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  1. #1
    urugol's Avatar
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    SL900 - 1050 Conversion

    I thought it would be good to start up a quick thread on this conversion I am about to attempt. I haven't found a lot of data on this conversion, so any advice as I'm going along is welcome, after all this is my first attempt at anything like this

    Ok, so I picked up another 900 a few weeks back with a blown piston. I have a good 900 with low comp numbers so the plan is this;

    Update my existing 900 to 1050 - this project.

    Hone and re-ring existing cyls/pistons and move to more recent 900. You're prob thinking that's too convoluted, but my existing 900 is in much better cond and I will probably keep that to complement my Pro, this other 900 is just for this season.

    I received my parts in the mail today, and I am pretty happy with it. 009 Cylinders freshly honed to 0.5 oversize spec and brand new Wiseco pistons. I also have the domes, heads, cooling rail in the shipment. Carburetor will be upgraded to 40mm Keihin as per 97 SL1050 spec. I will be looking at doing this as a bolt on, I haven't thought of Impeller pitch or CDI (my assumption is that CDI stays the same).

    So far what I have done;

    Removed existing heads/domes
    Installed oil block off kit - the 2 skis are the same year/color on a tandem trailer. One is already on premix so I rather not confuse myself when filling up!

    To be done;

    Clean up new carbs, I have new kits for them in case.
    Install primer kit
    Remove 900 pistons.
    Install new pistons
    New domes/heads
    Fresh gaskets
    Set of Tau Ceti F/As
    Put it all together, torqued up as per service manual
    Might give the red bits a coat of dupli color as well
    Run er in!
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  2. #2
    urugol's Avatar
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    I noticed that 2 of the Pistons have the number 4265D on them, the other one is stamped 3301A. Also, as per the pics 2 Cyls have the number 1 whilst the other has the number 1+ stamped on it. I'm not sure if this is significant or not, it all looks exactly the same.
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  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Might want to review the specs for the 1998 and 1999 1050 models (SL and SLTX) and the Service Bulletins. Always good to check whether there were any changes or updates to the specs or settings compared to the 1996/1997 versions.

    Someone on here might know what the ignition advance curve differences are between the SL900 CDI and the 1050 CDI.

    The red line RPM limiter was 6800 RPM for both models in 1997 & 1998. By 1999 it was 7200 RPM.

    According to my service manual the 1997 1050 still had 38mm Keihin CDK-II, and 1998 had 40mm Keihin carbs

    BTW, full throttle cruising range per the manual drops from 50 miles with the 900 to 40 miles with the 1050 That's 20% less range from the 47 liter fuel tank

  4. #4
    urugol's Avatar
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    I think you may be thinking about the 97 sltx 1050, that model kept the 38's but the SL1050 was 40's in 97 (at least that's how I'm readying the manual). I checked the jet sizes against the 40's and they check out stock 158,152,152. The bigger jet/carb/piston setup would explain the 10 miles difference in cruising range, it's big but I don't care if I can cover 40 miles quicker! It also looks like the rpm limiter is the same as the 97 900 so I'm not certain I need to do anything with the CDI, which is a shared component according to the parts database.....
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  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by urugol View Post
    ...The bigger jet/carb/piston setup would explain the 10 miles difference in cruising range...

    It also looks like the rpm limiter is the same as the 97 900 so I'm not certain I need to do anything with the CDI, which is a shared component according to the parts database.....
    20% difference in fuel consumption between the 900 and 1050, yet only 11% difference in rated power (119HP vs. 107HP). That implies that the 1050 is less fuel efficient per HP at WOT - about 90% of the fuel consumption per HP of the 900

    I don't know the Keihin carburetors very well, but perhaps the 38mm Keihin's are more fuel efficient than the 40mm
    Or perhaps the 40mm high speed jetting is effectively richer for some reason.

    Interesting that the 1997 1050 engines in the SL and SLTX are rated for the same max power output (119HP), but one uses 38mm Keihin and the other uses 40mm.

    Since you will have both carb sizes on hand, perhaps some day you can do a comparison between the two carb sizes on the same engine. How fast can you swap a set of carbs to do back to back comparisons?

  6. #6
    urugol's Avatar
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    Quote Originally Posted by K447 View Post
    Interesting that the 1997 1050 engines in the SL and SLTX are rated for the same max power output (119HP), but one uses 38mm Keihin and the other uses 40mm.

    Since you will have both carb sizes on hand, perhaps some day you can do a comparison between the two carb sizes on the same engine. How fast can you swap a set of carbs to do back to back comparisons?
    That is a very interesting observation. The sltx/900 carbs use the same jetting as well so this is a mystery. If this is true then I should not see a power difference between the carbs and get more range - though I find it hard to believe

    Maybe I will swap carbs to compare, I can swap them almost with my eyes closed now

  7. #7
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    You more than likely won't gain any peak RPM with larger carbs, but you will gain throttle response and acceleration. I ran 40mm carbs from a 1200 on my 900-1050 conversion. I didn't think the fuel consumption was too bad..especially compared to when I put triple pipes on it, along with 48mm carbs...yikes!

  8. #8
    urugol's Avatar
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    Quote Originally Posted by PolarisNut View Post
    You more than likely won't gain any peak RPM with larger carbs, but you will gain throttle response and acceleration. I ran 40mm carbs from a 1200 on my 900-1050 conversion. I didn't think the fuel consumption was too bad..especially compared to when I put triple pipes on it, along with 48mm carbs...yikes!
    Did you change the 900 CDI on your conversion?

  9. #9
    urugol's Avatar
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    Looks like a carb rebuild is in order!
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  10. #10
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    Quote Originally Posted by urugol View Post
    Did you change the 900 CDI on your conversion?
    All the parts app's group the 96-97 900/1050 together-same ignition parts-CDI.

    The later model 1050 still had a 64-6500 operating range.They're CDI # replaces all older #'s,probably reliability.

    Just my opinion. I think the higher rpm's the 1200's run is in the exhaust.
    My incomplete testing on a 700-changing rpm's,caused a loss of torque.

    I suggest running it with the current cdi and see how it runs.


    I changed carbs on the 700 with a larger prop,from 38's to 40's (with accel pump ),with the engine under a heavy load from the prop-I gained 100 rpm.
    With a stock prop,I think the rpm's will be the same.

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