1981 Johnson 70hp (J70ELIM) Running porely at idle

I got this motor on the back of my skeeter bass boat last year and it doesn't seem to run correctly expecially at idle. seems like it is only running on one cylinder at idle seems to be running ok at any other speed.

First things first did the compression test and 150psi on all cold and 115 on all warm no difference in psi on any of the three cylinders.

So I took my timing light to check timing first and its ok other than it moves around but when it is by the timing mark it is spot on TDC.

moving timing light from each of the three cylinders the light lights up fast and the same and didn't seem to skip a beat.

Old plugs didn't look that great so I changed them and that didn't help. Ran the boat for a bit and took the plugs out to see what they looked like and the top one was black and oily like it should be and the middle and bottom ones where like brand new still just wet not to bad but wet.

I started the engine back up and decided to snuff out a carb one at a time and see what happens. close choke flap on cyl. #1 engine dies, started it back up closed choke flap on middle carb cyl. #2 and I can't hear a difference in the motor no matter how long i run it, and same goes for bottom carb cyl. #3 no change in motor that i could hear. So I'm confident it is only running on cyl. #1 at idle it seems to run great at any speed off idle.

So i moved on to the carbs did a link and sync, didn't think that would help and it didn't took carbs off and blew threw the jet that is at the front/top of the carb and the jet at the back/top of the carb and both were clear. blew threw the neddle and it was clear. blew threw the passage that is in the bottom of the carb that looks like it goes to the jet that is at the front/top and it was clear. only jet I didn't check was the one that is in the bottom of the bowls the one that the needle sucks through i think, im not for sure but is that the idle jet?

I put the carbs back on did another link and sync still not any better.

Im not a carburator guy as they are before my time (Im 23yr old) but I know the basic functions and have rebuilt a few of them just not on boats. This is my first boat and I am confident I can fix it just need some help and advice.

Which jet is the Idle jet and why would the timing bounce around? These are my two questions for now. I'm out of town for two weeks cause of work so I have plenty of time to research This website is great and helped me go in the right direction with my lower unit that is leaking water any help would be great guys thanks.

Re: 1981 Johnson 70hp (J70ELIM) Running porely at idle

Get a spark checker at Auto zone/OReilly and check the spark on all your cylinders, sounds like a few of them aren't hitting by the clean plugs.

An easy way to check for no gas is to squirt a small amount of gas into each carb and see what it does, dies, that carb is good, picks up that carb isn't good.

Have a fire extinguisher right there when you do this just in case, seriously.

Your comp numbers are backwards, comp should be higher when hot, that is odd but 115 is still good.

I have found that just blowing air through a jet doesn't really do anything, you have to remove the jets and physically clean them with a stranded copper wire, just peel wires back till it fits and work it in and out a few times, seen jets that look factory fresh that weren't.

I have an '81 50 and my idle jets are the ones on the front, the mids are on the top back and the high speeds are the ones in the float bowl, clean them all, do one carb at a time and keep the cover screws with the jets so you don't mix them up.

Re: 1981 Johnson 70hp (J70ELIM) Running porely at idle

awesome I will try the spraying the fuel in the carbs when I get back in town in two weeks(going to be a long two weeks at that). Fire extinguisher is always ready had bad experiences with cars. I got an adjustable spark test but ran out of time last night as I had to leave early this morning. Im assuming it is carbs since it seems to run ok off idle but I will definantly check spark to make sure thats not it. I did try checking spark the old fashion way with letting it jump from the wire to the plug but I only tried on #1 and it wouldn't even start so I just went and bought a spark tester but didn't get back to it before it was too late.

Thanks for the advice any other advice would be great guys.

Re: 1981 Johnson 70hp (J70ELIM) Running porely at idle

If your motor is idling on one cylinder, it must be a dang good cylinder (not doubting you, just saying mine idles great on 2, but won't run on 1).

Not sure exactly what you mean by "moves around"?

Spark test is a good idea, but I suspect you're right about the carbs. Set your spark tester gap at 7/16".

The idle jet is the one on top in the middle, the one over to the side is "off-idle," and the hi-speed jet is in the carb bowl, behind the drain screw.

Could be flooding through worn float valves, but I wouldn't bother guessing -- just go ahead and order 3 carb kits from iboats, take 'em off & soak 'em overnight, blow 'em out with compressed air, put 'em back on with new kits. About $30 and some chemicals, well worth the time. She just always seems happier with fresh carbs.

Click on the "top secret file" at the top of this forum -- the "carb rebuilding" thread shows how to make a jet removal tool. Don't take a chance on mangling the jets with a regular screwdriver.

Re: 1981 Johnson 70hp (J70ELIM) Running porely at idle

Thanks J texas I think that what I will do is just go ahead and rebuild carbs as it seems it hasn't been done in a while I am planning on dumping some money into it anyway been saving for a little while now.

What I mean by the timing jumping around is looking at the timing marks from the carb side the timing marks will be off to the right of the indicator by almost 50 to 70 degrees then bounce back to the timing mark but it is off to the right more than it is infront of the timing indicator like it should be Im not sure maybe a bad ingnition part but I really have no clue it doesn't help by changing cyl. it just moves them further away from the indicator which I suspected. I checked the coils and made sure they were wired correctly to the power pack #1 or/bl #2 or and #3 or/gr. I am just hoping that the timing bouncing like that isn't causing the idling issue. I do know when I rev it up the timing comes back to the timing indicator and is steady where at an idle it bounces like that.

Re: 1981 Johnson 70hp (J70ELIM) Running porely at idle

Hey anyone thats reviews this thread just wanted to let yall know that i cleaned the carbs and put kits in them and the motor runs great better than ever. Money well spent can't wait to get to the lake this weekend.

THANKYOU EVERYONE AT IBOATS FOR ALL THE HELP!!!!!!!!!!!!!!!