Engine(39)s die, then are fine. Arrggghh-gctid390709

[Mileskb]

I have had the symptoms for two seasons and we thought we figured it out last season. But... based on yesterday... apparently not.

As I am looking for every angle, I'm just going to post what happened in hopes someone comes up with a new idea.....

Merc 470 on '79 Santiago. Full tank of fuel.

1. Head out from Coronet Bay... down south to Camano Island and then head back...

2. Cruising at 20-ish mph at 3000-3200 rpm... purrrrrrrrr

3. Get back up around Skagit Island, been out about 75 minutes cruising at this point and the engine dies.

4. It will idle, but any load (into gear) and it stalls.

... but wait there's more..

5. I light up my 2005 Honda 4, 15 HP Kicker... to head back...

6. After about 15-20 minutes of putting along nicely.... it dies.

7. I am able to start it, let it puch along for a minute, it dies, I restart... eventually... it doesn't want to start either.

8. It's been 20 minutes since I tried the main engine... so why not??? It starts right up.. purrs like a kitten.

9. At the pier I had to maneuver forward/reverse a few times and was worried it would stall at an inappropriate time... but it was just fine.

10. When I got home flushed both engines... they fired right up and ran fine. I use a bucket to flush the kicker so was able to put it into gear as well... all just fine..

To set the hive mind in the right direction... As the only thing the engines have in common is Gas... I checked both screens.

The in-line on the kicker and the fine mesh screen that is in the side of the carb on the 470. Both SPOTLESS....

I do have a water separator which I will pull next... but wanted to get the hive mind opinion.. The fact that BOTH engines, completely different (other than they are engines) acted essentially the same, the only common thread is the fuel... so I started with filters.. and came up empty...



Thanks in advance for any thoughts..

Miles

p.s. I just love these 60 degree and raining type days... (sarc) LOL !!!! Man was it nice out yesterday...

[Guest]

To truly eliminate the fuel system as the issue, do you have a way to hook up a portable tank (e.g. outboard tank) to the outboard? You would leave the original fuel system hooked up as is, then wait for the trouble to surface. When it does, switch over to the portable tank and verify if the problem comes back or not.

You said the pickup screen looks ok--do you have a check valve on the main line? Perhaps that is clogged/sticking? How's the fuel filter? Have you checked the water separator yet? How old is the fuel?

[Guest]

This story may or may not help your search, but it sounds similar:

My brother commuted 80 miles each morning in a VW bug. Occasionally his car would sputter and die and he'd drift over to the side. After a few minutes, he'd start it up and continue. He noticed it usually happened when he was low on gas.

After tearing through everything a couple of times and finding it all up to spec, an old timer asked if we'd checked the gas tank, and told us a story that sounded like ours. We took off the tank and found a length of clear hose which had swollen up while soaking in gas so that it looked like a long jellyfish. Someone had siphoned gas and lost the end of their hose in the tank. It would float around the tank harmlessly, for the most part, and then occasionally block the gas outlet and be held on by vacuum. Letting the car sit released the vacuum and released the hose. And the chances of it happening increased when the tank was more empty.

[Mileskb]

Well I may have solved the problem, but I won't really know till we head out again.

FWIW in response to the questions..

Fuel is reasonably new.. it's s 60 gallon tank and as you can see below I checked all the filters.

I like the secondary tank idea. A bit of a chore to swap the main engine, but could do the kicker easily.

So here's what I have so far today...

1. Both fuel filters were clean.

2. Took off fuel separator and it had nice clean gas in it.

3. Cleaned vent.... Ding Ding we may have a winner...

The vent was not "clogged" per se.. but it was restricted. A assumed it was ok because as a test a month ago when some gas expanded out of the full tank inlet instead of the vent I blew into the inlet and gas came out the vent... While it had flow, it was apparently clogged, just not completey. When I removed the vent from the tank side and blew into it... I could blow air through but it was hard to do. I can't really get to the through hull fitting, but I flushed it both directions and a bunch of stuff came out until it was clear. The only thing I had to flush it with was a garden hose, so I then blew air from my compressor and will await for it to dry before I hook it back up. Any moisture should drip completely out overnight.. I did test and it was much easier to blow through the hose now.

Additionally, and I didn't think about it at the time... When the first sign of "somethings wrong" happened I looked at the gas gauge and it was pegged just before the engine quite. Later, when we were putting in, I noticed the gauge was at 3/4 tank, which seems correct based on prior performance.

Can someone confirm/deny that if the vent was clogged, the pressure in the tank would cause the gauge to max out?

Also can someone can agree/disagree that I might be on the right track that the vent has been the issue, or anything else short of something actually floating in the tank.

[Chief_Alen]

Sometimes you may overfill the gas tank and gas comes out the vent tube, the vent tube may have a bend or loop and gas will stay in the tube in effect cutting off air to the tank as it empty's.

[Mileskb]

Thanks Chef,

That may indeed be what happened. I know fuel got into the vent, and while there was a spot that dipped just low enough to hold a little, which should slosh back into that tank or evaporate over time, but add the clogged vent, even though not completely blocked vent.... and I think what you described is exactly what happened.

FWIW... I just hooked up the vent and assumed (again bad idea) that I'd have to "prime" the carb a bit as I had the separator off earlier today.. so I just opened the throttle and figured I'd have to turn it over a few times to get it primed..... lo and behold... it just started!!! It's NEVER started that easily from a cold state. After about 30 seconds of warmup at about 1500 rpm, I dropped to idle... and it purred like a kitten. Again... hasn't done that from a cold start ever either. Usually takes about 2-3 minutes before it will idle.

Hopefully if the weather holds we'll go out tomorrow and try it again. Could a clogged vent have interfered that much? I guess I already know the answer to this question, but still would like to hear if anyone thinks it could still be something else.

[Guest]

If you suspect a clogged vent, you can crack the gas filler cap open to verify. You might even hear the rush of air back in.

[Mileskb]

Optimus wrote:
If you suspect a clogged vent, you can crack the gas filler cap open to verify. You might even hear the rush of air back in.

Good idea... If the problem hasn't been solved that's an easy enough test... wish I would of thought of it yesterday... pretty obvious really...