Well, if I recall correctly, this is not the first time you've fooled around with a KDX snorkel hoping for a good outcome.
The engine has the ability to produce big, enjoyable, and satisfying power in the upper end. But such power requires a lidless airbox and proper carb/EFI mods to be realized.

You are now making power that is at or over the stock injectors' capability. If you cannot make 12.6 - 12.8 ( inclusive ) AFR for all RPM points at WOT, you've reached the end for the stock injector. Running Duty Cycles of %100 or more is not an optimal situation.

The 34mm throttle body would certainly create more power in the low-mid range - this would be more "fun" power during "normal" riding.. But we do not know if it will allow the same top end as the 38mm..

 

I forgot to mention. I installed new 270cc injector (compared to 220cc oem) with new throttle body. But fuel settings are just a touch richer compared to previous setup. I feel OEM injector could work as well.

 

From previous testing in here, I remember 28 hp being doable but 30 hp runs the stock injector near %100 duty cycle.

 

BTW, I assisted in a year-long tune development project, for a particular mod combo on the Indian Scout. Best performing AFR was found to be 12.53.

 

I also needed a dyno tune again after fitting the replacement ApiTech Ecu, this time returning to lidless. The Top end was regained. Thanks for pointing that out KLXster.

It does have an occasional backfire that needs eliminating but not sure where to start.

 

Any chance you could share this recipe?
I would love to do a 351 kit and use this as a base line.
I have done some GM tuning in the past but I have the tools to do that.

 

What information do you need? My mechanical aptitude is rather limited, but I can try provide some info, even if I have to ask my mechanic for it.

The bike is lidless, 330cc kit with cams, APITECH Standalone ECU (no piggy back), secondary throttle plate removed, full performance exhaust (Norofumi Indonesian brand), stock air filter. That's it

 

Thank you!
I have been looking at the APITECH ECU for a bit.
How close is it out of the box?
​​​​​​Can you share the .bin file for your APITECH set up?
I Have a 2024 and I would like to go 351 but I don't want to give up any drivability.
Thanks again!

 

For those who consider bigger throttle body (TB). There are 2 caveats:

1. I've realized that there is a rubber intake manifold between TB and cylinder head. This manifold has 34mm inlet to match standard TB diameter. So when I installed 38mm TB there was a step 38mm->34mm right before cylinder head. As you can imagine it doesn't contribute to smooth and fast intake flow.
2. The cylinder head intake window has oval shape with wider diameter = 31mm and smaller diameter = 33mm (which is somewhat smaller than 34mm TB). Standard intake manifold tapered from circle 34mm to oval ~33.5 / 31mm to match it.

I had a spare standard intake manifold and tried to bore it to 38mm, but it's hard to bore rubber. Also when you bore the rubber finishing becomes rough and I believe gasoline which will fly through it will destroy it eventually. Long story short - this manifold was trashed.

Fortunately there is another (and the only) Kawasaki model which comes with the same engine, but 38mm TB - Ninja z250sl which is somewhat common here in Indonesia. So I've bought intake manifold from it - part number 16065-0125. The only potential disadvantage is that it has a bit more depth compared to standard. But in the end it fits well. The inlet I measured is 40mm (maybe 1-2mm error and actual is close to 38mm as it matched my 38mm TB perfectly without any step) and outlet is 34-31mm to match cylinder head.
Takeaway:

1. if you run (or planning to run) oversized throttle - you will likely need z250sl manifold 16065-0125
2. Unlikely TB larger than 38mm will be useful - it will be hard to find appropriate intake manifold and also standard inlet window for the cylinder head is 31*33mm.
   
   
   

 

I would consider talking to TSC first about his ECU discovery project which may be more reliable.

I was concerned about the reliability of the API TECH after reading limited information online which wasn't in favour of it. I also spoke to Keng Engine who simply said in regards to the device "Not Strong".

Ignoring all this, I bought and fitted one, and as great as it was, it failed within 6 months.

I was able to get another one under warranty, although I incurred another customs import fee, and will see how it goes.

The DynoJet may be a good option, although its still a piggyback.

I don't know what the .bin file is you request. I guess it's something my Dyno tuner would have on his computer, as the ApiTech needs to be dyno'd

A guy here in Vietnam also fitted 355kit with ApiTech and has done over 10k km's without issue so far. He too went through a multitude of experminatal ECU's and insists the ApiTech is the best. He also says the waterproofing of the API is "primitve" and may well have been what caused my first failure... I don't know.