Honestly, feel like an idiot having missed this. Oh well, live and learn.

When the boat ran great on the top end back in September, it was still running really rich at cruise so I took jet out of it. Then changed some of the metering, and took more jet out of it because of those changes and really screwed it up.

I think starboard was more tolerant because idle transition was richer - the idle on that engine was richer compared to port. It too started to go lean with RPM.

Will be interesting to see what happens next time out.

I got ya and feel your pain. I once burned 100+ tunes on my Camaro trying to get the WB02 happy before I realized I had a vac leak.

Is drilling out the vac passage a possibility?

Yes and it’s already done. The opening for the vacuum source in the baseplate was there, but it wasn’t drilled through to the underside of the base plate. Pic for reference:




I checked it with air before making any changes - completely blocked. I drilled through it and now the well for the PV diaphragm is connected to vacuum.

These carburetors were used on a blown setup that the previous owner had lots of trouble with. These were not blower carburetors - just standard issue Demon 850s. The baseplate is factory Demon. My thinking is that it was a quality control problem - I found similar quality issues with the metering blocks (mentioned in another thread) so this isn’t all that surprising.

I know how to setup a carburetor but this situation had me doubting myself. Nothing that I was doing seemed to work. This was a big “ah ha!” moment - should work as intended now. The fuel curve might need some attention, but now that the PV will work as intended, I’ll be able to get better data if a change is needed.

I also ordered a set of PV blowout protection kits to make sure the PVs don't get damaged from backfires. My carburetors were made circa 2009-2010 (during Holley's purchase/selling of BG's assets) and should have had the check valves on the primaries - another clue that I missed.

Are you SURE this is the carb? Would you gain anything from swapping carbs. Maybe it’s an issue with vacuum serving the carb, fuel, timing, etc.

You could very very quickly minimize your list of potential issues by seeing if this follows the carb.

Good catch !
Thinking out loud round table talk…..if there is no vacuum to pv, then it’s open right ? If it’s open it adds much more fuel so should be rich when the pv is supposed to be closed.
Your thoughts ?

From my experience aftermarket carb components are a PIA and just complicate things. A boat basically idles, runs part throttle at cruise and WOT.

I took out the fuel dump PV`s and just used larger jets. The fuel curve was much happier.
You say it starts to open at 1500rpm , so basically its open most of the time running , why not just jet up 5-8 sizes and meter the fuel better, eliminate a potential issues.

I fell down that rabbit hole myself. Apparently the PV was stuck ON and he leaned the jets to compensate for the over-rich condition at cruise. Now that vacuum passages are open, I believe he's putting the jets back to orig and starting over.

Okay. Cool.
Well, then sounds like he’s probably good to go. :thumbs

Pretty sure the carb has the majority of the fault. Vacuum wasn’t being served - the base plate wasn’t drilled through.

These are great carbs when they work. Trouble is that they’re from a time where BG went way down on the quality control side of things.