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1985 Johnson 70 HP

I had similar problems with an '83 70hp evinrude. Turned out to be the fuel line from the tank. The squeeze ball had a crack in it. Also replaced all fuel lines with the new "ethanol resistant" hose as it was all cracking and disintegrating from the new ethanol gas.
The hose and primer bulb appear to be in good shape. I did just replace the ends because they were cheap. When I pump up the primer bulb it gets hard and there are no apparent leaks in any of the fuel lines or connections. I have also tried swapping lines and tanks with my kicker motor and it had no affect. I am taking Wednesday off work and going fishing so I will see how it runs then with my most recent changes and adjustments. I will also try adjusting the timing pickup point and see what that does. If it still wants to die when I accelerate my next thing to try is obtaining some 75HP carbs with adjustable needles.
 
I tried to respond last night don't know were it went The fuel tanks are at the same height as the power head two tanks two hoses all is new same result from both I'm reluctant to go tearing into it and spending $$$$$ something changed it most certainly is a fuel delivery issue or vacuum leak it seems to me that a stuck or malfunctioning check valve could absolutely play hell with the motor I would assume you changed the fuel pump check valve when you changed the VRO pump? as far as the port I mentioned it would make sense that it drains the box so what would it hurt to try capping it just to see?
I also remember reading that the wrong temp plugs could mess with it? but it seems unlikely a plug that is to hot would do this however that is the one thing that I did just change? and now that I think about it
seems to me this all started after the plug change have you messed with plug temps?
 
Well I had the boat out today and there is no improvement. Adjusting the floats had no effect. Adjusting the roller to allow more advance didn't help, in fact it was worse. I really think it is simply starving for gas. Once I give it a shot with the choke it will take off. At high speed it runs fine. I am beginning to believe the rebuilt powerhead I bought was in reality a 75 horse rather than a 70. Since its rebuilt it could even be bored oversize. I really think the carbs I have are incapable of supplying enough gas at low speed. I am going to try and locate a set of 75 HP carbs. If that doesn't work I give up. This has gone on too long. I will steer clear of any 3 cyl OMC in the future that's for sure.
 
I agree with racerone,it is probably somthing simple overlooked.you say adjusting float and roller for advance made it worse,try reversing those two things one at a time and see what happens.If you revers one of them and it gets a little better then that should give you more of an idea where to look.DONT GIVE UP!!!
 
Let me clarify, adjusting the float had no affect at all. Advancing the timing more before opening the throttles made it worse. I have the roller adjusted as far as it will go the other way now and it still wants to die. It is not getting enough gas. I have found a set of 1985 75hp carbs on e-bay that allegedly came off a running motor. When I get them I will see if they make any difference.
 
I got my 75 hp carbs and I checked them over and cleaned them out thoroughly. Floats are set to spec and are working properly. Since I had a set of brand new needle valves and retainers I took out the old ones and put in the new ones. I put everything together and did a complete link and synch. I fired it up on muffs in the driveway and set the low speed needle valves per a procedure I found posted by Joe Reeves. It seems to run fine at idle in the driveway at 1100 RPM which usually gives me an idle speed of 700 RPM in the water in gear. I believe I have everything set up according to spec. I just need to get it in the water and see if it willl accelerate properly. Wish me luck as I have run out of ideas.
 
Took it out on Lake Erie last night. Still runs like crap at low speed. What a difference between running on muffs in the driveway and running with the motor in the water. The increased back pressure on the exhaust really affrects how the motor runs. I did a stupid thing by putting the plastic air box back on the carbs. I should have left it off so I could do adjustments on the needle valves while I was on the water. Now here is a dumb question, if I turn the needle valves counter clockwise that gives it more gas right? I just want to be sure because it definitely needs more gas. I am going to leave ther air box off next time and I think I should be able to get some improvement. I can't think of anything else to do. It seems to run great once I choke it to give it enough gas so the high speed jets can take over. I get 25 to 28 mph at 5000 RPM with 2 people total in the boat. Is 5000 RPM the correct WOT speed for this motor? I currently have a 13 x 19 prop.
 
My last night experience was one of my customers' 150hp outboard bogged down at high rpm. I simply replaced the fuel hose and primer bulb and the problem went away for 20min at high rpm and continues to occur again. I can now 100% sure that the fuel system need to be looked at, that including inline filter clogged, clogged high speed jets in the carb, bad fuel connector to motor, ruptured fuel pump diaphragm etc...Most of the time problems are caused by the most unreliable items that are made out of non lasting material; rubber, plastic, etc...If these items are not yet thoroughly checked out twice after compression and spark tests are done with good result, do so before going into too complicated matter such as increase orifice in carbs, etc...
Good luck to all and happy boating.
 
Turning that mixture screw counterclockwise will indeed richen up the mixture...
With your wide open being 5000 rpm your prop pitch should be ok.... but since you have tried everything else, maybe a 17" prop may also be worth a try..
The 17 should put your wide open to close to 5500rpm and this may just be enough to lessen the load on the motor to get you over the point bogging down..
 
Turning that mixture screw counterclockwise will indeed richen up the mixture...
With your wide open being 5000 rpm your prop pitch should be ok.... but since you have tried everything else, maybe a 17" prop may also be worth a try..
The 17 should put your wide open to close to 5500rpm and this may just be enough to lessen the load on the motor to get you over the point bogging down..
Thanks for the info. This just might work.
 
DON'T GIVE UP!!!!

I spent three years troubleshooting the EXACT same problem on my 1982 75 hp. I did EVERYTHING you did and more. Finally, one night after tilting the engine up with the cover off I noticed fuel dripping from the round connector that houses the metal filter screen on the fuel pump body. It turned out 25+ years of fuel and heat had warped the plastic and was allowing air to be sucked in, leaning out the engine. I put two zip ties over the connector and it works perfect.

Amazing how the simple, cheap things drive us batty. Check yours out!!
 
DON'T GIVE UP!!!!

I spent three years troubleshooting the EXACT same problem on my 1982 75 hp. I did EVERYTHING you did and more. Finally, one night after tilting the engine up with the cover off I noticed fuel dripping from the round connector that houses the metal filter screen on the fuel pump body. It turned out 25+ years of fuel and heat had warped the plastic and was allowing air to be sucked in, leaning out the engine. I put two zip ties over the connector and it works perfect.

Amazing how the simple, cheap things drive us batty. Check yours out!!
I have already replaced all the hoses, clamps, zip ties etc associated with my fuel and oil system. My fuel pump is a VRO pump and I dont see any metal screen on it. There is a plastic filter with a plastic screen for the fuel and a long conical screen thingy for the oil. I will however double check everything for leaks.
 
FINALLY, after 2 years it is running right. I got the boat out on Friday and I had put on a 13.25 x 17 prop and opened the needle valves 1/4 turn. It ran great in the driveway but still wanted to stall when I put it in gear and tried to accelerate. You can't learn much running on muffs in the driveway. So I poped the cover and opened the screws 1/8 of a turn at a time until it would finally take off without stalling. It ran pretty good but would still bog occasionally so I opened them another 1/8 turn and then it finally would take off without bogging. The new prop seems to help it get up on plane quicker and it runs great WOT at 5200 rpm. It also idles and runs much better when approaching the dock. Thanks to Racerone for the suggestion to employ the adjustable needles for low speed. Thanks to Ciscokid for encouragement. Thanks to Tonyaus for idle screw and prop advice. Thanks to everyone who tried to help.
 
Jet A .067 Diameter.jpgcarb 328279.jpgJet A and B.jpgJet B.jpg

Hi Guys,

I have what a believe is a 1984 Evinrude 70 HP with similar issues.

I have the motor in a barrel and it idles fine and it will run like a charm on the lake at WOT. However, it will stall during transition from idle to WOT. If I press the enrichner once or twice as it begins to studder it will get past that part on the acceleration process.

I have cleaned the carbs and done the link and sync and read posts on various forum on this subject till my eye were tired. I have had the motor to a dealer and one other guy that is supposed to be good with outboards. They say the motor is noisy and is not worth putting any more money in.

It has 120 PSI on all 3 cylinders with 1 PSI.

I am just about ready to deep six the thing. I noticed that one of your guys mentioned something about drill out the jets about .002. I have attached a few pictures. Which jet needs to be enlarged to get better transition from idle to WOT?

Any help would be appreciated.

Thanks,

John
 
Hey All,


I have 1985 70HP Johnson. Revs are perfectly fine at idle, good compression. When under load, it takes a very long time for acceleration. Very gradual. Barely any throttle response. What you thinking, fuel flow in carbs or something else?
 
Hey All,


I have 1985 70HP Johnson. Revs are perfectly fine at idle, good compression. When under load, it takes a very long time for acceleration. Very gradual. Barely any throttle response. What you thinking, fuel flow in carbs or something else?
Start your own thread. This one is 6 yrs old
 
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