Carby question on 5.7 l mercruiser

[brett62]

Have a question on a Holley carby sitting on top of a 5.7L 350 mercruiser.

At the bottom of the carby there is an inlet that has vacuum and find it surprising that it’s allowed to sit there and suck what every it feels like.

I see that the flame arrester has a pipe that is not in use also. Would it be afair assumption to say that a hose is missing from this picture?

I don't believe that mercruiser's came with Holley's installed. Bought the boat not long ago and did not notice it.

Can any mercruiser specialist explain what is going on here?



IMGP2362.jpg

[Bustedoff]

Is it the vacuum port for connecting to the distributor?

[captain rednut]

Hi Mercruiser defiantly never use or recommend holly carbies on inboard engines in pleasure boats as the original proven 4 barrel rochester carby is very safe and efficient with fuel usage.
Hollies are very thirsty.
cheers cr

[brett62]

Is it the vacuum port for connecting to the distributor?

I checked that and no connection to the distributor.

[brett62]

Hi Mercruiser defiantly never use or recommend holly carbies on inboard engines in pleasure boats as the original proven 4 barrel rochester carby is very safe and efficient with fuel usage.
Hollies are very thirsty.
cheers cr

I didn't think they did. This is the first mercruiser Ihave owned.I will seriously consider changing the carby over. It certainlylikes to drink. At 3600 rpm I am doing 20 knots and sucking 42 LPH. I will tryand find out which Rochester should be living on top. The person I brought the boat fromhad just installed a new short motor and the original motor was set up withEFI. The mechanic that did the job said they perform better and are morereliable with a carby so on went the carby. When I purchased the boat it onlyhad 50 hours on the new motor and I have added another 25 hours since. Alwayshad concerns with the fuel burn as I should be getting around the 37 L atcruise.

[Fed]

The top port could be from a mechanical fuel pump I think they had a hose running from below the pump diaphram to the carby in case of a break in the diaphram.
Fully agree with putting it back to a stock standard state.
Get on to iboats and chase up achris in the mercruiser forum he's a good bloke with all things mercruiser.

[brett62]

The top port could be from a mechanical fuel pump I think they had a hose running from below the pump diaphram to the carby in case of a break in the diaphram.
Fully agree with putting it back to a stock standard state.
Get on to iboats and chase up achris in the mercruiser forum he's a good bloke with all things mercruiser.

I will chase up achris get his advice. I am also unsure if the fuel pump is correct also. Does not look like any thing I have seen on a mercruiser.

[Fed]

Have all your serial numbers ready.

[brett62]

Hi Mercruiser defiantly never use or recommend holly carbies on inboard engines in pleasure boats as the original proven 4 barrel rochester carby is very safe and efficient with fuel usage.
Hollies are very thirsty.
cheers cr

Jim I would like to thank you for coming around this morning and checking out my rig. The advice given by you with the years of experience was certainly an eye opener on all the items that you raised and left me feeling rather flat. I certainly will be going with all of the points raised and look forward to your plan of getting the motor right.

I would also like to thank Gary (Spaniard_King) for putting me onto you.

Anyone after a marine engine repair company I would recommend that you get hold of these people.

Thanks again Jim as you have just defused the time bomb that my family and I ride in.

[DATCOL]

Hi Brett I may have a suitable Rochester carbie that I can sell you as I got a couple with my Caribbean that I bought with a Mercruiser V8 GM 5.0 L motor Cheers COL