305 running rough, loss of power

[James Francis]

This is a strange one...the engine has been performing great. On a recent run getting up on plane I used my Lenco trim tabs ( electric) for the first time this season - about 2 seconds after I pressed the switch to activate the tabs I heard a loud pop in the engine compartment. The engine started to misbehave terribly immediatly and I had to limp home. As soon as I got up over 1500 RPMS the engine who lose all power Could the draw for the tabs have really effected the ignition circuit of the engine?

I first thought fuel but I took off the the separator and there was not a drop of water in the bowl.

Any speculation ?

James

[stonebreaker]

Look for a burnt or shorted wire. Are you carbed or fuel injected? Also, correlation does not prove causation - don't rule out something else, it could have just been a coincidence that the problem occurred as you used the trim tabs. A "loud pop in the engine comparment" needs serious investigation.

[charmc]

Stonebreaker is right. I'd carefully trace all wiring located near the engine. A loud pop is a serious indicator of malfunction; the dropoff in engine performance is more evidence that it is serious. An ungrounded circuit, loose wire touching something, an overload ... Check every circuit; don't assume that it must be the new trim tabs.

[James Francis]

Although I am not certain it is the tabs - It just seems too coincidental that it happened simultaneously - The boat has acted like this before but I don't remember the popping sound. Although I chased the problem as if it were fuel related, it turned out to be in the ignition system. The points and cap look good but I think I might swap out the ballast and coil as a test. Other than that I will check the ignition switch and make sure it is not effecting 12 volts at the coil.

The boat has a 4 barrel quadrajet. Again, I don't think it is fuel ( new fuel pump, clean fuel, new filter) but I will test the engine on a fresh tank of gas from a portable and another new filter to validate that assumption.


Jim

[charmc]

It's not necessarily the tab power draw itself, but adding the tabs means some wiring was added to what was there before, and there could have been an overlooked error, like a poor ground, open circuit, wires chafing, etc. which could be draining power.

A less likely, but possible, cause could be a hairline crack somewhere, like in the cap. I had an engine suddenly lose power at night, saw spark arcing from the side of the cap. The crack was hairline, not visible, but the high voltage current went right through.

I think you're right, it's more likely to be electrical than fuel related.