Need help from the carb gurus

I have a 77 kz 1000 with a 1075 kit with v&h 4into1 and k&n pods. The carbs are 1975 vm 28's. The carbs were supposed to be professional rebuilt when i aquired them. I have had them apart, and they are very clean inside. The jets are 117 main's and 17.5 pilots. The problem i'm haveing is on the #4 carb. I have a colortune, best tool in the world by the way, and i can get the idle circuit set on the other 3 carbs, but the #4 carb is grossly rich, to the point that i can take the idle screw out and it is still too rich. I took the carb back apart and rechecked the air bleed and blew carb cleaner and compressed air through all ports, and everything is flowing as per design. I swapped the pilot jet out with another with no luck. Its is as if there is too much fuel being sucked in through the pilot circuit. The pilot jets are brand new, so no garbage, but i still blew some carb cleaner through them. I see there is a small welch plug in the pilot circuit. Is it possible that it is leaking and drawing in extra fuel through the float bowl, I know the quadrajet jet carbs were notorious for welch plugs to leak. I checked floats and it is a little high but not any higher then the other three. Any help would be greatly appreciated. I have exhausted my experience.

oppie501 wrote:

I have a 77 kz 1000 with a 1075 kit with v&h 4into1 and k&n pods. The carbs are 1975 vm 28's. The carbs were supposed to be professional rebuilt when i aquired them. I have had them apart, and they are very clean inside. The jets are 117 main's and 17.5 pilots. The problem i'm haveing is on the #4 carb. I have a colortune, best tool in the world by the way, and i can get the idle circuit set on the other 3 carbs, but the #4 carb is grossly rich, to the point that i can take the idle screw out and it is still too rich. I took the carb back apart and rechecked the air bleed and blew carb cleaner and compressed air through all ports, and everything is flowing as per design. I swapped the pilot jet out with another with no luck. Its is as if there is too much fuel being sucked in through the pilot circuit. The pilot jets are brand new, so no garbage, but i still blew some carb cleaner through them. I see there is a small welch plug in the pilot circuit. Is it possible that it is leaking and drawing in extra fuel through the float bowl, I know the quadrajet jet carbs were notorious for welch plugs to leak. I checked floats and it is a little high but not any higher then the other three. Any help would be greatly appreciated. I have exhausted my experience.

checked floats and it is a little high but not any higher then the other three --- Was the service float bowl fuel level checked by means of the clear tube test?

The upside-down-on-the-bench measured float height is notoriously inaccurate.

Good Fortune!

Is choke plunger fully closing on #4 carb when choke is OFF?

Is #4 pod over-oiled? Could remove the pod and test run. Sometimes a pod will obstruct entrance to the pilot circuit air passage intake port.

Good Fortune!

Thanks, I pulled the pod filter and no luck. I checked the float height on the bike with the clear tube in the drain hole. It acts as if the air bleed is obstructed, but when I blow carb cleaner through it there is no obstruction. I can actually seat the air screw and the engine doesn't die, but the colortune indicates that the fuel shuts off which makes no sense at all, since the bleed screw has nothing to do with the amount of fuel, only how much air mixes in with the fuel. Pullin my hair out. The choke plunger is seated the same as the other three carbs.

Doesn't the air carry the fuel? Therefore with no air passing through the carb would there be any fuel drawn into the combustion chamber?

My engine runs just great on three cylinders...

Will mention a couple of things.

Possibly the pad at bottom of choke plunger is worn or damaged, and failing to block fuel entry into enrichener circuit when the plunger is down, which would result in an over-rich air/fuel mixture.

Possibly the float vent is obstructed, resulting in "vapor lock." Could blow compressed air backward through the vent hose into the float bowl, to assure the vent line and vent passage are clear.

The image below describes a good method for assuring all pilot circuit passages are clear.

If turning the pilot air screw produces no change in engine rpm, there is likely something wrong inside the carb.

Tapered tip of pilot air screw should be in visibly good condition.

The default pilot air screw position is 1.5 turns out from lightly seated.

Good Fortune!

[Click on image to enlarge view.]

Hey Patton you r the genus of the day. It turns out the choke plunger was hanging up a little and not seating all the way when the choke was turned off. The carbs were totally rebuilt with new choke plungers and all. Should I put a little oil on the choke plunger body or will they wear in. I pushed it down with a screwdriver and whamo problem solved. I put the choke on again and it did the same thing, the others went right down but that one hung up just a little. Any suggestions is surely appreciated, Its not nearly as easy to get to when the tank is on it.

oppie501 wrote:

...choke plunger was hanging up a little and not seating all the way when the choke was turned off. The carbs were totally rebuilt with new choke plungers and all. Should I put a little oil on the choke plunger body or will they wear in. I pushed it down with a screwdriver and whamo problem solved. I put the choke on again and it did the same thing, the others went right down but that one hung up just a little. Any suggestions is surely appreciated, Its not nearly as easy to get to when the tank is on it.

Could apply PBBlaster to the choke plungers and work the choke lever while helping #4 to seat each time.
Such lubing may resolve the issue by reducing any friction between the plunger and its channel.
Doesn't hurt to periodically lube the external carb workings.

Good Fortune!

Nice one Patton