I have two 588 ci N/A motors and the starboard motor seems to backfire or miss while cruising. It seems to do it the most around 3500 rpms. It will not make the noise at idle. What could it be? The motors have very low hours. The motor runs great and doesn't loose power, just makes funny noise.

Thanks!

Loose carb/bolts.
Maybe getting air in the fuel line....do you see your fuel psi drop at or right before the pop?
If your running MSD ignition, make sure you have the vented style caps....Mine were not, and had rust/corrsion inside.
Good luck, let us know what you find.

two of the plug wires had small cuts in them. I am replacing all the plug wires and plugs. Which are the best plugs/ wires to use?

thanks!

I have the MSD wires...never had a problem with them.

Might be a lean condition. A rocker arm adjusted to tight? Had this happen with mine. Figured it would of showed up initially, but it showed up about after 4-5 hrs. Also, maybe a weak or broken valve spring. I know you said they have low hours, but just a thought. If it only does it at mid throttle only, disregard the last two ideas.

Taylor spiral pro wires from Summit or jegs. If this is carbed I would be thinking jetting in the primarys or wrong power valves. If fuel injected how is fuel pressure when the noise starts?

BT

Is it ok to use NSG plugs? the motors run fine now. Thanks for all the help!

bad gas try octane booster untill next fill up change water sep.

Ethanol fuel issues?????

Been a few of those around here. Fuel filters clogging, pumps having issues etc. Just a thought. . . . .