I assume that there is some differences between the carb repair kits. Otherwise Tillotson would have saved the money and made only one kit The individual parts may appear similar but some parts may have differences in thickness.
Most of their Carbs have two different kits available. The Basic is just the gaskets for the pumper and metering diaphram, where the Complete has the metering needle, needle seat, fulcrum arm, spring and some orings for the high and low speed needles. The basic kit is the same Tillotson part number while the Complete Kits vary from carb to carb.
Given that the pump diaphragm is driven by pulse pressure from the block, I see no reason to think they can’t flap fast enough. Also the fact that the fulcrum and tension springs are adjustable (setting POP OFF) means that it is, in fact, variable/dynamic or how could it influence the carbs performance just like a Float level does in a Bowl. Personally I have noticed a difference in tuning the high and low speed needles when the metering diaphragm stretches and distorts. Its much less consistent through the rpm range.
Sorry if this is a bit off topic.
You and me are both speculating, but, it’s hard for me to believe that, at 14,000 RPM, that needle could open and close 233 times a sec., that that diaphragm could flex 233 times a sec., that the fuel flow could stop and start 233 times a sec. That’s what I base my theory/assumptions on.
Apparently, I was never a good enough driver/tuner to feel the difference in pop-off pressure that others felt. I have read that people say they can feel the difference between 10 psi and 11 psi. My theory; you need some pop-off, 10 psi is some, and with my limited tuning ability, I never noticed a difference if it was higher or lower, within reason.
You know, I feel like the only reason these carburetors have pop-off at all is because the carburetors are meant for chainsaws and such, and chainsaws are often stored in different positions. If they didn’t have the needle and seat, fuel would flow out of the tank into the engine and that’s not good.
Follow-up; think about a model airplane engine, they have no carburetor, no pumper, no metering diaphragm, no needle and seat, just a pressure differential. They don’t need a carburetor, they don’t idle much, they mostly run at a constant RPM.
Both right imo. The pump diaphragm ( thin fawn one) can and does operate at 233 /sec.
The metering diaphragm ( thick black one) and the needle can’t and don’t.
The needle valve is opened by the metering diaphragm ,through the operating lever ,acting against the spring.
The metering diaphragm is moved by the depression in the inlet tract, not by crankcase pulses.
I tend to think that pop off pressure setting is over rated but as with many other things people who go/ went a lot faster than I ever did , say it matters.
Although we are meant to set pop off to say 10 psi. the actual fuel pressure in the carb never reaches anything like that, maybe 2 psi. (EC Birt) if anybody doesn’t know. www.kartpulse.com/article/60/setting-tillotson-carb-popoff
Here’s someone who seems to know what those things are doing in the carburetor. Care to show us your documentation on your observations?
I think what @d-i-y80 is saying is that the metering diaphragmn is activated by the pressure differential in the venturi vs. the atmosphere not the pulse of the crank. It merely holds up the main needle allowing fuel to flow to the jets. The pulse diaphragm does rely on positive and negative pressure changes to move fuel from the tank to the carb. Think of a kid kart, tank sits on top of the engine so gravity does all the work. I the case of a shifter or LO-206, they use an external pump to send fuel to the carb. Tillotson just combined the carb and the pump into a single unit. As I understand it, Alky carbs use a double diaphragm pump carb due to their higher fuel delivery rate demands. Within the pump diaphragms are little flaps that only allow fuel to flow in one direction (similar to a reed valve), they don’t need to move a lot of fuel just more than they could without it.
Its funny you brought up model airplane engines. I have several years of experience with RC cars. The biggest difference between Kart and RC is a rotary intake vs. a Reed Pedal. Even then, that has only changed in the last decade or two. As for fuel delivery, the demands of an RC engine are quite small compared to a 100+ cc engine, hence the need for a pump. Both work on the same principal, pressure differentials. Lower pressure inside the intake pushes air and fuel into the engine. Only with higher consuming engines, atmospheric pressure have to be augmented with a pump.
What are you guys using for engine mounts? I have a 5* Odenthal slider that I used with the x30. It put the KA pretty high and up in my elbow. So I got a flat OTK mount and a shorter chain (from a 104 to a 100). The flat mount would work fine and give a lot more elbow clearance but the chain gets into the top of the clutch guard. I could easily clearance the guard on the mill but I’d rather not mod the engine if I didn’t have to. Just wondering if you guys have any better ideas or just deal with the annoyance.
I’m afraid I can’t agree with you on that! I have no data to support this statement, but I can think of no reason why, If a Yamaha ran at full throttle all the time, it would need a carburetor.
We use the same Odenthal 5 degree that you were using. I just try to move the motor as far back as I can. Most of the time, my daughter has no issue with hitting her elbow on the motor, but she has on a few of the rougher tracks.
Good sectioned diagrams showing fuel flow ,how it works etc. at https://tillotson.ie service manuals/HL series as an example.
Also article ‘Setting Tillotson Carb Popoff’ - Kartpulse. by the late EC Birt. carb ‘guru’ and Tillotson consultant. Should be on here somewhere. www.kartpulse.com/article/60/setting-tillotson-carb-popoff
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Thats was my concern Tony. However, if the part number is the same my assumption is it should be the same spec and work in either application.
Zach, I think the size of the motor package is going to make it a challenge to eliminate your elbow/arm hitting the motor. On the good side it doesn’t seems to get that hot. I also hear a little chain slap on the stand but I don’t think that happens under load when the tires are on the ground.
The carb rebuild kits for the X30 and KA100 should be different, unless there is a spec change I missed. The difference between the kits is at least the pump diaphragm. For the KA, the diaphragm should be .07mm, while the X30’s is .1mm. The Tillotson part number for the KA diaphragm is 237-223 and the X30’s is 237-162.
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I moved it back on the angled mount and have a short o-ring in the mail right now. Should be here before practice this weekend. If it’s still a problem I’ll notch out the clutch cover. Worse comes to worst I’ll just have to buy another cover if tech decides to be difficult.
Yea, the shear size of it is a bit surprising. Side by side comparison with the x30 makes it look comically large. Yours must run cooler than mine. I sat in the seat with my suit down while I moved the steering shaft up and I proceeded to burn my arm multiple times on accident. Because you’d think I’d learn on the first time… but no. With the flat mount the chain was 3-4mm from the guard at a relaxed state. Any bounce at all would’ve torn up the chain and guard. So I just put the angled mount back on until I can get a solution to it.
Is there a spec plug for the KA? If not you could use one of the shorter ones you find on KZ’s.
I know this is semantics… but I’m curious how we can say the frequency of the carb diaphragm(s) match the frequency of the pulse?
I think it’s unlikely, otherwise different thickness of these would have limited effect especially on the pump diaphragm.
The metering diaphragm moves with vacuum. While that vacuum comes in pulses, I’m inclined to believe that really the diaphragm, needle etc move with gross changes in vacuum.
Who can 3D print a transparent pumper carb?
There is a specific plug to run, however it does not stick up too high from the motor. The size of it is large so it has area to cool it since it is air cooled.
Obviously, tech could be picky, however the supplement rules from SKUSA does say it it ok to trim the clutch cover for chain clearance.
Where did you see that at? I just read through the pdf and the supplemental rules and didn’t see anything about clearancing for the chain. Just an alternative cut on the side
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