octane and 2-strokes

[ruffdog]

That was then. Look up "power valve". The exhaust port timing is controlled in every modern 2-stroke dirtbike the past 25 years. Lots of discussion on KTM forums as to the most desirable spring to control the opening for different conditions. Beta adjusts theirs with a threaded shaft making changes in the woods very easy.

The last RD400 was the first I remember having a power valve in the exhaust.

Yamaha had the YPVS power valve and other makers had theirs too:

Two-stroke power valve system - Wikipedia

 

[etpm]

That was then. Look up "power valve". The exhaust port timing is controlled in every modern 2-stroke dirtbike the past 25 years. Lots of discussion on KTM forums as to the most desirable spring to control the opening for different conditions. Beta adjusts theirs with a threaded shaft making changes in the woods very easy.

The last RD400 was the first I remember having a power valve in the exhaust.

I didn't know about the power valve. Thanks. Though I really liked 2 strokes at first I became disenchanted with them for several reasons, the main ones being poor fuel economy and the oil sheen from outboard motors. Things have really changed since my RD 350.
Eric

 

[Oaktree]

I really liked 2 strokes at first I became disenchanted with them for several reasons, the main ones being poor fuel economy and the oil sheen from outboard motors.

Not to mention the smell of the exhaust.

 

[Kyle_in_Tex]

Castor Bean oil smoke....yummm.

 

[Kyle_in_Tex]

RD400, no power valve.
RZ350, power valve and liquid cooled. Plus catalytic converters for American models.

 

[MossRoad]

Not to mention the smell of the exhaust.

I always found the smell of 100 octane burning in my RD400 mixed with the oil thrilling.

 

[not2old]

I didn't know about the power valve. Thanks. Though I really liked 2 strokes at first I became disenchanted with them for several reasons, the main ones being poor fuel economy and the oil sheen from outboard motors. Things have really changed since my RD 350.
Eric

I too was concerned about fuel mileage when I took my 1999 Husky 360WR to Baja. Turned out I used less fuel than another guy riding a Yamaha YZ450. My 2016 TE300 uses even less and using Amsoil at 50:1 neither one smoked.

 

[not2old]

Castor Bean oil smoke....yummm.

Yes, I miss that too!!!!!

 

[MossRoad]

I too was concerned about fuel mileage when I took my 1999 Husky 360WR to Baja. Turned out I used less fuel than another guy riding a Yamaha YZ450. My 2016 TE300 uses even less and using Amsoil at 50:1 neither one smoked.

If I one day put my RD400 back together, I'll try that. Otherwise, I'll have to contract out to the county to fog for skeeters just to make it legal.

 

[big bubba]

as a footnote to pre ignition & octane count. my 4x4 Toyota 4 cyl began to ping a lot after hitting 200k. previous, went w/87 but gradually pinging got worse. took me a while, but figured with that mileage, carbon build up hot spots on piston caused pre ignition with lower octane.
been using 91 ethanol since & the pinging has completely disappeared.

the original engine (never opened) now has 305k & runs like new, compression still holding 185 to 200 psi.
glad i discovered the higher octane advantage & non ethanol before damage to pistons.
like modern tractors & vehicles, i will never own one w/regen or all the damn sensors, etc.