The Solex 4a1 factory manual is almost 180 pages long - 70 of those describing changes that happen to the carburetor over the years. You can identify some changes by looking at the fuel bowl vent (from none, to vacuum operated and ending up with electrical - see the image above), presence of TN choke (the Y shaped device at the carb's front face) and the sort of choke pull off it uses. Here is the list of the changes with the reasons given by the manual.
| jan 73 |
|
bypass bore deeper by 8mm |
|
to improve bypass characteristics |
| mar 73 |
|
idle speed air jets smaller (100 from 110 before) |
|
to improve starting and bypass during slow acceleration |
| may 73 |
|
new throttle valve body and larger idle speed air jets (110 from 100 before) |
|
to improve cold start and bypass characteristics |
| may 73 |
|
metal pulldown housing with screw |
|
to facilicitate adjusting procedure for starting gap |
| may 73 |
|
metal pulldown housing with o-ring |
|
to improve sealing of adjustement screw |
| jun 73 |
|
plastic self-locking nut for accelerator pump |
|
to faciliciate adjustement |
| oct 73 |
|
increased voltage to idle-speed shut off valve (3v from 0.5v before) |
|
to prevent afterruning of engine |
| nov 73 |
|
ball of intake valve |
|
for better sealing and avoid starting and bypass faults during slow acceleration |
| jan 74 |
|
TN-starter |
|
to improve cold start and warmup characteristics |
| jan 74 |
|
new TN insulation flange |
|
to introduce TN-mixture into intake |
| apr 74 |
|
new float |
|
to increase closing force |
| sep 74 |
|
accelerator jets changes |
|
to improve direction of jets |
| july 75 |
|
more robust TN-starter |
|
to prevent failure of expansione element |
| jan 76 |
|
thermo-lag valve instead of electro-magnetic |
|
to improve engine operation immediately after cold start |
| jul 76 |
|
central idle speed |
|
to simplyfy idle-speed adjustement |
| july 76 |
|
accelerator pump with stroke limiter, adition of cam disc |
|
to limit quantity of injection |
| july 76 |
|
stabilizing bore for idle-speed |
|
to prevent surge when decelerating |
| july 76 |
|
pre-atomizer with slot, larger main jets 97.5, ball under mixture tube |
|
to improve starting and bypass |
| july 76 |
|
jet needle "B 4", raiser pipes shortened to 15mm and calibrated to 1mm. Air valve weight increased to 112g (75g before) |
|
to improve bypass characteristcs |
| july 76 |
|
new central idle-speed flange |
|
to introduce TN-mixture and idle-speed mixture via same grove |
| oct 76 |
|
locking plug for TN-starter |
|
to prevent adjustement |
| oct 76 |
|
locking plug for idle-speed screws |
|
to prevent adjustement |
| april 77 |
|
adition of sliding block to stage II spring |
|
to prevent broken spring |
| sep 77 |
|
fuel return with pressure regulator |
|
to eliminate fuel level fluctuation |
| sep 77 |
|
external vent system |
|
to shorten hot start time |
| sep 77 |
|
choke with 2 screws |
|
to prevent release |
 |
|
|
|
|
