Sudden death at higher rpm

[Mark S]

Happy Fathers' Day all you fathers!

Today we had three generations on Weetamoe, the youngest being two and a half year old twins, and we thought we'd take a short motor tour to get them acclimated. The engine started and idled normally and all gauges, oil pressure, temperature and ammeter, reported normal conditions. After casting off, we cruised out of the mooring field at 1500 rpm and I increased rpm to 1900 after entering Salem Sound. 1900 is as high as our engine will go when forward is engaged. We have the Indigo prop on a Pearson 35.

Everything was totally normal until quite suddenly the engine almost quit, and probably would have quit, except I throttled back to 1000 rpm and it seemed then to run normally again. I increased engine speed slowly and again it almost quit. We turned around and went back to the mooring at 1000 rpm. I didn't think it wise to run the risk of needing assistance with the little ones aboard.

Back on the mooring, with the reversing gear in neutral, I slowly increased engine speed from idle, around 700 rpm, past 1000 rpm, and when approaching 1500 rpm it started to die again.

I am theorizing:

1. Fuel starvation from an unknown cause.

2. Air infiltration at higher rpm in an unknown location.

3. Failing electric fuel pump.

Any thoughts would be appreciated. We are planning a trip down east to Casco Bay the week after next and I probably won't have any time to do much myself between now and then. There's a guy in Marblehead with a lot of Atomic 4 experience that I probably will have to have make repairs, but this site always has a wealth of information and experience that may prove helpful to him if not to me.

Thanks.

Mark S

[CalebD]

Must have been great to have 3 generations on your boat!

I don't know enough to know the answer to your question. All I can do is guess.
How clean is your fuel tank?

[Mo]

When you have symptoms like that one of the first thing you should do is check your fuel filter / water separator. Typically, engines in boats that are not used frequently can develop fuel issues.

Yesterday my phone rang about 6 times (only two were A4's and others were power boats ...most with the same problem as you describe. I instructed them all re: fuel issue.

Water in fuel will give you symptoms as you describe as well however it will sputter and run good then sputter until the filtering is overcome.

So now what I just tell these guys is:
-suck the bottom of the tank to remove water and crud
-change fuel filters.
-there is a possibility that the carb will need cleaning as well.
**the ultimate cure for tank / fuel issues is have the tank cleaned.

In my honest opinion, this is where you start.

[Mark S]

Thanks for your thoughts, Mo.

The carb was rebuilt a month ago and the fuel filter is brand new. I checked the fuel and water separator a month ago and emptied only fuel. We have probably two and a half hours on the engine since then and have had no troubles.

This problem came like a bolt out of the blue. One minute the engine was running as ever. The next it was dying. I suppose these symptoms could easily be caused by something partially blocking the fuel line, allowing enough fuel to run the engine at 1000 rpm but not enough to run it much faster.

Mark

[Mo]

Mark,
Did you add fuel to the tank since you did that work? I had water in my fuel back a few years ago and it got there via me pumping water laddened gas into a jerry can from a service station...then poured it in my tank. I was heading for a trip down the shore and the problems started about 20 minutes following that.

There was no wind and I was motoring out onto the Atlantic to pick up the sea breeze early. At first I was getting a couple of sputters then it shut down. Restart was a non issue as it fired up right away...this went on and on and it started to get really bad with loss of power, couldn't throttle up without stalling...so within an hour I was puttering along just at idle...it idled OK. (My boat will do 3.8 to 40 kts at idle in no wind)

...so as I was in the swell I went through a bunch of things...and I was not thinking fuel as the problem because the engine runs almost every day.
-checked spark
-changed points and condenser (I now have EI)
-changed coil
...sick as an animal leaning in over the engine in swells at this point.
-finally I pulled the water separator and there was water.
-new element put in and it ran fine for another 20 minutes and started again.
-pulled and drained filter again...more water.
-changed element and inline for 3rd time and it ran half decent but still not perfect.
-after we arrived at our destination we anchored and carried on with the trip stuff...kids to beach etc.
-next morning I put a hose in the tank and hooked up electronic fuel pump to suck the bottom...water had settled and I pumped out about a pint....never had trouble since.

I didn't think I had a water problem at all until I checked the filters.

EDIT: If ethanol fuel is in a tank sitting it tends to dissolve the layer of stuff on the lining of the tank that accumulates with normal gas usage for years on end. Those particles mix into your gas and can foul your filters and carb as well...FWIW

[Dave Neptune]

Fuel IF

Mark, sounds like your running out of fuel. Does she still run smooth when you reduce the throttle? If so a fuel pressure gage would tell you volumes.

If you have the "water separator~~polishing filter set up I'd first change out the polishing filter and check the pressure while doing so. If everything is working fine the main filter should be plugging before it ever gets to the polishing one~but the small one is cheap and easy to R&R, An easy test is to attach a clean piece of hose to the pump end of the filter and try blowing through it and compare it to a "fresh one"

I'm gonna bet fuel pressure if she is running good at reduced throttle.

Dave Neptune

[edwardc]

Sounds like you're having problems right around the transition point to the main jet. This suggests that the main jet is partially clogged or obstructed with gunk.

If, by chance, you have an adjustable main jet, you can do a quick, crude clearing of the jet by cranking the jet all the way closed (counting the turns as you go), and then opening it back out to where it was.

[Mark S]

This forum is so good because the people are so good.

Mo, I have not added gasoline since the work was done. Dave, the engine runs fine at 1000 rpm. The problem only starts when I get up to 1500 or so and then it just dies unless I throttle back down to 1000 and then it picks up again just fine. Ed, I'm intrigued by your thought that the problem occurs in transition from one jet to another.

I bit the bullet and called the man. I wish I had the time to investigate all these suggestions because they're good ones.

Thanks.

Mark

[Sony2000]

Is the valve on the fuel tank opened fully?

[roadnsky]

Mark-
Given your comments back to everyone's ideas, I'm with Ed.
Sounds like a clogged hi-speed jet. (Main jet)

The good news is that it's easy to remedy.