4000ft Above Sea Level Carb Settings 4.3 Merc

[nmelche]

I occasionally pull my boat to my in-laws mountain house that is roughly 4,000ft above sea-level. My Searay has a 4.3 Merc engine with the 4 barrel rochester quadrojet carb. I have an extra carb that I would like to setup just for this altitude. Anyone have any suggestions as to what jet size I should use for that altitude? Thanks!

 

[ScottinAZ]

I occasionally pull my boat to my in-laws mountain house that is roughly 4,000ft above sea-level. My Searay has a 4.3 Merc engine with the 4 barrel rochester quadrojet carb. I have an extra carb that I would like to setup just for this altitude. Anyone have any suggestions as to what jet size I should use for that altitude? Thanks!

without knowing what is currently in the carb, its difficult to know how or if you will need to rejet. Best option would be to run it, and see how rich its currently running at that altitude. My GUESS is that you will need to go one to two jet sizes smaller, but only running it will find out for sure. Thankfully for you, all Quadra-bog jets are the same, so you can source them easily and cheaply from somewhere like Summit Racing. You can likely get a small assortment kit from them for a reasonable price when trying to get the right ones. I would bet that they also have metering rods should you need to change them as well.

 

[nmelche]

without knowing what is currently in the carb, its difficult to know how or if you will need to rejet. Best option would be to run it, and see how rich its currently running at that altitude. My GUESS is that you will need to go one to two jet sizes smaller, but only running it will find out for sure. Thankfully for you, all Quadra-bog jets are the same, so you can source them easily and cheaply from somewhere like Summit Racing. You can likely get a small assortment kit from them for a reasonable price when trying to get the right ones. I would bet that they also have metering rods should you need to change them as well.

Ran it last weekend and it ran incredibly rich and had a hard time hot starting. I had the same thought, just buy a set and experiment with different jet sizes. Just wanted to see if someone had a good suggestion before I wasted a bunch of time. Thanks!

 

[todhunter]

Try posting on the forums at Cliffs High Performance. Cliff Ruggles posts frequently hand he may be able to help guide you. He also carries high quality QJ parts.

 

[Scott Danforth]

You are down 12% or more on power. From a jet standpoint, you will need to go smaller (leaner) the the 4000 elevation

 

[dubs283]

Just wanted to see if someone had a good suggestion before I wasted a bunch of time.

The mercruiser factory manual for your engine has a jetting chart for your carb/altitude. This is of course a starting point and does require teardown and installation of different jets but ime the charts are pretty spot on for naturally aspirated carbureted engines

 

[achris]

From the Merc service manual... (and Merc don't suggest any change other than a prop to get the engine back to recommended WOT RPM below 1525m)