4.3LX Mercruiser Carburetor

[Dump]

I have twin 4.3LX two barrel carburetors on Mercruisers in a 1991 Sea Ray Sundancer. Three questions; how difficult (and expensive would it be to convert to 4 barrel carburetors? Would the increase in power be worth the expense, and finally, how would this affect fuel economy at norma cruising speed?

 

[bluewater19]

Re: 4.3LX Mercruiser Carburetor

I did this to my bluewater 19ft cuddy cab. You will increase your flywheel hp from 175hp to 190hp. This translates to a jump from around 160hp to 175-180hp at the prop. These figures are from a mercruiser manual. Mercruiser rated motors at the flywheel in 1991. I installed a holley vacum secondary on my boat and found that part throttle fuel economy to be better than with the 2bbl. As long as I stayed out of the secondaries!<br />Top speed went up from 38mph to 42-43 mph on the gps. I don't know what it would do on a heavy boat like yours. I didn't have to change props because it was running at the low end of recomended max before and and now it is at the top end of recomended rpm. I say in my case it was worth the swap. I liked it so much that I am doing the same swap to my 2003 glastron but this time I am using the carter/webber 4bbl because Bondo, the 4.3liter guru on this board says this carb is easier to tune and that is what mercury put on there in the first place. We'll see!!!!

 

[Dump]

Re: 4.3LX Mercruiser Carburetor

Thanks Bluewater. I going to show my ignorance which isn't an uncommon occurrance. What do you mean by "secondaries" and also, do the intake manifords need to be chaged to accomodate the switch to the 4 barrels?

 

[Bondo]

Re: 4.3LX Mercruiser Carburetor

That's an Awlfully Tall Title to Step Into bluewater19...... <br /><br />Dump,<br />Ya, What he said......<br />You'll Gain a Solid 20hp from Each motor....<br />The Swap is a Really Easy one...... <br />The Most Inexpensive way is to Find a Merc. Take-off, Used..... <br />New, Aftermarket, would be around $500. or so....<br />IF Your motors are 1991s,<br />You'll need the Manifold with Six(6) bolts on each side for a Total of Twelve(12) hold down Bolts........ There is a newer one, the Vortec Style, It has Only eight(8) hold down bolts.....<br />And, Yes, I Love the Merc/Weber/Carter/Edlebrock Carb... Easy to Tune... Easy to Service....<br />Economy ???.....<br />A 4bbl runs on Only the front 2bbls when you're Idling, on Up to around 3500rpms(when the Secondaries come in).......<br />If you Prop the boat to Run 4600rpms at WOT.......<br />Then Cruise at about 3000/3200rpms......<br />You Should be able to pull in a Good gph......<br /><br />I've got Mine Running Clean, but not Lean.....<br />And I have to pump gas Out of the tanks, Every weekend....

 

[bluewater19]

Re: 4.3LX Mercruiser Carburetor

That is why you are the man.<br />What kind of top speed increase do you think I will get on the 2003 glastron after swapping the 4 bbl?<br />I peg the speedo at 55 (57-59 on gps)and run 4800rpm with a laser II 23 pitch right now with bone stock 2bbl.

 

[Bondo]

Re: 4.3LX Mercruiser Carburetor

I peg the speedo at 55 (57-59 on gps)and run 4800rpm with a laser II 23 pitch right now with bone stock 2bbl.

It appears you're Under-Proped Now......<br />With those #s... A Bigger Prop,+ the 4bbl Should get you to the other side of 62.....<br />Maybe More....