I have a 1998 Sea Ray 37 EC with 454 7.1 Horizons inboards.when I start engine cold they run great for hours. When I stop engine for 3-4 hours they won't stay running. backfire, no idle try everything.wait 3 more hours there cold and they start right up and run great. they will also start if started back up in 1-2 hours after running. just had plugs, wires ,cap and rotor replaced. And the real mystery is its both engines act the same. I also changed all fuel filters and running new fresh gas. Ive had 3 professional mechanics look at it and they scratch their heads,.........Please suggestions..