Kadrons stumble under load

[ched]

My setup is dual Kads on 176 motor. Originally ran fine as delivered but recently the car stumbles and sligh backfires under load.
Engine revs perfectly under no/ light load. I dont believe its an acc pump problem because it stumbles unde gradual acc under load Any advice ???

[Bruce2]

plugged idle jet

[ched]

After careful looking. I found one accel pump not squirting. I have ordered a rebuild kit and will see if that handles the problem once installed

[ched]

Ok I have rebuilt both carbs. Engine idles smoothly but stumbles and almost dies when I try to rev it even under no load . It will not rev over about 2 000. starts up and idles without hesitation. Fuel pressure is a little high at 3.5 psig but that is not a new issue. could this be an ignition problem?

[ched]

Ok Progress one of the carbs didnt have the emulsifier vent properly seated so now it reves strong an pulls good a low rpm but stumbles at high rpm under load Im not sure of the main jet sizes but they are the same ones when it ran strong theoughout rpm range vent is 40 28

[FJCamper]

Hi Ched,

Do you have your balance tubes connected between both carbs?

Here's a quick-check list.

Be sure both accel pumps are squirting evenly. You might be missing an accel pump checkball, which lives under the brass accel pump nozzle tube.

The linkage is allowing both carbs to open up to full throttle.

Remove the carb tops and insure that both main jets are the same size and fully seated, and the floats are working smoothly.

There is a rare condition in which the air correction jet is loose under its pressed in plug. You have to have the carb off the manifold to check this, just shake the carb and listen for the loose tube. Remove the float first before you shake it.

Make sure both idle jets are the same size. They have a number stamped on them, generally you want a G45 or 55.

Your needle and seat valve might be sticking on one side, causing flooding or starving. By the way, these have sizes too. Some times they are mismatched. The size refers to the two holes in the brass valve. Look for a stamped number.

A not-so-rare problem is the accel pump nozzle being bent down too far into the carb throat. At high speeds, the intake velocity will siphon gas right out of the nozzle and cause top end misfires due to too much gas.

Let me know if how you're doing

FJC

[ched]

Thanks, I do have a balance tube installed. The check balls are in place. The main jets are as per original and not stamped as to size. they were furnished by AJ Simms who makes his own for the Kad setups he sells. Needle and seats are new from the rebuild kits I installed. Idle Jets are same as mains ( not marked). The car acts as though the mains are too small as it stumbles at hi rpm under load which can be momentarily remedied by a "squirt" from the accel pumps. It pulls strong under load a low rpm.
My next step is to replace the mains with a known size probably 130s . I have semi hemi heads which I understand demand a little richer mixture.

[FJCamper]

Hi Ched,

Let's focus on the high-speed or "power circuit." You have a small "annular discharge ring" (ADR) just above the venturi. It is in itself a venturi that accellerates airflow past the main power circuit, sucking fuel directly from the float bowl. The ring is held in place by an external screw. Loosen the screw and remove the annular discharge ring and blow it out clean. A partially clogged ADR will cause the carb to fail to deliver enough fuel above 3000 rpm.

[ched]

I will do it ! I did however remove and clean thes parts as part of rebuild but WILL double check. I did find that one of these ADR assemblies was not clicked in place accurately on one of the carbs and things improved see my posn september 23.
Thanks for your suggestions

[ched]

Took one carb off and re cleaned main jet AND the ADR assembly paying particular attention to the small fuel passage. It fixed the problem 95% so Ill do the other carb tomorrow. Thanks to FJ for this tip.

[ched]

Late update: 2nd carb had a very slightly restricted main jet. a #55 drill bit pushed through and cleared it. Now 100 % OK. I had previously soaked the jets in solvent but somehow one was not completely cleared. Lesson learned !!! Soak em and mechanically clean also !!!