1971 johnson 85 hp troubles

[skidoocory]

I have a 1971 Johnson 85 hp that I am having trouble getting started. I have read many treads and the service manual to help trouble shoot. Motor will run for short time (30 seconds) then shut down and backfires through exhaust. Seems like timing issue?? My main question is when I test the Amplifier it shows as being no good (tested by using test light on pin 5, blue wire to coil and cranking over). But I still have good spark to my plugs. I wanted to get another opinion before I spend a couple hundred on the new amplifier. I did just read and old tread on how to test the amplifier using a different method. Will try when I get home. Anyway thanks in advance, Cory.

 

[tashasdaddy]

Re: 1971 johnson 85 hp troubles

you have to have 3 things for it to run, compression, spark, and proper fuel/air mixture. did your motor set up this winter with fuel in the carb? you have spark to the plugs, it could be 3 things, compression, but it has enough to fire off, the flywheel key is sheared, but it would run rough. i think you have dirty carbs, as the #1 problem. see the sticky at the top of this forum on carb cleaning.

 

[F_R]

Re: 1971 johnson 85 hp troubles

It is always tempting to blame the mysterious "black Box". But that probably is not your problem. Pull the flywheel and clean up the distributor cap, check plug wires continuity, check points gap, and clean up the area and re-lube the anti-reverse cutout ring. Flywheel and crank tapers must be clean and dry and use a torque wrench to tighten the flywheel nut to 100-105 ft/lbs. If you are still trying to run the original surface gap plugs, trash them and put in a set of QL77JC4 plugs gapped at .030.

 

[skidoocory]

Re: 1971 johnson 85 hp troubles

Thanks for the advice. I just bought the boat and the motor is a mystery. I did pull compression, and all cylinders are between 118lbs and 125lbs. That was done dry because of the motor not running. My gut is telling me it is something in the timing. I will follow your instructions and let you know how I make out. Thanks again.

 

[skidoocory]

Re: 1971 johnson 85 hp troubles

Sorry, I forgot to mention I rebuilt both carbs and set all the needles the same to get it running. Thanks again

 

[tashasdaddy]

Re: 1971 johnson 85 hp troubles

do you have an OEM manual? as F_R said pull the flywheel.

 

[JB]

Re: 1971 johnson 85 hp troubles

If the "backfires" are loud bangs rather than coughs I think you are getting heat related crossfire. That would be in the ignition system.

If they are really coughs or sneezes the engine is running out of fuel and it is a fuel supply problem. What happens if you pump the primer bulb when it is trying to quit?

If it runs well for 30 seconds it is not a carb problem.

 

[skidoocory]

Re: 1971 johnson 85 hp troubles

Thank you for your suggestions, Here is an update. Yes I do have a service manual to help out. I removed my flywheel and cleaned and inspected everything. I did find the notch on the bottom of the rotor was almost missing completely and that was allowing the rotor to move much more then it should. I thought for sure that was it. I set both sets of points to 10 thousand (per manual). I brought the number 1 cylinder to top dead center on the compression stroke. Pointed to about 4 degrees before top dead center. Seems correct according to book?? Tested it again and the same thing. Only it farted over once and makes a loud bang, pop out of exhaust. I am sorry to keep asking for help but the book seems to have run out of help.

 

[Lakester]

Re: 1971 johnson 85 hp troubles

Flywheel and crank tapers must be clean and dry and use a torque wrench to tighten the flywheel nut to 100-105 ft/lbs.

hello,

why so high? isn't factory spec for flywheel nut... 70-85 ft lbs?

i would think 85 is more than enough!

also to note: factory calls for specific key to keyway alignment on these engines. i would be sure to run per the specs...

regards,
lakester

 

[Lakester]

Re: 1971 johnson 85 hp troubles

Motor will run for short time (30 seconds) then shut down and backfires through exhaust. Seems like timing issue??

hello,

well, imo... to run for 30 seconds seems like a long time to me. then to just shut down, well... hints of running out of gas. too lean and a backfire?

will it start back up once it dies? or if u pump it?

how did it run before u rebuilt the carbs?

regards,
lakester

 

[skidoocory]

Re: 1971 johnson 85 hp troubles

I bought the boat not running so I don't know. Once it fires over it usally won't refire for a couple minutes. I am not sure but I think I am going to look further into the fuel today. Make sure its getting fuel correctly.

 

[HighTrim]

Re: 1971 johnson 85 hp troubles

Are the points not suppose to be set to .020 on that motor? After that follow Joe Reeves advice for setting the carb from the FAQ

It is early and I have just started my coffee

 

[ckgreenman]

Re: 1971 johnson 85 hp troubles

A buddy of mine bought a 1971 85HP that seemed to have similar problems. It would run for about 30 secs to a minute and then just quit immediately as if the key was turned off. No sputtering. Once it died it would not start again until it sat for a few minutes and then you fire right up again only to die 30 seconds to 1 minute later.

We ended up swapping the motorola box for a known good OMC box on a 60HP and that fixed the problem. Now we need to figure out something for the Trim/Tilt

Not saying this would fix your issue but it worked in our case.

Good Luck.