'78, 70 hp jonhson cuts out when put on F or R please help

[imported_newbieboater]

jsut pick up a boat with a 1978 70hp johnson outboard, runs fine at home with muffs... able to put in Forward or Reverse but when put in water motor cuts out once i put it on Forward or reverse... please help...thank you

 

[DJ]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

Your engine is probably running on less than three cylinders. They will appear to run fine, on the muffs. Muffs provide no essential backpressure for proper diagnostics.

Things to check, in order.

1. Compression. Should be over 100 and within 10 psi of each other.

2. Spark. Should get a good strong blue spark.

3. Look at the plugs, they all should look similar.

 

[imported_newbieboater]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

thanx DWJ, i have recently takin the plugs out, one of them seems to be darker than the other once...sorry new to boatinf but thanx for the help. at the dock today a friendly baoter came up and suggested that it might be the linkage, does it sound right.

 

[DJ]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

newbie,

Linkage adjustment may just mask a more serious issue.

Check the basics first, then we'll dive into other possibilities.

Compression testers are cheap and spark plug checkers are also cheap. Both tests are simple.

To test compression, do this.

1. Remove all three plugs.

2. Disconnect the fuel line.

3. Move the control to wide open throttle.

4. Isert the compression tester in #1 (top cylinder).

5. Crank the engine over 5-7 revolutions.

6. Record results.

7. Repeat process for cyl's. 2 & 3.

 

[Silvertip]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

You need to start with the basics. Compression check, spark check, and a check of the fuel system. Fresh fuel. Was the engine stored for a long time without being run. Carbs are probably all gummed up and need rebuilding. When done with that, a link & sync should be performed. You need a service manual for the engine. All of these procedures are far too detailed to go into here. Check your local library -- they sometimes have them to check out.

 

[imported_newbieboater]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

tanx will try that, when i bought the boat the previous owner mention that he just had it tuned up, and if i do remember right the compressions that he mentioned are over 100 and within 10 psi just like what you have said.

 

[imported_newbieboater]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

tanx SILVERTIP, i was just looking for repair manuals online.

 

[DJ]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

If it were mine, I'd recheck. No sense in going further if you have a sick cylinder.

Spark check is next, after that.

 

[tashasdaddy]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

just tuned yeah, 2 years ago maybe, did he give you the reciept? do what has been mentioned, and if it sat up for a while do the impeller, before you burn it up.

 

[imported_newbieboater]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

check plugs today, # 1 and #3 plug has some burnt marks on but # 2 plug stil new and clean, just like when i put it in.

 

[mikesea]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

I'll bet the carb isnt getting fuel,that float might be stuck closed.You can try the old tap tap..If the comp. is good and you have spark,look to carb.

 

[HavToNo]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

If one sparkplug is clean it it could mean that water is getting into that cylinder. Switch the plugs around and then try running it for 5 to 10 mins and see if the #2 comes out clean. I have a manual for Evinrude and Johnson outboards and it describes your situation perfectly.

 

[imported_newbieboater]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

Your engine is probably running on less than three cylinders. They will appear to run fine, on the muffs. Muffs provide no essential backpressure for proper diagnostics.

Things to check, in order.

1. Compression. Should be over 100 and within 10 psi of each other.

2. Spark. Should get a good strong blue spark.

3. Look at the plugs, they all should look similar.

finally got around to do this...

compressions are as follows, 130, 125, 130
#2 plugs is still new... CAN IT BE COIL PROBLEM.
fresh gas (regular)and oil mix (west marine twc-3) of 50:1 ratio IS THAT RIGHT RATIO.
fuel in all cylinder.

 

[DJ]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

Compression is OK.

Do you have spark on #2? Spark should jump a 1/4" gap with a strong blue spark. Spark checkers are cheap.

 

[tashasdaddy]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

idle has to be set high on muffs, there is no back pressure on the exhaust on muffs, the engine will idle lower when in the water. if idle set to low the engine will cut out when put in gear.

 

[imported_airxsteel]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

fresh gas (regular)and oil mix (west marine twc-3) of 50:1 ratio IS THAT RIGHT RATIO.

Yes sounds correct. I have a 140 HP 1979 Johnson too that had the same issues. These guys are right on the money. Plugs are the cheapest things to buy. I bought four new ones for mine. That is the easiest thing to check.

 

[imported_airxsteel]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

by the way, shouldn't really matter but.....

Make sure your using Champion plugs in that Johnson.
Good luck.

 

[freddyray21]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

I had a 50hp evinrude did the same thing. As someone already said they need to idle higher on the muffs. Best way to set the idle is with the motor in the water. You might not have anything wrong with compression, fuel or spark. If it isn't idling high enough in the water it will die when you put it in gear. Do the simple things first before tearing into it.

 

[Walker]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

Forget all this about setting the idle higher on muffs. You have a clean plug so you have either a fuel delivery problem, no spark, or water intrusion into that cylinder. Have you done a spark test yet?????????????
If you have spark my best guess is that your carb is clogged. If you clean one, clean all 3.
You get that cylinder to pull its own weight and your idle/shifting problem will probably take care of itself.

 

[DJ]

Re: '78, 70 hp jonhson cuts out when put on F or R please help

Forget all this about setting the idle higher on muffs. You have a clean plug so you have either a fuel delivery problem, no spark, or water intrusion into that cylinder. Have you done a spark test yet?

Agree 100%.