TM KZ10C sanity check

2 Stroke Kart Engine Forums
1

New here, already got a ton of info from you guys, happy to join!

I’ve been using TM since forever and I’ve raced the 9B, 9C, 10, and now the 10C. Using it on a 2023 CRG Road Rebel but I’ve only been playing around with jetting and temperatures since a year or so. I’ve picked up alot already and I’d like to share some info in search of a sanity check on the current jetting.

This will be the third time I’m hitting the track this year after a new top end.
Mixing 1:25 with Vrooom Factory oil (I’m in the Netherlands) using E95 mostly.

These are the pictures after 2 days of open practice at 1020hPa, 17 to 20C, used about 25 liter.

IMG_1921
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IMG_1930
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IMG_1928
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IMG_1927
IMG_19271920×2560 550 KB

IMG_1924
IMG_19241920×2560 428 KB

IMG_1952
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IMG_1946
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This is my verdict and I’d like to know if I’m heading in the right direction.

After the first day and after piston inspection, I noticed some detonation although unaudible. EGT of 669C.
I upped the mainjet from 175 to 178, not much difference. I also witnessed the carburetor overflowing when idleing/low revs. When on track, the carburetor is emptied and I experience no issues whatsoever. Didn’t figure out the issue yet.

Second day I began with main 180, which brought the EGT back to 625 average, a much safer setup. Carb overflowing was ofcourse still happening, what resulted in sputtering and bogging while idleing or at low RPM. I cleaned the return-fuel line and the fuel pump as a whole, and checked if the fuel circuit-nozzle inside the carb is freely moving up and down. Will only be able to check this upcoming sunday when starting the engine.

Current setup:

DQ268
K98 3.5
180 main
50 valve
1.5 airscrew
70 idle jet (this is what my mechanic said would work…?)
60 pilot jet

About to use (because the jetting app says so and I didn’t have the 269 laying around earlier… :-)):
DQ269
K98 2.5
175 mainjet
50 valve
1.5 airscrew
70 idle jet
60 pilot jet

What’s your conclusion of this piston and cilinder? And how can I address the overflowing carb properly?

2

That bore has a lot of time showing which makes me wonder how much time is on the bottom end. I’m not 100% convinced the damage to the piston is from detonation, it looks more like it could be subtle piston/head contact.

The carb overflowing is interesting. You could try cleaning the inlet needle and seat with toothpaste to help them seal. Generally the fuel pump should not hold the needle open.

3

Added two new pictures to show cilinder head and plug. Bottom end has seen 4 pistons, I think. This is the third piston I’m putting in, also the last one before a bottom rebuild. How did you notice?

4

You’ve got a wrong balance on your carb.
With the K98 you have to run DP and not DQ. You are too lean in the in middle and that is why you are detonating.
Assuming you are using regular fuel and a temp of 20’C , change the piston and try this 2 setup:

DP267
K98 - 2.5
178 main
50 valve
1 - 3/4 airscrew
52 idle jet
60 pilot jet

DP267
K23 - 2.5
172 main
50 valve
1 - 3/4 airscrew
52 idle jet
62 pilot jet

The above configs are very similar with the k98 more leaner than the k23.

5

My old 10c ran flawless with this at 20c:

DQ269
K23 3 clip
175 main
60 idle
CD1 emulsifier
1.5 out on airscrew

11.5mm float height

6

Thanks for the replies. How do I notice a lean middle-transition to WOT on track?

Regarding DP or DQ, everybody in this area is using DQ for these types of engines. DP would be too rich, as I’ve been told on and off track. I get where you’re coming from, I thought the DP would fit better but there’s something lacking (it might be experimenting with different setups) in my judgement.

I do not have a K23 on hand yet, I do play around with a K27 or a K93.

7

Those that have already answered are more familiar than I am with the fuel you use in your country, as the fuel seems to be a limiting factor here. That said the engine obviously needs more fuel, and a DP tube will accomplish that. I wouldn’t be concerned with going “too rich”, as you’re already at the point of too lean…which one is worse?

The K27 is a richer needle that could be worth trying. It’s actually a step richer than the K23 due to the longer taper.

What do you currently have your squish and ignition advance set to?

8

Do you mean 5% ethanol, not 95%?
If so, to put that into perspective E5 (5% ethanol) requires approximately 2% more fuel than ethanol-free gasoline for the same lambda, which is about the same air density change as 5C change in air temp.

9

K98 works better with DP than DQ.
I would try a go at the config that I sent you with the K98.

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10

Sorry I used the wrong pronounciation, it’s either E10 (10% Ethanol) or E5 (5% Ethanol.) I’m always using E10 as my mechanic claimes it doesn’t matter? I am reading a lot here about fuel quality and what to go with, so I might switch to E5?

11

fuel matters a lot actually :confused:

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12

Drop me a DM I have ntproject jetting software I can run some comparisons and give you graphs.

What airbox are you running?

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13

10% Ethanol needs almost 4% more fuel, which is like the air temp dropping from 20C to 10C for you.

Ethanol is good, in my opinion, but you need to know how much you have in your fuel mix to account for it.

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14

From what I can read from my gauge, the squish is 0.9 (it only has 1 decimal…). There is a bit of clearance to 0.8 but it’s definately not 0.80… if it helps.

I cannot check the timing as I don’t have these tools. I imagine it to be close to ‘stock hobby driving’ setup as that’s what I asked my mechanic to do when I brought it in.

I will try the K27 needle this weekend and report back.

I would like to replace the piston myself as I’ve done it on motorcycles and watched this procedure a lot on the usual channels.
Would you recommend it?

15

if you can’t get squish or timing right, it might be an issue.

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16

Fixed carb overflowing by dismantling/cleaning fuel pump and freeing up/remounting return hose.

EGT’s back at 670, even with a 185 main jet. I think there’s a leak somewhere, might be at the crankcase because using brake cleaner at the carburetor while idling isn’t doing anything to the RPM’s.

Thanks for all the responses :slight_smile:

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17

Check there is a seal on the slide valve cap.

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