ATC350x vs XR350R vs XL350 Head Swap?

[ps2fixer]

I just ran across a basket case XL250R bike and learned about the dual carb setup they have. According to my research the XL350R had 30hp vs the 350X @ 27hp. I have a 350x bottom end with a bad top end so was wondering if anyone has tried to swap them out? Figured this might be an interesting "upgrade" maybe for the 350x.

Either way, I know the xl250r isn't going to fit, but I have plans for the engine, so the rest of the bike is going to be parted out, so if anyone has one, shoot me a pm for parts. I'm keeping the engine and electronics required to make it run.

There is a XR350R for $400 local to me, so I'm half thinking about grabbing it if the top end would swap to the 350x bottom, or the whole engine has the same base mounting points.

In case someone here has experience with the XL/XR dual carb setup, should both carbs open at the same time, or one slightly delayed? Mine has 1 that opens to about 1/4 open before the second kicks in.

[onformula1]

The xr 350 head is not a bolt on, but I have read it can be done with a lot of work, but the 350x has a good head design.

The bottom end is very different as far as mounting points.

Yes the carbs are progressive.

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[ps2fixer]

Thanks for the info, i won't bother with the XR local to me then since I don't have a good contact with a machine shop to do the extra work (or access to the machines).

Bummer on the mounting points, figured it could be an interesting swap

Kind of wonder if the dual carb setup is any better than a single. Non-the-less it is a new interesting thing to me, dual carbs for a single cyl, just about like when I learned the 350x had dual exhaust ports.

BTW if anyone was wondering, I'm planning to throw the xl250r engine in a 200x roller, lots of fab work but shouldn't be too bad. Wasn't really impressed with the 200x power, so hopefully the xl250r will be enough for me to take a liking to it, if not it might be up for sale TF2016 :). Of course the 200x's i have were beat to snot, so they probably need the top ends re-done.

[onformula1]

That dual carb set-up was nothing special.

Al Baker (RIP) at XR's Only had a kit to remove the duals.

Conversions are interesting, sometimes fun..LOL, but a 200X can be modified to be pretty quick. Plus they kick forward.

[RIDE-RED 250r]

Yep, the old 350x was kind of ahead of it's time for ATV's. You mention the dual exhaust ports, that is because it is a 4-valve head. That's a pretty significant performance bump for a thumper. Ever run a 350x (4-valve) against a Warrior (2-valve)?? No contest. :cool:

Mickey Dunlap is cranking out a new big bore kit for the 350x now (500cc) and for what you get, it is priced very reasonable. If my wife were ever to allow me to mod her 350x, Mickey is the man I would be looking up.

Early Yamaha Raptor 660's ran dual carbs. If I'm not mistaken they have abandon that approach in subsequent model years.

[ps2fixer]

Yea I understand it is a 4 valve, but I came from the 4 valve cars before atvs. The cars only have 1 exhaust port per 2 valves, the dual ports I never saw before around 4 years ago till I learned about the 350x and wanted one badly (have 2 + 4 bottom ends and 1 top end and 1 top end that is jb welded up pretty bad and the head studs are shot for the exhaust). Trying to get a spare engine up and going for my two machines for pretty cheap as I'm self employed and can't afford a whole lot unless things took off a bit faster.

I was really hoping the mount points would be the same on the xr350r, since $400 into the complete machine, and parting out the rest would make the engine more or less free. Don't really want to have to fab up the 350x frame if I ever have engine probs though.

Thanks for all the input so far

[Poco Loco]

If your gonna go through the hassle of a head swap, go the full monty and do the early xr 500.217887 I did it back in1987. Its still running.

[ps2fixer]

Is the XR500R head a direct bolt on to the 350x cyl, or what all is required? Parts for that engine are so much cheaper!

Only issue that comes to mind if it is a direct bolt on, the head is designed for a larger engine, so the combustion chamber would be larger, which would lower the compression ratio?

[onformula1]

I have not tried it myself, but I have a buddy that is currently spec'ing it out and it doesn't look good without a lot of work, with what is looking like no real gains, besides the large chamber size.

If you do a search I think there is a few threads on here I read years ago.

The 350X head can be made to really flow a lot and can handle 500cc, so for me why change?

[HairyJR]

Besides the loss of compression with the larger xr500 head cc volume, I also believe you need to use the xr500 cylinder bore size as the valves might hit the smaller 350x bore diameter. Try this thread by "Swigin" covers a lot of the issues to install. I don't remember all the details as was done almost 30 years ago....

http://www.3wheelerworld.com/showthread.php/78141-ascott-500-head-swap-onto-a-350x-with-pics?highlight=ascott

"HJ" 217938 :beer

[Poco Loco]

Harry Jr is right. I had the 350 sleeve pressed out, then bored the cylinder, then press in a 500cc sleeve. You adjust the compression with a custom made piston. its a 500cc piston with the top milled down and valve pockets cut in. If you dont mill the piston it will slam the head...not good