Carburation for TM KZ10 144cc Fun 56 Upgrade

I’m at my wits end and could do with some sound advice from my fellow karters.

I run a TM KZ10 6 speed shifter limited to 14000 rpm with the Fun 56 upgrade kit, which takes the bore to 56mm. I run 98 octane fuel with the standard PVL ignition system.

I’ve run with a Keihin PWM carb -seized engine twice
I’ve run with a 30 Dellorto carb - seized engine twice
I’ve run with a SC2 38mm Smartcarb - seized engine twice

Everything and everyone has suggested that it’s running lean and/or it’s my fault for fluttering the accelerator just after WOT.
I’ve now purchased a 39.5 Dellorto which I’ve yet to try.
Would like some help on jetting this beast for long track racing. My raceway straight is about 700mm which is where most of the seizures have occurred.

I don’t have much more hair to pull out

Bad gasoline. 98 RON is not enough for this application. It’s fine for a sprint circuit.

For a long-circuit race, try C12 or avgas. It won’t make as much power as a 3% oxygen 100-AKI unleaded fuel, but it’ll survive.

So it’s a detonation issue?

John, seizures not withstanding, what is your assessment of the SC2?

It’s almost certainly detonation.

At the moment it’s difficult to assess the SC2 because my judgement is clouded. I did purchase another metering rod to richen the mixture, but engine seized with that change also.

Using Avgas for racing purposes in Australia is not available, but we do have Powerplus 102 NE which I have used before

Are you suggesting that because the engine is now 144cc, it needs that better fuel?

Seized multiple times on different carbs… what’s the ignition timing set to?
98 racing fuel should be OK but it doesn’t hurt to have some octane left over for a little bit of protection, especially if it’s locking up that much.

Do you have pictures of the pistons and cylinders of the previous lockups?

People run KZ on the banks of Daytona every year with the 30mm Dellorto. Honestly even with the larger bore I’d say pause on running the 39.5mm for now (They are harder to tune) and get it dialed in on the 30mm.

So with that said, what jet combinations were you running with the 30mm? Do you know what the head volume is with the “fun” kit?


Ignition timing is 1.1mm, squish 0.97mm
Pit advice, and it’s been varied, say ditch the 144cc barrel and go back to 125cc, others say it’s driver error, others say go bigger and to be honest when you’re desperate, anything and everything is on the table.
Not sure what the volume is for 144cc

These are the settings from when I purchased 30mm from Mondokart
Clip position 3
Max jet 180
Idle jet 60
Emulsifier B48
Gas valve 50
Needle valve 300
Floats 9 gr
Pulveriser DQ268

But I have used other combos.

John, nobody I know here in Australia running a gearbox on road circuits uses 98. Many of us in Victoria use the Elf Race 102 since AvGas was banned. Some the VP equivalent. You may also need to look at reducing your ignition advance. If you’re prepared to stick with the 30 mm Dellorto, get in touch with the Queensland Superkart Club. They have a number of members running stock KZ on road circuits.

What settings (main jet, needle etc.) on the 30 mm Dellorto have you (unsuccessfully) tried?

180 is a decent sized jet. 1.1mm is conservative on advance.

That’s why I’d like to know what the head volume is. If it uses the same head as a KZ, then you have an engine with more compression.

Does sound like going up in octane is a good idea. At least until you rule other things out.

Do you have pictures of the piston crowns? The pic you shared has me thinking along the lines of skirt clearance being too small.

Suffice to say, the issue might not be jetting at this point, with so many seizures and variables it’s hard to say for sure.

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Also, what EGTs are you hitting, where on the track are you seizing (as in anything in common), what top speed are you hitting down the main straight and what sprockets are you running (front and rear)?

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What oil are you running, and at what ratio? When and how are the seizures occurring? End of long straight? At WOT, or after you come off the gas?

What are your minimum EGT’s?

I think you have an opportunity to richen the early stages of the throttle range. K28 needle, richer atomizer, and richer pilot emulsifier.

Tom, thanks for that.

These are the settings from when I purchased 30mm from Mondokart
Clip position 3
Max jet 180
Idle jet 60
Emulsifier B48
Gas valve 50
Needle valve 300
Floats 9 gr
Pulveriser DQ268

Tom, egt readings range between 428 and 567
Top speed coming over the top of the hill (where most seizures happen) at Barbagallo is around 130kph.
Last seizure was after 3 laps and was just about to pull in the clutch and coast into pits to read spark plug.

Front sprocket 20t
Axle = 20t

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I’m running Maxima k2 at 20:1.

Seizures occurring end of straight, coming off gas
Minimum egt 428

In the Dellorto 30mm, I was using:
A K28 needle
A B48
A DQ268
Clip 3 position

Which ones do you suggest I use in Dellorto 39.5?

James, the Fun kit included a new barrel, new KZ10 head insert and new piston.

The attached image shows bottom only 3 laps, top right maybe 20, top left maybe 10 laps
Barrel bore size honed to 56.005mm
Piston dia 55.93mm

Piston tops dont look lean to me. I suspect 0.12mm is a bit too tight clearance for this kit

Have you checked what the cylinder/piston clearance is when the head is torqued on ? Some cylinders go out of round when measured with the head. I have seen 0.01-0.015mm. If so take it to a machinist / machineshop and have the cylinder honed with a torq plate. The torq plate has to be tightened / manipulated so that the cylinder is distorted to same dimensions as with the head you are using

I would increase the piston to wall clearance to at least 0.15mm

In my iame 175sse I tested clearances below the factory minimum 0.13mm. The motor ran fine while warming up but seized after I gave full throttle for few laps. The motor was not running lean. Clearance was just too tight for the piston - no room for expansion

Looser is safer if you have tuning issues. I Have run my sse loose as 0.18mm with no side effects


John, just like Mikko has said, I was going to suggest you look at clearances. We’ve had a number of surprise seizes with our CR125s (Stock Honda) on our road circuits, and the view has been wrong piston for the barrel even when sticking with the stated tolerances in the tech book. Things just get so hot with the longer stretches of WOT and while it may have survived a sprint circuit, long circuit has pushed the limit.

Your EGTs seem very low (I would have thought at least 650C). And if you’re running 20T front and back, you can’t be anything like 14,000 in G6. You should be close to 160 km/h in G5 at that RPM. Are you pulling 14,000?

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Thanks Mikko, you’re the first person to suggest piston/barrel clearances, even my pit advice has not explored this option and to be honest I’ve never questioned the plater and honers tolerances, I assumed they knew.

I’ve managed to catch and advise my barrel plater/honer before returning back to me

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I will add that whoever saw those crowns and said it was too lean should probably not be consulted for engine issues in future.

Verify the correct skirt clearance and ensure that it is correct for the piston choice. Cast vs forged pistons usually have different clearances.