Logo

Carburetor

Gradyrook61

New member
Hey, Rookie boater here who has a 1986 Grady white with the gm 305 4v engine. I have just finished normal maintenance. Oil change, plugs,wires,cap rotor fuel filter, water separator. My question is this. My boat runs great but I only achieve 32-3400 rpms at wot. I'm only getting about 25mph. I'm thinking I should be running about 4- 4500 and about 40 mph at wot. I'm not a mechanic by any means but I'm capable of most wrenching fixes. What could be holding the motor back? I wish I new what carb came stock on this boat. I have a mercruiser 2barrel and i thi k from what I've read so far it may have come with a Rochester 4 and for whatever reason was swapped out. My boat weighs 3750. Would changing out the 2 to a 4bbl help my issue? Thanks in advance people!
 
re: "I'm thinking I should be running about 4- 4500 and about 40 mph at wot."....
Did it ever when you owned it? In 1986 GW made boats from 19 up to 25 ft. What do you have? BIG difference between a 19 and a 25...( and the ones in between for that matter.) At 3750# sounds like more like a 22 ft.
 
re: "I'm thinking I should be running about 4- 4500 and about 40 mph at wot."....
Did it ever when you owned it? In 1986 GW made boats from 19 up to 25 ft. What do you have? BIG difference between a 19 and a 25...( and the ones in between for that matter.) At 3750# sounds like more like a 22 ft.

Hey Captain Bob, you are on the money. 22ft GW. It's only my 2nd boat ever. I have never had it up to 4000 but my boating friends have told me it should run 40mph
 
...................
Hey, Rookie boater here who has a 1986 Grady white with the gm 305 4v engine. I have just finished normal maintenance. Oil change, plugs,wires,cap rotor fuel filter, water separator. My question is this. My boat runs great but I only achieve 32-3400 rpm at wot. I'm only getting about 25mph. I'm thinking I should be running about 4- 4500 and about 40 mph at wot.
WOT RPM is a test RPM as to determine if the engine/drive are geared and propped correctly.
WOT RPM is NOT to be sustained for any duration...... unless of course you want to shorten the life of your engine!

In order to perform a WOT RPM test, the hull must be clean, the gearing must be correct, the prop must be in full tune and the engine must be healthy and in full tune!

I'm not a mechanic by any means but I'm capable of most wrenching fixes. What could be holding the Engine back?
Have you looked to see what the ignition advance is doing at around 3,200/3,400 RPM?
A lazy ignition advance will hinder performance.
You should be seeing approx 28* @ 3,200/3,400 RPM.


I wish I new what carb came stock on this boat. I have a mercruiser 2barrel and i thi k from what I've read so far it may have come with a Rochester 4 and for whatever reason was swapped out. My boat weighs 3750. Would changing out the 2 to a 4bbl help my issue?
At 4,000 RPM (just above ideal cruise RPM), your 5.0L SBC will pull in approx 293 CFM @ 83% VE.... and approx 353 CFM @ 100% VE.

Hey Captain Bob, you are on the money. 22ft GW. It's only my 2nd boat ever. I have never had it up to 4000 but my boating friends have told me it should run 40 mph
See above re; WOT RPM!


If I'm correct, in 1986 OMC had not yet introduced the Cobra drive.
By chance is this boat equipped with a Stringer Drive?



.
 
Back
Top