With my 300DA, Marine Power Crate motors, 350, 310HP Carb models, 70 hours on both engines and new Holly 4150 Carbs, the Port Engine suddenly developed a problem that I am pretty certain traces to the Carb. It starts and idles fine, choke works well and comes off properly as it warms up. All linkage checks out properly. I typically idle out of the No Wake Zone at the marina, then go to about 1400 RPM to get farther out to the main channel. All still works fine and smooth. Then I typically go to 2000-2100 RPM for a low cruise speed. As I advance the Port Throttle, slow or fast (doesn't matter which) the engine felt like it completely died the first time, and I started to turn back toward the Marina. Then I realized the engine was running, but at near idle speed. Jockeying with the throttle got it running up around 3000 RPM and again it ran fine, so I continued the pleasure cruise for the day. I could throttle back to 2000 fine and it would keep running smoothly, and back up to higher RPM, but if I brought it back down to 1400, then tried to go up to 2000 again, it would seem to die every time. I have repeated the test several times and it is consistent. Get it past that point jockeying the throttle, and it will run fine again. It also runs fine at full throttle. Its a lot like a HUGE bog, but it doesn't come back the way a bog usually will and it came on suddenly. I checked to see if the vacuum secondary's were opening all of a sudden and causing it by rigging a camera so that I could clearly see the butterfly's as I advanced throttle, and they were not the cause. At the dock under no load, everything seems fine.
I have checked timing and that sort of thing, but since mechanical things don't fix themselves as you go faster, I'm pretty certain it is something with that Carb. Anyone have any thoughts or experience there? I can rebuild it easy enough myself, but wonder what to look for rather than just changing parts. Thanks.
I have checked timing and that sort of thing, but since mechanical things don't fix themselves as you go faster, I'm pretty certain it is something with that Carb. Anyone have any thoughts or experience there? I can rebuild it easy enough myself, but wonder what to look for rather than just changing parts. Thanks.