Carb questions

[MANIC MECHANIC]

The boat I just bought (used) has what is supposedly a Holley 750 non-marine carb, with vacuum secondaries and manual choke.
http://www.***boat.com/image_center/data/520/11912004_0423dialajet0005-med.JPG
http://www.***boat.com/image_center/data/520/11912004_0423dialajet0004-med.JPG
Can anyone identify this carb?
Can it be converted to a marine carb? (I intend to run the engine cover)
Are vacuum secondaries acceptable for a jetboat?
The black rubber hose going to the vacuum port between the fuel supply lines is the vent from the mechanical fuel pump...that's not where that line belongs...is it?
Any info would be appreciated.
Tim

[Hotcrusader76]

From the looks it's definitely a vacuum secondary that's been converted to 4150 along with external adjustable jetting blocks. Those look like the old weber or moroso designs.
To answer your question yes it can be converted to Marine use but it won't be USCG approved. Not that it needs to be but the only conversion that can be performed is sealing the shafts and J-tubes.
Hope that sheds some light for ya.
~Ty

[shirkey4750]

Tim get the list number off the front of the choke horn, and post it and I will check ir for you.

[roostwear]

Looks like the old Dial-a-jet system. Never used used it, I went with the Holley Adjust-a-jet (Percy's). Adjust-a-jet works well, but I gotta figure if you run your boat in the same area, just jet it and use the money on something else.
As far as the Dial-a-jet, if it's working, leave it alone. If/when it craps out, go back to stock.
My.02

[bocco]

Originally posted by Hotcrusader76
From the looks it's definitely a vacuum secondary that's been converted to 4150 along with external adjustable jetting blocks. Those look like the old weber or moroso designs.
To answer your question yes it can be converted to Marine use but it won't be USCG approved. Not that it needs to be but the only conversion that can be performed is sealing the shafts and J-tubes.
Hope that sheds some light for ya.
~Ty
Hotcrusader76, can you elaborate on the marine conversion. I asked the Holley tech line about it and they said no way. Are the parts available to make the conversion? J tubes and shaft seals?
Thanks
Gary

[Hotcrusader76]

Yes Holley is correct in that a Non-Marine carburetor "can not" be completed converted to a USCG Marine. This is because of the baseplate (throttlebody) design. Marine carburetors have reversed butterflys and knotched shafts to prevent (not always successfull) fuel leaks. A Marine throttlebody has a very distinct primary shaft when veiwed from the outside, it's almost like a polygon shaped peice.
The only components that can be converted are the Marine J-tubes and sealing the throttleshafts, which is performed in a similiar fashion that the blowthrough carburetors are done. This is the only way to mimic the sealing capabilities of Holley's Marine carburetors and has proven far more benifical than the Marine version itself.
There has been alot of debate on Auto vs. Marine and alot of good and bad info has come out of it. I will say that if you're looking for a USCG approved version then get the Marine. If you just need to pass a visual inspection than the converted Auto will do just fine and prove to be just as safe if not safer than the Marine.
Some other "not so good" options on Marine carburetors:
1. fuel transfer tubes on primary metering blocks- prevents leaking on warped metering blocks but the tube leaks itself after a winter season due to dry rotted seals.
2. non-adjustable needles and floats on 90% of Marine Ford 600cfm Holleys- Why I don't know..must be insurance reasons
3. Primary metering block emulsion tubes- not an optimal component for the emulsion circuit on performance machines.
Hope that helps...
~Ty