1995 Sundancer with 7.4s carb questions

[270win]

We just picked up a 1995 330 DA with 7.4 v drives. When the boat has sat overnight (or small week) the port engine has to be spun over to prime the carburetor, maybe 10 seconds or so, then pump the throttle a few times and starts it. Once it’s running it runs well.

Until yesterday, it was great all day but we came back to the slip for an hour to avoid some weather. When we fired it back up it started fine but as we were idling out the port engine quit. I restarted it (and it quit) about 3 times before it finally wouldn’t even try to start, just turns over. The P.O. told me the choke was probably adjusted too tight and that I might need to back it off. I did that, still nothing. It’s not getting fuel and I believe the fuel pump has failed.

BUT- when I removed the flame arrestor I discovered that the engines have Holley style carburetors. I think the boat is supposed to have QuadraJet carbs. Anyone see this before or did MerCruiser ever install Holley carbs?

 

[hottoddie]

The Holley carbs are aftermarket replacements and if in good condition should be fine. Do you have the fuel pumps that are mounted on the seawater pump which is belt driven. They are notorious for failing and the worst design ever conceived by Mercruiser.

 

[270win]

The Holley carbs are aftermarket replacements and if in good condition should be fine. Do you have the fuel pumps that are mounted on the seawater pump which is belt driven. They are notorious for failing and the worst design ever conceived by Mercruiser.

No, these are the old school big block Chevy mechanically driven fuel pumps.

 

[hottoddie]

Several things could cause your problem. Have the spin on fuel filter/water separators been changed? I'd be inclined to have the carburetors removed and cleaned. The fuel pump may have failed but if the engine runs up to high rpms I doubt the fuel pump is the cause.

 

[HawkX66]

Holleys have mechanical accelerator pumps. Disconnect the throttle cable, pump the linkage and see if there is any fuel coming out of the nozzles. If not, either you're not getting fuel to the carb which you should have already checked, or your needle and seats might be clogged or you might have a stuck float. Either way, if the carbs are an unknown I'd throw a rebuild kit at them that includes the needles and seats and the accelerator pump diaphragm etc.

 

[270win]

Several things could cause your problem. Have the spin on fuel filter/water separators been changed? I'd be inclined to have the carburetors removed and cleaned. The fuel pump may have failed but if the engine runs up to high rpms I doubt the fuel pump is the cause.

The fuel filters are new (+/-10 hours). My plan was to have the carbs either rebuilt or replaced (With Rochesters) this winter. I don't have a problem with Holley per se, but I do prefer to stay OEM.

 

[270win]

Holleys have mechanical accelerator pumps. Disconnect the throttle cable, pump the linkage and see if there is any fuel coming out of the nozzles. If not, either you're not getting fuel to the carb which you should have already checked, or your needle and seats might be clogged or you might have a stuck float. Either way, if the carbs are an unknown I'd throw a rebuild kit at them that includes the needles and seats and the accelerator pump diaphragm etc.

We did pump the throttle and saw no fuel. I planned to rebuild them this winter before I found out they're Holleys. Now I'm thinking I may swap Rochesters back instead.

 

[HawkX66]

We did pump the throttle and saw no fuel. I planned to rebuild them this winter before I found out they're Holleys. Now I'm thinking I may swap Rochesters back instead.

Holley is an excellent carb. Are they marine? If you pumped them and no fuel came out, did you check to see if there was fuel in the bowls?
If you're replacing them, look at the Edelbrock 1410. It's basically identical to the factory carbs.

 

[Wanderer 290]

Has fuel flow to the carb been verified? Have a gasoline absorbing pad, a flexible fuel line (hose) of the proper size and a small gas can available. Open the the fuel system where it connects to the carb. Routing the fuel line into the gas can with the flexible fuel line have a helper crank the engine and verify fuel flow.

If no fuel I suggest replacing the fuel pump and recheck. If there is not fuel flow start moving up line, the filter, clogged line.

Additionally, once the fuel line is disconnected at the fuel pump inlet blow into the line. Resistance to blowing should be minimal.

Take all precautions working around gasoline and gasoline lines.

 

[270win]

Has fuel flow to the carb been verified? Have a gasoline absorbing pad, a flexible fuel line (hose) of the proper size and a small gas can available. Open the the fuel system where it connects to the carb. Routing the fuel line into the gas can with the flexible fuel line have a helper crank the engine and verify fuel flow.

If no fuel I suggest replacing the fuel pump and recheck. If there is not fuel flow start moving up line, the filter, clogged line.

Additionally, once the fuel line is disconnected at the fuel pump inlet blow into the line. Resistance to blowing should be minimal.

Take all precautions working around gasoline and gasoline lines.

I used to do all the work on my boats and cars myself. These days I mainly pay someone to do the work. I got a MerCruiser fuel pump today and my guy is going to install it in the morning. As much as I have worked on them in the past, I swear it acted just like a fuel pump failure. We’ll know more tomorrow.

Where do you guys get your engine parts?

 

[270win]

Holley is an excellent carb. Are they marine? If you pumped them and no fuel came out, did you check to see if there was fuel in the bowls?
If you're replacing them, look at the Edelbrock 1410. It's basically identical to the factory carbs.

I didn’t check the bowls. Is the Edlebrock 1410 a marine carb. I also don’t know if the Holleys are marine carbs or not. They looked original but I don’t think that’s possible.

 

[hottoddie]

I didn’t check the bowls. Is the Edlebrock 1410 a marine carb. I also don’t know if the Holleys are marine carbs or not. They looked original but I don’t think that’s possible.

What makes a carb a marine carb is the addition of a return line from the fuel pump the the throat of the carb. It is there in case the diaphragm in the fuel pump fails the fuel will be routed to the carb and into the engine and not into the bilge that can cause an explosion hazard. That explains why a marine fuel pump has a return line fitting on the top of it in order to accommodate the return line. Other than the return lines both the carb and fuel pumps are the same as automotive. BTW if you install new carbs make sure they are 750 CFM rated for the 7.4s. The 5.7s use a 650 CFM.

 

[270win]

What makes a carb a marine carb is the addition of a return line from the fuel pump the the throat of the carb. It is there in case the diaphragm in the fuel pump fails the fuel will be routed to the carb and into the engine and not into the bilge that can cause an explosion hazard. That explains why a marine fuel pump has a return line fitting on the top of it in order to accommodate the return line. Other than the return lines both the carb and fuel pumps are the same as automotive. BTW if you install new carbs make sure they are 750 CFM rated for the 7.4s. The 5.7s use a 650 CFM.

Good info, thank you! I saw some Rochester carbs online from Sierra for about $365 each.

 

[HawkX66]

I didn’t check the bowls. Is the Edlebrock 1410 a marine carb. I also don’t know if the Holleys are marine carbs or not. They looked original but I don’t think that’s possible.

Yes. The 1410 is a marine specific carb and 750cfm which is what you need. A little more expensive, but brand new, never rebuilt/monkeyed with etc.

https://www.summitracing.com/parts/edl-1410

 

[PlayDate]

It is your boat.....Holley's are a major upgrade over the Rochesters. First they don't leak down and second when you pair them with an marine electric fuel pump you get turn key starting. OEM means a mechanical fuel pump that you have crank and crank to build fuel pressure and then it will leak down when it sits. Plenty of CSR threads where new owners complain about this.

The problem you have sounds like the fuel pump has gone bad not the carbs. Get the number off the airhorn of the Holley and check it. It should be a marine rated carb.

Also.....your boat should have a belt driven raw water pump with the fuel pump attached to the housing. As pointed out earlier.....this was a really bad design since it complicates routine impeller replacement. If you don't have this .....are these the original engines?

One last point.....I have never used the chokes on Holleys for marine engine applications. I rotate the electric control mounted on the side of the carb so that the choke stays open all the time. I suppose if you did a lot of really cold boating it may help on startup but practically ......it is only useful for a cold start.

 

[270win]

It is your boat.....Holley's are a major upgrade over the Rochesters. First they don't leak down and second when you pair them with an marine electric fuel pump you get turn key starting. OEM means a mechanical fuel pump that you have crank and crank to build fuel pressure and then it will leak down when it sits. Plenty of CSR threads where new owners complain about this.

The problem you have sounds like the fuel pump has gone bad not the carbs. Get the number off the airhorn of the Holley and check it. It should be a marine rated carb.

Also.....your boat should have a belt driven raw water pump with the fuel pump attached to the housing. As pointed out earlier.....this was a really bad design since it complicates routine impeller replacement. If you don't have this .....are these the original engines?

One last point.....I have never used the chokes on Holleys for marine engine applications. I rotate the electric control mounted on the side of the carb so that the choke stays open all the time. I suppose if you did a lot of really cold boating it may help on startup but practically ......it is only useful for a cold start.

I'll verify again on the pump style, the motors are original and have sequential serial numbers.

My boat's carb on the port side (Both Holleys) does leak down and has to be pumped up after sitting between weekends.

I'll make sure the chokes are turned all the way off.

The marine carbs I see listed by Holley don't look like mine. Mine look more like this except they're black-
https://www.holley.com/products/fuel_systems/carburetors/street_strip/parts/0-82751

I'll get the numbers and post them.

 

[PlayDate]

I'll verify again on the pump style, the motors are original and have sequential serial numbers.

My boat's carb on the port side (Both Holleys) does leak down and has to be pumped up after sitting between weekends.

I'll make sure the chokes are turned all the way off.

The marine carbs I see listed by Holley don't look like mine. Mine look more like this except they're black-
https://www.holley.com/products/fuel_systems/carburetors/street_strip/parts/0-82751

I'll get the numbers and post them.

There is a really easy way to tell if they are marine carbs. Look at the fuel bowl vents and non-marine point straight up....marine carbs J hook back into the carb.

 

[270win]

They are mechanical pumps, the carbs are Holley and they are marine carbs and this thing starts like it’s fuel injected now. Thanks for all the input!