[Ripperton]

Im fitting a 2023 KTM 125 SX TBI throttle body on my 2020 KTM 150 EXC.
I ordered the TBI throttle body assembly from a local KTM dealer on the 19th of December 2022 which ended up costing $1080 AUD
but took a bit over 2 months to arrive.
The injectors and clips are the same part number between the 2 bikes so didnt order those. The injector manifold was purchased seperately $30 inc.

 

[Ripperton]

Main reasons for doing this retrofit.
1: Remove the Oil Tank. Completely unnecessary, adds weight up high. Annoying dash light comes on too early. No bother mixing fuel like real men do.
Lowering center of gravity will make the bike even faster in single track without increasing power.
2: Injector Relocation. Entire bottom end runs cooler and improves fuel vaporisation and economy. Smoother transfer ports. Allows PreMix.
Taking advantage of the crucial heat exchange between crank, conrod, piston and fuel.
3: Run engine on PreMix. More reliable, no pump failures or blocked filters. Be able to adjust fuel oil ratio. Leaner fuel oil ratio makes more power.

 

[Ripperton]

First problem is ECU reconfiguration.
The TPI has a Hall effect throttle position sensor, the TBI has a 0-5v potentiometer. The ecu will need to be switched over to the pot type tps.
The throttle cable pullies are a totally different shape. The TPI opens quickly. The TBI opens slowly.

 

[Ripperton]

 

[Axzon]

Im fitting a 2023 KTM 125 SX TBI throttle body on my 2020 KTM 150 EXC.
I ordered the TBI throttle body assembly from a local KTM dealer on the 19th of December 2022 which ended up costing $1080 AUD
but took a bit over 2 months to arrive.
The injectors and clips are the same part number between the 2 bikes so didnt order those. The injector manifold was purchased seperately $30 inc. View attachment 112365

Interesting! We are running a 2013 150sx in MX2. VHM head, HGS header pipe. Has a Keihin PWK 38S carbi and some minor modifications. It is a 250f killer!.The 2013 150sx has a slightly longer stroke than the later 150sx bikes. But have started to wonder if there would be any advantage to convert to TPI or TBI? (I know it would cost a fortune to do... and perhaps i is not even possible?)

 

[hpc3]

Interesting! We are running a 2013 150sx in MX2. VHM head, HGS header pipe. Has a Keihin PWK 38S carbi and some minor modifications. It is a 250f killer!.The 2013 150sx has a slightly longer stroke than the later 150sx bikes. But have started to wonder if there would be any advantage to convert to TPI or TBI? (I know it would cost a fortune to do... and perhaps i is not even possible?)

You can skip the TPI - KTM is throwing that bad idea (for dirt bikes) out already. Keep the carb or maybe the TBI will become a good swap option. I kind of liked the Mikuni carb on my ‘17 300 after I figured it out. Much better than the TPI mess imo.

 

[Axzon]

You can skip the TPI - KTM is throwing that bad idea (for dirt bikes) out already. Keep the carb or maybe the TBI will become a good swap option. I kind of liked the Mikuni carb on my ‘17 300 after I figured it out. Much better than the TPI mess imo.

Thanks. The Mikuni stopped many buying a new KTM. Yes, it is fixable... sort of. But the lack of info from KTM stops us from going there. (If there is one thing I dislike with KTM it would be their reluctance of admitting their poor decisions, that then cost the owners of the bike money to try and fix).

So we keep on using the Keihin and making small changes on the bike/motor in search for some more gains.

 

[hpc3]

Thanks. The Mikuni stopped many buying a new KTM. Yes, it is fixable... sort of. But the lack of info from KTM stops us from going there. (If there is one thing I dislike with KTM it would be their reluctance of admitting their poor decisions, that then cost the owners of the bike money to try and fix).

So we keep on using the Keihin and making small changes on the bike/motor in search for some more gains.

See if you can find JD Jetting in your area. They are a U.S. company but really know the Mikunis. I have Keihins on my older bikes and they are decent. The Mikunis have a leaky pilot/bowl gasket from the KTM bike release that they never recalled/fixed. Once this is replaced (rubber/metal plate vs paper gasket) the Mikuni resolution is much better from the idle to main jet range. Almost electric motor good.

 

[Ripperton]

Thread has been HiJacked by CaveMen frothing about irrelevant ancient technology.
Lets keep it on topic.
I cant imagine what decision making catastrophe happened to allow TPI to go into production.
Probably some clueless management bigshot snuck into the design office and started throwing his weight around.
The cost of developing both a cylinder that houses injectors and an oil tank and pump would have been crippling when they already had 4 stroke throttle bodies lying around that they could have experimented with even if with only one injector. Could have jacked the fuel pressure up and lengthened pulse width to simulate 2 injectors.
The biggest tragedy was removing the cooling effect that the fuel gives to the bottom end ie the crank, conrod and piston and bearings and the heating / vaporising effect that the fuel; receives in return. Now forced to increase oil quantities injected to stop the bottom end over heating and turning to dust.
The other issue is the EXC range is essentially race bikes and therefore do not need the convenience or the excess weight of an oil tank which stores 6 rides worth of oil.
With the performance of a race bike you have to deal with the hassle of messing around in your workshop like a mad scientist mixing potions of fuel and oil for the sake of having the lightest possible bike.
All said Im going to need a team of boffins to sort out my ecu but I will have the only 150 EXC Premix TBI in the world for a year or 2.
This is my TPI muffler after only 45km hard enduro in the Watagans.

 

[DW]

I will give you 1 word as to why I believe ktm introduced tpi 2 stroke motorcycles. "Emissions".
The constant push of reducing emissions is why ktm went into tpi.
I gather the direct oil injection was to try and reduce the amount burning across the top of the piston. Out board boat motors have been doing this for while before ktm had a go.
Any dumb a-se can pre-mix the fuel and oil and run it through an injector in the intake instead. Just don't over mix the oil in the fuel.
TSP in Victoria have been making fuel injector re-location kits and oil pump bypass kits for the TPI bikes for a short while now. They also have an ecu re-flash to go with it as well.
Ktm probably would've done this in the first place if they weren't trying to combat emissions.
I take my hat off to ktm for having the balls to have a go with the tpi 2 stroke motorcycles in the first place.

 

[Ripperton]

Emissions is a noble cause but the maths is wrong and why do all TPI bikes belch great wads of smoke in a misguided attempt to stop piston failure.
The number of Enduro and Motocross bikes on the dirt AND the length of time they are running is a minority compared to the
demographic where emissions are actually important, being road users ie commuters and commercials.
Its Energica and Stark Varg that you should be tipping your hat to considering the half assed attempt KTM made in electric bikes.

 

[DW]

Ktm introduced the tpi bikes first into their road compliant enduro bikes. To be able to register a ktm 2 stroke dirt bike I believe they had to fall within certain strict emissions. The new bike probably passed these but had issues down the track. This happens, plenty of manufacturers have made lemons and or had bad designs, recalls, ect ect. The fact that they had a go and followed through with it is what I was taking my hat off too. They produced a fuel injected 2 stroke dirt bike. The japs didn't. I still love my jap bikes don't get me wrong, but usually they just wait till someone else makes something, copy it and then they try to perfect it.
I took interest in a project a few year ago where a guy was going to build an electric bike, would've taken my hat off to him too but I must admit the half assed attempt that ktm have done is a sh-t load better then what he ever achieved.

 

[Ripperton]

I have emailed 5 tuners around Sydney asking about TPS choices inside the ECU config program. One says there is no option to change from Hall effect to Potentiometer but the original tuner Harley says there is. Harley is currently moving shop and has no time to check configs or dyno run the bike so Im stalled.
Ive mocked the TBI body into the bike and it fits well although will need a stone guard as it is close to the chain.
A long fuel hose has to go back toward the air box, up and around to the tank. Third pic is the Hall effect magnet in the TPI TPS. Too difficult to fit this to the TBI body.

.

 

[Ripperton]

Im getting too many problems with the 23 throttle body like its going to be impossible to get the 23 potentiometer TPS to work with the 20 ECU and the cable pully is just another part I have to make myself.
So Im going back to my original plan of making an injector block that can be glued onto the original throttle body and use the 23 injector manifold. That way theres only one part I have to make and the tuning just got real easy. Theres plenty of high quality Aircraft Grade aluminium adhesives that will do the job.
Another interesting thing I learnt today out at the KTM dealer was that all 3 TPI bikes in the range have the same 38mm throttle body, 150 250 and 300 !!!
Heres the 3D model.

 

[DW]

Seriously Ripperton. Love your dedication, but watch this vid and call Tsp.

 

[Axzon]

Very interesting! I do not recognize the motor. Does not look like a KTM one. Will TSP have the kit for different make of bikes?

 

[Ripperton]

Seriously DW thats an old video and Ive already watched it.
Basically I dont like TSP injector relocation because it only moves 1 injector and the other one is in a weird place.
It doesnt optimise bottom end cooling or oil distribution or PreMix or fuel vaporisation.
I have contacted Dave asking about ECU tps type options but no response.
Im moving my injectors to exactly the same place as KTM have moved them after all the R&D they have done its the best place to put them.
Here is a pic of Billy Bolts bike with a modified TPI throttle body with 2 injectors arranged in a V downstream of the butterfly, which is exactly what Im doing except the injectors are arranged sequentially up and down stream of the butterfly as TBI is today.

 

[DW]

Never said video was new. Showing you that TSP have done injector relocations and have tunes which you've posted up that you're having trouble finding someone to tune.
You never know, maybe they have already done a full TBI conversion and just haven't put it into full production yet.

 

[Ripperton]

Cant believe I waited 2 months for the KTM TBI when I made this in 2 days.
Could do with finer resolution on the curve.
Consulting with retired Aircraft Engineer to find the right Aluminium adhesive.

 

[hpc3]

Cant believe I waited 2 months for the KTM TBI when I made this in 2 days.
Could do with finer resolution on the curve.
Consulting with retired Aircraft Engineer to find the right Aluminium adhesive.
View attachment 112542
View attachment 112544
View attachment 112543

Certainly admire your determination. One thing I haven't seen in the tuner space is a good ECM package for 2 strokes, especially since they don't have a lot of common sensors like the 4 strokers. Hopefully this will mature.