Can't get over 3000rpm

BoatingTimbo

Petty Officer 3rd Class
Joined
May 18, 2009
Messages
78
1985 32 foot Carver with twin crusader 350's 4-barrel carbs

Boats been running great all summer with regular use. Took it out yesterday and can't get it to run over 3,000 rpm with both throttles wide open. At about 3/4 throttle (3,000 rpm) it's got no more. Both engines identical and wasn't a issue two weeks prior when we were away for the weekend.

No missing or hard start, no overheating, idles perfectly and runs perfectly at 3,000 rpm -- wouldn't know anything was wrong except final 25% of throttle is dead.

Could it be fuel pumps?

Maybe 4 barrel secondaries not kicking in?

why would both engines be experiencing the identical problem?

any insight would be greatly appreciated.
 

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: Can't get over 3000rpm

Bottom condition? Have to ask, and it would affect both engines. End of season. Gap between running well and now?
 

BoatingTimbo

Petty Officer 3rd Class
Joined
May 18, 2009
Messages
78
Re: Can't get over 3000rpm

I dove down to check out the hull. perfectly clear, no growth at all. Minor barnacle growth on shafts and prop but nothing that would cause this kind of drag.

Ran fine three weeks ago with no hint of any issues developing.

Seems the second stage of 4-barrel carbs are not opening or fuel pump not supply at higher RPM's (3,000 +)
 

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: Can't get over 3000rpm

Doesn't seem like the last two should affect both equally unless it is in the controls. Bad fuel? Check filters?
 

Capt Ken

Commander
Joined
Jul 30, 2002
Messages
2,269
Re: Can't get over 3000rpm

It's going to be the bottom for it to affect both engines the same. Just a light film of slime will prevent one from planing. Been down that road too many times.
 

hottoddie

Seaman Apprentice
Joined
Feb 26, 2011
Messages
40
Re: Can't get over 3000rpm

If single fuel tank could be fuel filter, bad fuel or defective anti siphom valve. If 2 tanks most likely running gear fowled. Minor barnicles on shafts, struts and props will cause major drop in performance. Clean them first and go from there.
 

Tommyfmu

Seaman
Joined
Sep 16, 2009
Messages
63
Re: Can't get over 3000rpm

I've experienced the same; fouling a lot, so had her hauled and cleaned. Still had similar problem, not able to exceed 3000 rpms. I found that it was due to clogging in the port carb. Holley 4 barrel 750cfm with auto choke. During rebuild it was found that many of the multiple jets ended up being clogged with traces of water due to ethanol most probably, and perhaps not quite enough Startron treatment, or fuel filter needs changing; haven't changed it yet so will do so this weekend. With such a heavy boat, if one carb is bad, the sheer weight of the boat would keep the other engine from reaching higher rpms too, thus not exceeding 3000rpms in either, imho.
 
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