OMC 460 running rich at idle after higher rpm

[Trevthefox]

Hey guys, sorry for the long write up. Let me know if you have any ideas. Thanks in advance.

I have a '89 460 king cobra. Everything was completely rebuilt and she runs pretty damn good. The only issue we've been having is when we lower the speed/rpm coming off of plane. The engine seems to be running very rich. You can see the black exhaust and you can smell it pretty strong and the engines runs a little rough at idle. (this only happens when coming off of a higher rpm). The carb has been rebuilt a couple times during the process of us rebuilding the engine and followed we the instructions exactly. Float levels are parallel and idle needles have been set according to the manual.

Mind you, I don't rebuild carbs professionally but I'm pretty handy and can follow instructions. I'm pretty sure I did it the right way but obviously with these issues I'm starting to 2nd guess my work. I'd hate to send it in to a carb shop and waste money only to learn it was a simple mistake that i'm overlooking. The Carburetor is a 4 barrel Holley 650 CFM.

To temporarily solve the problem I wired up a fuel pump cut off switch at the helm so when I come off plane I can kill the fuel pump. I put the engine in neutral and let it run out of gas until it dies. Then when I start up everything is back to normal. When the engine starts to run out of fuel and burn through the excess, the rpm rises on its own and then dies.

My only guesses are: bad floats or float levels, need to adjust idle fuel/air mixture, or bad carb altogether. The electric up doesn't shut off automatically when it hits a certain psi, but its only rated at 5 psi just like manual recommends.

Any ideas?

 

[Scott Danforth]

Who rebuilt the carb? A Holley carb is as simple as a toilet. the key is to chase every passage with a piece of wire

650 is a bit small. What are the airhorn numbers?

If you had a backfire, you could have ruptured the power valves

Which Holley carb? 4150 or 4160?

What kind of check valve for the accelerator pump? Check ball, or orange mushroom?

If orange mushroom, did you trim the installation *** off it after you pulled it thru? If not, it's holding your float.

Use the float bowl sight glasses to set float height. Your secondary float could be too high

 

[Trevthefox]

Who rebuilt the carb? A Holley carb is as simple as a toilet. the key is to chase every passage with a piece of wire

650 is a bit small. What are the airhorn numbers?

If you had a backfire, you could have ruptured the power valves

Which Holley carb? 4150 or 4160?

What kind of check valve for the accelerator pump? Check ball, or orange mushroom?

If orange mushroom, did you trim the installation *** off it after you pulled it thru? If not, it's holding your float.

Use the float bowl sight glasses to set float height. Your secondary float could be too high

Hey Scott. I rebuilt the carb and it was pretty simple like you said. All passages were clear and I followed a couple vids plus the manual to make sure I wasn't missing anything.

I don't have the air horn numbers handy right now but I can find it. The list number was 50470 and its a 4160 Holly Carb.

I don't think it's backfired lately but is there a way to check the power valve to see if it's been ruptured?

It has the umbrella type check valve. And thats something I never replaced. I don't think it was in the rebuild kit so I just reused the old one. Maybe that's the issue.

Unfortunately my carb doesn't have the float bowl sight glasses so I'd have to install them or just take off each bowl and adjust the height