ESE's works engine tuner

[RMS eng]

Indeed. Nevertheless, you should pay attention to the flow through that carb because plenum pressure will drop during the inlet phase and you want to keep that drop as small as possible.
From what I can see, the tract length between the carb and the plenum is quite large, and so is the inertia of the mixture column in it. Though the flow through it is more or less constant, which lessens the inertia's influence, shortening it won't hurt. It will also create more room for an air filter (or should I say vacuum cleaner bag?).

Maybe, but the inflow at the butterfly body looks terrible. I would suggest losing the whole butterfly body and fitting a short, well-rounded bell mouth instead. The better shape and reduced column inertia will promote max.power and overrev. Moreover you may be able to close the inlet earlier which will give you back your low-end torque and simplify setting the carburation. And you will have one less servo system. You know my view on construction in general and on racing equipment in particular: every part that you can leave out, doesn't cost anything, doesn't weigh anything, and never breaks down.

By the way, a 30 mm carb may sound large to you folks, but over here we run 32 mm carbs on 50 cc engines, and they behave quite civilized with them (and make some power as well).

your tracks must be big to run 32mm carbs on your 50s,they would be shit on our small kart tracks,and worse in the wet.

[RMS eng]

That is the quote of the century!!!!!

thats how most of us build race bikes ??

[Frits Overmars]

your tracks must be big to run 32mm carbs on your 50s,they would be shit on our small kart tracks,and worse in the wet.

They lap the entire field on kart tracks. With a 5-speed gearbox.

[RMS eng]

They lap the entire field on kart tracks. With a 5-speed gearbox.

what do they lap,do you have a photo of your kart tracks

[dinamik2t]

Just a notice: is there no room for a bigger corner radius for the aux passages? Increasing that would give some extra hp I think!

[jasonu]

thats how the experienced builders build race bikes ??

Fixed it for ya....

[TZ350]

OK today in A grade without Kel all we could do is watch.

Points Race 1 ... 2-stroke 4-stroke 2-stroke.

Points Race 2 ... 2-stroke 4-stroke 2-stroke.

The two 2-strokes were Derbi 80's in RS chassis, great little bikes and the 4-stroke was an FXR

With Kel out until November the only saving grace for Team ESE is that the FXR was tuned on the Teams Dyno.

[Buckets4Me]

With Kel out until November the only saving grace for Team ESE is that the FXR was tuned on the Teams Dyno.

that and the 50 kept going all day

[wax]

D you guys race the 50cc am6 mineralli over in new zealand

[Frits Overmars]

what do they lap,do you have a photo of your kart tracks

This tight enough for you?

[TZ350]

that and the 50 kept going all day

Your right, there were two Team ESE 50's

[TZ350]

D you guys race the 50cc am6 mineralli over in new zealand

Not many around .... this is NedKellys, I think its an AM6

[wax]

I have an mhr mallosi team cylinder for one of these bikes. Brand new in the box I was hoping you guys raced a few as I wish to sell it

[TZ350]

... the inflow at the butterfly body looks terrible. I would suggest losing the whole butterfly body and fitting a short, well-rounded bell mouth instead. The better shape and reduced column inertia will promote max.power and overrev. Moreover you may be able to close the inlet earlier which will give you back your low-end torque and simplify setting the carburation.

I will give it a go, I already have a short bellmouth ready to try.

Closing the valve at 75° ATDC will give reasonable power and a friendly engine. Exceeding 85° aTDC may make the engine bad-tempered. Trying disks with 75°, 80° and 85° will get you in the ballpark. I wouldn't bother trying intermediate values.

The std timing for a GP125 is 55 ATDC (GP100 is 45) and I am currently running 85. EngMod2T suggests that with a 2L plenum (I have 1.5L) that 75deg ATDC would be good for the bottom end without loosing much of the top, so I will take your suggestion and start there.



When I first tried the plenum idea I made a short belmouth.



And the inlet tract was opened up to 32mm



The inlet closing point was 80 deg ATDC and with the short inlet tract at 5-6,000 rpm there was quite a resonance hole that I called the Blarrrs.



I tried closing the inlet earlier but even at 45 ATDC I still had the Blarrs and no top end. The Blarrrs were only cured by extending the inlet tract but now it was too long.



I wanted to be able to continue to close the inlet at 85 deg ATDC and also shorten the inlet tract for better top end. The Butterfly arrangement was much shorter and controlled the blarrrs by changing the resonance of the intake system.



When I first tried the plenum the engine was making 20hp and the plenum did not realy improve things.

I think the plenum will only show a real advantage when the engine has been developed to the point where the F4 Class Restriction of a 24mm carburettor is truly strangling the engines breathing.

To see if we had reached that point now we are at 30hp I wanted to try a bigger 30mm carb as that size was an easy match to the existing inlet tract.

[TZ350]

I have an mhr mallosi team cylinder for one of these bikes. Brand new in the box I was hoping you guys raced a few as I wish to sell it

We are restricted to using non competition parts, aftermarket road going sports bike parts might be OK but race stuff is a definit no no.

I don't know much about the different after market kits, is your cylinder kit "Race" or "Road Sport"?