1978 johnson 9.9 stalling on top end

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

have not ran the float drop test yet. will do asap though. thanks

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

Just checked the float drop and looks like it's droppin fully. Moves a little over an inch. Pulled the main jet and I was wrong before about the kit having a new main jet. It is the old one. It is a 56. I don't know if that's right or not but it's what is in it. I'll try again lookin up the size for a stock 9.9. Hopin that's a 15 hp jet and will solve haha. Currently soaking the carb in mineral spirits to try to break the stuff free. Will blow out in morning and see. Also pulled the top core plug out (the large one) and it looks good inside. I'm assuming there isn't anything behind the core plug normally???

 

[Haffiman]

Re: 1978 johnson 9.9 stalling on top end

While having the carb down and in pieces, do the following:
Put a plastic hose on the tube going up in center of the carb.
Block the end where the main jet is.
Try to 'suck' at the plastic tube.
If any leakage, it will not suck fuel but air when running.

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

took the boat out today and checked it over good. I noticed that there is an orifice to the left of the mixture screw (when looking at it from the front) This carb had a rubber stopper sorta thing in it so I removed it. Started garbling and sputtering so I put my finger over it and it ran just like always. I played with the throttle and moved my finger around on the orifice to get it just right and boy does this thing fly!!! I've had a few newer 15 hp jons but this one will dust them all haha. It's definitely the carb. I dunno what this orifice does tho and what should be in it. Seems like there should be a ball valve or something that changes position as engine load goes up. Can anyone help me out....I think I've narrowed it down really close. Thanks.

 

[Haffiman]

Re: 1978 johnson 9.9 stalling on top end

It is the air inlet for the idle/intermediate circuit. What was inside, may have been a piece of the gasket #41.
Remove and readjust your needle valve.

 

[SalmonAssassin]

Re: 1978 johnson 9.9 stalling on top end

Im having the same problem with a 70hp evinrude.. ive replaced coils,diaphram,plugs(Gapped), all fuel lines and plastic connections, new tank ,new bulb, cleaned carbs (No new jet) But they were spotless inside, Im stumped too... If you figure it out let me know..

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

removed the needle and cleened/blew out with 100# air and readjusted....and nothing. Still stumped tho. It had a rubber cap like a small vacuum tube block off cap.

 

[the machinist]

Re: 1978 johnson 9.9 stalling on top end

Some of the 9.9/15 carburetors have a vent on the lower side to relieve pressure inside the float bowl. Some are just a hole, while the later ones have a black plastic Tee. If so equiped, these need to be open to the atmosphere. or you will not be able to draw enough fuel in fast enough

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

this hole is on the top front side right next to the mixture screw above the carb mouth. Is this the air inlet for the mixture screw? Can't find a diagram that shows exactly. Thanks.

 

[Haffiman]

Re: 1978 johnson 9.9 stalling on top end

What probably happened when you got it running was that you managed to get the main circuit 'started'.
Did you ever check that it is no air leakage in the tube in the carb throat?
Remove the main jet and double check!!

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

ran it by poking a tiny hole in the rubber cup that was inserted into the hole next to the mixture screw and it ran EXCELLENT. What does this mean for the carb? Am I missing something there that throttles air or is it just coincidince that it worked?? Thanks. Haven't checked for air leak yet on the main jet

 

[Haffiman]

Re: 1978 johnson 9.9 stalling on top end

ran it by poking a tiny hole in the rubber cup that was inserted into the hole next to the mixture screw and it ran EXCELLENT. What does this mean for the carb? Am I missing something there that throttles air or is it just coincidince that it worked?? Thanks. Haven't checked for air leak yet on the main jet

'Poking' that hole might have just created enough vacuum to get the main jet system started.

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

So if I just started up the main jet system, what do I need to do to make this thing work right as from the factory. I sorta see what you;re talkin about but kinda having trouble visualizing it. It ran EXCELLENT today after poking the hole in the rubber "cup". Ran 22 on the water. Any recommendations? Can I get more speed out of it? Thanks!

 

[Haffiman]

Re: 1978 johnson 9.9 stalling on top end

Not being at the engine makes it a bit difficult.
It might be an air leakage in the center tube down to main jet, it might even be that the center tube has been slightly bent pointing outwards, the air flow gets pushed down the tube and not creating a 'drag' of fuel up. It might even be something 'stuck' inside the air channel. What seems to be for sure is that it is a carb problem.

 

[the machinist]

Re: 1978 johnson 9.9 stalling on top end

If I understand this correctly the rubber part you a referring to is #315232 "Retainer, Needle Valve". This is simply a rubber insert that is inserted into the needle hole, when you thread the needle valve (idle jet) into it the needle threads conform to the rubber & keep it from backing out. Like in the old days where there was a coil spring between the needle head & the carburetor body.

I don't understand how a small hole in this (which would allow some air into the idle side) would have any effect on the high speed running. However if this hole is making a difference, you have a problem with the carburetor, like internal passages plugged & or the needle tip bent or broken.

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

No I have that part. It's actually a 1/4" hole right next to the needle valve. If you look at a diagram it doesn't label it or show anything in it. It definitely has a slight suction on this hole as you can put your finger over it and change the way the motor runs completely. It looks just like a black rubber vacuum line block off for an old vehicle carb vacuum secondaries turned inside out and pressed into the hole. Still researching.

 

[AlTn]

Re: 1978 johnson 9.9 stalling on top end

the high speed jet <orfice> is part no. 322752 id. no. 38 for the 9.9, for the 15 hp. the part no. is 322293 id. no. 54....this 1/4 " hole you refer to being next to the low speed mixture needle....is this located on the top, rear of the carb where the needle enters a small metering "well" with 3 small holes ?..if so..there should be a small metal disc <core plug > blocking that opening and no vacuum should exist there

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

No the hole is on the front face of the carb where the silencer mounts and would normally cover the mouth of the carb. The hole is at the 11 o'clock position to the mouth of the carb......just to the left of the mixture screw knob if you're looking aft. Thanks.

 

[OptsyEagle]

Re: 1978 johnson 9.9 stalling on top end



Are you talking about the hole I marked "Hole #1" in my picture? I don't think I have anything in that hole on my carb. I don't recall anything rubber that could be poked.

 

[AlTn]

Re: 1978 johnson 9.9 stalling on top end

there's no hole there on the '78 9.9 I've worked on...did you note the original main orfice size for a 1978 9.9 ?