Adjusting Accelerating Pump - query

[JohnLiles]

Hi All , have just had some Solex 40 P 11 4 carbs rebuilt , and while they are on the workbench I want to check the injection quantity from the Accelerating Pump.
I have read about how to do this from the Registry and I also have the Workshop Manual Supplement that specifically deals with these carbs . I made up and calibrated my own little measuring cylinder marked off in 0.3 ml quantities.

As checked , the carbs are delivering 0.3ml at each injector nozzle for every 2 full strokes of the accelerator pump . The position of the adjusting nut on the adjustment rod judged by thread emerging appears to look same as it was before I had carbs rebuilt , so maybe the person doing the disassembling and reassembling had made a note of that.

Query - the workshop manual page SF15 says the delivery at each injector should be 0.45 ml for every 2 full strokes 'warm season' setting and 0.65 ml for every 2 full strokes 'cold season' setting.

However for the Zenith 32NDIX carb , the manual says the delivery should be 0.2-0.3 ml , no mention of warm / cold season.

So it looks like my Solexes have been set to deliver Zenith quantities . As these carbs applied to same 1600cc engine , drawing in same amount of air , using same mechanical fuel pump , I dont understand why there should be twice the difference in amount of fuel injected by Accelerator Pump .

Can anyone advise on this before I start altering the delivery up from 0.3 ?

[John Brooks]

They will work, but may be prone to an occasional "pop" when you first push the pedal. I always set mine for cold ..5-. 6. I have always treated them like on and airplane engine. Rich is better than lean.

[David Jones]

John,
I set both my Solex's at the factory recommended settings for warm weather as the car gets driven much less in cold weather. I then do a road test and if I can stamp on the gas at around 2500 to 3000rpm and there is no hesitation I call the setting good. If there is a hesitation I turn the nut in a half turn then try again. Once they respond properly I call it good and leave them alone. Each engine will require it's own setting especially now after so many possible changes could have been made to the engines since they were new.

[JohnLiles]

OK , just to check I am doing things right

1 carbs are on the workbench ,with no banjo connection to a fuel line , can I just pour fuel in down the central ( between the barrels ) brass riser tube which is the vent to float chamber ?

2 do I tighten up the nuts on the threaded pump rod to increase delivery ie shorten the effective length , or do I loosen them off to lengthen effective length , only got about quarter inch to work with if I do that ?

[Paul Lima]

My experience with modern fuels in my S90 Roadster is much better with lower settings than originally recommended. Your current setting is about what I run and recommend.

[John Jenkins]

The fuel we have now is much more volatile so not so much is needed to go down those manifolds to get volatilized. I set the quantity to about .35 cc for two strokes for my local guys when they have trouble and that seems to work if all else is well. If the idle mixture is really correct then a sixteenth of a turn out may be needed to take care of a stumble off idle. Richer is better than leaner when those 40 mm butterflies open up.

[WilliamVaughan]

question 1) Yes, then do a few pumps to get air out of pump system.
question 2) The former. When you move the nuts toward the throttle shafts the injection volume increases. Nuts out at the tip of the push rod yields virtually no injection volume.

You can make a graph of injection volume versus distance between outer most nut (lock nut) and end of shaft, measured with a small scale. Done on bench is easiest. Use mineral spirits in place of gasoline to keep the stink down.

[Doug McDonnell]

FYI the accelerator pump reservoir on Solex carbs is not filled automatically from float reservoir like on Zeniths. the suction created when pedal pushed all the way down fills it on back stroke. One of the reasons it is harder to start with dry Solex carbs. Even if you are using electric or manual priming pump you need to depress the gas pedal fully a few times. Something I didn't know until recently.

[Richard Shilling]

The ventures are smaller in diameter on the Zeniths than the Solexes. The air velocity is higher in the smaller ventures, which helps the dispersal of the gas. If the weather is moderate and all is well in the engine - timing, distributor advance, etc., the lower discharge volume is fine as long as the engine accelerates under full throttle with a flat spot. More discharge and aiming (see below) can go a long way to curing flat spots on the Solexes.

It is possible, but not easy, to aim the accelerator pump discharge tubes on the Solexes to squirt directly into the space between the side of the venturi and the butterfly. This reduces or eliminates the possibility of a flat spot. If the discharge hits the side of the venturi it takes a while to get down into the engine which can cause a flat spot.