Connecting fuel line to carburetor

T

TheSTRdude

Member
Feb 3, 2022
59
Boat Info
1995 Sundancer 330
Engines
twin 7.4L mercs w/ V-drives
1995 mercruiser 7.4 - it’s in a 330DA. Had to remove the carburetor - reattached and can’t get fuel now.

wondering what I’m missing as I feel like it’s simple. Everything worked fine before. Tried starting fluid and engine will only run when it’s sprayed in. Is there an O-ring between the fuel line and carburetor that provides suction? Or does the line just go straight in and tighten?
 
Why did you remove the carb? Rebuild?

the pump pushes fuel up to the carb
The pump sucks from the tank

did you close any fuel selector valves when you pulled the carb?

the line to carb should be steel loosen the fitting wrap a rag around crank a few seconds should get some gas on the rag
 
hughespat57 said:
Why did you remove the carb? Rebuild?

the pump pushes fuel up to the carb
The pump sucks from the tank

did you close any fuel selector valves when you pulled the carb?

the line to carb should be steel loosen the fitting wrap a rag around crank a few seconds should get some gas on the rag
Click to expand...
This helped - fuel is indeed pumping. Gas on the rag…. Now what?
 
Pump is working
Carb float is likely stuck up
Did you have the carb apart?
 
Carefully pour a couple of tablespoons of fuel into the vent pipe. That's the bologna-sliced tube sticking up between the primaries. If it runs for a few seconds on that, then there's something wrong internally in the carb. Possibly got the float/needle assembly skewed.
 
Tap the top of the carb just next to the inlet fitting
Use a small hammer lightly
Or the handle of a large screwdriver
May free the float

else take the inlet apart and be sure nothing got in the fitting
 
Update: it’s either the fuel pump or the raw water pump.

Can anyone tell me if the cam lobe in the raw water pump should be able to be spun by hand?
 
TheSTRdude said:
Update: it’s either the fuel pump or the raw water pump.

Can anyone tell me if the cam lobe in the raw water pump should be able to be spun by hand?
Click to expand...
I'm not sure how the raw water pump would be associated with your fuel delivery issue. That, and I can't picture a cam lobe in the raw water pump. The mechanical fuel pump would run off the eccentric on the end of the cam shaft accessed through the side of the engine block. The raw water pump is belt-driven.
 
Nater Potater said:
I'm not sure how the raw water pump would be associated with your fuel delivery issue. That, and I can't picture a cam lobe in the raw water pump. The mechanical fuel pump would run off the eccentric on the end of the cam shaft accessed through the side of the engine block. The raw water pump is belt-driven.
Click to expand...

maybe it’s a v drive thing? The raw water pump looks like this:

https://nuwavemarine.com/mercruiser...Mj_FsiToCeeAIhK9zHnqU9h7XgrvIFMAaAtBQEALw_wcB

The little lever on the end of the mechanical fuel pump sets in that “inner metal space” and is actuated by the little camshaft lobe inside it.
 
hughespat57 said:
watch this...
that chamber should be filled with motor oil to prevent the shaft and roller from wearing out.
But yes it does rotate on the eccentric shaft of the shaft.
It should be clean and a snug fit.
https://www.hardin-marine.com/s-894-sea-water-pump-vst-fuel-system-0k147349-and-below.aspx

Click to expand...

this is helpful. Going to grab a fuel pump tomorrow and possibly a new raw water pump. Planning to see if the new fuel pump moves significantly different than my one in my hand currently. If that’s not it… probably raw water pump. Yay.
 
I agree with @BillK2632
Be absolutely certain the carb is not the issue before you throw a $1k at a water pump.
When you tested at the fitting Post 2 & 3 you got fuel at the loosened fitting.

If the ecentric is worn you typically get enough fuel to idle, just not enough for WOT.
The ecentric rarely suddenly fails completely, they wear out from poor or lack of oil.
 
I’m pretty sure it’s not the carb.

First thing I did was use a mechanical pump to get some fuel moving out of the line. Attached to carb, tried starting with starting fluid - it started for just a moment and quickly died once starting fluid burned off. Not getting fuel.

replaced fuel filter and primed it - same thing.

removed fuel line from the carb and wrapped a rag around it, at advice from a mechanic - cranked it. A little fuel came out, this is what I was referring to in previous posts.

I attribute that mostly due to some residual fuel from me pumping. Mechanic said it should be a hard pulse. I put it into a Coke bottle, attempted to start - no fuel at all.

That’s how we’re here now - fuel pump or raw water pump.
 
Your not going to be able to easily turn the raw water pully, given a) the impeller is squished in there pretty good, and b) the fuel pump lever that rides that eccentric bearing takes some force to compress.

There are two set screws / plugs on the side of that pully housing. Lower one is to drain the oil, top one to fill. While your there, I would suggest checking fluid, or better yet - drain, flush with some oil, then top off. This oil (a few ounces worth) can get diluted over time, thin out, and trash that bearing.

Your fuel pump should have a separate clear tube (maybe 1/4”) coming of the pump running up to the carb. There should _not_ be any fuel in that line. If there is, the diaphragm in the fuel pump is ruptured. This normally results in flooding out the motor as the gas simply bypasses the floats and gets dumped down the carb.

If your trying to start for the first time from winter layup - its gonna take a bit. I have to crank mine over for 10seconds, pause, and repeat around 4-5 times - so total cranking time maybe 40-60 seconds. Takes a bit to draw fuel all the way through the system.

Coke bottle is a good testing strategy - did you crank it enough though?

Did you change filters this season? If so, those need to get primed/filled as well - additional cranking time.

Worst case, use a minivac hand pump, connect to the fuel line at the carb, and vacuum (suck) fuel through the system up to the carb. Basically manually priming the entire fuel system.

At times I wish I had an electric fuel pump - but the mechanical works great. If you need a new mechanical one, you have an option (at your own discretion) of using an automotive one. Just match it up and make sure the level length and travel distances match up. You may have to swap over the fittings, and optional spray paint it black.
 

Attachments

  • 1B4D9034-FA60-46D1-A194-0164E9296C96.png
    1B4D9034-FA60-46D1-A194-0164E9296C96.png
    248.1 KB · Views: 60
Does the oil chamber for the eccentric take gear oil or regular motor oil?
 
I believe they call for Merc high performance gear lube oil. I think I used a heavy weight gear lube oil from valvoline (its what I had onhand). dont recall if it was synthetic, but it was in the blue bottle.
 

Attachments

  • 43135162-E215-4846-A448-9592837A8D3E.jpeg
    43135162-E215-4846-A448-9592837A8D3E.jpeg
    33.7 KB · Views: 61
Raw after pump and fuel pump replaced… still not getting fuel. Banging my head against a wall…
 
You must log in or register to reply here.

Forum statistics

Threads
113,118
Messages
1,426,544
Members
61,035
Latest member
Lukerney
Back
Top