Solex p40-II Idle metering jet orientation

[Greg Greer]

I can only get my # 4 cylinder to idle by slightly backing off the idle metering jet by about 1/6 of a turn counter clockwise. My other idle metering jets are turned in completely and run fine. I have tried switching this jet with other idle metering jets, however, it is the same story. It will only run if the jet is backed off about 1/6 of a turn. I can turn this cylinder on and off just by this slight turn.
My mixture screws are turned consistently out, however #4's mixture screw only has an effect when the idle metering jet is backed off the slight 1/6 of a turn. I have cleaned this circuit with lots of carburetor cleaner and idle air bleed is clear. I cannot detect any air leaks or ignition issues. I have good compression and spark. The engine runs fine off idle range. The questionable JET IS #9 in the first pic and Letter g in the second pic. Any advisement appreciated.

[Greg Greer]

I can only get my # 4 cylinder to idle by slightly backing off the idle metering jet by about 1/6 of a turn counter clockwise. My other idle metering jets are turned in completely and run fine. I have tried switching this jet with other idle metering jets, however, it is the same story. It will only run if the jet is backed off about 1/6 of a turn. I can turn this cylinder on and off just by this slight turn.
My mixture screws are turned consistently out, however #4's mixture screw only has an effect when the idle metering jet is backed off the slight 1/6 of a turn. I have cleaned this circuit with lots of carburetor cleaner and idle air bleed is clear. I cannot detect any air leaks or ignition issues. I have good compression and spark. The engine runs fine off idle range. The questionable JET IS #9 in the first pic and Letter g in the second pic. Any advisement appreciated.

[Model Murdering]

Hi Greg,

Idle jet woes are always annoying. Having to back off indicates a restriction. I know, Captain obvious.

Did you use a new jet or just other jet?

Did you gently insert a sizing tool into the jet and determine that it is clear and unobstructed. It doesnt take much "shclevarnique" to restrict the flow. Generally a white crystalline clod in the bore will not be deterred by carb spray. If this doesnt clear up the problem, remove the jet and use your pocket mirror with a good light to get a good look in the idle jet bore. There may be a foreign object hanging in the bore.

Once the obvious is eliminated ...

I also have seen repeated working of idle jets pound the idle seat back further into the carb housing, necessitating the set back you have described. Too much depth means the perpendicular cross flow bore can be misaligned vertically and possibly occlude. This can be difficult to ascertain cramming ones head in from the side, so you may have to have carb inhand.

It's not a new thing for old carbs. Look at both the face of the jet or seat for any excessive tattle tale marking or marring. Another clue is that the jet in question may appear to sit deeper in the housing than the others

If it doesnt leak, mixture screw still meters, and the plug burns correctly; only you will know.

Good luck,

Bill