DA 50 w/ KS 86 canister non-linear throttle

[shall36]

I have a DA50R with the KS 86 canister. I have a real "hump" in the throttle. It will jump from 4500 to 5500 rpm. I guess this is an issue with the length of the header pipe? How long should the header pipe be and how should I go about tuning (my guess is that I have to cut on the header pipe)?

Thanks!

[swheaton]

what size prop are you running?

[shall36]

I believe it's a 23x8.

[shall36]

I measured the pipe and it's 8.5" from center of the port to end of the header. Will cutting the header pipe have the potential to solve this problem?

[Dan J]

Did you try a throttle curve?

[zzw26n]

shall36,

What length servo arm you using? what servo you using? post a picture too. I run a short servo arm on mine (4 DA-50's) and no issues with throttle curve. Only thing to watch for is what RPM band you canister kicks in, very large jump in RPM then.

[shall36]

I'm using a throttle-throttle mix (5 point exponential) to try to straighten out the power delivery. I'm pretty sure the jump is due to the canister. It may be the case that the power band peak issue can't be resolved. I know the smaller 2-strokes with tuned pipes rely on cutting back on the header length to get the exhaust tuned properly. I'm not sure what effect cutting my header pipe back would do. It's not that I want more power, I just want to minimize the jump caused by the power band.

[Olli-Matti]

I asked KS about the header length when I were in the process of installing my
KS 86VS-4 canister and DA50.

The reply was:
We recommend the muffler # KS 86VS-4 for the engine DA 50 R. You get the best results with a neutral header-lenght from 200-260 mm (the neutral distance from the flange-plate to the end of the header)

I have a header length of 255mm (10")and it has worked just fine. Transition is very linear, with
no jump caused by the canister. I do have a normal p-mix to counter the effect of butterfly carb though.

Unfortunately I haven't tried any other lengths because 10" has worked just fine.

[krayzc]

is there a pic coming of the set-up shall36?

[DATech]

Hello
I would not recommend going to a shorter header. Normally, the KS canister likes a header in the 10" to 12" range. The larger the prop load (lower rpm), the longer the header. The smaller the prop load (higher rpm), the shorter the header.
With props normally used on the DA50, shorter than 10" can lead to over heating and a step in the throttle transition.

[shall36]

Alright! Some great responses here.

I took pics, just need to post them.

Sounds like my header pipe is a bit short. It measures 8.5" from center of flange to end of pipe. A slightly longer pipe might work better.

Conversely, I could drop down to a 22" x 8 prop. Not sure I want to do that.

Sounds like I need to find a 10" header pipe? The setup I have came from Troy Built Models.

I haven't had problems with overheating and it's been in the mid to upper 90's here in Orlando.

Thanks!

Hopefully, I'll have time to post pics tonight.

[shall36]

Quick question...when we talk about header length, how are we measuring the length? Do we measure on the outside of the pipe?

I measured the header as the crow flies.