Home › Forum › Ask A Member › 1976/77 OMC 9.9 & 15 carb needle valve bearing
- This topic has 17 replies, 9 voices, and was last updated 7 years, 12 months ago by
rudderless.
-
AuthorPosts
-
May 5, 2017 at 1:55 pm #57145quote FrankR:Good job, and good report. I always just shoved the new one in with a rod or punch till it bottomed out. Don’t know if that is the approved way or not. Thanks.
Frank I will always take your way as the approved way any day!
May 6, 2017 at 4:18 pm #57201quote joesnuffy:Retiredoz,you may be right . I am guessing your talking about the cup seal being not used in 79? I do know that it seems like the carb was changed 3 times in a serious way for basically the same power head that was used on 9.9s from like 75 to 91ish to 95ish other than the ignition systems going from points in the 75 then 85 and 91 were also different from each oher I am guessing both were a type of cdi type set-up for 85 and 91. I couldn’t tell much of a difference when setting up the motors regarding ignition systems other than getting the timing of the carb butterfly opening at the correct time with relation to the magneto plate rotation. The big difference to me on slow engine idle was how well the 95 carb performed much better than the 75 85 and 91 carbs.
Again, the whole carb was redesigned in 1987, so the plastic cup seal question discussion only applies to the 74-86 models with the aluminum body/tin float bowl. The question is how engineers were able to eliminate this seal without making other changes to the carb body that would help prevent outside air from entering the mixing chamber through the needle valve/carb body threads. The idle circuit plumbing was changed on these style carbs sometime around 1980, the fuel was drawn up the to idle circuit through a brass tube that ran right up through the venture. The older carbs had a cast in passage in the carb body instead of the brass tube. So, I am guessing this change was simply a cost savings, but the change would not seem to be a substitute for the low speed needle cup/seal.
The "modular"/CPS carbs were introduced in 1987, and that is when all the trouble/reliability issues began. What once was a simple, reliable carb, was now troublesome, and more complicated. The low speed needles on the newer carbs threaded directly into the plastic tops, the plastic threads posed much more interference/tightness when threading the needles in place, which also created more plastic debris floating around. I’m "guessing" this tight interference fit was how the engineers justified not adding some sort of sealing system to the low speed needle.
To be fair, the modular carbs got many improvement over the years, but still not as simple and reliable as the original style.The modular carbs were changed again when the engines were redesigned in 1993. The 1993 carbs had a design flaw which created an air leak in the plastic top, the only fix was replacing the carb assembly. Needless to say, all these carbs should have been replaced free of charge, but many of the defective carbs that were replaced are floating around on dealer’s shelves now, I see them for sale every once in awhile. It was with this new engine/carb design in 1993 that the needle valves were moved to the side of the carb under the engine cover. I suppose one could argue both sides of the debate regarding this being an improvement. I suppose it does keep the owner from easily messing with the mixture, but also makes it more difficult to make minute adjustments that might actually be necessary depending on temp/weather conditions. These 93 and newer carbs will not fit on the older models. The choke linkage is different, and I don’t think the older air box will fit onto the newer carbs. I really can’t think of any reason why one would want to replace the simple reliable carb design with one of the newer style carbs, I don’t think these new carbs offer any idling advantages when compared to the original design.
May 7, 2017 at 3:40 pm #57249Thanks Fleetwin that clears it up for me. Always appreciate your knowledge.
I haven’t worked on many of these motors so I don’t have a lot of knowledge of them and opted to sell all 3 of mine while in Key West this winter which is where I stored them on a military base in the storage lot last summer. They were all 3 salt water engines (not my favorite) that were given to me as non-working by a fellow camper we camp with. I fixed them up and got them running and was using them on a 11ft boston whaler I purchased down there from the guy that gave me the motors. He owns a marina in RI. I sold the whaler this winter also to a liveaboard. Someone that is good at repairing small outboards can stay as busy as they like down there because like 1/3 the town lives on mainly sail boats moored on moorings down there and dingy to land daily. We normally camp on base down there for a few months in the winter with a water view. I have made friends with a few of the liveaboards and help them from time-to-time with their dingy motors and make a few bucks in the process.
Thanks for the help,
JoeMay 11, 2017 at 12:51 am #57479Now THIS, is a topic right up my alley.
I have fixed about 100 of these over the last 3 years. Not as many as some of the gurus of this forum, but to add my $0.02.
I agree, the carb change WITHOUT the low speed needle bearing seems to show up in ’79. HOWEVER, I JUST NOTICED that depending on the production line between 1974-1978, you MAY have a carb with a smaller mouth on the back of the carb. I only noticed this on the 9.9 carbs….haven’t handled enough 15hp carbs to notice a difference. The 1974-1978 motors seem most sensitive to the carb configuration.
Some production models have an AFT carb barrel with a smaller diameter. Did anyone know this?
My conclusion as to why later (as in, post ’78) carbs across the board DON’T need the low speed needle bearing has to do with the the orifice plug. These change depending on year.
NOW, granted, the ORIFICE PLUGS primarily affect the lionshare of fuel for high speed (which I surmise, affect top end power), we all know that the main jet controls the lionshare of fuel, and perhaps the low speed circuit, sort of, provides fuel in concert based on this orifice plug…? I would assume this mirrors when they introduced leaf valve shims, and a tuned exhaust.
But I’ve got about 50 9.9/15 carbs here, and there are a lot of variations of these carbs, despite what M.E. parts lists indicate.
I have had to transplant so many different combinations of 15hp carbs on so many different 9.9/15hp powerheads, that I don’t bother to use service manuals on initial test tank calibrations just to get the motor running. For instance, the old service books say a 9.9 uses 1 turn out, a 15hp uses 7/8th. Well, try putting an ’89 carb on a ’77 model or vice versa. Watch what happens. There is no rhyme or reason, in many instances, the low speed needle needs to be 1.5-2.5 turns out. Now the low speed needle TAPER seems to be the same across all years. Forget about post ’92/’93 models (totally different).
WHAT I LOOK FOR is if the motor starts easily or does it run in an odd manner (i.e. , inconsistent starting, bogging, bad idling, etc.). 99.9% of the time, REGARDLESS of what ‘generation’ of powerhead/exhaust housing combination you have, and whatever carb you are putting on it (in the 15hp variety), if the motor is running odd, it’s probably because the carb is missing that low speed needle bearing.
KEEP IN MIND, I am talking about if your ignition system & fuel system are fully rehabbed (which they are before I try anything), and there aren’t any bizarre situations going (i.e. air leaks somewhere). AND timing is set correct in terms of a typical link and sync (more difficult on the old metal cam follower style motors…plastic cam followers, while not as durable, are far easier to calibrate).
May 13, 2017 at 10:35 am #57632After rebuilding the 1977 9.9 carb with the new needle bearing installed as i posted ,it ran and idled well in a barrel.
Then when i next did the 1976 15 carb, when i went to use the screw removal maneuver, i did not feel a bearing down in there. HUH? I looked with a flashlight,slid a piece of safety wire down the side of the hole to see if i could hit one,i did not. I swear it was missing. Not to mention the new needle bearings in carb kits are a clear color ,the original one i found in the ’77 9.9 was brown,much easier to see with a flashlight.
So i figured the bearing was missing and installed one exactly as i did on the 9.9. It won’t idle now ,and did before the rebuild,how odd. The slow speed needle is at 1.25 -1.5 turns out. The only other things i did on the motor was to set the carb sync better. i put fresh plugs in and rebuilt the water pump and removed the t stat and checked to see if it was stuck. I did check the timing and one cylinder was off a bit and i plan on trying to get that closer before his next outing. i also removed the new needle retainer as it was so tight i could not turn the needle by hand. I replaced it with the old one ,turns fine now.
I guess i will remove the needle bearing since it idled well before? As i recall this carb had been rebuilt before as it had a plastic float. Or did i damage the new bearing when i installed with it sitting in place on the needle? Maybe i should have put a bit of outboard oil on the sides of it so it would slide into it’s location in the hole better.
I did clean the carb very well with a soak in BRP Engine Tuner ,checked all passages carefully with the smooth end of small orifice drill bits and blew dry.
Anybody have some idea what i did wrong.
*** Also would like to hear how you guys install the new needle bearings*** Thanks ,Jim PSB"Some people want to know how a watch works, others just want to know what time it is"
Robbie RobertsonMay 13, 2017 at 10:57 am #57633When you say wont idle, do you mean stalling out?
I install those small needle bearings by just putting it on the needle and pusing it in without the larger retainer first. Then I install the needle with the rerainer and it goes to where its supposed to.
If it is stalling try backing the needle out more. Sometimes I have to set them at 2.5-4 turns out. May not be the originalcarb on that motor?
Just fixed a 9.9 and needed to replace the carb because the original was toast.
Well I have a bin full of these carbs – used one withthe needle bearing. However, I found some without and with different main jet orifice jets. One had a #40 with a short inside main pickup tube, another had #51 with a long pickup. I tried swapping the main jet orifice jet and the motor ran erratic. Swapped back and ran coompletely fine.
Further confusing is ME says for 1975, it uses a #51 carb. Well it wouldnt run right with this one on it, even when on a long pickup tube version.
My guess is as good as yours as to why these changes were made year to year. Maybe corresponds to the leaf plate shims and tuned exhaust updates? This was a 9.9 motor and carb, 1975. Perhaps to promote better idle but then again the 9.9’s didnt get these updates like the 15 until ’89?
May 13, 2017 at 11:14 am #57634Well, first, are you working on a 76 15hp, or a 77 9.9hp? I guess it does not make much difference carb wise though. The engine idled OK before the carb job, correct? I guess I’m wondering why you pulled the carb apart if it was idling OK. In any event, it won’t idle now….Does it seem too rich, or too lean….Will feathering the choke help it idle? Or, if it is too rich, perhaps you can turn the needle valve almost closed without it leaning out much.
There is the possibility that something else went wrong while doing the carb work, although that doesn’t seem likely. I guess the simplest thing to do would be to try a different known good carb….
I can’t imagine it would do any harm to add one of the cup seals on a carb that was not equipped with it originally, but who knows….Perhaps the cup seal is covering/blocking a fuel/air passage messing up the idle. So, I think it best to try peeking inside to ensure the cup seal is properly installed….If so, go ahead and remove it, then try running again….I suppose it is possible that someone installed a newer carb on this engine….
Let us know, this IS an interesting topic, sure hope we can get some clarification on the cup/seal usage…May 14, 2017 at 2:32 am #57680Many needle adjusters have a spring to hold the screw adjusters position. Since the threads are tapered and the spring pulls the adjuster against the threads the needle adjuster will normally stay in the center of the jet opening. Like in the needle tip being concentric with the passage.
Without a spring loaded needle adjuster and the needed running clearance at the threads the needle tip can orbit or become non-concentric in the jet or passage opening while adjusting or just in normal operation from vibration. That "bearing" as its called keeps the needle tip in the center of the jet opening.
When I received my motor in a box there were two needle bearings in there. One was sideways with a hole pierced through it…
-
AuthorPosts
- You must be logged in to reply to this topic.
