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Help Looking for Info - Yamaha 250 single

Discussion in 'Yamaha 250cc Singles' started by minimac, Jan 7, 2018.

  1. minimac

    minimac Active Member Premium Member Contributing Member

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    I know this site doesn't cover scooters specifically, but I can't find any info and sources for parts. I'm trying to build a mildly enhanced performance engine for a scooter I'm building for long distance touring competitions. The runs I'm looking to compete in are limited to 279cc It is a liquid cooled, fuel injected(throttle body) four valve 250 single that originally was in a 2006 Morphous (Maxam) Yamaha scooter, but it only puts out 20H.P. The motor will be put into a chassis from a 400 Majesty with custom body work, dustbin fairing, Malossi variator, and custom made gearing for a bit better top end. The engine is supposedly physically the same as the 400- also a four valve- with only the bores being different. The problem I've run into is this engine, and the Maxam scooter, was only imported into the U.S.A. for three years and only one into Canada, so info here is virtually non-existent. I know it was sold until 2012, but beyond that, I can find nothing. Reading through the varios threads on this site, there are some real cleaver people here. I'm open to any and all ideas, suggestions, links, etc.
     
  2. gregt

    gregt Well-Known Member Premium Member

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    That engine appears to be part of a range - with the 400 - that is unique to the scooter side of Yamaha.
    Bore and stroke are different to the good 250's and i'd suspect that the general level of tune reflects a low margin of strength for modifications.
    In the big stuff from Yamaha for example, the Vfour cruisers which use the same basic engine as the V Max are severely detuned to the extent of weaker valve springs to match the softer cams.
    I'd be pretty careful just how far I went with this, it could get expensive very quickly.
     
  3. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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  4. minimac

    minimac Active Member Premium Member Contributing Member

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    Thanks for the quick responses. I was even checking ATV/UTV engines. There seems to be plenty available for them, but the 400/250 must be orphans. About all of my Googles turn up is a variety of spark plugs, oil filters, high dollar mufflers, and some aftermarket body parts. I guess I'm going to be restricted to doing a clean up bore, good valve job, and maybe a port and polish. Maybe some knows of someone with some experience with this engine. I know it's a long shot, but if I stumble on some magical combination, I'll be sure to post my results.
     
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  5. Mike Fulcher

    Mike Fulcher Active Member Premium Member Contributing Member

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    If the engine has a four valve head you are half way there already. Some of these type engines are generic, & used with different specs for different applications. some are so restricted to conform to Gov. regulations etc it is not even funny.
    To illustrate what I'm saying, I have come across even Jap manufacturers putting restrictor plates in the intake manifolds & fitting the engines with extremely constipated exhaust systems.
    Throw away the exhaust for a start, start with a header pipe at least the same diameter as the exhaust port, & use a large capacity straight through sound absorbent type muffler. Now the intake side, use an intake manifold of at least 10 percent bigger diameter than the intake port, open up (taper up) the cylinder head to match, & replace the inlet manifold with one at least 2 mm larger venturi dia. than fitted as standard, same with the carb.
    If you can source a higher comp. piston this will also help immensely.
    Now what sort of transmission does your scooter have? if its a CVT you will need to change the centrifugal weights & springs to allow for a higher RPM engagement speed.
    Finally your bike may be fitted with an electronic RPM limiter, get rid of it & fit a very easily available after market unlimited RPM CDI.
    All the best.
     
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    Last edited: May 25, 2018
  6. minimac

    minimac Active Member Premium Member Contributing Member

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    I think I can safely bump the compression ratio up .5 to 11:1 and still be good running readily available gas.I'm thinking the biggest gains will come from replacing the restrictive exhaust, as you stated. I already have a new Malossi variator ready to go with an assortment of rollers to try. I also plan on trying a couple of different springs in the clutch to fine tune it. There's no replacement for displacement, but I'm going to have to have longevity and dependability as a major concern, as opposed to all out power. I'll look into possibly having it sleeved and a custom piston. I think I could realistically see about a 20cc increase without sacrificing too much, (other than cash), especially since the only difference between my 250 and my 400 is the bore. I might be able to have a shop near me reflash the ECU, also. Lots of big ideas, but a small pocketbook! On the plus side, I have almost two years to get this all together and sorted, though. Thanks for the interest!
     
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    Last edited: May 26, 2018
  7. minimac

    minimac Active Member Premium Member Contributing Member

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    I've located the sleeve I need and a shop to install all my parts, but Im having trouble figuring out how to spec out the piston I'll need...i.e., how do you figure the best location for the pin? How does it effect rod angle, or doesn't it matter that much?
     

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