4.3 Mercrusier carb questions

[Newbie@boats]

97 Merc 4.3 no history of carb repair or replacement. Boat was always difficult to start cold-like first initial start at the ramp. No matter which different way I tried with the throttle.

So I had an Amazon gift card I’m sure you can already see where this is going, and I bought a carb off of there. Installed it and now the boat fires up without any throttle just one pump back to neutral and it lights right off.

I know it’s a cheap Amazon carb, but I replaced both upper and lower gaskets with OEM gaskets-I have the spacer between the carb and manifold. The issue I’m having is I have a choppy idle. Any thing off idle smooth and no issues. I’ve played with the air fuel screw but I cannot get the choppy idle to go away. I’ve had great luck with carbs off amazon previously so I figured I’d give it a try with their return policy I can get my money back.

That’s the only thing I’ve changed minus the coil when that failed at the beginning of the season. As a side note the carb came with an oval gasket and a gasket with 2 holes punched out. I reinstalled the gaskets the way I found them originally, 2 holes upper and lower. I am wondering if I should of used the gaskets that came with it cause that’s how that carb is designed to run? I don’t have much experience with carburetors.

 

[matt167]

Amazon carbs will generally ‘work’ as in you wouldn’t be stranded…probably. They are often not machined perfectly and/ or have messed up jets. You’ll probably have to open it up and tinker with it anyway. You’ll probably get it working but you could probably get your original working just as well

 

[Newbie@boats]

Amazon carbs will generally ‘work’ as in you wouldn’t be stranded…probably. They are often not machined perfectly and/ or have messed up jets. You’ll probably have to open it up and tinker with it anyway. You’ll probably get it working but you could probably get your original working just as well

I agree. We used to have a carb rebuild shop in our town but he’s no longer around.

I am more then willing to send my original carb out to get rebuilt, I’ve found a couple places online that sell rebuilt merc carbs, but I can’t find any reviews on them and I am very mechanically inclined but never been in a carb like this. I’ve been in plenty of quads/dirtbikes carbs before

 

[nola mike]

I agree. We used to have a carb rebuild shop in our town but he’s no longer around.

I am more then willing to send my original carb out to get rebuilt, I’ve found a couple places online that sell rebuilt merc carbs, but I can’t find any reviews on them and I am very mechanically inclined but never been in a carb like this. I’ve been in plenty of quads/dirtbikes carbs before

You could help us by letting us know which carb you have, but both the mercarb 2bbls and the weber 4 bbls are easy enough to rebuild.

 

[Scott Danforth]

every amazon carb is junk in a box. doesnt matter what its bolted to.

take the original carb, reach out to Cliffs or Mikes if you cant rebuild it yourself. https://cliffshighperformance.com/ or https://www.carburetor-parts.com/

 

[Scott06]

You could help us by letting us know which carb you have, but both the mercarb 2bbls and the weber 4 bbls are easy enough to rebuild.

I’m thinking it’s a mercarb based off the two hole gasket and oval holed gasket he mentions, which usually both come in the kit.

97 Merc 4.3 no history of carb repair or replacement. Boat was always difficult to start cold-like first initial start at the ramp. No matter which different way I tried with the throttle.

So I had an Amazon gift card I’m sure you can already see where this is going, and I bought a carb off of there. Installed it and now the boat fires up without any throttle just one pump back to neutral and it lights right off.

I know it’s a cheap Amazon carb, but I replaced both upper and lower gaskets with OEM gaskets-I have the spacer between the carb and manifold. The issue I’m having is I have a choppy idle. Any thing off idle smooth and no issues. I’ve played with the air fuel screw but I cannot get the choppy idle to go away. I’ve had great luck with carbs off amazon previously so I figured I’d give it a try with their return policy I can get my money back.

That’s the only thing I’ve changed minus the coil when that failed at the beginning of the season. As a side note the carb came with an oval gasket and a gasket with 2 holes punched out. I reinstalled the gaskets the way I found them originally, 2 holes upper and lower. I am wondering if I should have used the gaskets that came with it cause that’s how that carb is designed to run? I don’t have much experience with carburetors.

When I did my mercarb a few years back on my 3.0, it came with both oval and two holed gaskets. Oddly enough the factory mercarb gasket was two holed, even though there was a single oval hole in the intake… so I thought I’d try the oval gasket , which I think is actually for TKS carbs, wouldn’t idle for chit and the response to changes in mix screw in a normal manner. Went with the two hole and it worked.

does it respond to changes in the mix screw and is the idle speed correct? If idle speed is too high maybe be exposing g the transition circuit. Would also very ignition timing is good and cap rotor etc are in good shape and you have a strong spark on gap tester.

if the carb doesn’t respond to changing idle mix likely you Got A bunk carb. Seems like from reviews on these they are 50/50.

if you have rebuilt dirt bike or other carbs it’s the same thing. Get a good carb kit from mikes and I use a cheap ultrasonic from harbor freight, which has improved my rebuild quality dramatically. I do 2-3 carbs a year between all the lawn equipment, boat, outboards, and my 65 pontiac.

 

[Newbie@boats]

It’s a 2bbl merc carb.
The air/fuel screw does change the way it acts but I feel as if I have to make a lot of turns for it to make a difference. From fully screwed in to like 4 turns out for it to make any type of noticeable difference.
I’ll look into those websites, will probably send my original carb out to get rebuilt.

Was mainly curious about the gasket set up if that could be causing my issue, like I said boat runs excellent other than the choppy idle, which I can hear on the muffs but can’t really tell when I’m in the water.

I did check the timing cause I was curious and it seemed to be lighting up when the line on the balancer hit the mark on the cover or was very close to it.