The Onan on the 345 started to give me some problems this weekend also.
It ran fine with both AC's on for about a half hour, then surged a couple of times, then flat died.
During the carb rebuild a month or so ago I installed a clear filter just before the Onan fuel pump. The filter body never fills with fuel, I therefore suspect it is pulling air in from someplace -- possibly the old rubber fuel lines are starting to deteriorate.
Also, during the rebuild I noticed that both of the needle adjustments were worn badly (velocity errosion from air being drawn in?). This, coupled with the fact that I could not find a "sweet spot" for either of the needle adjustments leads me to suspect that air is being pulled into the fuel system.
I plan to trouble shoot the system by taking fuel from the pressurized side of the rear electric fuel pump and feeding the Onan fuel pump with this pressurized gas, rather than having the Onan pump pull the gas all of the way from the main tank in the rear of the vehicle.
I'll keep the forum posted on my efforts.
"Suck it up, spend the bucks, do it right the first time."
WBCCI # 1113
Trailer '78 31' Sovereign
Living Large at an Airstream Park on the Largest Lake Totally Contained in Texas
Texas Airstream Harbor, Inc.