bad miss

[Bob Moss]

I have a89 trophy with a3.0 omc . I have replaced the dist. cap,rotor ,points,condenser,wires, alternator,coil,plugs, all fuel filters, i have cleaned the carb an reset jets at 2 1/2 turns. boat will idle good for awhile then start missing . she will not run over 3600 rpms. Im going down today to replace fuel pump. i have also replace the prop. anybody have this problem, i could use the help. THANKS, BOB

[mikie]

Any chance you could have gotten water in your fuel tank or really old gas? Odd that it would run okay for awhile and then start missing. Even if you change fuel filters, if there is water in there you will get more to the carb.

Another thought, when it starts missing look down the carb throat and see if there is excess gas dripping in - float could be sticking.

[Sandtiger]

Sounds like it might possibly be your ignition. 'Runs fine for a while and then misses'; could be that some component in your electronic ignition is warming up and breaking down when warm. I'd have a mechanic check it out. Right now it sounds like your on a witch hunt and replacing more than you'd like to replace.

[3bees]

If it is popping back it should be ingition. Check for any play in dist shaft. Also this happened to me, when my big block popped back it sucked water into pistons. just to be sure take out plugs and crank to see if any water got in.

[ericjp]

Sounds like it's running rich. The plugs might be fouling out. What happens if you rev it in neutral? Doe's it idle fine for a few minutes?

[Bob Moss]

I have changed the plugs checked for water in the fuel ,checked for waterin the motor. yesterday she started fine but could not get but 3500 rpms. she started missing after a warmup. Thanks for all the help,BOB

[mikie]

When you say it won't go above 3500, are you running in gear under load? If so, you said you changed the prop - are you sure it's the right diameter and pitch?
Did you look down the carb throat when it started to miss to see if the float was stuck?
Looks like you replaced all of the ignition parts except the coil - might want to replace it - could be breaking down after warming up.
The only other thing I can think of offhand is to put a timing light on the motor and make sure the timing is correct and advances when you rev up, and put a dwell meter on the points to make sure the dwell stays steady. If not, then distributor could be bad.
Sorry, just reread you're post, see you already replaced the coil.

[Bob H.]

Assuming you replaced all of those parts AFTER the problem surfaced you need to take a new approach. Here's some ideas: 1) look for a loose clamp on fuel lines, especially around high temp area's - vapor lock; 2) look down carb throat for fuel during normal idle and when problem pops up - visually check quantity under both conditions - this may provide an indication of misadjusted floats or stuck needle valve; 3) Fuel tank vent - are you sure it's clear? A partially blocked vent will produce the symptons you're having and spring to early summer is when critters like wasps like to build nests in fuel vent lines; 4) electric or mechanical fuel pump? Electrical can get finicky before they die - you can put a gauge in the fuel line to check pressure; 5) Although not characteristic of the symptons but you've been playing in the distributor, check timing and dwell before the next run to prevent causing secondary problems.