1986 Johnson problem

[jeldreth]

Hello everyone. I have a 1986 V4 Johnson 140hp outboard on my boat. In my yard and with the muffs on it runs great. 6000 rpm and sounds great. In the water it sounds great but WOT only gets me 2000 rpm and that's it. I know nothing about outboards except how to mix the gas and run it. Please educate me before I take this for service so I don't get taken advantage of. Thanks in advance.

 

[Walker]

Re: 1986 Johnson problem

What's the history on this motor?? Did you just get it, or when was the last time it ran right??
Compression, fuel, spark
All three are neede to run.
Start with a compression test, then do a spark test on all cylinders. Let us know what you come up with

 

[jeldreth]

Re: 1986 Johnson problem

Thanks Walker. I've had the boat for 5 years and never had a problem with it. Always properly winterized. It always ran strong. I've never done a compression test so I'll have to read up and buy the equipment. Would a loss of compression cause it to run great out of the water but not reach WOT underway. Can you explain to me what the effects of lost compression are?

 

[Fl_Richard]

Re: 1986 Johnson problem

6000 RPM out of the water, no load and muffs... Are you crazy!!!

 

[Walker]

Re: 1986 Johnson problem

OUt of the water the engine has no loads to overcome other than its own friction. You motor could probably turn 6000 rpms on only 2 cylinders.
A lack of compression in one or more cylinders is a lack of available force. Burning (expanding) compressed fuel/air mixture is what creates force to push the piston back down. Low or no compression means the force is not applied to the piston top but is leaking out through the haed or past the piston rings.
It sounds like you probably have fouled carbs but the compression and spark tests are things you neeed to do to systematically pinpoint your problem to either compression, spark, or fuel.

 

[itstippy]

Re: 1986 Johnson problem

Don't run it at 6000 RPM on the muffs. Nothing over fast idle on muffs. Gotta be in water so there's backpressure on the exhaust and load on the prop. Do what Walker says and post the results. You can get a compression tester for about $25 and a spark gap tester for about $5 at any store with a decent automotive department. Both are easy to use. The test results give the guys here valuable trouble-shooting clues. Free professional advice!
Lost compression or spark in one or more cylinders means they're not doing their share of the work and the remaining healthy cylinders are dragging them along. On muffs with no backpressure or load the motor can hit 6000RPM but it can't do it under real conditions. If that's what's going on the compression & spark tests will tell you who's loafing and why.

 

[itstippy]

Re: 1986 Johnson problem

You guys type & think faster than I do.

 

[tashasdaddy]

Re: 1986 Johnson problem

if you want to blow up that engine keep reving it, it can also cause dieseling whitch means you can't stop it only by removing the gas line a hope it doesn't throw a rod out the side. compression test remove all plugs, put in forward gear full throttle. insert guage, turn engine over about 4 times, record reading and cylinder #,, test spark, and record results. should be blue and jump 7/16 of a inch. post results. this tells us the condition of the engine, then we go from there.

 

[jeldreth]

Re: 1986 Johnson problem

Hey guys. Thanks for all the advice. I didn't realize I could do damage by revving high while not in the water. It was only for a second but from what I hear now, that's enough to kill it. Thanks for stopping me from killing my motor.

Ok. The advice you gave paid off. Went home and tested spark. removing both plug wires on the right side of the motor made no difference in the way it ran. I had no idea that this motor could run, albeit poorly, on only two cylinders. I found a loose ground connection to the coil pack for those cylinders. Cleaned and tightened the connection and put it in the water. Ran like a champ, with one exception. I took a long run at 4200 rpm. When I throttled down, the engine stalled and when I went to restart, the battery was almost dead. Switched to the auxillary battery and noticed that the voltage meter was at 13.5 to 14 VDC at low rpm, but at higher rpm dropped to about 12. Any suggestions?

By the way, if I didn't say it berfore, you guys have been a fantastic help. Thanks for helping me have a great day on the water.

 

[OBJ]

Re: 1986 Johnson problem

First as always, check your battery connections are clean and tight and do this all the way back to the engine. Check the connections at the terminal strip on the starboard side of the engine where the yellow leads from the stator mate with the leads from the reg/rectifier. Since the tach is still working, it sounds like a dirty connection....probably at the batteries or the battery switch.

Don't over look the connection at the starter solenoid either. This is where the charge wire (red) from the rectifier goes to.

 

[tashasdaddy]

Re: 1986 Johnson problem

another happy ending.