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'77 Johnson 70hp (70EL77S) Issue

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Adam Taylor

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Hello everyone. I'm new to this site and new to outboards. This is my first boat and I'm trying to learn as much as possible and these threads are really helping alot. Now to my problem. When I bought the boat the guy told me that it would idle all day long in a barrell or on the river but as soon as you give it throttle it would die. I fixed that problem by putting a longer fuel line between the fuel pump and the fitting on the lower pan, which got rid of the kink in the line and allowed more fuel. The boat ran for 3 Sundays with no issues. Today we go out and it runs fine for most of the day until this afternoon when it was time to bring it in. I turned the key and it fired right up as usual, I push the throttle stick forward and it goes into gear and dies. I put it back in neutral and fire it up again. Push the throttle forward and it doesn't die but even with throttle stick pushed to full throttle, it runs as if I'm at a "no wake" speed. I continue like this up the river trying to get back to the landing, playing with the throttle to see if I can get it to open up. I get to an area on the river where I can pull aground and check the motor out and I back out of the throttle once again to let another boat pass. When I push the throttle forward to cross the river it opens right up and accelerates like normal and ran fine all the way back to the landing. When I get there I have to wait on a few boats to launch. While I'm waiting I test it out a couple times and it acted up again but started running fine when I got ready to accelerate onto the trailer. Any advice would be greatly appreciated.
 
Intermitent problems such as what you've encountered will drive most of us nuts. However, on general principles check the compression on all cylinders (100+ psi & even on all cyls?), then (with the spark plugs removed), check to see if the spark will jump a 7/16" gap with a strong blue lightning like flame... a real SNAP on all cylinders.

If the above checks out as it should, I would strongly suspect that debris has broken loose within the carburetor float chambers and is getting drawn down into the high speed jets. The jets are located in the bottom center portion of the float chambers. Clean the carburetors.
 
Ok, well I checked the gap on the plugs and they were at .030". I also noticed they are Champion L77JC4. As I read in another thread, they are supposed to be the Champion QL77JC4. I plan to get a set tomorrow. I also read in another thread that if there are problems then I should try the .040 setting. I set them to .035 and it ran great for a few minutes then started the same as before. I pulled the plugs and set them to .040 and now as soon as I give it throttle while it is in gear it picks up a little speed but as I advance the throttle a little more it dies. Like I said I am getting the proper plugs tomorrow and a compression gauge to check the compression and a spark tester with an adjustable gap. I want to try everything else before I go into my carbs. Any more advice would be greatly appreciated.
 
The only difference between a L77JC4 and a QL77JC4 plugs is that the "Q" plug is a supressor plug designed to quiet ignition noise, etc that would interfere with any electronic equipment you might have aboard.
 
Compression checked out at 130 on top and bottom cylinders and 125 on the center one....havent checked the spark yet, I have to get a spark tester when I take my lunch break today. I will post results as soon as I know something. Thanks again.
 
I got good spark on all three coils while running it with "rabbit ears". Havent been able to check the spark under load but when I took it out again this afternoon, it ran fine for about 90 seconds until I caught a little bounce crossing another boats wake and then it started spit and sputter and lose power. I have replaced the plugs and have good compression on all three cylinders...... Any further help would be greatly appreciated.
 
I've jumped a few wakes myself... that bounce can be fairly bone jarring at times. It would be unlikely that the bounce would affect the fuel system or compression as both of those areas are taking a beating on a constant basis anyway. The spit and sputter scenario, then a loss of power would lead me into the ignition system.... loose wire, frayed shorting out wire, tight but dirty connection, that sort of thing.

Did the engine dies out completely or just loose power? If just a loss of power, how much loss?

Describe the appearance of the spark plugs.... which ones appear alike, which one(s) differ.
 
Carburetors are also the oil pump on your motor so running with a suspect fuel system is " taking a risk "----------You must be absolutely sure that fuel system is clean and free of blockages.This means taking carburetors apart for cleaning .Removing high speed jets threaded into the float bowls.Cleaning all the small fuel lines and fittings in the hoses.----------Not complicated to do and usually not much money invlved in doing this job. Install a fuel pump repair kit too.
 
When I crossed the wake it just lost power and would only run at about 20% speed at WOT. But thats only if it runs good after starting. This morning when I took it out, it would completely die out as soon as I put it in gear. I fished using my trolling motor and when it came time to bring it in, it would run fine in gear until you tried to push past about 25% throttle. Hold it at a "no wake" throttle and it will run all day, push past that point and it dies. Thanks again for your help.
 
Adam Taylor said:
it would run fine in gear until you tried to push past about 25% throttle. Hold it at a "no wake" throttle and it will run all day, push past that point and it dies. Thanks again for your help.
Click to expand...

That indicates a possible problem such as debris becoming drawn into a high speed jet (clogged carb) or a badly sticking timer base (retarded spark).

Also.... I have encountered intermitent problems such as you're describing and found that the interior of the fuel lines were deteriorating in very small partiucles that would gain access to ther float chambers. Eventually those floating particles were drawn into the high speed jet resulting in a loss of power to the related cylinder.
 
Engine NOT running, observe the movement of the timer base as someone slowly moves the throttle from it's full retard position to ite full spark advance position (up against the rubber stop). It should not stick anywhere but rather move smoothly thru that range.

You may need to turn the propeller somewhat to shift into gear when advancing the throttle lever.
 
Timer base moves smoothly. Should it hit the rubber stopper before you reach "half throttle"? I pulled the hex head screw from the bottom of the float chambers on all three carbs and what looked like dirty water came from the top carb. The other two looked like normal fuel/oil mix. I flushed the chambers out with carb cleaner. I will post results after I put it back on the water.
 
Timing hits full advance before throttle opens all the way !-----------Did you use a 3/16" diameter shank screw driver to remove the high speed jet found behind the drain plug.---It must be cleaned / inspected to be clean.
 
Pulled the idle jets and cleaned them. Couldn't get the high speed jets out so I pulled the float chambers off so I could gain access to the jets. I cleaned the chambers and jets and put them back together. Took the boat out after work yesterday and it runs better than it has the entire time I have owned it. Thanks for everyones advice and I hope someone else can learn from my problem.
 
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