9.9 Johnson Carb Question

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This topic contains 74 replies, has 10 voices, and was last updated by Avatar outbdnut2 2 years, 2 months ago.

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    outbdnut2
    US Member - 2 Years
    Replies: 1139
    Topics: 57
    #59129

    I’ve wasted way too much time on this motor lately. I’m going to loan my friend a motor to fish with for awhile and let his 9.9 sit for a week or so. AT this point, I need to get in a better frame of mind to work more on it.

    Also – 9 motors followed me home last week from a batch of about 30 a friend came up with cleaning out his Dad’s garage. I’m anxious to see which can be restored and which are parts motors.
    Dave

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    optsyeagle

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    #59187

    I can’t say it will fix your problem but if I was having a slow idle problem I would definitely remove the welch plug and the slow speed needle bearing and clean them cavities out well and replace them with new ones. It is not difficult to do and the parts are maybe worth $10 in total. Keep in mind that the slow speed needle bearing is made of plastic and plastic parts are not fond of carb cleaner. A little is fine but maybe someone soaked that thing in carb cleaner over a few days. Not sure a plastic bearing would hold up well with that. In any case, just replace it. Might as well replace the retainer needle valve as well. It is also made of plastic and is critical to maintaining a good seal. If air sucks past that it will never idle well.

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    outbdnut2
    US Member - 2 Years
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    Topics: 57
    #59199
    quote OptsyEagle:

    I can’t say it will fix your problem but if I was having a slow idle problem I would definitely remove the welch plug and the slow speed needle bearing and clean them cavities out well and replace them with new ones. It is not difficult to do and the parts are maybe worth $10 in total. Keep in mind that the slow speed needle bearing is made of plastic and plastic parts are not fond of carb cleaner. A little is fine but maybe someone soaked that thing in carb cleaner over a few days. Not sure a plastic bearing would hold up well with that. In any case, just replace it. Might as well replace the retainer needle valve as well. It is also made of plastic and is critical to maintaining a good seal. If air sucks past that it will never idle well.

    Thanks for the info about that bearing. Up until I came across this thing, I never hears of one being there. I will try another know good carb (borrowed form a good running motor) and if the good carb works, I will take the welch out of the bad carb. I have a lot of various size welch plugs left over from many carb kits where I didn’t need to pop them out, so I’ll find something that works. Is the bearing and retainer in OMC or Sierra kits? or do I order that separate?
    Dave

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    optsyeagle

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    #59609

    Sorry for the delay. They should all be in a kit but you can order them separately as well.

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    joesnuffy

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    #59670

    I have noticed that magneto timing on these motors is also very important to get them to idle correctly. When the carb roller cam follower is lined up with the timing index mark (not really sure what mark on timing plate is called that roller rides on to open carb) the carb butterly should be shut and be on the verge of opening once you advance the timing a tad more. The carb butterly has to be shut when lined up with that timing index mark to make the carb use the low speed circuit correctly at idle speed on those particular motors. I have almost pulled my hair out getting mine to idle correctly that was a crucial part of it.

    The bearing needle valve and the needle valve retainer must also be in good condition for a good idle. As someone mentioned carb cleaner destroys them. I destroyed a brand new needle valve retainer in seconds with carb cleaner.

    Good grounds on all ignition components are also critical as you mentioned. All 3 of mine were salt water motors and the grounds especially for the ignition coils had to be cleaned up with sand paper and a file. If in doubt thoroughly clean all the grounds then you can rule that out. The component might be bad but not the ground.

    Just my 2 cents and I hope that helps,

    Joe

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    outbdnut2
    US Member - 2 Years
    Replies: 1139
    Topics: 57
    #59686

    Thanks for the tips Joe. I’m thinkin’ next week I’ll dig into that motor again. Had to stop to get some other stuff and other motors done, and to get in a better mental state regarding that motor, as I’ve spent too many hours on it curing this and other problems. That timing mark/roller cam alignment is correct, but it’s at the far end of the adjustment, which on this early 9.9 is a screw tightened into a slot on the part that has the arrow on it. Thinking more about it, there could well be some slop in the linkage from the rollercam to carb throttle plate that is messing up the adjustment. This does not have the adjustment screw on the roller assembly that later models have. To take up slop in the throttle linkage, the only way I see to do this is to bend the small rod that links the roller to the carb throttle plate. I’ve seen this bending of a rod as a standard procedure on some automotive carbs I’ve rebuilt.
    Dave

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    PugetSoundBoater
    US Member - 2 Years
    Replies: 979
    Topics: 135
    #59689

    All those cam follower rollers that i have dealt with have slop. What i do is get the roller touching enough to take the slop out before it hits the mark. It takes patience to get it right.

    "Some people want to know how a watch works, others just want to know what time it is"
    Robbie Robertson

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    fleetwin
    US Member - 2 Years
    Replies: 2715
    Topics: 33
    #59706

    The throttle cam pick up is adjusted by loosening the two little screws that secure the throttle cam to the mag plate. One screw hole is slotted so the cam can be moved in and out. Some of these screws are pretty tough to get at without removing the flywheel….I would not bend the link rod to make the adjustment, would be pretty tough to get it right.
    For now, I would just make sure the throttle is closing completely at idle….I would not be too concerned about the throttle plate starting to open too late…But, the engine surely won’t idle if the throttle plate is not closing completely at idle.

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    PugetSoundBoater
    US Member - 2 Years
    Replies: 979
    Topics: 135
    #59714

    I use those small ignition wrenches on the adjusting bolts for the cam. I had to grind one thinner so it would fit in there,it is a tight fit as you know.

    "Some people want to know how a watch works, others just want to know what time it is"
    Robbie Robertson

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    joesnuffy

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    #59722

    Great tips and advice from everybody. Keep us posted.

    Joe

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    outbdnut2
    US Member - 2 Years
    Replies: 1139
    Topics: 57
    #59725

    Last week I ground a wrench thinner so I could loosen the throttle cam bolts. I’ve got it at the far end of the slot (throttle cam sticking out toward the roller all the way), and it is now about .010 inch from touching the roller when at the arrow. The throttle is closing completely at idle – I checked that the first time I took the carb apart. The idle seems to go bad with decreasing throttle just as the throttle plate goes completely shut. I will pull the welch plug and check the bearing on the low speed needle and see if I can further clean passages while the plug is out, there could still be some stuff in the idle gas passages. I cleaned a lot of junk out of the carb – so much dark brown stuff crystalized around the float needle, that it was seized up. Also will check compression – haven’t done that yet because after a lot of effort I have it running so darn good at fast idle and above.
    Dave

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    fleetwin
    US Member - 2 Years
    Replies: 2715
    Topics: 33
    #59773

    The symptom you describe was a common one on many of the older 9.9/15s I worked on: The engine would fall flat/maybe stall while decreasing the throttle slowly and the engine was relying more on the idle circuitry. I usually had to readjust the idle mixture a tad rich to compensate. Your throttle pick up is a bit late/retarded (.010 between roller and cam at pick up point), but this would cause the opposite condition: rich at midrange. The only other thing I remember is that some of these earlier throttle linkages were prone to sticking (throttle plate not closing/sticky), this can be due to all the crazy add on safety linkage. So, just because there is a gap between the roller and cam does not mean the throttle plate is closing completely.
    So, does the engine idle OK now? Is this midrange thing the only problem? If idle is still NG, I would look for a different carb to try. If the engine idles OK with a different carb, then we can dig deeper into this carb…

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    outbdnut2
    US Member - 2 Years
    Replies: 1139
    Topics: 57
    #59780
    quote fleetwin:

    So, does the engine idle OK now? Is this midrange thing the only problem? If idle is still NG, I would look for a different carb to try. If the engine idles OK with a different carb, then we can dig deeper into this carb…

    I haven’t worked on it for a week or so, but still have the bad slow idle. I was thinking about, as you also suggested, trying a different carb, but the only similar motors I have to rob a carb from are 15 HP models (have 5 of them from a failed resort) and these are 1989-1991, where the 9.9 is a 1977. My 15s have the larger diameter cam-follower rollers, and the carbs are a bit different, but look like they will bolt right up and can be made to physically fit. To temporarily swap carbs between these motors, will this give me a fair idle comparison? I know the only difference between 9.9s and 15s back then was the carb, but there were several carb changes over the years these were made.
    Dave

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    garry-in-tampa
    Lifetime Member
    Replies: 3147
    Topics: 30
    #59792

    There were also differences in the reed valve opening and the exhaust tuning. I don’t mean to discourage you, but the 9.9 model always seemed to idled better than the 15. . . 😕

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    fleetwin
    US Member - 2 Years
    Replies: 2715
    Topics: 33
    #59793

    The later model 9.9/15 carb will bolt on up to 1992. You could just use your roller and link instead of whatever is with the later carb. We are talking about dead idle here, so the cam should not be touching the roller and pick up timing is not an issue. I am not sure just what the initial needle setting is supposed to be on those later plastic top carbs, might be different than the 1977 spec.
    And yes, there were several changes made that distinguished 9.9s and 15s during the years, but I don’t think that will affect any given carb’s ability to give an OK idle.
    So, give it a try, will only take an hour or so…..

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