New 5.7 vortec sucking air at caburetor, replaced everything and still not fixed!

[stoverdr]

I bought a vortec 5.7 short block and put on a new intake and carburetor Edelbrock 650 cfm and MSD Ready to Run distributor and coil. Timing is set at 10 degrees BTDC as required. Boat idles perfectly, throttle response is decent but sometimes sluggish from idle. I can hear it sucking air at idle and adjusting the left side idle mixture screw does not affect the idle. Put the boat in the water and it will almost get on plane going backwards. Try to go forward and it sounds like it running on 4 cylinders. No power, won't come close to getting on plane and sucking a TON of air through the carburetor. Any suggestions are great;y appreciated. Been working on this for months.

 

[tank1949]

Base gasket may not be a perfect match for carb and intake manifold. I had similar problem years ago on quad-jet. Only by carefully examining both did I see problem. Gasket was slightly torn or gouged out. It is either base gasket or manifold is not seating correctly. I am surprised that you found an 4 b intake for vortec heads. They usually went on TBI or EFI, but I also suspect aftermarket hot rod and marine mfgs finally caught up. Get some starter fluid and spray around edges of manifold and listen for RPM increases. If none, pull carb. Good luck!

 

[stoverdr]

I used new gaskets when putting it together, after a million hours on the internet, I found out about the felpro 98000t intake gaskets that have the metal plate in them. Just put them on and it didn't change anything. I bought a rebuilt marine carb from ebay and when it's installed, it's sucking a lot of air at idle. Went and bought a brand new Edelbrock and you can barely hear it but it's still sucking air at idle. I've put and replaced several gaskets and adapters between the carb and intake.
I'm not certain about your comment regarding the use of vortec heads with a carburetor, can you elaborate?

Thanks

 

[Scott Danforth]

which Edelbrock calibration? you could have bought the 1409 and simply bolted it on.

was it a reputable company selling on ebay, or someone simply selling a carb?

 

[stoverdr]

It seemed to be a reputable company, but you never know. As an instant replacement, I went to the parts store and bought an Edelbrock 1905 and thats whats on there now. With all new gaskets

 

[stoverdr]

The 1409 carb is out of stock everywhere I looked.

 

[Rick Stephens]

Seeing as how that isn't a marine carburetor you just built a bomb. Not good. Definitely need to get rid of the 1905 and get the real thing.

And not to just toss that out, why marine carburetors are different: a boat is a bucket. Gas fumes sink. Any leakage on a car part, like a carburetor or a fuel pump just drips out on the road. In a boat, it fills your boat full of fumes making a bomb. Your 1905 carburetor is externally vented. A 1409 carburetor is internally vented. If it leaks, a 1409 will leak down the intake and flood your motor but not turn your boat into a fuel air explosive.

 

[Scott Danforth]

the 1905 is not a marine carb. the 1409 is available nearly everywhere. Jegs has 11, even available on multiple Amazon outlets

ignoring the potential for the 1905 to turn your boat into a bomb. did you plug the two big vacuum ports that normally go to the power brake booster and other vacuum accessories?

 

[Rick Stephens]

the 1905 is not a marine carb. the 1409 is available nearly everywhere. Jegs has 11, even available on multiple Amazon outlets

ignoring the potential for the 1905 to turn your boat into a bomb. did you plug the two big vacuum ports that normally go to the power brake booster and other vacuum accessories?

You gotta admit though, as often as it happens, plastic boats burn really well.

 

[Bondo]

You gotta admit though, as often as it happens, plastic boats burn really well.

Ayuh,...... but Alotta nasty black smoke,........

 

[stoverdr]

all vacuum ports were capped on the new carb and not present on the 1409. The 1409 was sucking in a TON of air at idle, the 1905 was very little. And I guess I only looked at Edelbrock's website for the 1409.

 

[Rick Stephens]

I think I got the best price for my 1409 at Summit Racing.

I'd consider using spray carb cleaner if you think you have an intake leak. Spray around and listen for motor changes.

 

[Scott Danforth]

sometimes they simply blow up while on the water

 

[stoverdr]

I have gone all around the intake with the spray and it's tight.

 

[tank1949]

all vacuum ports were capped on the new carb and not present on the 1409. The 1409 was sucking in a TON of air at idle, the 1905 was very little. And I guess I only looked at Edelbrock's website for the 1409.

I hope that you have a marine fuel pump too! There is a big difference.

 

[stoverdr]

I have the red marine Holley.

 

[tank1949]

I have the red marine Holley.

If you tried the spray on carb base AND intake manifold and no rpm increase or decrease, and carburetor is marine, perhaps what you are hearing is air being sucked into the carb. normally?

 

[tank1949]

sometimes they simply blow up while on the water

That's not good. Happen to friend's boat right next to restaurant, while we were eating together, but we were not in boat. We watched it BOOM. Scarred the crap out of me!!!!! I always include fume sensor in any I/O or straight drive boat. But nothing beats use marine grade, observing and a good nose. I even request fellow anglers to lift bilge hatches on my boat before I turn on blowers.

 

[Bt Doctur]

Did witness a refueling explosion a few years back pretty impressing to to 2 men fly thru the air with their feet still on the deck

 

[tank1949]

did witness a refueling explosion a few years back pretty impressing to to 2 men fly thru the air with their feet still on the deck

not good!!! I learned to turn off eveything at battery switch too befor fueling.