Solex 4A1 Upgrade

[ctaylor738]

I just completed a mini-upgrade of my 280C's carburetor to the later choke pull-down, which post 1973 carbs already have. The reason I did that is because I found that the old-style dashpot was not holding vacuum and the part is NLA, so I needed to upgrade.

Special thanks to Gympie, who provided parts from his 4A1 collection, and advice from his considerable experience.

The pull-down adjusts the choke opening for engine load, so if it isn't working, running during warm-up is going to be crap, which mine was.

I also found that the dashpot that contols the secondary flaps was toast. This means that under full acceleration, the flaps would open and allow more fuel and air than the engine needed.

So the bottom line is that my choke and secondaries were not working correctly, AND I had two giant vacuum leaks at the rear base of the carb. Still haven't got the choke adjustment quite right, but fixing the vacuum leaks has improved the idle and general performance and the new pull-down has improved warm-up running.

Gentlemen - if you have a 4A1, check those dashpots at the rear of your carb -- they are a vacuum leak just waiting to happen.

[mpnye]

The CHOKE HOUSING update was listed in SI's back in the EARLY 70's . . .

Chuck,
Thanks for the kudo! Only happy to help.

[ctaylor738]

Finished adjusting the choke gap. Thought I would share how I did it. It is simplified from the procedure in the manual, because you do not have to simulate a cold engine.

Tools needed:

Very small screwdriver
Vacuum pump
1.5 mm allen wrench.

- With cold engine, as in sits overnight, remove air cleaner.
- Open/close throttle with linkage quickly. Observe that choke flap closes completely
- Disconnect the pull-down's vacuum line from base of carb
- Apply vacuum to pull-down with pump. The pull-down should hold vacuum and the choke flap should open slightly.
- Measure the gap between the front of the choke flap and the vertical surface of the carb top plate using the 1.5mm allen wrench as you would a feeler guage.
- Adjust the gap by turning the screw on the back of the pull-down unit. In = smaller, out = bigger.
- Reconnect vacuum line, replace air cleaner.

If you have the old-style pull-down with the dashpot and by some miracle, it is still holding vacuum, then the procedure is the same, except that you adjust the gaps by closing or widenening the "jaws" of the "V"-shaped linkage that attatches the dashpot to the pull-down.