1974 Johnson 85 hp wont idle.

[Basscat 1]

I have a 1974, 85 hp Johnson outboard that I cant seen to get it to idle. It will run a few seconds and die, sometimes longer. It sputters a little bit of smoke and then dies.<br />It also will cut out occasionally at higher rpms out of the water, but not to noticeable. It runs great on the lake at mid-top end. (50mph)<br /> I have completely rebuilt both carbs, all the electrical, even tore down the power head and replaced all the gaskets and seals. I checked the reed block assembly, replaced the fuel pump, changed coils, spark plugs. During the tear down I found the lower crank bearing was bad and replaced it. I also found the spaghetti cord torn, (I thought I found the problem) and replace it.<br /> I inspected the seal rings on the crank and found them ok. I ran a compression check on each cylinder and found them all equal, but I don’t recall the readings.<br /><br />The only gaskets I didn’t change during the tear down was the Outer exhaust cover and inner exhaust cover gaskets. It appears to have been leaking, and I plan on changing them. I noticed in the forum somebody had a blocked exhaust that caused them idle problems. <br />I did notice that all 4 plugs will carbon up quickly. Could exhaust restriction be the problem?<br />If anybody can help me turn over a stone that I haven’t thought of, I would appreciate it. <br />Thanks.

 

[OBJ]

Re: 1974 Johnson 85 hp wont idle.

Hello Basscat and wecome to the forums.<br /><br />Couple things come to mind....do you have an OEM manual to do a good sync and link with? Check both throttle plates are closed when in neutral and both choke plates are wide open.<br /><br />What's the engine temp like at idle? Does it warm up or stay cool. If it's staying cool, combustion won't be the best in the world. If it stays cool, replace the t-stats.<br /><br />Have you checked the spark? Each spark should jump at least a 7/16" gap with a hot thick white spark.<br /><br />And I would replace the exhaust cover gaskets. If they are leaking out, the will eventually leak in. You could get water blowing into the cylinders when running. Keeps everything nice and clean but the engine don't run worth a crap... <br /><br />Keep us posted and I'm sure some of the other guys will throw in some ideas also.

 

[Basscat 1]

Re: 1974 Johnson 85 hp wont idle.

Thanks for the reply. Starting with the carbs. I did a good sync, as did a buddy of mine who has been working on outboards for 20 years. He was the one who thought it might be leaking air in the power head. One thing I forgot to mention. You can block off the lower carb with a rag and will idle much better, and even longer.<br />I havent checked the temp at idle. What should it be, a where would I check it using an laser heat detection gun, (if you are familiar with this)?<br />The spark appears to be fine. We replaced all ignition parts one at a time. I replaced the coils with new ones.<br />I did notice also that the outer exhaust cover seem to be leaking water. I tightned the bolts and it quit. Again I plan on changing the gaskets. Is the water leak normal at this particular place? I wouldnt think so.

 

[OBJ]

Re: 1974 Johnson 85 hp wont idle.

I would think that if you block a carb off and it idles better and longer, you have a fuel flow problem. The vaccum created by the engine is literally pulling in the fuel as compared to the fuel being sucked in by the low pressure area created by the throat of the carb. What you might try is some premix in a spray bottle. Get the engine running and when it seems to want to die, give the carbs a squirt. If it continues to run, start checking the fuel system. You may have also missed a plugged jet if you didn't soak the carbs and remove the jets for inspection. Always follow up with compressed air.<br /><br />The engine temp should run around 143 to 145 at idle as measure on the flat areas on top of the block.<br /><br />The exhaust cover gaskets do have a history of being leakers. Best thing to do is remove the covers, throughly clean all gasket areas. Put a coat of gasket sealing compound on the new gaskets and re-install covers. Torque all the bolts evenly with a torque wrench....'bout 8ft lbs. I believe it is.

 

[Basscat 1]

Re: 1974 Johnson 85 hp wont idle.

Quote,"The vaccum created by the engine is literally pulling in the fuel as compared to the fuel being sucked in by the low pressure area created by the throat of the carb."<br /><br />Could you explain this a little more? I thought that the engine is supposed to pull a vaccum and draw the fuel in. Thanks.

 

[Basscat 1]

Re: 1974 Johnson 85 hp wont idle.

Just bringing this back to the front page. Maybe somebody can help.

 

[dolluper]

Re: 1974 Johnson 85 hp wont idle.

Try this link<br /> http://science.howstuffworks.com/two-stroke2.htm

 

[Basscat 1]

Re: 1974 Johnson 85 hp wont idle.

After a closer inspection, I believe I have finally found the cause of my idle problem. It turns out the reeds were not sealing. One of the reed blocks was even rusted and pitted. Somebody suggested replacing the reeds with Boyesen reeds. Do these really make a difference in performance? I know my factory reeds are bad and I will need to change them, but I am wondering if they will be worth the money? I have read that it will change the performance of the motor, but I would like to have the opinion of somebody who has actually made the switch. What exactly do they come with? I will need the block for sure and of course enough reeds to change the both sides. I should be able to obtain the reed block from a friend of mine, but I was wandering do they come with the new reeds?<br />By the way, the light trick worked. I used a flashlight in the dark and was surprised how much light you could see around the edges.