Carburetor losing prime

[Captain Pauly]

I have an issue we have been chasing for a year and we are baffled. I have a 1994 Sea Ray 400 EC. It has twin 454's. The Starboard Carburetor will lose prime after sitting for a few days. The bowl in the carb is dry and the fuel separator is empty. There is no fuel or fuel odor in the bilge. We are convinced that the fuel is being drawn back to the tank somehow. I have to fill the separator with fuel and re-prime the carb and then engine starts fine and runs fine. If I start the engine everyday it has no problem, she fires right up and runs great. It takes a few days for it to drain back to the tank. I have replaced the fuel pump, the water pump (it drives the fuel pump), and the carburetor. We switched the fuel feed lines to rule out blockage in the pickup tubes and tank and have confirmed that there is no obstruction in the vent. We also pressure tested the fuel lines. There are no leaks in the lines. We are very baffled by the carb bowl being sucked dry. Any and all input is welcome we are out of ideas.
Thanks, Pauly

 

[HT32BSX115]

Re: Carburetor losing prime

We switched the fuel feed lines to rule out blockage in the pickup tubes and tank and have confirmed that there is no obstruction in the vent.

howdy,

Welcome aboard!


When you "switched" fuel lines, did each engine get fuel from a different tank (2 fuel tanks?)

If it's a single tank, is there a separate fuel pickup for each engine? And if there is, is there 2 anti-siphon check valves on each tank?

Did the carb "go-dry" after the switch?


Regards,


Rick

 

[alldodge]

Re: Carburetor losing prime

I have an issue we have been chasing for a year and we are baffled. I have a 1994 Sea Ray 400 EC. It has twin 454's. The Starboard Carburetor will lose prime after sitting for a few days. The bowl in the carb is dry and the fuel separator is empty. There is no fuel or fuel odor in the bilge. We are convinced that the fuel is being drawn back to the tank somehow. I have to fill the separator with fuel and re-prime the carb and then engine starts fine and runs fine. If I start the engine everyday it has no problem, she fires right up and runs great. It takes a few days for it to drain back to the tank. I have replaced the fuel pump, the water pump (it drives the fuel pump), and the carburetor. We switched the fuel feed lines to rule out blockage in the pickup tubes and tank and have confirmed that there is no obstruction in the vent. We also pressure tested the fuel lines. There are no leaks in the lines. We are very baffled by the carb bowl being sucked dry. Any and all input is welcome we are out of ideas.
Thanks, Pauly

:welcome: to iboats

With the carb going dry my first thought is it has a leak, which is not uncommon.

Now the seperator is a real puzzler unless the antisiphon valve as HT32 mentioned. Have you check the gear oil in your sea water pump? Fuel pump may be leaking back into the pump and if bad enough could be putting gas into the raw water system

What's you engine serial number?

 

[Captain Pauly]

Re: Carburetor losing prime

Rick Thanks for the input. The boat has 2 tanks with switches that will switch fuel for either tank to either engine. Selector switches do not change the issue. On the Starboard tank I have a separate fuel line for the generator with separate anti syphon valves and separate pick up tubes. We switched those fuel lies and it did not help the issue. I was told today that I should replace the anti syphon valves to see what happens, apparently they can go bad. Thanks again.
Pauly

 

[Captain Pauly]

Re: Carburetor losing prime

All Dodge,
Thank you for your input. We have checked for leaks in the carb and cannot find any, also there is no gas in the bilge so we have ruled out leaking as the issue. The gear oil is full in the pump. Your questions are good ones as are Ricks. They are in the ball park as knowledgeable mechanics have asked the same questions. It's a head scratcher for sure. Will try replacing the anti siphons and see what happens Engine serial is OF228272.

Thanks again for the input

 

[alldodge]

Re: Carburetor losing prime

All Dodge,
Thank you for your input. We have checked for leaks in the carb and cannot find any, also there is no gas in the bilge so we have ruled out leaking as the issue. The gear oil is full in the pump. Your questions are good ones as are Ricks. They are in the ball park as knowledgeable mechanics have asked the same questions. It's a head scratcher for sure. Will try replacing the anti siphons and see what happens Engine serial is OF228272.

Thanks again for the input

Will look forward to seeing what you find. The serial number is for an Alpha stern drive

 

[Bondo]

Re: Carburetor losing prime

All Dodge,
Thank you for your input. We have checked for leaks in the carb and cannot find any, also there is no gas in the bilge so we have ruled out leaking as the issue. The gear oil is full in the pump. Your questions are good ones as are Ricks. They are in the ball park as knowledgeable mechanics have asked the same questions. It's a head scratcher for sure. Will try replacing the anti siphons and see what happens Engine serial is OF228272.

Thanks again for the input

Ayuh,.... Fuel can Not siphon out of a carb, it can't jump the air space at the needle valve,...

It's Got to be leakin' into the intake,...

'n if the tanks have anti-siphon valves, the fuel Can't go back into the tank,...

 

[Captain Pauly]

Re: Carburetor losing prime

Ayuh,.... Fuel can Not siphon out of a carb, it can't jump the air space at the needle valve,...

It's Got to be leakin' into the intake,...

'n if the tanks have anti-siphon valves, the fuel Can't go back into the tank,...

Bondo Thanks for entering the discussion. I like the input and I appreciate everyone who has weighed in on this because we are stumped. You have nailed our dilemma exactly. The bowl in the Carb goes dry, but so does the fuel separator. We had a Carter on the engine originally, it too lost prime. I appreciate any ideas. Thanks for weighing in>

 

[Fun Times]

Re: Carburetor losing prime

The boat has 2 tanks with switches that will switch fuel for either tank to either engine.

As a test, Are you able to close/shut off the switch completely so that no fuel is able to return back into the tanks. Then check your filter.

Another temporary test would be finding some clear fuel line so you would be able to see if the fuel is going back to the tank. Since it seems to take awhile to go dry, with todays technology, just set up a live camera so you can watch the fuel line from the comfort of your couch.

 

[Bondo]

Re: Carburetor losing prime

Bondo Thanks for entering the discussion. I like the input and I appreciate everyone who has weighed in on this because we are stumped. You have nailed our dilemma exactly. The bowl in the Carb goes dry, but so does the fuel separator. We had a Carter on the engine originally, it too lost prime. I appreciate any ideas. Thanks for weighing in>

Ayuh,.... Run/ test it with a remote fuel tank/ gas can to eliminate everything Up-stream of the fuel filter,...

 

[alldodge]

Re: Carburetor losing prime

I can understand the carb maybe but the fuel filter dry, really it's dry?

Is the filter new?

 

[MikDee]

Re: Carburetor losing prime

Ayuh,.... Fuel can Not siphon out of a carb, it can't jump the air space at the needle valve,...

It's Got to be leakin' into the intake,...

'n if the tanks have anti-siphon valves, the fuel Can't go back into the tank,...

I love this! :lol:

 

[Scott Danforth]

Re: Carburetor losing prime

I agree, you have two fuel issues.

A carb issue allowing fuel to leak out of the bowl
A fuel delivery issue allowing the supply to the carb becoming empty.

for the carb issue, a rebuild is probably needed.

for the delivery issue, I would work backwards from the carb and test every component until you hit the inlet of the fuel siphon tube.

 

[Captain Pauly]

Re: Carburetor losing prime

Ayuh,.... Run/ test it with a remote fuel tank/ gas can to eliminate everything Up-stream of the fuel filter,...

We will give it a shot Bondo. BTW I confirmed that the fuel from the carb is not going into the intake. Any thoughts there? That is a very puzzling piece of the puzzling puzzle.
Thanks for the input,
Pauly

 

[pyrotek]

Re: Carburetor losing prime

Wouldnt a slow leak just evaporate? I know you dont smell anything but I've had small engines evaporate gas in the garage and I won't smell it.

 

[funk6294]

Re: Carburetor losing prime

What type of filter are you running? Is it racor with a drain for the fuel or a standard screw in cartridge?

 

[Captain Pauly]

Re: Carburetor losing prime

We may have found the issue. We found a TEE fitting at the fuel shutoff / tank selector that had a small crack at both ends. This is a tapered brass thread so the tighter you make the connection the more air you would draw. Its brass and supposed to be forgiving, Obviously defective material It was probably imported. Buy in America, Made in America. Thanks for all the input folks. I appreciate it.

Pauly

 

[redneck joe]

Re: Carburetor losing prime

so did this fix it (by testing leaving it sit for a week or so)? My last boat had exact same issue (regular filter instead of separator) and I never solved it but would like to maybe help the new owners as they haven't figured it out yet either. We had single tank, dual lines.

So frustrating - as yours always ran fine unless sitting for awhile.

 

[Walt T]

Re: Carburetor losing prime

It's evaporating. Happens with some carbs sometimes. The overflow tube vents directly to the bowl and provides air that can cause evaporation.

 

[Captain Pauly]

Re: Carburetor losing prime

so did this fix it (by testing leaving it sit for a week or so)? My last boat had exact same issue (regular filter instead of separator) and I never solved it but would like to maybe help the new owners as they haven't figured it out yet either. We had single tank, dual lines.

So frustrating - as yours always ran fine unless sitting for awhile.

Redneck Joe, I am hoping this solved it. I will know in the next couple of weeks and keep you posted. It takes about 5 - 7 days for the fuel to drain back. So far we had a 5 day test. This week will be a 7 day test. and then i will do a couple more for peace of mind. This was a tough one!! we were loosing our minds trying to figure it out. There isn't allot to a fuel system, but holy cow was this one tough! By the way my Mistresses look similar to yours!