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mercruiser 1988 260hp fuel leak down

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searay57

Contributing Member
hi, i have a 1985 mercruiser 260hp chevy 350 block with edlebrock carb. my problem is after i shut off engine fuel leaks down carb and floods engine. i thought float and needle and seat were bad. borrowed a carb from a friend it did the same thing, bought an reman qjet of ebay it did the same thing, bought a new edelbrock did the same, bought a fifth carb and have same problem. i have two recore filters befor pump and a inline after pump. also pump is new. i am stumped.
 
Re: mercruiser 260hp fuel leak down

My 1994 5.7 Mercruiser blew black smoke, sooted up the transome a little, and was not the easiest to start. I pulled the carb and all the other accessories and replaced the long block. Reinstalled the carb (without doing anything to it) and it now runs like a top. It sounds like you have eliminated the carb. My point is, a worn out, low compression engine is not capable of burning the same amount of fuel it once did. Time for a compression check.
 
Re: mercruiser 260hp fuel leak down

Is there gas inside the fuel pump plastic hose going to the carb? Yes? Replace the pump.
 
Re: mercruiser 260hp fuel leak down

one modification thats easy and prevents the pressure left in the pipe to the carbi,causing flooding,is to make a bleed back pipe ,teed into the pump to carbi pipe,and fed back to the fuel supply before the pump.if its a say 1mm hole it wont affect the pump pressure,but will allow the pressure to bleed off when engine stopped.stops the hot engine from expanding the fuel left in the pipe,and pushing past the needle valve
 
Re: mercruiser 260hp fuel leak down

the block is new last year, and it fires up and runs perfect. the only time i have a problem is after i run at speed for a while and back it down to idle.
i was told the steel line after my filters and pump may be all gunked up and shedding rust that would clog all 4 needle and seats, makes sense. so i will r&r and report back.
 
Re: mercruiser 260hp fuel leak down

WHAT PSI IS YOUR NEW PUMP GIVING YOU ? Someone else asked and now i am.

AGAIN WHAT PSI IS THE FUEL PUMP GIVING YOU ?
 
Re: mercruiser 260hp fuel leak down

searay57 said:
the block is new last year, and it fires up and runs perfect. the only time i have a problem is after i run at speed for a while and back it down to idle.
i was told the steel line after my filters and pump may be all gunked up and shedding rust that would clog all 4 needle and seats, makes sense. so i will r&r and report back.
Click to expand...



A new 1985 engine, that makes a big differance. As mentioned, monitor fuel pressure.
 
Re: mercruiser 260hp fuel leak down

What is the symptom of the engine after run and shutdown? Strong gas smell and only way to restart is to open throttle full??? Do you see the gas dripping down the carb throat? Does spraying starter fluid help hot restarts? Will it just not fire until cooled down? I'm starting to fell like a dentist.:D
 
Re: mercruiser 260hp fuel leak down

I still believe its a carb problem unless the fuel pressure is crazy high. One other thing to check is EFFECTIVE float height. What I mean by this is not the normal measurement between the float and the housing, but the float height when all buttoned up.
In this case what I'm thinking is.... is the carb mounted square to the manifold, or is it on a wedge? If it should be one way and its the other, then the EFFECTIVE float height is off and fuel will spill into the carb.

Unfortunately, we're guessing here because you didn't give us a vital piece of information... i.e., did this problem start with the new block or did you always have this problem?
 
Re: mercruiser 260hp fuel leak down

i will check fuel pressure over weekend, the symtoms are it dumps gas down barrel of carb to the point of pooling up on throttle plate. floods engine and needs to be held at 3\4 throttle to restart. problem started this year with new block.
 
Re: mercruiser 260hp fuel leak down

I checked your profile and I'm fairly sure that with your setup (inboard) that you need to have a wedge under the carb so that the carb sits level relative to the WATERLINE (more or less) not to the engine.
 
Re: mercruiser 260hp fuel leak down

the boat in my profile is not the one i am having problems with. but you are correct that boat has a wedge to keep the carbs level.
 
Re: mercruiser 260hp fuel leak down

Marine carbs are level when. Only when you put a level across the motor on the hard. In the water the carb is never level.

This a marine carb ?

Everyone laughs and scoffs at my remarks when it comes to the rochester. I love em' yes love em'. They are simple and effective in a marine application. And i have had them on auto's .

But then again i just dated myself.

Ok do you really truly want to find the problem ?

Then you have to do something for us to help you !

Post pics, for me i want to see the fuel pump and i want you to follow the line from the pump to the carb with pics. I think i may have helped someone with a problem as yours.
 
Re: mercruiser 260hp fuel leak down

I have a Rochester quadrajet on my boat and I had one on my 1978 Camaro Z-28 back in 1978, doh, I dated myself as well.
 
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