1991 carburated 4.3 fuel pump output.

[Majorwood]

Hello, I am new on here. I did a search and found lots of questions regarding fuel pressure but none about fuel volume. I have a 1991 glastron 1900 that after 4 years of working on the floor finally put back in the water. It started and idled alright in the driveway but when I took it to the lake it acted like it was starving for fuel. It has new fuel line from tank to the filter, filter to the pump. New filter and I cleaned the pick up tube and siphon valve when I had the tank out and was redong the floor.
I am fairly confident that it's just after sitting for four years that it's just junk and gunk in the carb but I wanted to make sure that the fuel pump was moving enough fuel. I rigged up a hose from the steel line going into the carb, the hose runs to a qt size mixing cup. Crank the engine and with 8 "shots" of fuel from the hose I am at. 4 oz consistently. I do not have a manual for this boat or engine. I have no idea how many owners before me. The engine serial number is gone from the tag on top of the air cleaner. All I know is it's a 4.3/v6 alfa one, thunderbolt 4 with a 2 barrel carb in a 1991 Glastron 1900.

 

[itsathepete]

Just a guess but I would expect the fuel pump to be capable of 30 gallons per hour which is more than you need but without spinning at normal rpms it's hard to gauge. Clean or rebuild the carb first. It will need it.

 

[Scott Danforth]

The same fuel pump is on the 5.0 and 5.7 and 7.4

The pump will support twice the HP you can make with the 4.3

Generally mechanical fuel pumps either work, or don't.

If it doesn't work, $45 gets you a new Carter fuel pump

 

[Majorwood]

The same fuel pump is on the 5.0 and 5.7 and 7.4

The pump will support twice the HP you can make with the 4.3

Generally mechanical fuel pumps either work, or don't.

If it doesn't work, $45 gets you a new Carter fuel pump

Is there a specific marine Carter fuel pump you recommend? I read about how you don't use a automotive fuel pump in place of a marine one because of vapors in the engine bay.

 

[achris]

Is there a specific marine Carter fuel pump you recommend? I read about how you don't use a automotive fuel pump in place of a marine one because of vapors in the engine bay.

Not vapours in the engine bay, it's that when the diaphragm on an auto pump fails, it fills the sump with petrol. Shortly thereafter you become the first involuntary astronaut....

Chris...

 

[Scott Danforth]

Is there a specific marine Carter fuel pump you recommend? I read about how you don't use a automotive fuel pump in place of a marine one because of vapors in the engine bay.

the same fuel pump that is there.

most likely the M6973

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[Majorwood]

Just a guess but I would expect the fuel pump to be capable of 30 gallons per hour which is more than you need but without spinning at normal rpms it's hard to gauge. Clean or rebuild the carb first. It will need it.

Not vapours in the engine bay, it's that when the diaphragm on an auto pump fails, it fills the sump with petrol. Shortly thereafter you become the first involuntary astronaut....

Chris...

Get to space ... just slightly overdone. Lol

 

[Majorwood]

I tore down and cleaned the carb. Had issues on the first start up, the needle and seat that came it the kit did not want to seal. So some premium went into the crankcase I'm afraid. Put the old set back in and didn't have a a problem after that. I don't have the manual so I did all my adjusting buy gut feel on muffs in the driveway. Took it to the lake today still started hard... backed away from the dock and just let it idle around and get warm, made a couple adjustments to the throttle cable and the idle air screw. It seemed to be doing great, had my trim set high so I would plow through the water and ran at 15 mph for a good bit came back to an idle it was clean and crisp around 800 rpm by the tach put it into gear it would drop 100 or so rpms so I trimmed the out drive and pointed her out across the lake gave it the onion... she got up on plane beautifully I still had throttle left was moving along at 36-37 mph and she just shut down... she was still idling ... I pulled the throttle back to neutral listened waited then put it in fwd and tried to throttle up and she died. I have a 12 volt inline fuel pump that I used for troubleshooting fuel delivery issues at work, I'm going to rig it up and bypass the mechanical fuel pump and go out and see how it will run. If it gets up on step and stays there I know the mechanical fuel pump isn't moving enough fuel. If it still has the same problem I'll know there's an issue in the fuel filter head, the new fuel lines I put on, the anti siphon valve in the tank.

 

[Majorwood]

So its been a couple trips to the lake and still no smoking gun. I did hook up the 12volt fuel pump in line with the mechanical fuel pump and the boat would run for a longer period of time once on step.... some times. Came back got access to the fuel lines at the tank all clamps were tight removed and inspected anti siphon valve... no obvious issue with that. But I did find some odd build up on the seating area of the fuel water separator it felt about the the thickness of a couple sheet of printer paper, it didn't go all the way around so it may have been sucking air there. I also resealed all the fittings on the filter housing. I inspected the new fuel lines with a camera and blew compressed air both ways through them no issues. The lines were replaced when I did the floor. I'm stumped. I rigged up the 12volt fuel pump on the output line from the filter housing and started to fill a 5 gallon fuel can monitoring the fuel flow, after about a gallon or so I noticed a buzzing noise it wasn't coming from the pump. But fuel flow was being affected. The buzzing was coming from the anti siphon valve. I tried tapping on it with a wrench, no change. I swapped out the anti siphon fitting for a standard one and tried again. Fuel flow was definitely improved I let it run for the same amount of time to make sure something wasn't in the tank, bid not have any other fuel flow issues. So I used compressed air and blew through the valve in the direction of flow and it will block flow off completely depending on the pressure you put on it... and I have no idea at what point it does that but I'm going to guess the spring is weak and is allowing the ball to act as a check and cut off my fuel.

 

[achris]

That filter gasket surface is a prime candidate for an air leak, and it sounds like the anti-siphon valve is working as required.

I don't have a valve in my fuel line, but then once the line leaves the top of the tank it doesn't drop below that level before getting to the filter fitting on the engine, so it's not actually needed...

Chris...

 

[itsathepete]

Well sounds like you found your problem. Hopefully that takes care of it

 

[Majorwood]

Took the boat out yesterday and it ripped! No issues. I am going to put a anti siphon valve in the line from the tank to the filter because getting to the fitting at the tank is such a chore.

 

[Bondo]

Took the boat out yesterday and it ripped! No issues. I am going to put a anti siphon valve in the line from the tank to the filter because getting to the fitting at the tank is such a chore.

Ayuh,..... That kinda defeats the purpose of it,.....

The idea is to keep fuel in the tank, in case of a problem,....

 

[Majorwood]

Well .... no. The spring pushes the ball against the seat to stop fuel from flowing back into the tank causing the fuel system to loose prime.

 

[Scott06]

Well .... no. The spring pushes the ball against the seat to stop fuel from flowing back into the tank causing the fuel system to loose prime.

No that is not how an antiphon valve works. It is supposed to prevent the tank from siphoning out into the bilge in the event of a fuel line leak, hence why it is located right on top of the tank … yes there is a cracking pressure like a check valve u reference but that is not the purpose of it

 

[achris]

Well .... no. The spring pushes the ball against the seat to stop fuel from flowing back into the tank causing the fuel system to loose prime.

What you described is a check valve.

An anti syphon valve is installed the other way. It will allow a 'small' flow but if the flow exceeds the spring pressure (if the fuel line is damaged and allowing fuel to free flow) it pushes the ball against the body, stopping flow...

Personally, I don't like them and if the fuel system was designed correctly in the first place it doesn't need one...

Chris...

 

[Majorwood]

So my back ground is heavy equipment and over the road trucks so this is my best guess on how this goes. We are both right. The anti siphon works both ways. The spring is strong enough to close if there is a leak but will open when it is exposed to vacuum from the fuel pump. It also closes to prevent fuel draining back to the tank and losing prime in the fuel system. Either the way the one that I had wasn't working correctly or is damaged in some way. I will reevaluate replacing it with the in line valve because of the potential for a fuel leak.

 

[Majorwood]

What you described is a check valve.

An anti syphon valve is installed the other way. It will allow a 'small' flow but if the flow exceeds the spring pressure (if the fuel line is damaged and allowing fuel to free flow) it pushes the ball against the body, stopping flow...

Personally, I don't like them and if the fuel system was designed correctly in the first place it doesn't need one...

Chris...

That 35 gallon tank would have to pull out of the bottom to have enough head pressure to seat that ball against the spring and stop flow.... and then the boat wouldn't run at all. My best guess is if the tank had a straight through fitting and the fuel system expressed a leak it would alow fuel to slowly leak out creating a dangerous build up of gasoline vapers in the bildge. The spring in the anti siphon valve is compressed by the negative pressure (vacuum) created by the fuel pump pulling on the ball alowing fuel into the line and up the pick up tube to the pump. But if the engine is off the spring seats the ball and fuel can't flow.

 

[jonny rotten]

I have almost the same boat. 1990 Glastron 19 cuddy with a 4.3
I'm no expert but things I've done.
Carb rebuild a few times
New fuel pump. Should shoot clear across the boat with the metal line disconnected at carb.
There is an inline filter in the carb that gets clogged, clean every year
This year I was having trouble starting after winter layup. After some testing and troubleshooting the 6 inch line from fuel filter to water separator dried out and cracked. Must have been sucking air. Replaced it and it fired right up.
I just replaced the floor and seats last year. She's like a new boat all over again. I left one of the back to back seats out. So much more room