KA100 Tips, Tricks and Tuning

If in the bottom photo that is the ring gap, then the locator has definitely gone. The gap is supposed to be in about the 2 o’clock position on the inlet side.

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“Blueprinting” in the US for KA has just been setting the timing and carb. It’s not like it was with the Yamaha or anything, I think we follow the same rules as Australia for our KA stuff. We just say Blueprinting because that was the big thing in Yamaha stuff, but it’s really more like a general race preparation, making sure everything is set right

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That one is going to be expensive unfortunately. How many hours on the motor?

It needs a head at minimum and maybe a cylinder unless you get lucky and still have enough wall thickness to save it.

My brother and I both had KA’s blow up this year unexpectedly. Mine the builder said the pin pushed in on the piston allowing the ring to spin and tear up the ports. I had to buy a cylinder to get mine healthy again $675 plus the rest of the rebuild costs.

My brothers the builder said he left debris in the ring channel when he pulled it apart to clean it causing the ring to not seat completely and eventually caused ring failure which looked much like this one. Needed head replaced to get his healthy again. Thankfully he got away without cylinder but he will need one on the next rebuild now.

Your carb settings for the blowed up one seem rich on low and lean on high base on my experience. Could have had it too lean up top.

When it comes to the blueprinting topic…there’s still some validity to what guys are using for stones to get the best possible seal for the bore (wall clearance , etc) along with attention to detail in the rest of the components. There’s info out there to where you can set your carbs, timing and squish close enough but how attentive to detail are you when you are setting this all up? If you feel you are 100% mechanically incline and can execute to plan than you can likely make a KA run pretty competitively but if you just kinda have an idea it’s best to leave those details to the guys that really know what they are doing.

Yep, that high end looks way too lean. You should be starting out at 1 and 1 unless your engine builder has a preferred setting. Make small changes. I’ll go in 2m increments.
Assuming you had a stock plug in the motor.

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4 posts were split to a new topic: Ignition Timing Discussion

in regards to testing pop-off, has anyone experienced leakage from the top cap screw? i’ve noticed that when I test mine that it does leak from the screw, but when I take the carb apart and test inside it fine.

They can warp with time, especially if you’re a little heavy handed with the screw. Keep a spare cap or two, you can make it a preventative maintenance item if you like.

Correct, spare cap. Updated my post

As someone considering the class, how much of a difference is a blueprinted or P1 motor going to be vs the stock motor?

Very little. There is almost nothing you can do to “blueprint” the KA. As I’ve noted, I ran a stock engine the first season it was here and finished on the podium at USPKS multiple times.


Evan, I don’t have a lot of data, but I ran my first season with a stock KA. These motors are very consistent. Most of my competitors ran stock motors as well. Like anything mechanical and mass produced I am sure there are some examples that have a little more than others and ones that have been given once over might be slightly better still, but there are probably better ways to spend the difference (roughly $500), track time and tires comes to mind, that will probably make you faster than a blueprinted motor.


Blueprint on a KT100 is quite a different thing from a blueprint on a KA100.

A few years ago I had a new HPV. Before racing it I pull it apart, just to check the tolerances, no need whatsoever. Port timing, cc’s’s, ignition timing, crankshaft run out, everything was right where it should be. I changed nothing.

Some have charged as much as $500 to blueprint a KT100, but if somebody says they can blueprint your KA 100, it better not cost more than $100, and even that is high. Of course if there’s machine works involved (and they better be very specific about what needs to be machine) then it’s going to cost more. Knowing how the Italians are with kart engines, I doubt very seriously if the engine will be anything but perfect. You know, I’ve heard of people charging outrageous amounts of money to blueprint a HPV. There’s a sucker born every minute. And at least one crook to take advantage of them.

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The way I look it… With these newer engines “blueprinting” and working with a specific builder is like a service plan.

There’s definitely value in being able to call up someone who can help on those days that things just aren’t running right.

It may not reduce your lap time on your fastest lap, but it can turn a crap weekend at the track into a solid one.

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I’m having trouble understanding the context in which you use the Term blueprinting. My understanding of the term “blueprinting” seems to be at odds with yours. I think your use of the term could more accurately be replaced with with the term “tuning”.

As an example; I always considered myself a good builder and tuner, but I had neither the equipment, the inclination, nor the skills required, to “blueprint” engines, in my understanding of the word “blueprinting”.

We have the same understanding. However you’re more likely to get tuning support from a builder who has blueprinted your engine.

I would caution people to be very suspicious of a tuner who would tell me he’s going to “blueprint” your KA100. I would have them define what they mean by the term “blueprint”, and the cost. As far as that goes, assurances you’re getting a good engine, and the cost of that assurance, in my opinion, should be part of the deal. Any extra cost for that service should be dialed into the price in the first place. I know I wouldn’t let any engine out the door without knowing whether it was suitable for the purpose intended.

I have more than one horror story of “blueprinters” and what they have done.

The topic of “blueprinting”, or “fiching” as they say in the UK, a modern, spec kart engine seems to crop up in multiple threads. I call it “new engine prep”, but who really cares, it’s just semantics. In the context of today’s kart engines, this is what “blueprinting” is, or at least it’s what I do:

-factory piston wall clearances are too tight for best performance, so I re-hone the cylinder to re-size it until I get the clearance I want, along with the crosshatch angle and surface finish I want (this differs from engine to engine).
-I replace the piston ring if necessary to get the proper ring gap.
-I reset the squish gap.
-crank end float is usually too tight as well, so I either re-space the main bearings or change the crank spacing itself.
-cranks are usually perfect from the factory (this has not always been the case), but I will true the crank if needed.
-set the timing on engines with non-fixed timing
-take apart and ultrasonic the carb, rebuild it, set fulcrum height and pop-off
-break in the engine on the dyno
-power test on the dyno and compare to known, winning engines
-repeat any of the above steps if the power isn’t what it should be

So, it’s a fair amount of work. Is it worth it? Yes, especially because I only charge a nominal fee if the customer bought the engine from me. There are sizable power gains to be made from this process. It’s just a fact. My dyno is calibrated off of stock engines, and the power gains after “blueprinting” are undeniable. And, as engine packages are on the market for a while, builders figure out more things to make a series of marginal gains that eventually add significant power. I don’t sell snake oil; I tell customers all the time that the engine is a distant 3rd (after driver and chassis) when it comes to speed, but you might as well get the most out of your engine and eliminate that variable.


Crank end float.

I have always worked to a figure of 0.008 inch.
I had no problem with setting up this clearance for the ’ industrial based ‘engines where the crank is free to slide through the bearing inner race, nor with the well worn 2 strokes (a/c 100s) where the crank was free to do the same.
However at one stage I bought a brand new TKM BT 82. from the factory and took it apart with difficulty.
The C4 bearings were a tight fit on the crank and I had to make up suitable pullers to split the crankcase.
I am assuming this is normal for a new engine.
In such a case how do I achieve or measure end float?
I appreciate that the bearings have axial ’ float’ within the bearing which may be more or less than 0.008 inch when assembled to crank and case, so that if the crank width is correct relative to the cases then the whole of this axial clearance in the bearings will be available to measure as end float , and the crank can be moved ‘in and out’ by hand to measure the float.
So that under ideal conditions the maximum end float available will be equal to the axial clearance within the bearings, and any variation from ideal will reduce or remove the end float?
Can you explain just what is happening when we measure end float and where the ’ movement’ we are measuring is taking place?

Are you familiar with what engine builders have to do to a KT100 when they “blueprint” it?

I have what I think is a good understanding of what the word “blueprint” has stood for in the past. If the definition of what it means has changed, I have no knowledge of that.

The word “Billet” is a word whose definition (In the past) I totally understand, but even that has changed, it is now used to distinguish “cast” aluminum from “extruded” aluminum. In fact, using the word “billet” throws all the extruded “aluminum alloys” into one category. There is a significant difference between 6061 and 7075, both in strength and machine ability. Not to mention suitability for the application!!