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1990 8hp Johnson won't idle/stay running

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bcontento

Contributing Member
I was sure I posted this last night, but I don't see it. Sorry if it duplicates.

I have a 1990 8hp Johnson that ran fine a couple of years ago, then started acting up (surging, hard start, bad idle) and then it sat since then. I decided to get it back on the water. The motor will kick over (hard) with some starter fluid but will not run for more than a couple of seconds (even by misting some starter fluid to the carb throat). Here is what I've done to try to work through it:

- new correct plugs
- testing spark (jumps gap)
- replaced fuel pump (Sierra 18-7350)
- cleaned and blew out fuel line from pump to carb. With the primer bulb, I get good fuel squirt from that hose
- removed carb, opened it up and cleaned it out and blew it out best I could without a rebuild kit

no difference. Is the next step to do a full rebuild on the carb? Other ideas?
thanks all!
 
First thing is quit using starter fluid. These engines run on a mix of gas and oil to lubricate them. You'll fry the piston using that stuff.
 
Yes clean the carburetor.-------There may be a wee rubber tube inside that needs replacing.---Item # 26.--------And clean all small holes that feed fuel up that tube.
 
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As I've experienced on these motors that have "slept" a while, it often takes more than one shot at carb cleaning, and be very thorough with the cleaning: As experts will tell you, it takes more than spraying and blowing. Make sure to drive something like a strand from a wire brush through every jet and little hole you can see, and DEFINITELY use a rebuild kit. You won't do a complete clean up without removing both welch plugs (that come in the kit) as they give you access to the tiny ports that may be clogged after that period of time.
If you want to put the potential ignition problem out of way, just pour a bit of mix in both cylinders through the spark plug holes (a syringe is ideal for this) and see if it fires up for second or two.... If it does, back to work on the carb! Good luck.
 
thanks guys. I only used a tiny bit of starting fluid a couple of times. No worries there and I've squirted some mix into the cylinders to keep them lubed. I'm going to tear the carb down again fully and see how it goes.
 
ok, so for a guy (me) that has torn apart and rebuilt "real" carbs (like big four barrel holleys and such), I'm embarrassed to say I know why it's not running and that I missed it the first time I opened the carb up. The main needle valve operated by the float was completely stuck shut and the rubber tip was half-broken (all the way broken when I pulled it out). Needless to say, rebuild kit is on it's way.
 
bcontento said:
ok, so for a guy (me) that has torn apart and rebuilt "real" carbs (like big four barrel holleys and such), I'm embarrassed to say I know why it's not running and that I missed it the first time I opened the carb up. The main needle valve operated by the float was completely stuck shut and the rubber tip was half-broken (all the way broken when I pulled it out). Needless to say, rebuild kit is on it's way.
Click to expand...

Yeah the kit is a must after a long period of inactivity, particularly that needle valve.... Glad you found the issue, let us know when it runs like a top!
 
ok, got the carb rebuilt and reinstalled and got her running. I have two issues. First, it wont idle low and stay running. As I understand it, there is one mixture adjustment screw (on the left top of the carb on mine). I think I read somewhere that it should be about 2-3 turns out, but I think I'm more like 4-5 right now to get it running. The other adjustment screws seem to be on the throttle linkage. One is the stop underneath the linkage and one if against the cam roller. Is there a good adjustment procedure someone can link me to?

Second, I've got a broken bit. The plastic "arm" that the throttle roller rides on snapped in the middle (in my hand in the photo below). I haven't been able to find a good diagram of this area. so this is going to be a little confusing to explain. It's actually got me stumped. One one end there is an alen screw that threads threw a hole in this piece (under my thumb in the photo...can't see it) and appears like it would screw into the main body. However, the spot on the main body has a little indentation (red circle in second photo) where the screw would tap in but it's not cut through (there is no hole all the way through). All that happens if I tighten the screw in is that it pushes the arm away from the main body. Is that what is supposed to happen? If so, then the piece that "broke" off can't be fixed/attached at the other end (yellow circle) otherwise it would naturally break off.

Lastly, the motor got really hot I think. It's pissing water great so I know it's pumping, but after running it for a few minutes (granted, much higher revs that I think it should be at idle in neutral), it was noticeably hot. I'm green when it comes to outboards. is this normal?

Any help here would be appreciated. A diagram. A part I can order. I way I can fix it. How I can adjust the idle down and smooth.

20170714_185426.jpg

20170714_185627.jpg
 
racerone said:
??-------That is an adjusting screw and it moves / changes the shape of the cam !!
Click to expand...

ok, I'm good with that but how was the OTHER end attached? It needed to be some kind of hinge but I assume it wasn't Was it just thin plastic that was flexible, hence the breakage?

Any guidance on tuning the carb correctly?
 
ok, so I found a photo of the cam (similar to mine but not exact) and have a much better understanding of how that looks/works.
cam.jpg
 
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