Hi
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.
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.
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
K98
Clip position 3
Max jet 180
Idle jet 60
Emulsifier B48
Gas valve 50
Needle valve 300
Floats 9 gr
Pulveriser DQ268
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?
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)?
These are the settings from when I purchased 30mm from Mondokart
K98
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.
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?
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
