1987 Johnson 8hp frustration

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davesko
Posts: 82
Joined: Thu Nov 10, 2016 9:48 am
Location: Hershey Pa

1987 Johnson 8hp frustration

Postby davesko » Wed Sep 06, 2017 10:06 am

Hello all, I have an 87 Johnson 8hp that won't run without the primer. It's a plastic topped carb. I have cleaned it very well 3 times now and put a kit in it. I paid close attention to all passages and still no go. This motor is new to me and was like this when I got it. I took the carb off my other 8hp and put it on and it runs perfectly. Also I checked for cracks and warpage in all plastic parts. What am I missing???? Thanks Dave

crosbyman
Posts: 637
Joined: Tue Mar 10, 2015 11:39 pm
Location: Montreal Canada

Re: 1987 Johnson 8hp frustration

Postby crosbyman » Wed Sep 06, 2017 12:15 pm

doesn't take much.... did you blow dry all & any hidden passages/cavities

check for warpage on a flat surface

fleetwin
Posts: 1965
Joined: Mon Mar 09, 2015 4:27 pm
Location: Rhode Island

Re: 1987 Johnson 8hp frustration

Postby fleetwin » Wed Sep 06, 2017 12:19 pm

Well, don't feel alone, these stupid carbs are a royal pain in the neck, why the heck did they change from the almost bullet proof carbs with the metal bowls? Oh well, guess we all know the answer....
So the engine runs OK with an alternate carb, good info, and it has always run like this since you got it....That stupid primer has three positions, off, enrichment for warm up, and prime....I am assuming you are pulling the primer knob half way out to the enrichment position to keep the engine running.
The initial problems with these carbs was the funky rubber hose that connects the main jet plastic fuel pick up to the carb low speed tube. These hoses disintegrated, created an air leak causing the engine not to run on its low speed circuit. The hose debris also had a habit of plugging the idle pick up tube also, so the engine wouldn't idle even after hose replacement.
Does your engine still have the original plastic top set up:
http://www.marineengine.com/parts/johns ... Carburetor
The ill designed low speed needle is hidden behind the air box, so the air box must be removed in order to make adjustments.
Replacement plastic tops have the side mounted low speed needle:
http://www.marineengine.com/newparts/pa ... OMC0436342
So, if things are mismatched, there might be a problem...
Will the engine run on its own (no primer) at higher speeds? Keep in mind these engines won't run at high speeds without the air box/gasket installed, they will be lean which is normal.
Finally, and I guess I should have led off with this, synchronizing these crazy engines is another lesson in over engineering. Unlike just about every other OMC outboard, these carbs are designed to idle with the throttle valve "cracked open" just a bit, which is what that spring loaded screw is for on the throttle arm. There is a base timing setting as well, which requires checking TDC and a timing light. Do you have the synchronization instructions? Final adjustments are "ticklish" at best, because slight adjustments in the needle valve often require a tweak of the cracking screw as well.
You mentioned this engine runs/idles OK with a different carb. What style carb are you using as a substitute? Metal bowl carb from an older model, or similar style plastic top carb?
Sorry to post more questions than answers here, there are just many possibilities. Feel free to post pictures if that will help. D

davesko
Posts: 82
Joined: Thu Nov 10, 2016 9:48 am
Location: Hershey Pa

Re: 1987 Johnson 8hp frustration

Postby davesko » Wed Sep 06, 2017 2:58 pm

Thanks Fleetwin, It does have the updated cover with the side screw, I have to wonder if the wrong top gasket was used. The carb I'm using that makes it run is an old style and it ran all day in all ranges. I checked for warpage and cleaned and blew out everything again no difference. Btw my air box is missing so once I get this sorted I will have to get one. It almost looks like someone tried to rebuild this carb years ago and gave up, I'm ready to get another old style carb and call it done. Thanks again,Dave

davesko
Posts: 82
Joined: Thu Nov 10, 2016 9:48 am
Location: Hershey Pa

Re: 1987 Johnson 8hp frustration

Postby davesko » Wed Sep 06, 2017 3:01 pm

I just discovered that if I hold my finger over the carb inlet it runs perfect, almost like a choke.

fleetwin
Posts: 1965
Joined: Mon Mar 09, 2015 4:27 pm
Location: Rhode Island

Re: 1987 Johnson 8hp frustration

Postby fleetwin » Wed Sep 06, 2017 5:07 pm

Where do you have the side mounted needle valve set to? I looked in the instructions with the updated cover kit and it says the low speed needle should be set to three turns out as an initial setting. The original style top gasket does supercede to the later style that is used with the updated cap, but perhaps someone used the new style cap and old original style gasket...Might be worth investing in a new gasket.. Have you looked at the plastic cap closely? These are easily cracked, which will create an air leak. Is the screw/plug and gasket in place where the original style needle valve was once found? If not, there would surely be a big air leak....
OK, the engine works OK with the old style carb, so I agree the problem is most likely with the carb or sync/link....
Have you followed the sync/link instructions for setting up the cracking screw, etc? Keep in mind, the engine probably will not run/idle if the throttle plate is completely closed. I'm sure we can get this sorted out without reverting back to using an old style carb, but you will definitely need to find an air box, gasket, and proper hardware in order for the engine to run right.
Partially covering the carb might be drawing fuel up through the high speed circuit keeping the engine running, so we can't make too many conclusions except that there is fuel in the carburetor bowl.

davesko
Posts: 82
Joined: Thu Nov 10, 2016 9:48 am
Location: Hershey Pa

Re: 1987 Johnson 8hp frustration

Postby davesko » Wed Sep 06, 2017 5:46 pm

Thanks Fleetwin, I just got a manual, air box and hardware. I am going to check the air fuel screw setting, pretty sure I have it at 1 1/2 turns out so maybe that will make a difference. Will keep you updated. I know how to do link and sync on the old ones but this is my first experience with a newer motor. Thanks again Dave

fleetwin
Posts: 1965
Joined: Mon Mar 09, 2015 4:27 pm
Location: Rhode Island

Re: 1987 Johnson 8hp frustration

Postby fleetwin » Wed Sep 06, 2017 6:39 pm

Dave, this is a completely different animal from the conventional OMCs, read the synchronization section and let me know if you have questions...
Yeah, seems like 1.5 turns is way too lean, try the three turns out setting and see if that helps any.....

davesko
Posts: 82
Joined: Thu Nov 10, 2016 9:48 am
Location: Hershey Pa

Re: 1987 Johnson 8hp frustration

Postby davesko » Thu Sep 07, 2017 1:34 pm

Fleetwin, Thanks for your help! I cleaned the carb yet again, adjusted the air/fuel mixture to 3 turns and followed the sync instructions and low and behold it runs like a top!!!!! Thanks a lot, Dave

fleetwin
Posts: 1965
Joined: Mon Mar 09, 2015 4:27 pm
Location: Rhode Island

Re: 1987 Johnson 8hp frustration

Postby fleetwin » Thu Sep 07, 2017 4:01 pm

Cool!


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