Engine idle down issue

[Chris58]

I have a 5.0L 305 year 2000 carb Thunderbolt V ignition engine serial# 0L628970 in a Chaparral SSE with a Mercruiser outdrive. Last summer it start having issues with the engine rpms cutting out without warning. The symptoms are pretty consistent. Starts easily, idle out of our creek into the harbor (about 15 minutes) power up to 3500 rpms (about 37mph) for about 30 minutes, then all of the sudden the rpms drop to 1200 and the engine almost chokes out. I can slowly rev back up to about 1900 but if I go to 2000 or higher it cuts back down to 1200 again. If I put the transmission in neutral the engine will rev to 3500-4000 with no problem. If I turn the engine off and let cool for 30 min or so, boat starts back up with no problem and will power up to 3500 like nothing is wrong and may stay that way for a while. All gauges look normal at all times, temp, oil pressure, battery, etc. Any suggestions?

 

[alldodge]

I'm thinking fuel delivery problem.
Dump the contents of the fuel filter into a something clear and see if you see anything but clean gas.
Remove the gas cap when it does this and see if you hear air being sucked in.
Check the tank anti-siphon vale for a restriction
Listen for the fuel pump and to see if it is still running and/or bad sound coming from it
Get a vacuum/fuel pump tester and check fuel pressure at the carb, should be 4-7psi

 

[Scott Danforth]

Im thinking chunks of stuff floating around in the fuel bowl on the carb

 

[Bondo]

I'm thinking fuel delivery problem.

Ayuh,..... Welcome Aboard,... I have to agree with AD, 'n Scott,.... Sure sounds like a lack of fuel delivery to Me too,...

 

[Chris58]

Thanks all. Will get to work and hope that's it. Cheers.