ESE's works engine tuner

[TZ350]

Which is why I had a pin with an offset centre section made. 20mm ends with a 22mm centre offset .75mm to reduce the stroke 1.5mm.

Now that's a very good idea, thanks.

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[TZ350]

You don't need a power jet. What you want is a carb off a 95-96 RS125. Didn't have power jet, those were the last years that the bikes were setup to run leaded fuel. If you get the powerjet carb you'd be looking at $1500+ because you then need to run tps, the full loom and cdi. You can't just block the powerjet off because then it cocks up the whole fueling of the thing!

Hi K14 we are getting one of those IngTech ignitions to try out that you told us about. I think the race version we are getting can switch the power jet.

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[sonic_v]

Hi Sonic, thanks for your input, carb's and diffusers. Can you tell us more? A picture or discription would be very helpfull. I am very interested in how this is done.

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The ica 100cc kart engines use diaphragm carbs with a choke size of 24mm. However by the carb exit they have diffused out to 27/28 mm. They bolt directly to the engine manifold and appear to diffuse out in area even more but hard to tell as the profile shape changes to match the reed block. This ibea carb is particularly good. http://www.out2win.com/catalog/images/ibeal5.jpg

The replacement world championship class is now called kf2 and these engines are 125cc with reed induction and powervalves. They use the same 24 mm carb design. the l6 carb shown here is homologated for this class. http://www.out2win.com/catalog/ibea.html

People are claiming 38hp plus for these engines. Clearly the carb is not holding them back too much!!!!

The 24mm carb rule is not the limit in horsepower development for a bucket that people think it is provided you use a diffuser. A 30mm at most area inlet port for a disc valve is all that is required with a nice tapered diffuser. Any bigger than 30mm will be a waste of time.

[TZ350]

People are claiming 38hp plus for these engines. Clearly the carb is not holding them back too much!!!!

The 24mm carb rule is not the limit in horsepower development for a bucket that people think it is provided you use a diffuser. A 30mm at most area inlet port for a disc valve is all that is required with a nice tapered diffuser. Any bigger than 30mm will be a waste of time.

Thanks Sonic_V thats very interesting, very encouraging, seems like Thomas and I are on the right track.

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[sonic_v]

This is the homologation document for the ibea L6 carb as used for the kf2 kart class.
http:http://www.j3competition.com/downloa...mologation.pdf

You can see that it opens out from the 24mm choke to 28mm at the exit.

[k14]

Hi K14 we are getting one of those IngTech ignitions to try out that you told us about. I think the race version we are getting can switch the power jet.

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Yes but still, the powerjet is for unleaded fuel. It is useless for running leaded. Stick to a 95-96 and you will get better results.

[sonic_v]

Yes but still, the powerjet is for unleaded fuel. It is useless for running leaded. Stick to a 95-96 and you will get better results.

Why is a powerjet useless for leaded fuel ?

[k14]

Why is a powerjet useless for leaded fuel ?

The whole carb was re-engineered to run unleaded petrol. The powerjet stops mid rev detonation which unleaded fuel is very bad at causing. The standard powerjet on a rs125 runs from around (I don't have my manual with me, will check when i get home) 8000rpm to whatever cut off you program it to do, there are 4 different cut offs which are selectable with different plugs into the loom. I think standard is 12600 and they go up in 200rpm steps from there. It also has a throttle position sensor that complicates things more in regards to on/off of powerjet. The way I understand it is that the way powerjet works is totally detrimental to achieving a good fuel mixture across the whole throttle range. You can perfect the fueling with the standard jetting configuration and because of the leaded fuel not have to worry about mid throttle opening/rev detonation.

The powerjet wasn't bought in till 1998, they changed the bikes to unleaded in 1997. You can still get leaded kits for the 125s and with them come a standard non-powerjet carb and 96 (or a kit) loom.

[TZ350]

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Well this is a cockup......and won't be seen at Taupo, too wide, it sticks out wider than my feet.....

But it sure looked the business, probably the Worlds first ever Suzuki GP125 fitted with an RS125 38mm carb.

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[Buckets4Me]

you just need a nylon plug for the end of it and no nead for sliders that side

[TZ350]

This is the homologation document for the ibea L6 carb as used for the kf2 kart class.
http:http://www.j3competition.com/downloa...mologation.pdf

You can see that it opens out from the 24mm choke to 28mm at the exit.

Thanks Sonic_V that's very usefull, now we know we are on the right track, just getting it all to fit is the problem.......

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[TZ350]

you just need a nylon plug for the end of it and no nead for sliders that side

I'll put a nylon plug in your end........

Given up on that big carb idea, but have a much more devilish..............plan

but will probably not be able to get it done before Taupo.......

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[sonic_v]

I'm not too sure I would subscribe to the idea that a Kartsport engine spends little time in the peak power range there Sonic.

I am of the opinion that it is quite the opposite actaully!

One of the many things a Kart does well is hold it's corner speed!

You are just plain wrong on this one SS.

On a typical kart track the karts are geared for 65mph at the top revs - 20,000 rpm. Now as at most the peak power is at 13,000 rpm, this equates to a speed of 42 mph. The engines are well into their power by 10,000 rpm ie 32 mph. As karts can corner so fast and have high exit speeds they exit just about all the corners in the power band and because the gearing is so low they absolutely rocket out of corners.
By the time the kart is 30yds down the straight the revs are already well beyond peak power speed. At high revs (beyond 15,000) these engines are producing very low bmep and are only making a reasonable amount of power due to the high revs.

It is equivalent to riding an rs125 honda race bike in only first gear whilst being geared for 42 mph at peak power and then just holding the throttle and letting the engine rev for ever.

PS I was a 100cc kart racer for many years.

[sonic_v]

I am pretty sure that most "fixed gear" Kartsport engines run around 1.25:1, for the very reason that a longer spread of peak power is desireable.

100cc Kart engines typically have crankcase compressions in the 1.40:1 region.

I realise that some Kart engines are very particular about set up (I have minimal experience with these), but i have never heard of a moder 2 stroke engine that revs 7000 RPM over it"s peak power, and has a static curve.

Why would a 2 stroke engine that revs to 20,000 RPM have high advance, when the peak pressure point at 20,000 RPM come a lot sooner that at 14,000 RPM?

The 100cc rules have always stipulated a fixed ignition.

Who says peak pressure comes sooner at 20,000 rpm?

It does not come sooner if your charging efficiency is well down compared to the peak power speed conditions. Also the cylinder is being poorly scavenged resulting in a high residual trapped exhaust gas content. This slows up the combustion rate.

[TZ350]

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Number two motor is ready to start going back together.

Pic-1 shows the big inlet port and the small roll pins that will accurately locate the copper spacer plates and under barrel fins. The mouth of the inlet port is built up with DevCon to direct the incoming charge up and over the flywheels.

Pic-2 shows the shortened cylinder studs and alloy TZ head bolts that I hope will expand at the same rate as the barrel and thereby reduce cylinder distortion.

Pic-3 the shortened studs will make it easier when the motor is in the frame to remove the cylinder head without scratching the gasket surface, which happened with the old long studs that protruded from the top of the barrel.

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