C30 Stalling Problem

[velowe]

Engine runs for 30 minutes in gear then stalls, as if it is out of gas. The rpm's slowly drop then stalls but if I put it in neutral, it remains running. It always starts right up but the next cycle becomes shorter - i.e. 10-15 minutes, then 5-10 minutes. I have done all the things that Don Moyer has suggested as follows -

Fuel side - new carb, new fuel hoses and vent hose, Facet pump new end of last season, new Racor, arrestor cleaned, no dirt in carb. I have bypassed the pressure switch to run the pump and it will pump 1 litre in a minute or less into a container.
Question - when I changed the fuel hoses, I used 3/8" ID hose to replace the 5/16" ones. Anyone know what effect this may have on the fuel delivery. I have conflicting info in my manuals - one says 5/16 and the other says 3/8. The local A4 dealer says it should be 1/4" ID??!!

Electrics - new plugs, points, condenser, rotor, cap, wires, coil, pressure switch.

General - compression is 101-103 psi on all 4 cylinders and 35 psi oil pressure. Gas tank was emptied and fresh gas with enzyme additive for Ethanol added.
Yesterday, I checked the exhaust back pressure on the exhaust flange and it is 1.0 psi but periodically rises to 1.5 psi and when it stalls, will read 1.0-1.5 psi.

I am open to all thoughts and suggestions.

[Dave Neptune]

Fuel?

velowe, it sounds as if you do have a fuel related issue. You seem to have all the guages however do you have a fuel preassure guage? Have you checked the fuel pick-up in the tank? It could be as simple as KRAP in the tank slowly plugging up the "screen" if so equiped. After you shut down the KRAP falls away from the screen and the process repeats itself.
There is also a chance that the tank vent could be plugged, if that is the case the more fuel in the tank the worse the problem will be, think about it.
I always recomend a fuel preassure guage mounted in just ahead of the carb, all you need do is look at the preassure and you will know if you have fuel being delivered PROPERLY at the correct preassure.

Dave Neptune

[velowe]

Dave,

Fuel vent hose was new last season but I pulled it and ran a fishtape thru it and there was nothing in it. I also cleaned the transom vent intake screen of spider webs. The fuel pressure gauge before the carb reads 6 psi when it stalls. I have replaced the tank pickup tube and there is no screen on it and the tube end is away from the low point in the tank. Tank was emptied and flushed with new fuel in the Spring, emptied and refilled with new fuel and an enzyme additive for Ethanol fuel.

Vern

[sastanley]

velowe, You are stumping me right now.

[hanleyclifford]

Let's try to eliminate some items. Next time the shutdown occurs, before you try a restart, open the main jet plug and drain the contents into a small container. If the engine has been starved for fuel you will get to know it.

[Dave Neptune]

Hmmm!

Vern what you are describing does sound fuel related as with an eectrical/ignition related problem will usually shut down abruptly.

If you are showing fuel preassure at the guage I would suspect that there is something floating around in the fuel bowl or the emulsion well that is plugging up intermitently however doubtful.

How do the plugs look? If the are sooty (black soot) you could have an overrich condition which could be fuel preassure related~~ie a bit high(6psi) and the float could be forced open enough to cause an overrich condition. All of this doesn't mean that the float couldn't be sticking closed as well but the plugs would look light grey or creamy in color.

This is a bit baffling~~one more thing to check would be the dist cap. look for moisture building up.

Check the fuel line from the guage to the carb, if something is floating around in there it could cause an intermitant problem and you would still show adequate preassure.

Get back to us after looking at the plugs.

I have seen on a few occasions the condensor being week and slowly break down as things warm up~~this to may be worth a try. Most everything else in the ignition circuit will be an off/on senario.

Dave Neptune

[dvd]

I would say its a fuel related problem. Clogged fuel filter or clog at the fuel intake at the tank. The fact that it runs for a while and then runs for shorter periods of time is the key. Something is clogging the fuel delivery and when it stalls the clogg loosens up enough to restart and run for a shorter period of time until it clogs again.

dvd

[velowe]

Dave,

I was down at the boat today and checked the plugs. #1, 2, and 3 plugs were clean - insulators white and no soot on the gnd contact. #4 had some soot but that is the cyl. that seems to not burn completely and has 100-101 psi compression. Plugs were new a week ago.
When I drain the fuel bowl, there is nothing that could clog the jet.
The distr. cap had no moisture in it. Cap, points, condenser, rotor and wires are new.
Fuel hose from gauge to carb is also new. All hoses from the tank to Racor to gauge to carb are all new. Racor is also new. I changed the hoses to 3/8"ID from 5/16", thinking it might help the fuel flow. A4 dealer here says hose supposed to be 1/4"ID. Manual says 5/16" in one area then says 3/8" in another area?? Not sure what it should be.

Vern

[velowe]

dvd,

Racor was drained 2 weeks ago and there was only a few bits in it and a minute amount of water which is what the Racor is supposed to catch before it gets to the pump.
The pickup has no screen to clog and it is located well above the sloped tank bottom where there may be some debris. When I drained and flushed the tank in the Spring and looked in thru the 3"D sending unit hole, the tank bottom had no obvious buildup in it. I took a wire and ran it back and forth across the tank bottom just below where the pickup sits and found no buildup as it made scratchs in the tank bottom. Tank looks to be aluminum.
This weekend I hope to use a jerry can(bypassing the tank) to feed direct to the Racor, pump and carb.

Vern

[ndutton]

I don't think the fuel hose size has anything to do with your shutdown problem. My A4 is plumbed with 1/4" fuel line throughout and it runs great.

Suggest the following tests:

1. Temporarily connect an outboard fuel tank with fresh fuel from the corner gas station directly to the Facet fuel pump and do a run test. If the problem persists you can eliminate the fuel tank and filter as causes. If the problem goes away, then the tank/filter is where the issue is and I suggest the next test:
2. Reconnect the fuel tank and try running with the fill cap open. This will determine if the tank vent is the issue.

The outcome of these tests will give us more to go on.

[velowe]

Neil,

I was curious as to whether the 3/8" hose is too large and affecting the pressure in some way.
The Racor is new so shouldn't be a problem and has been drained a few times and I found nothing that should cause a clog in the line.
The vent hose was new end of last season. To be sure, I removed it and ran a fishtape thru it with a rag attached and found nothing clogging it.
I will use a separate tank this weekend.

Vern

[ndutton]

Yeah, it's a process of elimination.

The reason I suggested fuel from the corner gas station is I think there's a far better chance of getting clean fuel there than at the marina fuel dock.

Other thoughts:

If your auxiliary tank run test with the tank connected directly to the pump inlet is successful, consider adding the Racor as the next test, kinda work your way back to the tank one component at a time.

Your 6 psi gauge reading before the carb seems high to me, like 30 - 50% high. I'm wondering if the float valve is being overpowered and the carb bowl is overfilling. You could actually gravity feed the fuel for testing without the fuel pump by connecting the outboard tank directly to the carb. You'll need a squeeze bulb to prime the flow.

[Kelly]

shot in the dark

It seems like you've cleaned/replaced most fuel and ignition related items, except the condenser (don't neglect this one, as mentioned before).

I'm just shooting in the dark here but could this scenario also be explained by some mechanical binding that bogs the engine down? How about a stuffing box pinching the shaft as things heat up? The engine seems to run alright in neutral when the RPMs start to drop.

The portable fuel tank connected directly to the carb will be a good test. It just seems that everything on the fuel side is ready to go - at least from my vantage point a million miles away.

[roadnsky]

I was curious as to whether the 3/8" hose is too large and affecting the pressure in some way.
The Racor is new so shouldn't be a problem and has been drained a few times and I found nothing that should cause a clog in the line.
The vent hose was new end of last season. To be sure, I removed it and ran a fishtape thru it with a rag attached and found nothing clogging it.
I will use a separate tank this weekend.

Vern-
When you changed out the hose to the larger size, did you also change the HOSE BARBS?
If not, it's possible some air is "bleeding" into your fuel lines and could be taking the long trip to the carb which would account for both the timeframes you're seeing and the RPM drop and stalling.
It also might explain the high 6PSI reading on the gauge?

Double check all connections and hose clamps.

[ArtJ]

Vern-
When you changed out the hose to the larger size, did you also change the HOSE BARBS?
If not, it's possible some air is "bleeding" into your fuel lines and could be taking the long trip to the carb which would account for both the timeframes you're seeing and the RPM drop and stalling.
It also might explain the high 6PSI reading on the gauge?

Double check all connections and hose clamps.

I am wonderng if my shutdowns have been related to hose connections.
I have long suspected that the shutdowns have been related to the
fuel pump and carb losing prime, then requiring a bleed. I have suspected
bad fuel, but only found one particle this spring when needed half choke
to idle.

Regards