2000 70hp Johnson semi start/ won’t stay running

[SJproline24]

So I have acquired this motor which has been sitting for 13 years. So far I have replaced the following new plugs, new fuel tank, all new fuel lines, removal of vro and went premix with conventional fuel pump, and rebuilt the carbs, new primer selonoid valve and gasket. Replacing ignition switch tomorrow.
Problem— motor ran for 20-30 minutes no issues many times on land with earmuffs. Go to the ramp starts up and runs for ten mins then it shut off. Got it running again and it stayed running to the point I was able to run the motor out to the bay and back prob30-40 mins all stages of throttle(wot, middle and just above idle).seemed to run pretty well imo. Get back to dock sat idling for a few minutes and I shut it off. Would not start back up. Cranks, sometimes fires for a few seconds but won’t stay running long and dies out. Have to advance timing at throttle to get running though.always.
Pulled plugs and saw spark on all three cylinders. At a loss of where to go now.
Any advice on what direction to take or what to look at.
Greatly appreciate any advice. Thanks.

 

[racerone]

You have to wonder why it sat all those years.----Post compression values.

 

[jimmbo]

After you remounted the carbs did you check/verify the Sync between the Carbs and Spark Timing? Also, how did you set the Idle speed? What Rpm is the Engine Idling at in gear, in the water?
When you checked the spark, did you verify that it could jump a 3/8" gap on all cylinders?

 

[SJproline24]

Boat was grandfathers then given to another family member. Who used it for a few years he had a kid and parked it.life showed up we will say. Didn’t have time for it. Just trying to resurrect it. Long family history with engine. Will have to do compression test. Haven’t gotten there yet. Haha Jimbo I didn’t. Don’t have manual. Didn’t do any of that just got the mark on cam that pushes on carb cam lined up. Boat doesn’t have tac to know what rpm I’m at. New to all this boating stuff but pretty mechanical.how do I go about all that “syncing”. Apparently it’s not just hooking the connecting rod and having the cam on carb meet that mark on the other cam linkage piece.
Edit: also I just pulled plug and watch for the arc grounded to engine. How I used to check for sparks on cars.

 

[jimmbo]

You need to get a Service Manual specific to that Model/Year of Motor

 

[SJproline24]

You need to get a Service Manual specific to that Model/Year of Motor

How do I know what model it is, I don’t see any markings on tag on boat or on flywheel
Edit. Never mind I got it

 

[jimmbo]

When I said specific, I meant a Genuine OMC/BRP Service manual

 

[SJproline24]

Yeah man will do. Thank you for all your insight so when I get that manual I can get back headed in the right direction.

 

[racerone]

Did you make sure that the high speed jets ( orifice plugs ) are clean ?---They are found way inside the carburetor bowls.----Often over looked.

 

[SJproline24]

Did you make sure that the high speed jets ( orifice plugs ) are clean ?---They are found way inside the carburetor bowls.----Often over looked.

Yes

 

[Chris1956]

A lot of OMC products of that era had plastic carb bowls. Those often warp, don't seal well and cause issues.

When she dies and won't start, does she have spark? Does your overheat alarm work? Does it sound?

 

[racerone]

I don't think plastic carburetors were ever used on the 3 cylinder 70 models.

 

[SJproline24]

Doesn’t have plastic on carbs, it had buzzer for oil. But deleted it when I went conventional fuel pump. Haven’t heard overheat alarm yet. Pisser works fine. Have to get spark testers to check if I lose spark.

 

[saltchuckmatt]

Spark jump testers....here's a low cost one.

 

[racerone]

Some will argue.----But if a motor has sat for 13 years it needs a new impeller.

 

[saltchuckmatt]

Doesn’t have plastic on carbs, it had buzzer for oil. But deleted it when I went conventional fuel pump. Haven’t heard overheat alarm yet. Pisser works fine. Have to get spark testers to check if I lose spark.

Get an IR gun and test head temperature maybe alarm is dead.

 

[racerone]

Test the overheat horn.---Install new impeller.

 

[SJproline24]

Update- I disconnected the kill wire on ignition switch and was able to get it to start and run. Just had to choke it off to shut it off. So now we are headed in the direction of key switch, power pack, or bad wire in harness.

I left out I have already replaced the impeller.

 

[saltchuckmatt]

Take your multi meter and find the culprit....nothing but time to find it. Good luck!

 

[SJproline24]

Got it! Threw in new ignition switch and she’s alive again!! And she shuts off and starts back up. Time for water test. Thanks for everyone’s input! Greatly appreciated.