Topic: Primary carb circuits 500 four Keihins

[paulbaker1954]

I strongly suspect I have a blockage somewhere in the primary circuits of at least 2 my 500 four carbs causing rich mixture at low revs

Adjusting the pilot air screw makes no difference to the poor running which is why I have this suspicion

By the way I have checked all other possible causes plugs,points,coils,compression,timing, valve clearances.......

Does anyone have a schematic or know of an exploded view of where air and fuel goes in the primary circuit so I can check if anything is blocked

[flybox1]

If you have a blockage in a fuel delivery circuit, it will cause you to be lean 
What evidence do you have that it is running rich?
when was the last time you pulled your carbs for a thorough cleaning?
Stock intake and exhaust, assuming by your profile pic?
What size jets? what IMS setting?
Are they clean and clear?
Is the fuel level in your carb bowls accurate?

[paulbaker1954]

Evidence is plugs 1 thru 3 are showing rich whilst 4 is a nice tan colour plus the pilot air screws make no difference to the problem even at 3 turns out

Carbs were rebuilt last winter and all o rings replaced but not the jets or emulsion tubes as these looked clear but to be sure I have on order a set of new jets and float valves and needles as not a bad idea to change them

Jets are standard at 40 pilot and 100 main by the way and before anyone comments gloat levels are spot on

I am thinking of having carbs ultrasonic cleaned but was just wondering if there is some way to vheck the primary air circuits

[flybox1]

Evidence is plugs 1 thru 3 are showing rich whilst 4 is a nice tan colour plus the pilot air screws make no difference to the problem even at 3 turns out.   OK....is this from general riding, or from a specific throttle position plug chop?

Carbs were rebuilt last winter and all o rings replaced but not the jets or emulsion tubes as these looked clear but to be sure I have on order a set of new jets and float valves and needles as not a bad idea to change them  No need to change out the originals.  Remove, clean, and put back the originals

Jets are standard at 40 pilot and 100 main by the way and before anyone comments gloat levels are spot on  Great

I am thinking of having carbs ultrasonic cleaned but was just wondering if there is some way to vheck the primary air circuits.  Ultrasonic is good, but get your hands in there.   Pull, inspect and clean the parts not touched by the Ultrasonic cleaner.  Spray carb cleaner followed by air in all passage ways.

THEN....two last items.
1. Once all other maintenance items are done, complete a vacuum sync of the carbs.
2. New D7EA plugs, and a idle plug chop.
Post a picture of all the plug tips/insulators for us to see.
This will give us a clearer picture of what is really going on with your A/F mixture.

[jonda500]

subscribed!  I have #35 pilot jets in my 500 (needle clips #4 from the top, mixture screws 5/8 turns out), but since replacing the emulsion tubes and two temperamental inner floats I now seem to be just a tad lean...
John