2 stroke 399 Kohler Bogging

[turbulence63]

I have an 1971 8x8 argo. I just changed the engine and put in a 2 stroke 399 Kohler rebuilt that used to be in a 6x6 before i did the rebuild. I had some trouble getting the carb set up ...but know it starts and idles nicely. But the big problem is it is very slow and boggy at full trottle under load. When not under load it screams fairly well. My argo is an 8X8 and wondering if its too underpowered with the 399. Although it originally had an old 4 stroke 17 Hp Tecumseh and the 399 is approx 25-28 hp, so i figure there should be plenty of power to get some speed.

Not sure if its the jetting or the clutch. But as I mention it idles great and responds well when not under load.The Carb is a Tillitson HR 40A

Would anyone have any suggestions ...i have the same clutch for that 399 Kolher that came with a 6x6 argo.

Barry

[Bazooo guy]

Try and set the high speed needle when its under load at wot.
Open it in 1/8 turn increments till you get the performance at top end.
Set the low speed at idle.
2 strokes make the best power in the upper rpm range.
I rev my rotax between 5000 and 7000 and it runs strong.
Idling for long periods or low rpms will foul plugs.
If your exhaust has too much back pressure it wont suck enough fuel at higher rpms.

[turbulence63]

Hello Bazoo Guy

I am fairly new to these engines and this was my first rebuild ...still learning much.

You have been pretty good at all the advice you gave me in the past threads. In fact It was your advice that got me to the end of this rebuild. Hats off to ya Bazoo Guy

I will go through those procedures you mention...but I do need to know how to tell if there is too much back pressure in the exhaust.

Thanks alot Buddy.

[Bazooo guy]

Glad i could help...
The exhaust is very important on a 2 stroke.
Heres an article to help you understand how it works.
Engineering Acoustics/Sonic Supercharging of 2 Stroke Engines - Wikibooks, open books for an open world
I have some pics of mine in my gallery and its quite simple to make.
Y pipes are equal length


The 90 is larger on the exit end into a canister/expansion chamber





Its not pretty but it works.

[turbulence63]

My friend you just pinpointed the problem.

I need to change the exhaust muffler ...the one on there is the original from the 17Hp Tecumseh 4 stroke that was changed to the 2 stroke 399 Kohler.

Something I should have noticed but ...still learning!

Right On!! Bazoo Guy

PS: any idea where to find an exhaust that would fit my 399 Kohler and run proper.

[Bazooo guy]

Depends how you need to route the exhaust.
Look for a snowmobile canister type that you can modify like this one.

1998 Polaris XCR 440 Indy XC Exhaust Canister Muffler | eBay

I used this type.

http://www.ebay.com/itm/1996-Snowmobile-Polaris-XLT-XCR-Exhaust-Pipe-580-Triple-600-Can-Motor-/110992298740?pt=Snowmobile_Parts_Accessories&hash=item19d7a812f4&vxp=mtr

[teeko]

Bazooo guy has helped me with my Kohler rebuild as well. Where are you located? Any snowmobile wrecker will have old pipes and cans that can be modified to your application. Something else to consider. Use the clutch that came with the 400 and not the 4 stroke. The weights will be different cased on teh operating rpm range of the motors. If you have secondaries (the larger diameter clutch or driven clutch) from both machines, use the one off the 400 as well as it will be matched with the primary (smaller clutch or drive clutch) from that setup.