Reed valve Sportfire/Trailfire...

[Mean Green]

It's been awhile since I've done any mods to a deere since the 4/6 into a new breed LF. I've been into hot rodding jetskis and have a new project in mind as the Kawasaki engines of the time have many similarities. One of these is the intake port shape and bolt pattern, and the 440/550 jetski manifold lines right up. During the "Heyday" of jetskis in the late 80's early 90's one of the mods that came up was retro fitting the piston port engines of the 440/550 with a bolt on adapter that incorporated reed valves. The only modification necessary to the engine was to drill "Boost ports" in each piston. These adapters were available through Johnny O's Racing and Goki. They pop up periodically on ebay. The one from Johnny O's is the one I'd like to try on this project as it utilises the reeds and cages from a Yamaha RZ350/YZF350 (Banshee), and I therefore can use the carb boots from the banshee as well. On my heavily worked jetski cylinders, this "bolt on" made a huge difference in starting, idle, and responsiveness. Here's some pics of both the adapters and some modified pistons I have from my JS550 jetski. Of course I won't be able to utilise the air box, but I don't plan on running powerjet carbs or dial-a-jets so this shouldn't be an issue. The additional fuel circuit in the affore mentioned carbs requires vacuum from the airbox to function. Anyways, if anyone has ever done this or heard of someone doing this please chime in!

Tracy

[Mean Green]

Thought I should show one of my "top secret" ported cylinders from a jetski with the reed adapter and dual SBN38 carbs....I have no intention of going crazy porting a fan cooled engine as cooling would become a issue. Just trying this to get a little "cleaner" response from the engine for low rpm trail riding.

[80spitfire]

Wow that's way cool you're using Kawi Jet Ski parts! I've got a handful of Kawi stand ups and I absolutely love them.

-Brian

[Matt]

Could you explain why this would make better power? I don't follow.

[a572mike]

I haven't heard of anyone doing this, but I've always wondered about it...

[Mean Green]

"Better Power" is an ideal choice of words. As the bottom of the piston skirt travels up past the intake port, it of course creates a vacuum and sucks in the fuel charge. On it's way back down it then forces this charge through the crankcase and up through the transfer ports. Unfortunately, there's a fraction of a second where the port remains open and part of the charge is forced back out the intake port. This momentarily reverses the flow of air through the carb creating a pulse effect especially at low rpm's. Reed valves stop this positive back flow and keep the air moving in one direction through the carb increasing efficiency. By adding reeds to a two cycle and eliminating the back pulse, throttle response and fuel economy are improved. This addition also opens up doors in the porting department as we are no longer restrained to the confines of making a choice between high end performance or low end driveability. You can hog out the ports for top end and not lose fuel charge velocity on the bottom end. (Velocity is air speed, high velocity is blowing through a straw, low velocity is blowing through a fire hose).

Anyways, besides not having a chassis yet, my one issue is clearance. Guess we'll cross that path when I get further along on this.


Tracy

[JDXspec]

The mod here is having low end torque (like a 76-78 LF) and the ability to keep the high rpms that the (80+)kawis like. Basically broadening the usuable power band. You could have say a 3500 engagement and still possibly have a 10,000 rpm maintance speed

Maybe thats why you don't see many 76-78 LFs racing (with pipes) because the reeds tend to "float" at high rpms which robs power. Makes a great trail eng but high rpm race eng not so much.

[nick80lf]

This is a little off topic, but I've always wondered if the starters that were used on the jet skis were the same as the snowmobile starters.

[jdrob]

I am just gonna give you my opinion ! If you run wide open all the time! WHY then would you need Bottom end ?? If you running a sportfire or trailfire clutching makes a big difference on the lower end to make up for what is lacking, plus a little tinkereing with your gearing helps too ! If you wanna go faster buy a newer sled ! Also your adding weight ! Now I understand reed cages don't weigh a ton but it is still added weight ! I guess it would make sense for a trail rider B/c you have more of a range of even power. Just seems to me a whole lot of work for little gain ? From my little knowledge the Kawi engines were built for High rpms and perform best there! When they built the trailfire it was for "trail riding " they didn't build a reed engine for it ! They clutched, geared and jetted to make trailable ! Just my .00063 cents

[Mean Green]

The significance of attempting to add reed induction to a piston port engine is to 1) Increase rideability while adding dual carburetors. If you open up the intake tract by 2,(dual vm34 carbs), you lose low end response due to fuel charge velocity. This mod is intended to regain that bottom end while enhancing top end performance. 2) By utilising reeds, I can machine boost ports (Holes, see pics in original post) in my pistons. This allows a greater fuel charge per cycle and more importantly, cools the bottom of the piston crown allowing me more timing advance and/or higher compression by reducing pre-detonation. 3) Nope, they certainly didn't build a reed engine for it. In fact, they never built any engine for it. The engine was built by, and designed by Kawasaki for their 1978 introduction of the Intruder model snowmobile. The design was offered to deere to assist in alieviating the heavy debt Kawasaki accrued by buying out Sno-Jet from Gastron in 1976. Deere engineers indeed adopted this powerplant, but per their own specifications. Low compression heads, single carb, and less timing advance were implemented to improve trailability, longevity, and compliance to low octain fuel commonly found by anyone purchasing a John deere snowmobile. While their kawasaki cousins enjoyed the benefits of higher performance, they also required more maintenance and availability of high octane fuel. 4) Most importantly, after having been a member of this sight for several years, and aboard during the "update" in 2005, I thought it might be refreshing for members to follow. Seriously, reading about barn finds, restorations, and helping anyone new to JD sleds is great. But after several years of rehashing the same things, perhaps something a little different couldn't hurt. 5) I'd buy a newer sled, but they all already have implemented case reed or rotory valve induction and that would spoil all my fun....

Tracy

PS: I have no idea about the electric starters. You would need to cross reference the Kawasaki part numbers from sled to ski.