1979 140 v4 low idle

[Joseph Wilson]

I have a 1979 johnson 140 v4. Starts up great, but won't stay idling in water. If I get it to idle, when I put it in gear it cuts off. I also noticed fuel leaking, it looks like its coming from the top carb and the air silencer cover. It runs great on the hose, but in the water no luck. I've pull the carbs off, they look good, maybe recently rebuilt (gasket look new). Any help would be appreciated.

 

[Goodoleboy]

Re: 1979 140 v4 low idle

Got a manual, Then try doing the link and senc thing. Back pressure on the exhaust while in the water is lowering your rpms.<br /><br />Should idel 750 or so in the water. And around a thousand on the muffs.

 

[Joseph Wilson]

Re: 1979 140 v4 low idle

Thanks for the help. I do have a manual, but I don't have a tachometer. Is there any info on this board for installing a tach on my particular motor? If not can someone point me in the right direction. Thanks in advance for any assistance.

 

[Tacklewasher]

Re: 1979 140 v4 low idle

Depends on the tach. I bought a used OMC one that plugged right into the control box and was the easiest to install. If you buy aftermarket, they are easy to install but you need to be sure to get an outboard tach and you need to know the pole setting to use (which I think is 6p for that motor).

 

[Solittle]

Re: 1979 140 v4 low idle

Your symptoms point to crud in the carbs. Check the procedures in your manual for rebuilding them.

 

[Joseph Wilson]

Re: 1979 140 v4 low idle

The carbs have been rebuilt recently. The needle and seat, float and gaskets are fairly new. I cleaned the carbs with carb cleaner, but haven't put the back on motor yet. I noticed on the air silencer there is a hole at the bottom, with a tube coming off the back. What is the purpose of that? If that tube is clogged could fuel leak from the air silencer cover? Fixing the leak problem is my first concern, once thats done I will address the idle problem. Thanks for the help.

 

[Solittle]

Re: 1979 140 v4 low idle

Your symptoms still point to crud in the carbs.

 

[Joseph Wilson]

Re: 1979 140 v4 low idle

Put carbs back on yesterday. Fired up the motor and it ran rough. Noticed fuel still leaking from air silencer cover. Could this leak be caused by something still in carbs? I cleaned them thoroughly. I noticed the first time I took the air silencer cover off that there was a build up of oil in the bottom of the cover. I'm not sure what to do at this point. Any help would be appreciated.

 

[Sherman]

Re: 1979 140 v4 low idle

Make sure that little tube at the bottom of the silencer is clear as it drains excess fuel back into the block. On my 79 115hp this tube got pinched closed by the bottom of the carb. The engine would barely run.

 

[Joseph Wilson]

Re: 1979 140 v4 low idle

Thanks for the info Sherman. I was not sure what that tube was for. Is it normal to have that much excess fuel from the carbs? Also would it hurt to run the motor without the air silencer cover on?

 

[Solittle]

Re: 1979 140 v4 low idle

Is is OK to run the motor at low rpm for short periods for troubleshooting etc. Not good for normal running.

 

[Joseph Wilson]

Re: 1979 140 v4 low idle

Pulled the hose off from the back of the air silencer and from the block. The hose was bone dry, no sign of any fuel going through it. Is there suction created to pull excess fuel from the air silencer via the hose down to the block? Also where does the excess fuel go? Does it go back to the fuel pump? I'm trying to figure out how that hose works. There was no blockage in it, but it may be blocked at either of the nipples it slides over. Again any help would be appreciated. Thanks in advance.

 

[imported_airxsteel]

Re: 1979 140 v4 low idle

I know this is an old post, however, I have that same issue with the exact same motor, 140 HP 1979. I even have a picture of the exact hose your talkiing about.

 

[emdsapmgr]

Re: 1979 140 v4 low idle

There is a nipple on the bottom front of the intake mainifold. This fitting is (should be) open through to the crankcase. The hose runs between this fitting and the lower airbox. During operation of the engine, esp when tilted for shallow water operation, some fuel/oil may drain from the front of the carbs into the airbox. This hose will suck the excess fuel/gas from the airbox back into the crankcase's bottom cylinder as part of the normal combusion process. This leaking may also happen when you tilt the engine up for storage. It is not normal to leak when running at normal speeds and normal trim attitudes. The engine will run lean if you run without the airbox. Either run with it on, or rejet your carbs.