Help with '87 40hp Johnson. Manual vs electric primer switch?

[noydb]

This motor ran fine till it ate some sand and chewed up the impeller. It then sat for 10 years. My BIL replaced the water pump and got it running again. I tested it with muffs and it would start and idle ok. I didn't try to rev it since it wasn't in the water. When I took it out for a test run, it would start idle 30 seconds then die. My bud tried pumping up the bulb and as long as he kept pumping it, it would continue to run and would even get up on plane and run at WOT. But as soon as he quit squeezing the bulb it would die. <br /><br />Looking things over later at home I noticed that the primer switch was in the manual position.<br /><br />Would that cause this symptom?<br /><br />Also I'm interested in suggestions as to what other maintenance I should do. Thanks.

 

[Mark42]

Re: Help with '87 40hp Johnson. Manual vs electric primer switch?

For maint, I suggest new sparkplugs and wires, the wire kits are available from your local dealer about $9.00 each wire. Also pick up the carb rebuild kits and clean out those old carbs. <br /><br />My guess is that your running problems are because the carbs are clogged up and need cleaning. I base this on the primer switch being in the open position and pumping the bulb keeps it running. This is because no gas is going through the carbs, but only through the choke. So my first suggestion is to remove and clean the carbs. Not hard because they are very simple design. <br /><br />If the carb work does not fix it, the next place to look is the fuel pump. Rebuild kits are available for that too if you need one.<br /><br />Before doing anything and spending any money, a compression check is a good idea because it will tell you the overall machanical condition of the motor. The PSI reading should be over 100, but more importantly is that the readings should be within about 10 psi of each other. If you get low or highly uneven reading, then remove the head and look for signs of a leaking head gasket. <br /><br />If the compression checks out good, a manual will be a big help, especially if you plan to keep that motor a while. The $30 invested is well worth the returns you will get from it. And in case you haven't priced new or used motors, they are big $ items. And that 40 is a nice balance between power and weight for any smaller sized craft.

 

[noydb]

Re: Help with '87 40hp Johnson. Manual vs electric primer switch?

Thanks, replacing the spark wires is just good PM on an engine that age. Should have already done that. So is rebuilding the carbs, will do that. I appreciate the suggestions.

 

[Jcrain]

Re: Help with '87 40hp Johnson. Manual vs electric primer switch?

Same thing happened to me. Sort of.... I didn't have the fuel line locked at the engine connect. It viberated off, engine died.But, I didn't notice this. I crawled out the back of the boat (Pontoon) and fiddled with a few things. but wouldn't start.I used a trolling motor to get to my dock, got a friend and my ski boat and pulled the pontoon to the loading ramp.As my friend an andi was loading the pontoon on the trailer, he noticed the fuel line hanging down. We hooked that up , put it back in the water and had the same symtom as you, run for about 30 seconds then die. Only way to keep it running was pump the bulb. I remembered the lever on the primer, flipped it back out of manual, and it started and ran like a champ. Oh, yeah, it's a 90 model 40 horse jonnie

 

[noydb]

Re: Help with '87 40hp Johnson. Manual vs electric primer switch?

Jcrain.<br /><br />Thanks! I think I need to do some more testing before I start rebuilding things. (still going to replace spark wires and rebuild carbs).

 

[noydb]

Re: Help with '87 40hp Johnson. Manual vs electric primer switch?

Just an update. Put muffs on after putting the primer switch in the correct position. Idled fine for several minutes. So on to PM.

 

[Jcrain]

Re: Help with '87 40hp Johnson. Manual vs electric primer switch?

Glad to hear that you got it idleing ok. I know I was happy when it fixed my problem.