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  1. #1

    650 sx engine mods - which to do first?

    Hi, what do you guys think of which mods to do first to a pretty much stock 1989 650sx, and in what order for best performance? I've changed the ride plate and grate, but no engine mods yet. Thanks for any thoughts!

  2. #2
    DPeteLand PeteSkeet's Avatar
    Join Date
    Jul 2008
    depends what you want... you can do many things.... spending from very little to a lot!

  3. #3
    Let's just say the most bang for the buck. Out of hole performance would be important, top speed probably second.

  4. #4
    Pro-pulsion's Avatar
    Join Date
    Feb 2009
    Ontario, Canada
    I'm doing up mine too, there are a ton of virtually free mods you can do to these skis. The exhaust mod from what I have heard is about the equivalent to a Factory Pipe Products exhaust. I'll get back to you with a list of mods later tonight.

  5. #5
    Thanks, that would be great. I took a look at your signature link, looks like you're busy with that ski! Just completely redid all the body, upholstery, graphics, etc. on my ski and now moving to the engine. Look forward to hearing from you on your list!

  6. #6
    thesepaperwings's Avatar
    Join Date
    May 2007
    South East Kansas
    You can get tons of speed with the free mods. I would start there and let us know how it starts out.

  7. #7
    Pro-pulsion's Avatar
    Join Date
    Feb 2009
    Ontario, Canada
    Well, I'm back for a few minutes so on with the info. First thing, read lol, here's a great thread that will give you most of the mods I'm doing and all for under $200.00

    There aren't any pics of the exhaust mod on this link but the link he provides is pretty good. I should have pics up of the exhaust mods I'm doing soon. I'm just waiting on a few more things before I start slamming it all together.

    Next thing that I can't stress enough, before you do any engine mods make sure you have a new gasket set in your hands. There's no point in disabling a perfectly well running ski to sit and wait on parts. You could do the vast majority of these mods in a day and a half if not less.

    So basically the free mods I am doing/have done are:
    - polish the exhaust ports
    - de-burr the spark plug ports inside the combustion chamber
    - polish the domes
    - de-burr the intake manifold on both sides if you don't plan to do any machining
    - de-burr the exhaust head pipe (again if there won't be any machining)
    - if you have your own drill hone, use it to clean up the cylinders just enough to restore the cross hatching
    - modify the exhaust as per the instructions here (also found in the first link)
    - remove the crankcase drain and plug the two ports
    - remove the drive rod from the oil injection and plug the lines (switch over to premix)
    - remove the injection fitting in the intake manifold and plug the port either by tapping it and threading in a small bolt wrapped in Teflon or an aluminum plug
    - remove the retainer plate holding the two carb bolts from inside the flame arrestor housing and use blue 242 Loc-Tite on those bolts (little less air flow restriction <--- I did this on my old 92 650 and it never failed)
    - cut out the center rib from the stock intake grate
    - sharpen the blades on the impeller
    - silicone all the seams between the ride plate, intake grate and hull

    There is one other mod that could be free if you can find the material and a welding buddy. But I'm not totally sure on that one just yet because I haven't gone through my list in awhile so I'll have to get back to you on it. It's another addition to the exhaust mod. Hope this makes for a good start.

  8. #8
    Wow, thank you for all this great insight and links. This will be extremely helpful to get me started! I appreciate your help!

  9. #9
    Pro-pulsion's Avatar
    Join Date
    Feb 2009
    Ontario, Canada
    Anytime, if you run into anything hard to figure out let me know and I'll do what I can to help. Have fun with it.

    All your gaskets and engine rebuild parts that you may need or want are very easy to get, I buy all of mine through here (already did the year/model search for you so what you see is for your ski)...

    Ah yeah, one last thought...if your ski has never been torn down then it is strongly recommended that you order up some new crank seals. 20 year old seals are only going to get worse and will fail with the higher output stresses.

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