1986 Johnson 40 hp bogs down at high speed.

[Daniel612]

I have a 1986 Johnson 40 hp with 145 lbs compression in each cylinder and a nice blue spark to both plugs. Engine idles find and works great until I try to get it up to plane. It goes up once in a while, but more consistently seems to bog down and "plow" instead of planing. When I push in the choke while at the highest speed I can go, the engine begins to die. My OB mechanic thought the problem was a bad gasket and so he replaced it. When I tested it that afternoon after he had replaced the gasket, I could get it up on plane. The next day, it bogged down at high speed and will not plane. I am thinking that it is probably the high speed jet or timing advance problem. Someone please help.

 

[fireman57]

Sounds like I would change mechanics and give the carbs a good cleaning and make sure my high speed jet is clean and my pickup tubes aren't clogged.

 

[Daniel612]

Fireman 57. Thank you for your response. I will clean the carbs and then, if necessary, rebuild them. Can I isolate the problem if I spray starter fluid into them while I am running the boat in the water? What are pickup tubes?

 

[fireman57]

If you go to ishopmarine.com you can pull up your carb diagram. The pickup tubes are the copper tubes that go into the bowl of the carb. There are small holes in the sides of them that can get clogged with the junk gas they sell now. You really can't isolate it with any spray and don't use starting fluid because there is no lube in it for the cylinders. You can use a bottle of premix gas and squirt it in the carb throat while running. Don't fall off the back because of your buddy's bad driving though.

 

[Daniel612]

fireman 57. I ran non-ethanol gas with sea foam in it. Let the motor run on the trailer in the water and cranked her up until it ran out of gas, then hooked it back up to the gas tank and it started running like it should. I took it out and it immediately planed, running like it used to run. I need to try it out tomorrow and see if it still runs at the high speed. Since I have no idea what kind of gas the previous owner used, I must assume that it probably had some ethanol in it. The thing is, each time the carb has been emptied and then run, it has planed. Then, after it sits for a day or two, it seems to go back to plowing. Could it possibly be the floats or a float in one of the carbs?

 

[rcbrownjr]

I'm having a similar issue with my 1986 Johnson 70. Idles just fine, will occasionally get on plane, but mainly plows. Good, consistent spark on all three cylinders, good compression, fresh non-ethanol gas with Seafoam. OB mechanic calls after opening up all three carbs, says that something in each carb is bent/cracked and all three need to be completely replaced. Says it's something in the carb that cannot be fixed by rebuilding. Could that happen to the copper pickup tubes and, if so, is there a way to repair and rebuild?

 

[fireman57]

The copper tubes usually don't go bad. If you look down at them you will see a smaller tube that is offset. Some people try to straighten it out. DON'T! It is like that for a reason. I would have no idea of what would crack in all three carbs to warrant replacement. You need to ask him specifically what it is and then start your own thread on this issue.
Daniel, I love Seafoam but it really isn't a substitute for dismantling and actually cleaning the carbs. It might have been a piece of gunk in a high speed jet that got dislodged but it could still be lurking in the bowl to create the same problem later. You can buy ethanol resistant gas line and replace them all. That is the first thing that I do when I get a different engine, then I take the carbs apart and clean or rebuild them whichever they need.

 

[rcbrownjr]

After talking to the mechanic, it looks like at least one of the smaller tubes broke off. Thanks for the feedback and apologies for hijacking the thread. Good luck Daniel.

 

[Daniel612]

Fireman57, I want to thank you for your excellent and informed advice. Today, the boat ran very well until I bogged down in shallow water and had to back up. The engine started plowing again and could not get up on the plane. So, I am going to take your advice and clean or rebuild the carbs. I think you are right about gunk in the bowl. It comes loose from time to time and then clogs the high speed jets again. I will also get some new ethanol resistant gas tubes. I have begun using only non-ethanol gas in all of my two stroke engines. Again, thank you for your comments as they are very much appreciated!

 

[fireman57]

No problem that is what everyone here does and how we learned about these engines. You said you bogged in shallow water. The lower unit didn't hit anything did it? Mud? Sand? Hope not because you might have spun your prop.

 

[Daniel612]

Nope, I shut it down immediately and backed out. I cleaned the carbs and took it out yesterday and guess what? She planed at about 35-40 mph with no problem. From now on I will never use gas with ethanol. And after I learn what I need to know with this smaller boat, I plan on getting a larger fishing boat next year. Something with a center console and a 150 hp outboard so I can take friends out as well. Again, thank you Fireman57, and thank you, too, for your service as a firefighter! I was a teacher for 40 years and am loving retirement now here in southwest Florida!