1989 70 hp johnson won't idle

I have 1989 70 hp Johnson that starts great in the driveway, but when I get it to the water -- it just grinds away.

I pulled the carbs and cleaned, and all looks well.

I changed the gas and went to a premium mix -- incase of water.

Tonight, I took a compression test -- 100 psi on all 3.

I poured some oil into each carb, took it to the lake -- bam, started right up, ran great and then died -- then would not start.

Pulled the plugs, poured some oil in -- and this time nothing, so my son tilted the motor up to mimic the driveway setting - and bam, it started and ran and idled while tilted almost all the way up -- just enough was still in to draw water.

As we tilted it down -- it would cough and sputter and die -- and then crank away with no ignition.

I already cleaned the carbs, and nothing appears to be sticking.

Any thoughts ???

Re: 1989 70 hp johnson won't idle

Welcome to iboats.....

What occurs to me is possibly a bad wire in the harness. Tilting the engine could be causing a short or causing a wire to "make/break" with the engine tilted. With the engine in the normal running position, try starting. If it does not start, try flexing the wire harness at the engine to simulate tilting. If the engine does fire while flexing the harness, you may have found the problem.

Also look at the fuel line in both the normal running position and tilt position. Make sure the fuel line is not getting pinched off in either direction.

One more thing, engines usually fire up a lot better out of the water than in. This is because there is no back pressure against the cylinders when out of the water.

Re: 1989 70 hp johnson won't idle

also remove the air silencer, and see if the carbs are flooding. tilting the motor would drain excess fuel off the carbs.

Re: 1989 70 hp johnson won't idle

tashasdaddy said:

also remove the air silencer, and see if the carbs are flooding. tilting the motor would drain excess fuel off the carbs.

Click to expand...

and if they are, double-check the float heights. check the operation of the float valves as described in "carb cleaning" (see "Top Secret" thread: http://forums.iboats.com/showthread.php?t=299680 ). Worn out float valves are difficult to detect visually -- if you can't get 'em to close off just replace 'em.

In the driveway it'll easily idle on 2 cylinders and you might not notice.

cylinder drop test: engine idling, pull then replace the spark plug leads, one at a time. Use an insulated or plastic tool (autozone sells a plastic "boot tool" made for this purpose, for a couple bucks). if there's no change in RPM, that cylinder's not making power. test it for spark first.

[hint: if this model has the 3-jet carbs and you accidentally switch the idle and off-idle jets, that cylinder won't idle -- don't ask me how I know]

Re: 1989 70 hp johnson won't idle

I pulled the carbs and popped the top cap over the low speed jets -- one carb and one jet seemed to be a bit clogged.

Also, one float seems to be sticking -- though I can't see why -- it appears to be clean: in the orifice, the needle and the float cam.

It closes ok, but when I slowly lift it slowly-- it seems to catch at about half way then pop up.

Not sure what this will do, for it doesn't seem to have an issue on closing, just when it is lifting. I put the carb's back on and I am still having lotso of idle trouble -- will buy rebuild kit tomorrow.

Meanwhile, if I screw the low idle screw all the way down, it seems to run, but then the RPM seems so high that putting it in gear causes a major clunk -- two fast. When I back the screw off, it just sputters and dies.

I will rebuild the sticking carb to see if that helps.

I followed the rebuild instructions, and could not blow air through the carb as it shouldn't-- but when I flipped it over -- I could (just as expected).

Not sure if I have a fuel flow issue or what, but this is driving me nuts. One last shot, and then a pro gets it.

Re: 1989 70 hp johnson won't idle

"Johnson that starts great in the driveway, but when I get it to the water -- it just grinds away." ---- set idle speed faster, then fine tune in the water with the motor in gear.

Re: 1989 70 hp johnson won't idle

mprobstf said:

...
Also, one float seems to be sticking -- though I can't see why -- it appears to be clean: in the orifice, the needle and the float cam.

It closes ok, but when I slowly lift it slowly-- it seems to catch at about half way then pop up.

Not sure what this will do, for it doesn't seem to have an issue on closing, just when it is lifting. ...

Click to expand...

sounds about right, but if it is sticking open while the motor's running, it'll flood that cylinder.