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Best air cooled motor for conversion
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1. The motor has a large crankshaft mass making the chassis want to stand up when leaned over with the throttle on (Gyro effect) just go and ride an old school big bore and you will see what I am talking about.
2. The air cooled big bores also had a lot of detonation issues with them. The modern pump fuels will make it just worse.
My choice would be a 81-82 Kawasaki KX250 if you are looking for power they ran more like 360cc than a 250. Or a KDX250 if you are looking for a wide easy to ride powerband.
The hardest part in this project is to going to be the expansion chamber will have to be custom fabed as well as the air boot will have to be custom made as the intake sits much lower than a 4 stroke intake.
The Shop
I -LOVED- this motor and recently got to ride one ,again, they really do Shred with the usual mods and good reeds.
This is ANOTHER project that I'm blaming on Newmann! Hopefully it'll turn out just as "perfect" as the last project I blamed him for!
That's a Newmann "sourced" gas-tank that looks BETTER than new. Now I understand how people build these bikes & DON'T want to ride'em; so, I'll be running a different tank at the races.
Braaaaap!
if you want a fun to ride air cooled 2 stroke in a modern chassis I would avoid the big bores. After all there was a reason why they died off. They were a handful to ride and less and less riders wanted to manhandle them around a track. When I raced the open class back in the 80's every time I had a chance to ride a 125 or 250 I jumped at the chance to go out and drag the grips through the turns and toss them around in the air. When my friends got back from ridding my 500's they would always be worn out and wonder how I raced that thing for 45+ minute motos.
My KX500s for BITD & Moto (late 90's thru 2004-5) were a blast to ride and more manageable than a lot of 450-4Ts I've ridden.
Still the best sounding 2 stroke i ever had.
few years ago I had an 82 465 and put last gen "right side up" cr250 forks on it, rebuilt the shock and linkages.
Very good motor in an agile chassis, quite light too, was a blast to ride
Wonder what was the lightest production air cooled 500?
The yz490 pinged like hell when hot,but I believe it was a squish band problem, cutting the head would prolly solve it.
No way i want to ride any of those engines again,and I raced them all.
Once we went water and coated life just was so much better.
Isn't air cooled slightly less powerful/mod because of the heat issues ?
And something I always thought, but why not both water cooled then air cooled to bring less liquid on the bike?
Pit Row
get your years straight, dammit
/sarcasm
You're welcome.
How much do you think 2 little radiators and a water pump impeller weigh? obviuosly the engine package gained some weight, but not as much as you want to believe.
It's the chassis that got heavy. Bigger frames tubes...bigger, thicker swing arms...bigger, thicker forks/springs...bigger, thicker triple clamps/steering stem...bigger, thicker shock...shock linkages...bigger axles, bigger swingarm bolt, bigger engine mounting hardware...more hardware in general...more plastic...hydraulic brakes.
all that stuff adds heft and small amounts of weight add up.
If you want a modern, lightweight, and fast open bike, here's the recipe...
. One Ktm 250 SX. One 300 SX big bore kit. One high compression cylinder head (S3 "stars" billet head). One taper bore carb. ...and a splash of race fuel. ( a large splash actually, like 50/50 or better)
properly tuned, that set-up is good for 55-57hp and will handle better than anything else you could possibly mangle together in your garage.
Even if you did make it run right (LOL) you still have a 4 speed transmission. The very last model did include a 5 speed, but dont let that confuse things. Just avoid IT at all costs.
The Yamaha "IT" engines were very good, too.
As has been said, a 250 motor would probably be your best bet.
FWIW, my YZ465 motor is stock other than a pipe and it runs without pinging and overheating on Avgas. Yeah, yeah, yeah, I've heard all the doom and gloom about Avgas but it's been 3 years on it now without a glitch.
My point is they can be made to run easily without modding the head. If it were to run pump gas their are plenty of vintage motor guys out there than can help you out. Eric Gorr is one of the most popular.
http://www.maicoonly.co.uk/maico-parts/engines.html
Team Green-I like what you're doing with the 125 but like the idea of a 250 KX even better....never had hardly any seat time on a 125 so it is 250s and up for this cowboy.
Regarding heating/wear versus water cooling again this would be a moto specific weapon...not for the desert or the trails. Just something that you put in practice and two twenty minute motos on...rinse....repeat.
Yes was talking Suzukis
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