Engine missing, help!

[73PennYan]

My boat engine has been intermittently missing at speeds from cruising to full throttle for 4 years. I only put about 5 hours runtime per year. The missing is audible but the boat doesn?t stall or bog down. I am looking for any suggestions on what to try to fix this.

The motor is a 1973 inboard OMC 250 hp (350 ci with Rochester Quadrajet and Mallory flat cap ignition). It does not have a water separator on it. So far I have changed the points and condenser, checked the timing, added dry gas, and changed the fuel filters in the carburetor and inline. The problem seemed to go away for most of a summer when I changed the points but it came back.

What should my next step be?
Change the distributor cap?
Change the coil?
Change the spark plugs?
Change the spark plug wires?
Add a water separator?
Check for a wiring issue?
Other suggestions?

The boat is on a local pond and I don?t have a trailer. There are a few mechanics that make house calls but this could get costly if they don?t fix the right thing first. I would like to try the easier stuff myself. Thanks!

 

[TiredoleBoy]

Re: Engine missing, help!

Have you checked for play in the distributor cam? Also is this a plastic bowl Rochester? I have also seen advance springs sticking causing missing, Also there is a possibility the condensor could be causing the points to foul. Are they pitted and dirty when opened? Where do you get your parts from. There is a difference between car and boat ignition parts.

 

[73PennYan]

Re: Engine missing, help!

Thanks, TiredoleBoy, for the suggestions.

The points and condensor (and all parts I have been using) are marine. I changed the condensor and points and I don't think the points are pitted or dirty but will check again. I will also check the springs on the carb. The missing starts with no change in speed or throttle position.

What is a plastic bowl Rochester? Is that the float? Also, how do I check the distributor cam for play? Thanks again.

 

[73PennYan]

Re: Engine missing, help!

The engine is still missing intermittently at planing speeds to full throttle. The points look good. I checked the ballast resistor. It is labeled 2 ohms and reads 2.2. The coil is a P&D UC-4X. It reads 1.5 ohms from plus to minus and about 10K ohms from plus to the center. I guess they are all right. I pulled one spark plug and it looked good. I am thinking that I should next replace the spark plug wires. What would any of you do next? Thanks!

 

[JustJason]

Re: Engine missing, help!

Is your fuel 4 years old if your only running it 5 hours a year????

 

[Isaacm1986]

Re: Engine missing, help!

Sounds like maybe just a good old tune up might help. New plugs, wires, cap, and rotor. This may not be the issue, but it is where i would start.

 

[73PennYan]

Re: Engine missing, help!

Is your fuel 4 years old if your only running it 5 hours a year????

There is definitely some old fuel in there. The tank is 36 gallons. I ran it pretty low and just put in 13 gallons with no improvement, though. I also changed both fuel filters last year.

 

[73PennYan]

Re: Engine missing, help!

Sounds like maybe just a good old tune up might help. New plugs, wires, cap, and rotor. This may not be the issue, but it is where i would start.

Thanks, Isaacm, I think that this is where I should go next.

 

[Haut Medoc]

Re: Engine missing, help!

The first thing i would do is add a water separater, it does not take much water at all to make an engine miss.....

 

[IES99]

Re: Engine missing, help!

The first thing i would do is add a water separater, it does not take much water at all to make an engine miss.....

Agree with Medoc about the water separating fuel filter and also do the electrical tune up. I think you'll be fine.

Good luck!
enjoy the boating

 

[dingdongs]

Re: Engine missing, help!

Try a portable fuel tank to isolate the problem to carb or electrical.could look at electrical system in the pitch black and see if its lighting up like a christmas tree.assume you've cleaned up all electrical connections first.

 

[73PennYan]

Re: Engine missing, help!

Thanks to all responses. I think the problem was with the fuel. Believe it or not, I think that using a can of SeaFoam fixed it. Every time out this year but one short one there was some missing before the SeaFoam. After I poured a can in the tank, I have taken 2 longer trips on the pond and onto Lake Ontario in calm water and choppy with no missing.

I think I might still do the tune up but it really is running great. I had tried dry gas without an improvement. I am still somewhat skeptical expecting the problem to return the next run but it is running the best it has in the last few years. I'll be adding some fresh gas in the next few days.

 

[JustJason]

Re: Engine missing, help!

Your best bet at this point would be to tune up the ignition system (cap rotor plugs wires points etc) fill it with fresh gas, and run the snot out of it. It's the sitting that kills it.