21V Cranks, but won't start after running hard

[Joeldc]

We had our boat (2001 21V, Mercruiser 350 MAG MPI) out on a lake at 7000ft elevation with 1200lbs of ballast and a wake shaper. The boat was working hard.

Side note....we're planning to get a different prop since we're at this elevation often. Probably replace our ACME 537 for a 1631.

While I was surfing, I noticed the engine get louder and the exhaust was more visible. I immediately dropped off the wave and we stopped the boat. When we tried starting it again it would crank, but not start. After several tries, I disengaged the transmission and gave it throttle while cranking. The engine started, but there was a squeal (maybe from the belt). We were anxious to get to the dock so we drove at low speed and the squeal went away. Boat started and seemed to run okay after that, but I haven't run it hard since.

Does anyone have any ideas of what happened? Thanks!

[TeamAllen]

Possibly Vapor lock?

[Joeldc]

Possibly Vapor lock?

Vapor lock sounds like a possibility. It would explain how the problem resolved itself. Is there any way vapor lock could cause the squeal that I heard? Thanks!

[gumby]

How much water was in the bulge. Sound to me like the belt was slinging water made the IAC go crazy. Ask me how I know. lol been down that road. Especially our hull.

[TeamAllen]

I would fix the vapor lock issue so you're not stranded on the lake. There are a load of threads and a TSB about it. The belt squeal could be numerous possibilities. Loose or misaligned belt, wrong or worn belt, stiff impeller, a failing bearing. Those are some ideas that I can think of.

There was a certain era where water could drip on the belts through the engine hatch. Owners were inventing a drip tray to prevent the problem. Not sure what year(s) that was an issue?

[Joeldc]

There wasn't much water in the bilge. However, if we stop the boat too quickly the wake will enter through the rear vents where there's a tube that drains it to the bottom of the bilge. I think the tube does a good job of keeping it off the belt, but there's still a chance the belt got wet and the bilge was pumped out before I noticed.

I've started it a few times with a hose in the driveway and it's been starting and running well. I was thinking about trying my luck at a lower elevation lake (4000ft) to see if the issue comes up again. I'll be keeping a close eye on the bilge and will do some more research on vapor lock before heading out.

Thanks for all the advice!

[gumby]

The stock location for the bulge pump is kinda off to the side towards the front of V drive. when the boat is heavy (filled ballast) the water cant get to the pump Before the drive pulley will go under water. When you empty ballast things go back to normal and doesn't look like there is much water in there.
I recommend you deleted the drain line to the bilge all together.( plug the hole) Get the pump as Low as you can in the bilge or add a second one at the rear by the rudder..I added a second one. The blower hose needs to go as high as it can before it drops to the bulge to keep water out of the blower. I have never had a Vapor lock problem. I DID insulate the lines from the filter to the pump. they run way to close to the oil pan (oil gets HOT) I used Pipe insulation from Home Depo couple bucks for the good stuff. (Cheep)

I cant say my bilge is completely dry. I am going to switch to glide this year see if that helps. Also I think I was getting a little water coming in the stock location of the hole for the bilge.(drain through hall) I put a check valve on that line also.

On the exterior I used a piece of rubber on the intake ramp to discourage water from just ramping into the blower box. I would much rather have a little standing water in the blower box than bilge full of water. @joeidc there should be pics of all of this on My profile under media tab "My Boat"

[Joeldc]

We took the boat out again at lower elevation (4000 ft). When we were launching and first started the boat it started then idled for a few seconds then stalled. It did this twice then I disengaged the transmission and gave it some extra throttle. After maybe 30 seconds I returned it to neutral and everything was fine. We spent 6 hours on the lake (38 miles). It pulled well and ran well with no starting or stalling issues.

The bilge pump is located next to the rudder. I checked a bunch of times, but there was barely any water in the bilge. However, before going out I noticed a large tear in the blower duct. It was below the high point near the vent in the back of the boat so it could have allowed water to enter. I fixed it with duct tape, but also made it a point to stop slowly to limit the wake from flowing into the vent.

I'm not sure if the original issue was vapor lock or IAC. The elevation could have been a factor either directly or indirectly by requiring the boat to work harder.

Gumby, your boat pics are great!

Thanks for your help!