting to see back to back dyno tests of them and the PSI carbs... (and any other people rate)... The Keihin's are only 150 pounds each, and if I knew for certain they offer an improvement I would buy them...

[Micah / AF1 Racing]

I tend to agree that the Kehin carbs are the best readily available carbs on the market....I use their 28mm PWK's on my Race RS50's and they jet very well.