1989 johnson 150 Fires up then quickly dies at less than 1500 rpms

[Caudfish15]

I've recently gone through a lot of electrical ignition issues. A mechanic recommended a new power pack based on his diagnosis; Stator and timer base checked out when tested. 5/6 coils have been replaced over the past year. Flywheel and key just replaced. Now I've replaced the power pack for the 3rd time. The motor finally fires up with ease, but immediately dies out. However; I can start it up while pushing the throttle forward and it will run great at 1500 rpms. Once I begin to move the throttle back to the locked position the motor will die after a few seconds. I'm thinking the power pack has solved one problem because I haven't been able to get it to start at all and had intermittent spark. Now seems to be firing on all six, but acts like there's a fuel issue.

Fuel pump, fuel lines, and carburetors have been replaced within the last year. After the carbs were rebuilt and a powerpack was replaced the last time the boat ran perfect with no issues until a few weeks ago when I lost spark due to a sheared flywheel key. The flywheel has since been replaced due to wearing on the slot that holds the key. I'm at a loss now, I've spent a lot of money and time on this motor. Wondering if the timing may be off causing this new symptom or if there's something else going on? Any help is greatly appreciated.

 

[jakedaawg]

You should not be shearing flywheel keys. are you using a torque wrench? Is the taper clean and fault free, lapping compound works well? The key does not hold the flywheel, it simply provides alignment purpose.

There are so many things that could be causing this I do not know where to begin...

Start with answering the above question.

2nd. post results of a compression test.

Then someone will steer you from there.

Also check that someone has not added a splice into the blk/yel wire to use as a ground for some fishfinder or whatnot.

 

[Caudfish15]

I haven't personally done anything with the flywheel, there have been 3 different mechanics who have pulled it and they say they applied the right torque. The most recent guy looked at the slot that the key fits into and said that it was too worn and would more than likely continue to shear keys. Now the flywheel has been replaced. After replacing the flywheel the mechanic tried to start it, but it wouldn't fire and had erratic spark. He ran test on ignition components and determined the stator and timing base was within speck so he said that the pack was bad. The guy said that once the new pack is on then it should fire and I need to test the regulator/rectifier to see if it's faulty and causing the packs to blow. Now I have fire, but won't keep running below 1500 rpms. I have not checked the black and yellow wire yet. Where is that located? Kill switch or on the motor?

Compression was checked last year and was in the range of 80-85 on all 6. I thought that was too low, but two mechanics said that was ok. Water pressure coming out of the motor is a good steady stream that isn't warm. When I am trying to get it down to idle speed I can push the key in for choke and it recovers some. There's an inline fuel filter that was put on last October when the carbs were rebuilt so it shouldn't have sucked anything up. Fuel lines are also new from the tank and into the motor. II'm going out Friday night to test things out again. I'd like to test the regulator and find out why this is my 3rd power pack since July. Others were Sierra and the new one is a CDI.

 

[jakedaawg]

How are you checking spark, what method?

The blk/yel wire goes from "M" terminal of.plug to the packs.

Are your pack/s properly grounded?

Are battery cabled clean and tight with a wrench? Wing nuts don't count, throw them away. All that can lead to pack or rectinier failure.

 

[Caudfish15]

I've checked the spark with a spark light attached to the plug and the spark plug wire. Last night I was on the water and did a cylinder drop test pulling off the spark plug wire and listening for a change. All spark seems to be good at this point. It continues to die when put back into the neutral position, but runs good when giving it gas. Pack is grounded well and battery cables are clean. Starts up well when giving gas, but dies when I pull the throttle back to lock position before putting it in gear. Acts like it's burning up the fuel, so I'm trying to adjust the idle speed, but I'm not quite sure on what I'm doing. I'm going to have a buddy try to adjust everything correctly tomorrow. I'm hoping that is the only problem. With all the trouble trying to get it to start before adding the new pack I wouldn't doubt that the mechanic adjusted things differently.

I need to find replacements for the wing nuts, just haven't done that yet. Do you think I'm right about the running out of fuel at the idle position? Would adjusting the linkage and screw help that problem?

 

[racerone]

I would remove bypass covers to inspect pistons and rings.------Some will argue, but I look at the basic facts.

 

[Bosunsmate]

Hows it idle on muffs? Any misfires? If so it might be a carburettor jet blockage