View Full Version : Mis-firing engine 1986 PCM 351

09-14-2013, 04:22 PM
Hey Folks, I'm a relatively new owner of an inboard, and love the excellent tips and advice on here.

Need help with a recurring problem on my 1986 Mastercraft Prostar 190:
- winterized it last year, and when I went to start it up this summer, really rough idle, and misfiring.
- didn't have time to do much on it, so took it to a shop, and they replaced the plugs, wires, rotor, points, cap - and adjusted everything.
- they also drained the old fuel and added new fuel, fuel filter, and fuel lines, plus changed the oil.
- Used it a couple times, ran perfect, then got busy and left it parked for about 6 weeks.
- went to take it out today, and same problem - running really rough, mis-firing, etc.

What should be the first thing I try?
I'm starting with some octane booster for the fuel, as its a little old now.

Any help would be appreciated. Thanks!

09-14-2013, 06:13 PM
I would start by replacing the old fuel and go from there , maybe looking for a lose wire or bad ground .

09-14-2013, 06:29 PM
Welcome to Team Talk dworsley. Six weeks shouldn't be so long that your fuel went bad, but it could be. You might try disconnecting the fuel line from the fuel pump (clamping it off so there is no leakage) and running the engine with a hose hooked to the fuel pump and the other end in a can of new gas. This would let you know pretty quickly if the gas in the boat tank is bad. You will just have to burn through what is in the carb.

My next thought is you are having problems with the advance weights and springs in the distributor hanging up and giving you way too much timing at idle. Check your timing at idle......should be 8-10 degrees. You should also visually check that the weights are moving freely. While you have the cap off, take a look at the contacts in the cap and on the rotor. If there is any build-up of crud, you can scrape it off with a screwdriver. Also visually inspect your points to see if the contacts are burned.

You should also look to see that your coil is mounted securely. If it moves it can make for a bad connection at the coil wire.

09-16-2013, 01:45 AM
Thanks folks, good suggestions. I'll try them out tomorrow.