Carb Problem

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Tuggle
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Carb Problem

Postby Tuggle » Tue Jul 04, 2017 11:09 am

After spending what I consider a small fortune on engines, transmissions, CARBS, etc. my port engine, after running about five minutes, begins to stall and stumble. Fuel pressure from start is reading a solid 5-6 lbs on both engines, gauge for each, after about five minutes at 2500 rpm's pressure drops to zero and engine stumbles, pull it back to idle for a minute and pressure rises only to fall back off again. First thought was a bad fuel pump, changed it out, no change. New filters too. This morning swap the fuel lines from port to starboard same thing. These carbs are brand new Edelbrock 1409's.
1975 32' Express, Twin 318's, Raw Water Cooled, Lake Lanier, Ga.

barkleydave
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Re: Carb Problem

Postby barkleydave » Tue Jul 04, 2017 11:45 am

For safety pressure test your fuel system. Do you smell fuel? What fuel pump you using? If electric it must be connected to Oil pressure sensor for automatic shut down with a ignition by-pass. If your oil pressure is low or sensor malfunctioning it will shut the pump down until oil pressure builds up to min. threshold. But you probably already know all this...


safe boating,
dave
1987 Marinette 29 FB Sedan
Retired Boat Accident UL and USCG trained investigator
Retired USCG Captain

Tuggle
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Re: Carb Problem

Postby Tuggle » Tue Jul 04, 2017 12:06 pm

Drained the tank and replaced with fresh fuel last week, no don't smell fuel, mechanical pumps. On face value it gives indications of a clogged fuel line or filter, good flow through line and filters new, this is the reason I ran the port engine off the starboard fuel pump and vice verse. Could there be a float in the carb that would release all pressure?
1975 32' Express, Twin 318's, Raw Water Cooled, Lake Lanier, Ga.

jralbert
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Re: Carb Problem

Postby jralbert » Tue Jul 04, 2017 12:25 pm

You probably did this but it doesn't hurt to double check: did filter change include the little one at the mouth of the carb (if the Edelbrock has one there)?
-joel-
former owner 1988 '32 FB Sedan
Chesapeake Bay
twin 318 / 240 hp
Potomac MD

Tuggle
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Re: Carb Problem

Postby Tuggle » Tue Jul 04, 2017 5:39 pm

Did not, will check in the next couple days though. Would a clogged filter at the carb cause a pressure drop?
1975 32' Express, Twin 318's, Raw Water Cooled, Lake Lanier, Ga.

jralbert
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Re: Carb Problem

Postby jralbert » Tue Jul 04, 2017 9:18 pm

Not certain about pressure drop (never measured fuel pressure) but a clogged filter is definitely one cause of the stalling issue you describe. With those filters clogged, it's hard to get the engine running above about 1500 rpm
-joel-
former owner 1988 '32 FB Sedan
Chesapeake Bay
twin 318 / 240 hp
Potomac MD

Fastjeff
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Re: Carb Problem

Postby Fastjeff » Wed Jul 05, 2017 6:25 am

Do you know what filtration your filters are? The one at the strainer should be coarse--around 30 micron--to stop "bowling balls". The one AFTER the fuel pump should be fine--10 microns to stop tiny particles. Some 1409 Edlebrocks also have strainer screen just inside the fuel line fitting, so check it as well (though anything coarse enough to be caught by it should not have gotten there).

Some people think one can slap a fine filter BEFORE the fuel pump and not have any problems--got into a major argument with a few who've done this and "Never had a problem" (or so they claim). "YET," I warned them, for all it takes is a load of crappy fuel from some pump (and THAT never happens, right!) Then there's the effect of ethanol gas, that tends to loosen up crud that was happily living on the bottom of your tanks for years, not causing any trouble. You need a coarse filter, changed regularly, to keep this stuff from plugging up the works.

The fuel pressure MUST stay above 5 psi at speed or she'll lean out on you. Good move putting pressure gages on your carbs!

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington

barkleydave
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Location: Kentucky

Re: Carb Problem

Postby barkleydave » Wed Jul 05, 2017 8:54 am

This is an interesting problem. Make sure we all know what the cause was!
Just a couple of thoughts...
Where are you pressure gauges located? are they before the filter on the output side of the fuel line?
If that is the case a clogged fuel filter would not cause a pressure drop. Actually it would create back pressure and readings would go higher.
If gauge is after the fuel filter a clogged filter would lower fuel flow and thus fuel pressure as fuel demand increases.
If none of the above then might be a problem with the float valve in the carb? If open then fuel bowl would not fill and no backpressure so in theory the fuel pressure would drop. But if that is the case...where is the fuel going?
How did you check using the other fuel pump? Did you remove it and install on the problem engine?
A weak pump could show 5 psi at idle but still not be able to keep up as fuel demand increases. (diaphragm problem) Is there fuel in the pump return line going to the carb?

Just guessing this is a good one !

safe boating,
dave
1987 Marinette 29 FB Sedan
Retired Boat Accident UL and USCG trained investigator
Retired USCG Captain

ddependo
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Re: Carb Problem

Postby ddependo » Wed Jul 05, 2017 9:23 am

often overlooked are the anti siphon valves. mine were clogged and drove me nuts until Fast Jeff said to check them.
Wayne
1973 32 express fly bridge
Chattanooga
"Southern Lady"

barkleydave
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Re: Carb Problem

Postby barkleydave » Wed Jul 05, 2017 12:16 pm

GREAT POINT I thought about it also that could explain it!
Run off of aux tank and I see what it does.

Dave
1987 Marinette 29 FB Sedan
Retired Boat Accident UL and USCG trained investigator
Retired USCG Captain