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  1. #1

    Bought a K&B 3.5cc outboard recently, wanted to do a Carb conversion

    So I ended up buying new in box K&B 3.5cc outboard, their standard model with the exhaust built into the bottom housing. However this is the much older model that uses an exhaust throttle , so I had a couple questions regarding this, but in general, I want to convert this outboard to resemble and function the way the current models do.

    So I placed an order with K&B as well, and I hope I didnt make any ill informed purchases.... So heres the list of stuff I bought.

    Products Ordered:
    -CARB NECK O-RING, K&B 3.5cc DF IB OB

    -EXH ADPT O-RING, K&B 3.5

    -EXHAUST ADAPTER, K&B 3.5cc (.21) OB

    -LOWER END HALVES, K&B 3.5 <------ (the model I have doesn't have a hole in the right side of the housing for the pressure nipple, so I bought these for that reason)


    -WATER & PRESSURE FITTING 10-32 thread


    -TEFLON GUIDE TUBE. K&B 3.5 OB

    -STEERING ARM, K&B 3.5 OB

    -CARBURATOR COMPLETE GOLD, K&B 3.5 DF IB OB

    Heres a picture of my outboard currently.
    Attachment 2075081
    Heres a picture I found of the same 3.5cc standard K&B outboard but in the newer rendition, I basically want mine to be exactly like this one. However I opted for the Gold carb instead of the black one. I purchased the steering arm thats on this unit too. However Im not sure what the deal is on that nylon mount in the front....
    Attachment 2075082

  2. #2

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    That is for the Dubro 3.5 adjustable motor mount.

    What will be your main reason for using this motor? Reason I ask is that the motor you have is very out dated. When looking for internal motor parts, this has the 12mm crank. The newer motors will have the 13mm crank. The motor will not be race competitive with the current motors available. If it is for play, have fun!
    Last edited by ob nut; 02-23-2015 at 08:51 PM.
    Mark Scott - just a nut for outboards
    A.D.I.D.A.S...

  3. #3
    Ron Olson's Avatar
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    Well, look who crawled out of the woodwork! Mark, I haven't seen or heard of you in ages! We need to talk sometime bud!
    IMPBA 17238 S
    269 Racing Team

  4. #4
    Quote Originally Posted by ob nut View Post
    That is for the Dubro 3.5 adjustable motor mount.

    What will be your main reason for using this motor? Reason I ask is that the motor you have is very out dated. When looking for internal motor parts, this has the 12mm crank. The newer motors will have the 13mm crank. The motor will not be race competitive with the current motors available. If it is for play, have fun!
    umm, wow thats a bummer because I certainly overpaid for this quite a bit then.... *sigh* lame.

    I wasn't planning on competing, this is actually my first build, ive owned a an RTR before and thats it, it was electric. But speed is still important for me.... I have a VS1 on the way. I mean, how much of a drag compared to newer ones? I mean this is why I mainly made this thread, to have someone perhaps give an OK on the parts I bought? is this crank going to impede my ability to install the new parts I bought?

    I was going to buy a pre-balanced and sharpened prop from Hyperformance too. Id like to get at least 40mph

  5. #5
    I could order the 13mm crankshaft from K&B for 29$

  6. #6

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    Since you have already ordered lot of parts from Mecoa you might as well proceed with the conversion! That being said the older K&B 3.5cc outboard was very usable with the exhaust throttle for fun running, the newer version had improved timing and a ticker sleeve in addition to a larger crankshaft. So if you want a 13mm crankshaft you'll have to replace the front end and bearings too!
    And the outboard crankshaft is timed for reverse rotation(CW)same as the old 3.5cc inboard with the side ventury.
    Last edited by coriolan; 02-24-2015 at 01:24 PM.

  7. #7
    ok, is 40mph attainable with the VS1 and this outboard?

  8. #8
    they havnt shipped the parts yet I could still get a refund.

  9. #9
    Ron Olson's Avatar
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    I've been seeing some good used K&B .21 OB's around for good prices. There was one in the RCU Marketplace.
    As far as motor mounts go, use a Du-Bro or Octura. Prather's are a pain in the butt to set up.
    IMPBA 17238 S
    269 Racing Team

  10. #10

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    If you can get a refund, go for it. Take that money and buy a more recent 13mm K&B. Preferable a SS. Better yet, get a OS outboard. The VS1 was built to run "stock" motor. With either the SS or OS, the VS1 should run high 40's to mid 50's with the proper prop and nitro % (50% or higher).
    Mark Scott - just a nut for outboards
    A.D.I.D.A.S...

  11. #11
    well, it ended up shipping right after I sent an email requesting a refund.... this is LAME. I really wanted the O.S. but im having trouble finding any that arent overseas, and on top of that I didnt really want to spend around 400$ for an outboard anyway.

    I mean, is the 13mm crank really that big of a difference, like can I hit 40mph with this current outboard with the carb conversion?

    Im considering just selling everything then and buying a UL-1. Great boat from what ive seen, and still 70$ cheaper than just the O.S. outboard, and in stock in numerous places. God I wish I didnt buy this outboard now! its brand new, I have the box and all the paperwork and stuff though.... how much you guys think I could get for it? im embarrassed to say how much I got it for.....

  12. #12

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    Even NIB it isn't worth much(not old or rare enough to be collector!), since it is not for racing don't get too fixated on that 40 mph number as when you run alone it really mean nothing. Speed will depend a lot on which type of hull,prop and fuel you use and how well everything is tuned.

  13. #13

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    See if you can return for a refund. There is one other item not listed you will need since you want to do this conversion. The prop shaft is different from the motor you have and the newer lower unit you purchased. The older one is clamped on while the newer is reversed thread. As Ron stated before, there is a 13mm K&B for sale here on RCU for under $100. Could be a good buy to just play with.
    Mark Scott - just a nut for outboards
    A.D.I.D.A.S...


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