Thanks for the good responses. I will pick up the spark plugs today and a new compression tester and try compressions again and see what I can with an endoscopic camera and report back.
Update. I did a compression check with a cheap tester without assistance, and not fully reliable, but all cylinders were between 120 and 135, except the one that lost its plug electrode recently (#3) and the one that lost the same a few years back (#5), which are side by side in the same head...
Attached is a photo of the sticker from the top of the flame arrester and another from the Tune Up Specifications from the Mercruiser Maintenance Procedures Manual for “1997 Gasoline Ski Series”. The plug type is what I am running, but the sticker say .035 gap and the manual shows .040. Not sure...
I pulled all of the plugs after the engine was failing to reach WOT and then backfiring on acceleration. They are all in need of replacement, but one (photo attached) was so bad, the electrode was completely gone. This is a carbureted engine, 1997, serial # OK146780. I was running AC Delco MR43...
On my 3.0 liter 140, the front mounts on my boat were secured to a cross member between the stringers. When the lag bolts stripped, I drilled out the holes large enough to drive lag bolt “shields” (used to put lags into concrete) in and the bolts snugged up fine. I ran that way for many years...
I would suggest a careful examination of the plastic body for cracks and also confirm that you did not have a leak at either the in or out hose. Sometimes the impeller is perfect till it is not. My experience with that pump on the same engine has been to change the impeller every 100 hours.
I have also heard rattling noises when idling too slow in gear that people smarter than me have said are coming from the damper plate, which is attached to the engine flywheel.
I have run a 5.7 liter Competition Ski with a Borg Warner velvet drive (fnr) behind a Walter V-Drive for the last 26 years and have fought belt squeal a lot, going through several serpentine belts, but your recording does not sound like belt squeal, although recordings are tough to analyze...
I see you mentioned you ”cleaned the tank”, but without removal, it is difficult to confirm you have all debris removed. The pickup tube can still periodically plug with debris, which then drops off as the suction reduces. You had two suggestions to run on a remote tank to isolate the problem...
Check out IslandExplorer’s post last Monday. Get the cable parts number with the parts lookup referenced by AllDodge, which should be available with Sierra cross reference. Your control is available on eBay.
Item #14 in the diagram is mercruiser 18-37809, which is a hairpin, rather than a clip type as shown in your photo. The mercruiser hairpin appears to also be readily available. I got a bit carried away chasing this down, but it was helpful for my application as well.
