As many of you know...

My modified Yamaha RT1/RT3 360 Black Widow bike has gone thru many different set ups with a Ported Piston Port Cylinder- 34MM Carb- Sleeper Pipe etc. and has been a constant project of mine to get the bike to the next level in performance and yet having it stay true to its roots in look and ability to perform aggressively in the Dirt to heading down the pavement when needed.

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So wanted to share some of my experiences around the Carburetor and what I have learned with this bike... By no means am I a Carburetor Expert- but knowledge is gained in my book by trial and error to see how changing one dynamic can play into getting the most out of your 2 Stroke motor.

I wanted to start this thread so others can share their successful tricks / experiences and certainly any question or challenges folks are having to get their bike running at optimum levels.


So.... I will start this out and share what I have experienced with my 360 Enduro in pulling/installing the same Carb I am sure is now 100's of times trialing different set ups and documenting each time the results to get the Carb at the PERFECT tuning to deliver maximum power and proper burn to achieve maximum throttle response.

Again this only my experience and with a modified engine/exhaust but the basic's are always the same.

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So the first step for me was to get rid of the old tired Flange mount Carb and stock manifold set up on the 71's and older model- and install a new 34mm Spigot mount with Rubber manifold.

This solved a couple of issues for me- Eliminated what seemed to be a never ending air leak and by moving the carb closer to the cylinder intake made a huge difference in the throttle response.

Most everyone understands the Pilot and Main Jets for the most part and know what they do when you decrease and increase the sizes.

These are fairly straight forward when considering especially in my part of the country 'High Altitude" but is also dependent on many factors from outside temps to humidity levels etc... that can make the engine run Ok to Good vs. taking it to a max performance in fuel and air mixture.

Here is a perfect graph of what each phase does in the Throttle opening-

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I know when you get into Slides- Needle Jets- Jet Needles /Clip Positions many are not comfortable or have never thought about what they really do and when they kick in thru the different throttle openings.

For me.... nothing makes me happier then my engine having the slight blubbering at 1/4 throttle and then have that instant burst of full power when you crack the throttle wide open.

So tend to jet my pilot richer then recommended and use the air screw opening or closing to best determine what is good... this bike is VERY Happy at 2 to 2 1/2 turns and not so much at a 1 1/2 to 1 3/4 so richer pilot jet is a must.

Then you can go to the next steps- Slide cutaway... and Needle Jets. I know this is an area folks get real nervous and may not fully understand but the graph above really simplifies the stages... again with this bike... a 2.5 Slide is much better on this bike in delivering the proper air intake at the start of opening the throttle vs the more stock 3.0 set up.

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I also run a richer Needle Jet (P-4) vs stock recommendations to deliver/control the fuel amount as the slide and jet needle start to raise... again like it to be a tad on the rich side so as it progresses thru the opening of the throttle stages there is plenty of fuel to take on the increased demand then fine tuning the Jet Needle and Clip position to dial it all in to 3/4 throttle then the final proper Main Jet.

Again- I know this is all just basic knowledge and thought I understood it well after all these years but as I began to try different things and see the differences with setups soon learned I did not know much!

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If I crack the throttle and it doesnt hesitate or stumble then im tickled at that point...Lol

Greg- Some questions...

That first change, intake mount, sounds like it may be a single, simple worthy change someone could make without necessarily going further and still enjoy a worthy improvement, you think?

In the image of the new carb I see no choke lever, is it hiding on the other side?

The new carb, w new mount - What factors influenced your decision for a 34mm, and would you recommend same for a DT1 250?

So basically you've improved flow and increased intake (fuel and air) delivery precisely to compliment the other powerband elements (transmission gearing and electric). What pipe did you choose to tune to?

Thank you.... That bike of yours is very cool man....