1978 johnson 9.9 stalling on top end

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

what is meant by the 1.5" float drop. Not familiar or maybe I'm just not remembering....def seems like a fuel problem though....somehow haha

 

[woodsyfeller]

Re: 1978 johnson 9.9 stalling on top end

A really good site for that series of outboard is here http://www.sschapterpsa.com/ramblings/OMC/OMC info.htm its an excellent resource for the 9.9 /15 hp motors

 

[Will Bark]

Re: 1978 johnson 9.9 stalling on top end

You set the float level when you "inverted" the carb, now turn the carb upright and measure how far it "drops"; adjust the other tab so that the float drops down as far as it will. Your engine may be calling for more fuel than the carb can supply at WOT. woodsyfeller gave you a great place to go and somewhere in there Leeroy will talk about what I'm describing. He is a master on the 9.9/15 hp engines.

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

does the 9.9 have a reed valve? I haven't yet seen a diagram of this if so

 

[Will Bark]

Re: 1978 johnson 9.9 stalling on top end

The reed valves are internal in the engine behind the carb; they rarely give any problem unless something gets in there and damages them or "sticky" fingers have to touch or bend them and then they are done.

 

[the machinist]

Re: 1978 johnson 9.9 stalling on top end

Check the mainjet, someone could have tried to increase the hp by just changing the mainjet to a 15hp. This will not work as you also need a carb with a larger throat to be able to accept more fuel.

Sorry, but I can not readily place my fingers on the sizes of these mainjets (Orfice Plugs as tghe factory calls them)

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

So i was looking at the pic of a restored 9.9 online and noticed that the fuel pump looks a little different in orientation than mine.....specifically that the small hose to the carb is coming out the top whereas mine comes out the bottom. Would this orientation cause any problems? I can't find a picture or diagram of an assembled pump to verify. Thanks again!

 

[Haffiman]

Re: 1978 johnson 9.9 stalling on top end

Fuel pump and lines will only come into question if engine performs with the hose and bulb hooked directly to the carb using bulb as pump.

 

[the machinist]

Re: 1978 johnson 9.9 stalling on top end

These fuel pumps have the strainer/outlet so it can be rotated into 4 different locations. It doesn't matter which one as long as the fuel lines are not kinked. Usually this outlet is placed differently on the rope start as compared to the electric start becasuse the electric start has a rectifier very close to the rear of the fuel pump.

As for the stalling, my things to look at are (1) running on a single cylinder, (2) carburetor not functioning properly (3) carb/timing plate cam (sync & link) needs adjustment (4) fuel line air leak (5) possible rusty ground at powerpack/coils to block

LeeRoy

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

I ran the boat today and tried removing the hood...changed nothing....removed spark plug wires one at a time....u know how that went....shocked the **** out of me! haha Got great spark all way up as far as i can run it. I did notice that it ran a little better though so I ran it thru its paces several times. As i slowly advance the throttle and watch teh throttle cam, as soon as the roller gets to the ramp on the throttle cam it bogs out and tries to die after about a second. I ran it slowly and quickly thru this routine. If I grab a lot of throttle quickly it will rev to the moon and then choke out and as soon as I let off the throttle it comes back to life at idle. Seems much like it's getting the fuel for a moment and then losing the adequate amount. But...since it revs to full for a moment before it bogs out when I quickly do it seems to me that it is able to pass fuel for a moment and therefore the jets aren't clogged. Fair deduction? I feel like maybe the fuel pump or float setup. Any opinions. I really hope this helps! Thanks in advance.

 

[Haffiman]

Re: 1978 johnson 9.9 stalling on top end

Is it bogging down due to lack of fuel or too much fuel?
Added:
Does it help choking it as you increase the throttle?

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

choke kills it instantly

 

[Rick.]

Re: 1978 johnson 9.9 stalling on top end

It would be a good idea to throttle it up let it die and immediately check the plugs to see if they are wet/dry/flooded. Although I don't want to lead you astray, I am of the opinion your issue is your carb. and cleaning it again would not hurt. For now I would probably leave the air silencer off as well to see if fuel is spitting out the carb. intake and you can see the position of the throttle plate easily. Rick.

 

[Haffiman]

Re: 1978 johnson 9.9 stalling on top end

choke kills it instantly

May be that 'someone' has been changing out your main jet or been a bit rough when cleaning it. Do as suggested and monitor the fuel flow through the carb, (without silencer box) when giving throttle.
Perhaps just too much??

 

[RandyJ]

Re: 1978 johnson 9.9 stalling on top end

Just subscribing. I've had the same problem with one motor and never got it fixed.... please stay with this until you fix it and post your solution!!!!

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

you can count on that. once i start a project i don't stop til it's done 100%!!! Keep me posted on anything you find.

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

doesn't seem to have any fuel spitting out of the carb. I run it without the silencer all time as i am always adjusting it. Adjusted fuel mixture screw from .5 turn all way to 2.5 turns very slowly and waited in between and seems to run best and smoothest at 1.5 ish. Still stumped.

 

[jmendoza]

Re: 1978 johnson 9.9 stalling on top end

I'll re-post the troubleshooting step, and until you try this, you are just spinning your wheels so read and get back to us once you have done this:

To eliminate the carb, hook up an external fuel source to it, thereby bypassing the fuel pump, ansd see if that cures it. Of course, you will have to gravity feed, or pressure feed by continually squeezing the fuel bulb.

This means running a fuel line directly to the carb. Later on, if you suspect the fuel pump, or an air leak in the lines, try using a shoirt piece of clear line between the pump and carb to see if you are getting air bubbles in the line.

A very common problem is a gas cap that is not open enough to vent the tank, and faded orings on the fuel line fittings, and hard fuel lines at the fittings not sealing.

 

[Will Bark]

Re: 1978 johnson 9.9 stalling on top end

stratos, refer to my post #18 I never saw where you even mentioned trying the float drop opening to see if you were using more fuel than the carb bowl could supply; did you try it and it not help?

 

[stratos201s]

Re: 1978 johnson 9.9 stalling on top end

yep. ran the clear line and got a clear stream (blue actually) to the carb. Removed the gas tank cap completely and replaced all the fuel lines. Will try the external fuel source asap and let you guys know. Thanks again