Is this a fuel problem?

[Still LauCo]

So a couple weeks ago, I had trouble starting the stbd engine after getting fuel at the gas dock.
I eventually got it restarted after limping back on one engine, right before I docked. It ran fine from there.
I figured I had a fuel problem, so I replaced the fuel filters on each motor.

Yesterday, the boat ran great on the way out to a bay. As we were leaving the bay, the stbd motor started to backfire when throttle was applied. (I didn't know fuel injected motors could backfire:huh

I kept it at idle, where it seemed to run fine. I put some dry gas in the stbd tank, and after about 3 minutes it ran perfect.
I then throttled back up, she ran great the rest of the day.

Does this sound like potentially a fuel problem?

 

[Still LauCo]

Anyone? Any idea as to what I should look for here, or could it simply be bad gas?

 

[osd9]

If you have etahnol fuel, adding dry gas is not recommended. Ethanol basically is dry gas.

Motors backfire for a lot of reasons.....a few of which are bad valves, timing, cracked heads, etc, etc....

It seems like you are only having trouble with the stbd motor. Do you have crossover valves for the fuel tanks? If so, try switching tanks.

 

[Hampton]

It does kind of sound like bad gas, or some other form of minor engine problem. I had that on my 1997 250 and fixed it with a new distributor cap, rotor, and wires. That fixed it after 2 hours of labor at the dealer didn't find anything wrong.

 

[douglee25]

It 'sounds' as though it could be electrical or timing related.

I would add startron to your tank first and see if things improve.

Doug

 

[ImpulseIII]

Will Startron cure an electrical or timing problem?:huh:

 

[fwebster]

When did you last change spark plug wires? Mid-90's Mercruiser ignition wires were notorious for breaking down. A quick check is to crank the engines with the hatch open at night and watch for arcing from any wire to the engine block or manifolds. It may surprise and scare you.

I did this on my old gas 390EC when it started randomly missing and was floored by what I saw. My engines looked like they had flashing Christmas tree lights hung on them. MErcruiser has had many different wire parts numbers superceded by improvements, so don't let a Merc dealer sell you a non-current set of wires.