Rebuilding Carburetors

From Citroen SM Wiki


A standard carb overhaul would replace all gaskets, O-rings, and the float valve/seat. There are also several drilled passages that are sealed off with lead bits. These are candidates cleaning during a deep overhaul.

Consider taking this opportunity to replace the old valve/seat with a Grose-Jet from John Titus.

Photos of the carbs and related materials:

Can the passages be cleaned?

Ultrasonic bath

An ultrasonic bath can do the trick. The ultrasonic bath may pulverize the deposits in the passages of the carburetor. By using this method you don't have to remove the seals of the passages (plugs).

The hard way

Like most carburetors there are passages (for drilling) that have lead plugs in them.

These plugs can loosen and fall out! leading to Danger

It seems to be primarily age-based, but it's not deterministic. Probably the less time running, the more likely.

But note that even if they are not loose, the passages may have accumulated debris that is very hard to remove.

These passages are hard to clean, and just soaking will likely not remove it all.

Sample Debris from one passage

So what are my options?

The plugs can be removed, the passages cleaned, and either plugs or screws reinserted.

Where are the plugs?

Seven plugs of note

One plug near accelerator pump
One plug near float bowl

Three plugs between barrels
Two plugs below float bowl and two plugs into the float bowl

Note that the lower plugs of these two are a front-to-back passage that should be (gently) cleared out. You will need to approach from the front to resistance and from the back to resistance as the passage in not perfectly line-drilled.

Two plugs into float bowl

The two into the float bowl can be replaced too for completeness, but don't seem to be as likely to cause problems.

Removing plugs

I (Brucem) used a 7/64" drill in a pin vise to ream out the lead, then an awl to get the last bits of lead.

Cleaning out the passages

Used a #36 drill in fingers only) to ream out the passage.

(Need to confirm drill bit size) Brucem 22:58, 2 October 2009 (UTC)

Plugging the holes

Two methods - Lead bits or tapping for bolts

New Lead Bits

One option: 4mm long pieces of 1/8" (3.175mm) diameter "Stay-Safe Bridgit", which is a low-temperature lead-free solder for copper pipe fittings. It is made by J.W. Harris Co. Cincinnati, Ohio. It contains Antimony, Tin, Silver, Copper, and Nickel. It comes in a 1 pound roll. Specification: Bridgit spec

  1. Put a drop of permanent Loc-tite (green) on plug aligned with hole
  2. Tap the plug in with a flat punch slightly larger than the hole
  3. Cover with a dab of Epoxy Steel J-B Weld.

Alternate lead bits

Consider Crossman .177cal pointed lead pellets

Bolts as threaded plugs

Tap the holes for 4mm brass bolts. Use a washer, of course. Holes into float bowl can be bolt-and-nut rather than tapped. Put a bit of red Loc-tite on the bolts.

This (threaded plugs) makes future rebuilds easier.