Pilots and Mechanics

[mschor]

Question: Why if the pilot jets are too big, like the ones from MikeXS, can't you just tune the mixture screw down a bit to make it work? I recall dealing with this last year, but I don't remember if I ever tried that, I just remember plugs fouling and then getting the right pilots. My carbs do not have the connecting passage to the main jet. If you're feeling generous, a description of how the carbs go about changing over from pilots to mains would be entertaining and educational as well.

[motoman]

Pilot jet sizing associated with flow VOLUME. Main jet metering is ADDED to pilot jet flow based on venture velocity which is based on throttle plate opening. Throttle plate opening location also starts fuel being DRAWN through main jet orfice.

[bikerphil]

Mike, the correct 45 pilot jets from MikesXS is Part # 200-3513, they are the BS 30/96 type which have the correct spray nozzle for our carbs. You may have had the VM type which will fit, but the nozzle type is wrong.

[TopCatGr58]

[mschor]

Sorry Phil I meant the K&L pilots, not Mike's. Thanks Motoman for the description, I was thinking it somehow switch completely over to the mains. I'm still wondering though why it's not a simple fix to screw in the mixture screw a bit with bigger pilots....is it because bigger pilots cause a rich condition in the mains range as well?

[3Phase]

mschor,

The Pilot fuel and air jets don't just feed the idle circuit, they also feed the transition/intermediate circuit.

If you look in the carburetor throat just upstream of the throttle plate you'll see a small cluster of three holes, those are the transition/intermediate ports and they are not adjustable with the idle mixture screw.

The only way to tune the transition/intermediate circuit is to change the Pilot fuel/air jets so they'll deliver the correct volume of fuel for your engine with the correct fuel/air ratio.

[bikerphil]

Mike, check out this diagram if you haven't already seen it....

[bikerphil]

Some more courtesy Topcat...

[mschor]

Ok, I get it mostly, fuel enters the pilot jet and splits at the transition passage but no screw to adjust there. Thank you, helps to have it spelled out ---& drawn out! An aside..... is the starter jet totally closed off when you shut off the choke...and any problems can arise there besides a clogged starter jet/passage? Since I last took the carbs apart, the choke lost its clicking into place, now is just a slide action. I was pretty sure I put the little ball & springs in correctly. I dont mind the way it works now as long as its not affecting performance

[bikerphil]

Yes the starter jet should be completely closed when the enricher (choke) is shut off. Only thing to go wrong would be enricher passage clogged which would promote hard starting or one or more of the enricher valves leaking which would cause a rich condition by not completely shutting off it's fuel flow. There should be 2 ball bearings and springs on the 1 and 4 carb bodies that align with the detents on the enrichment rod.

[mschor]

Gotit, will update after I pull the carbs one more time

[skids]

Mike, check out this diagram if you haven't already seen it....

When i made the drawings i thought air entered the holes in the sides of the pilot jets. This was proven false by some members. Also this was for older carbs 78 and 79.

[hamjam]

Pilot jet sizing associated with flow VOLUME. Main jet metering is ADDED to pilot jet flow based on venture velocity which is based on throttle plate opening. Throttle plate opening location also starts fuel being DRAWN through main jet orfice.

are you referring to the venturi here?

[motoman]

are you referring to the venturi here?

yup.......

[hamjam]

thanks a lot