70HP Johnson Idling problems

[ACAMACIAN]

Hello

I have a 96 70hp johnson that has idling problems when the boat is in the water. When in the yard on the muffs it starts right up and idles great. We fish tournments with this boat and while waiting for take off I have to keep the throttle on or fast idle on to keep it running. Trailering is a little difficult also as I have to come in fast to keep it running. When I took it to the mechanic he found nothing as it ran good on the muffs. Any Suggestions??


" THE ACAMACIAN "

 

[5150abf]

Re: 70HP Johnson Idling problems

Those engines are really sensative to dirt in the idle circuit of the carburator, I would say that is your problem, it is starting to get build up in the jet or pick up tube.

There should be a screw on the throttle linkage that lets you turn the idle up, be sure to count your turn so you can put it back if that doesn't fix it.

Just went through a very similar thing with my 50, started idleing worse and worse, turned out to be the pick up tube for the idle jet, now it runs like it used to.

On these engines the idle mixture can't be adjusted, all you can do is advance the timing to make it run faster but that won't work if it isn't getting enough gas, either clean your carbs or have it done, should clear up the problem

 

[ACAMACIAN]

Re: 70HP Johnson Idling problems

I had the carbs cleaned near the end of last year and it did the same thing, I figured that mechanic didn't know what he was doing as I brought it back to him and then he replaced the power pack, still the same.

The confusing part is it works really good on the muffs, but not in the water.

I am not great at this type of work. Would you recommend me taking the carbs apart and clean them myself. I have never done it before.


" THE ACAMACIAN "

 

[jtexas]

Re: 70HP Johnson Idling problems

in the water, there's backpressure on the underwater exhaust that isn't there on the muffs. It's very common for a motor to sound great then crap out when you put a load on it -- we've all been there.

This is an earlier model than yours, but I believe all the parts are the same -- you can see the idle set screw:

These are remarkably simple carbs, you can do 'em yourself, but I highly recommend getting a manual first. The factory service manual is best.

Don't take your motor back to the shop where you had it before -- that parts changer needs to go back to mechanics school.

 

[ACAMACIAN]

Re: 70HP Johnson Idling problems

Hey thanks alot. That pic looks exactly like it. So if I adjust the idle when it is in the water it should act a little better.

I will try that.

Thanks again

" THE ACAMACIAN "

 

[ACAMACIAN]

Re: 70HP Johnson Idling problems

One more thing. If it is a dirty Carb is there anything that can be sprayed in there that may clean it out. I see carb cleaner at the hardware store and I have used throttle body cleaner on my truck which worked good. Just wondering if anyone had any luck with a spray cleaner of some sorts.


" THE ACAMACIAN "

 

[tashasdaddy]

Re: 70HP Johnson Idling problems

no those items strips the lubrication of the surfaces of the 2 stroke motor. the only way to clean is remove dismantle. and rebuilt kit for each carb.
http://forums.iboats.com/showthread.php?t=244013 keep parts for each carb separated, and mark middle carb, as it is different than the top and bottom.

 

[dewangy]

Re: 70HP Johnson Idling problems

you may have an exhast leak under your engine cover causing your motor to starve for air,i had the same problem.