4.3 with aftermarket intake and carb

[wayne j]

Hey all, I bought a used 1990 Seaswirl Sable hardtop with an OMC 4.3. Love the boat, not so much the fuel consumption. The plugs read very rich, and it makes oil. Before I start going crazy trying to re-jet the carb I want to know if this carb is way too big. Looking at the decal on the valve cover, the boat came with a 2 barrel carb and my research says about 160hp and a 15-15 prop. It currently has an Edelbrock Performer intake with a Holley 4010. The HO option of this engine came with a 4 barrel and 220hp. I currently have a 15-17 stainless prop and the boat over revs (suspect I need a 15-19) looking up the carb, it is a 600 cfm carb, is this not grossly large for a 4.3? Thanks for any insight.

 

[Scott Danforth]

if your motor is making oil, you have a significant fuel leak issue simply pouring fuel into the motor.

that is not a carb size issue, that is a carb needs cleaning issue.

fix that.

 

[Bondo]

if your motor is making oil, you have a significant fuel leak issue simply pouring fuel into the motor.

that is not a carb size issue, that is a carb needs cleaning issue.

fix that.

Ayuh,.... Agreed,... or a ruptured fuel pump diaphragm,....

 

[jerryjerry05]

Yup sounds like it's dumping fuel into the oil.
The over rev?? What's it revving to?
The 15-17SS is about the same as a 19A
The 600 is probably OK The setup needs to be corrected.
How are the plugs burning? Carbon, soot or light brown? Pics?
Fix the carb, a professional rebuild is best.
Then go for a ride and check the rpms at wide open.
Remember load will add to the performance or lack of performance.
Check the drive and make sure it's the right one for the boat.
The switching and swapping of drive, you might have a v-8 drive??
It will affect the performance too.

 

[wayne j]

Ok thanks, have the carb apart and am rebuilding it this week. The plugs are super black and sooty. No oil residue on them. The over rev is 4800 rpm when doing 36 knots and still climbing. The boat comes out of the hole fine, the trim tabs help that I believe, but the boat seems to like a 25 knot cruise. At 25 knots I rev about 3800 rpm. Was thinking a stainless 19 pitch would help that out. Thank you all for your help.

 

[Bondo]

Ok thanks, have the carb apart and am rebuilding it this week. The plugs are super black and sooty. No oil residue on them. The over rev is 4800 rpm when doing 36 knots and still climbing. The boat comes out of the hole fine, the trim tabs help that I believe, but the boat seems to like a 25 knot cruise. At 25 knots I rev about 3800 rpm. Was thinking a stainless 19 pitch would help that out. Thank you all for your help.

Ayuh,.... Even if the carb is dumpin' fuel, that only explains the black sooted up spark plugs,.....

A Failed fuel pump diaphragm will cause the oil level to rise,....

 

[wayne j]

But shouldn't you see fuel in the line coming out of the top of ? Or can it just leak out the seal to the lever? I'm not saying it makes a liter in a couple hours, but it did come up on the dipstick during last season. Any idea what size jets should be in it?

 

[Scott Danforth]

What RPM do you get when you mash the throttle down and hold it on a day with moderate chop and your average load? you mentioned it climbs past 4800, however does it stop at 4900 or rev past 5500?

Is this only with you aboard and a nearly empty tank, or is this with 4 people and a load of fuel (average load)?

A carb simply dumping fuel will not only run rich, however it can dump raw fuel down the cylinders causing a hard start and dilute the oil with fuel. A stuck choke or a blown power valve due to a carb sneeze would do a similar job of causing it to run rich. If the diaphragm is ruptured, it would generally run up the bypass, however there is a possibility of simply the lever seal leaking.

when pulling the Holley apart for cleaning, note the power valve and jet sizes. someone could have a high power valve in there, requiring jets about 6 numbers higher than you should be running as the powervalve wont open. For example, I am running a #35 power valve on my 4160 on my boat.

I would guess your carb would have #45 power valve, 68 primaries and 79 secondaries as that is how the OMC 4.3's with the 4160's were set up. yours could be slightly different.

 

[wayne j]

4 people, full fuel, 4 prawn traps, trap puller, 2 electric downriggers, 4 mooching rods, 4 hali rods and 100lb mutt. Slight chop 35 knots and I throttled back because it was at 4800rpm and I read this motor should only go to 4600rpm. I have zero complaints about power. But the plugs get fuel fouled and I want to make a 80 mile run up the coast to Rivers Inlet this summer.

 

[wayne j]

Oh, plus ice and beer...

 

[Scott Danforth]

you still did not mention what it will turn, and yes, its common to have to back off the throttle on many boats when up on plane. However without knowing what it will do at WOT, we cant answer your prop question.

first and foremost, fix the fuel issue.

 

[wayne j]

Thanks Scott, I just don't really want to spin it past it's recommended RPM. I am already 200rpm over what I have read was the redline of the engine. Carb is going back together tonight and getting a couple sizes of smaller jets as well. Thank you guys for the info.

 

[Bondo]

Thanks Scott, I just don't really want to spin it past it's recommended RPM. I am already 200rpm over what I have read was the redline of the engine. Carb is going back together tonight and getting a couple sizes of smaller jets as well. Thank you guys for the info.

Ayuh,... The 4.3l motors are quite comfortable at 4800 rpms at Wot,....

It'll run for short testin' durations at 5200 rpms or better,....

Yer motor would be limited to 4600 rpms, only with the 2bbl. carb,.....

 

[wayne j]

Ok bondo, thanks again for all the info. Will be on the water this weekend to prep for a hunt on the Easter long weekend.