Perplexing Fuel Starvation

[dinsdale]

1993 Yamaha 225 outboard. Problems began last year. Engine would lose rpms progressively over about 4-5 hours of running time before bottoming out at around 11 rpm and not being able to carry any load. Counting last year, the boat has been looked at 5 different times for the same issue. Fuel separator was changed one time-ran well for about 4 hours. A few hoses/clamps were changed-ran well for about 4 hours. Most recently, they found clogged anti-syphon valves and changed another couple of hoses. Boat ran well for about 4 hours. I heard that I should check the tank venting by opening the fill caps. Are the tanks fouled? I could miss the whole season if this is true. It's just plumbing, I don't know why this is so hard to diagnose.

[Ken]

dinsdale,
Next time this happens, check the primer bulb - if it is collapsed, then fuel pump is having hard time sucking fuel due to vacuum in main tank or kinking of hose. Check tank vent hose and fuel line leading to primer bulb for kinks.
If bulb is not collapsed, try pumping it anyway a couple of times - if rpms come up, then I would suspect faulty fuel pump.
Good luck,
Ken K

[CLL2437]

I hate to say it but I'm glad to see that I'm not the only one with this problem. As I read more and more I see that others have the same problems as I do. I have replaced the whole fuel system and I still have the problem. I can shut mine off for under a minute and then start it back up and its fine for a while.

[Ken]

Charles,
If you have replaced the entire fuel system and still have the problem, then I would guess you're gonna have start looking at the ignition.
My fishing buddy had a similiar problem with his 95 C115 - but it would start acting up (loss of rpm and missing) very randomly, but did seem to be thermally related, i.e, would happen only after engine was totally warmed up - might go all day, might go fif**** minutes before problem would occur. Turned out to be bad CDI.
I would suggest you take a look at all electrical connections to the CDI and rectifier/regulator - you are looking for a bad connection that is opening up after the motor has warmed up. Grab every wire that has a connector on it and give it a little tug. Look for corrosion/rust on any connector.
Other than the above, you may have to replace the CDI, but that sucker is expensive - so make replacement the last thing you do.
Good luck,
Ken K