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  1. #1

    Default 1978 500 blue band - clean carbs?

    A few weeks ago it wouldnt start at all, so I took down the carbs and cleaned them - now it idles fine, but wont perform in the water. When going real slow in the harbor it lasted about 5 minutes under load, but hesitated and bogged down and died at the end. Managed to start it up and got to my spot. Tied it up and slowly increased throttle, it would pull hard on my lines, died when decreasing throttle though. Took it out again, going slow out of the harbor, immediately died when attempting to speed up out of harbor.

    At this point I tried to get back, but it wouldnt start unless I put the warmup throttle lever straight up. Couldnt get it into gear without dying. Squeezed primer bulb which seemed stiff, finally got it into gear by throttling up with the warmup lever and then putting it into gear. Limped into harbor and pulled the boat out.

    Gas is new, battery is fine. Have ordered new spark plugs, but still run on old ones.

    Did i screw up the carb cleaning? Just blew compressed air through the most accessible ports after removing bowl, float and needle. Do I need to disassemble it further to access additional valves / jets? Let it stew in gas for a few hours.

    I tightened up the fuel lines and replaced all carb gaskets after, but Ive yet to try it out. Any ideas?

  2. #2
    Join Date
    May 2015

    Default Re: 1978 500 blue band - clean carbs?

    Do the carbs have mix adjustments? If so open them another 1/4 turn.

  3. #3

    Default Re: 1978 500 blue band - clean carbs?

    Yep, I did so after last time, they are 1 3/4 out from seated now. I haven't been able to try it out yet though, I thought I'd ask here first because of how unpleasant it is to get stranded out on open water...

    Got a question though, took some pics of my carbs:

    Click image for larger version. 

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    I've understood that B is the idle mixture screw, it's the one that is 1 3/4 out from seated. What's the other screw? Is there any more adjustments possible on these carbs? They're tillotson carbs with a blue fuel inlet cover.


  4. #4

    Default Re: 1978 500 blue band - clean carbs?

    Sorry for bumping, but does anyone have an answer for my question above, about the carb screws?

  5. #5
    Join Date
    Sep 2010

    Default Re: 1978 500 blue band - clean carbs?

    B is the mixture adjustment.-----The " other screw " would have been removed during a proper cleaning of the carburetor.-------If it was not removed you need to revisit your carburetor cleaning work !

  6. #6

    Default Re: 1978 500 blue band - clean carbs?

    Thanks, it was removed and I blew compressed air into the orifice behind it.

    Took the boat out yesterday - it worked perfectly! Maybe a too little gas at idle, it died after idling for 5 minutes at the lowest possible gas. Fired right up again though, so no problem.

    A question about the mercontrol box throttle though - I think the cables might be worn out or misadjusted.

    When in neutral it's pointing straight up. When put in forward gear, 0-45 degrees angle from that point gives like 0-15% throttle, then 45-85 gives say 15-50% gas, and 85-100 gives 50-100% gas. Is this correct? Shouldn't the throttle be more evenly distributed across the range?

    Also, the plugs installed when I bought it were all NGK B9HS-10. I bought BUHW-2 since that was recommended. Why would the previous owners put in the NGK B9HS-10s, is there any benefit to it except they're a bit cheaper?


  7. #7

    Default Re: 1978 500 blue band - clean carbs?

    Max- Do yourself a huge favor and change the fuel lines on your motor if you haven't changed them recently. Mine (same motor) suffered disintegrating lines and clogged my carbs up with pieces of hose that looked like black fingernail clippings. May be attributed from using "gasohol" instead of "straight" unleaded. I think I paid less that a buck for a 15" piece of fuel line from an auto parts store. Much easier than taking the carbs off all the time.

  8. #8
    Join Date
    Sep 2010

    Default Re: 1978 500 blue band - clean carbs?

    ??----The first part of the lever motion put the motor in gear.----Then throttle is applied.----And it sounds very correct to me in the way it works.

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