280C Idle Adjustment

[ctaylor738]

Anyone have any ideas why my M110 (Solex) would idle a bit too fast even with the idle adjustment not touching the stop? It's like it's hitting another stop somewhere. It's not the linkage - disconnecting it makes no difference.

TIA

Chuck

[johan01]

Hi Chuck,

Solex 4A1? I believe your high idle is a result of internal and/or external vacuum leaks within the carburator itself.

The 4A1's have a natural tendency to warp -- especially the top cover holding the jets. Take a straight edge and see if it is indeed warped. Unfortunately, these carbs are difficult (if not impossible) to machine flat. [You can't rub it on a piece of sandpaper on glass]

Other than that, you may want to check the 4 idle/air adjustment screws -- these are usually hidden by a blue plastic plug.

I gave up on my Solex 4A1 and swapped a Weber 40 DCNF.

good luck,

[ctaylor738]

The car is running really well other than this, though. No backfiring or any of the other problems usually associated with vacuum leaks. I did have the carb apart briefly to check it and it looked OK.

The PO had the carb professionally rebuilt less than a year ago.

Is there any other stop or adjustment that would allow the primaries to close just a little bit more?

TIA

Chuck

[johan01]

Its possible that the Fast Idle Cam on the choke is not aligned or set-up properly (??).

I have a 659KB .pdf file that mentions this fast idle cam on the Solex. You want me to e-mail it to you?

regards,

[ctaylor738]

Thanks, I will let you know. I should be able to find it in my assorted documentation.

Chuck

[ctaylor738]

Just to close this out ...

It was in fact the fast idle adjustment. It is on the lower side of the carb on the engine side. You need a small screwdriver with at least an 8-inch blade to reach it. I backed it off and was able to adjust the hot idle down to specs.

Chuck

[pboboige]

Can you or someone post a pic (or schematic) of the fast idle adjustment? I can't find it. My 280c has a Solex carb and it idles at at least 2500 rpm. When I shift into Drive or Reverse it revs up even more.

The previous owner had someone rebuild the carb but I don't think they knew what they were doing.
The slow idle is adjusted as slow as it will go.

[cth350]

Just a fair warning...

I was looking at old threads to help somebody else recently and found one that pointed out there are something like a dozen discrete adjustments to make on that solex 4A1 carb. You really, really want to have the service manual pages handy before twisting and turning things. Also, you really, really want to make small and incremental changes while taking notes so that you can walk back a change, should it prove to be a mistake.

-CTH

[pboboige]

I really appreciate the help on this forum. The fast idle adjustment screw was missing. It's a 4-.70 machine screw. The idle is still fast but at least i"m in the ball park now.