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Simon B
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« on: 14 April, 2024, 09:23:20 PM » |
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The only plus to all this wet weather is that I’ve had plenty of time to work in the garage refurbishing some late PHH E3 Solex carburettors to replace the overly complicated solenoid equipped E2’s on our 1975 Coupe.
This is the first pair of Solex carbs I’ve rebuilt and I wanted to understand how they worked and setup as accurately as possible before installing.
I spent quite a bit of time tweaking floats and checking fuel levels and finally arrived at something I was happy with. Setting floats/fuel levels has been well covered in previous posts but I thought it might be helpful to share some ideas for checking accelerator pump operation as I didn’t find much info on the subject.
The original accelerator pumps were not fitted to carbs when I got them so I didn’t have any base settings to work from. That, plus my curiosity is my excuse for spending another wet day devising a way to measure the pumps output.
If you have replaced the diaphragm or rebuilt the carburettor this is a good way of checking the complete circuit and the exact quality of fuel delivered to each accelerator jet. If you decide not to go to the trouble of measuring the pump output, I think its still important to fill the float bowl with fuel and operate the accelerator pump several times, check for good output from each jet and check the brass plugs for leaks, three of the four plugs on my carbs leaked.
The pictures are fairly self explanatory, you simply replace the accelerator jet with the home made measuring device, two are required so that you can check delivery to both carb barrels at the same time.
They are made using 10ml syringe bodies, 4mm ID silicon vacuum hose (40mm long), bleed nipples (M6x1 x27mm long). 7mm lengths of the same silicon hose is pushed over the thread of the bleed nipples to form a seal against the top of the carburettor body. A seal is also required under the bleed nipple to ensure fuel is diverted up into the syringe body. I cut 2mm lengths from an imperial O Ring (3.53mm section) and dropped these into the accelerator jet locations before screwing in the bleed nipples. Care is needed positioning the O Ring material so it sits vertically in the location, one end seals the hole at the bottom where the accelerator jet would normally pass through into the carburettor barrel and the point of the bleed nipple bears against the other end. I tried to gluing the O ring material to a flat ground on the bleed nipple but it would not remain attached when unscrewed. I abandoned that idea and opted to simply fish the short bits of O Ring material out later, they generally dropped out easily enough or could be fished out with a pin.
The bleed nipples don’t need to be much more than finger tight, perhaps a fraction of a turn with a small spanner but be very careful not to over tighten and damage thread or the body where the jet passes through!
The accelerator pump should deliver equal quantities of fuel to each barrel, if there is blockage in one circuit or accelerator jet, you will likely get twice the quantity of fuel delivered to the other.
The pump only operates over the first 30 degrees of throttle opening, the technical spec for the E3 carb has a value of 7-9cc for 20 strokes, so a max of 4.5cc per barrel.
Set the carburettor up in a vice or prop up level with the top cover and float removed. Fill the float bowl to the normal operating level and operate the throttle lever a few times to prime the syringe bodies. Make sure there is no fuel leaking into the barrels or where the bleed nipples screw into the carb body. A spare syringe with a length of hose is useful for sucking out and zeroing the syringes after priming. 20 consecutive partial operation of the throttle lever should nearly half fill each syringe body with fuel. 40 and you should still not have filled each syringe body. Adjust the stroke of the accelerator pump arm to increase or decrease the quantity delivered. When I had finished checking both carbs, the lever movement was the same (4.5mm) although differing amounts of thread were showing on the lost-travel operating rod.
Leave the syringes full for perhaps 30 minutes and see if the level has changed to check the weighted ball valves are working correctly, i.e. fuel is not draining back, and to check the brass plugs for leaks. I replaced the plug seals on mine with some BS006 O Rings which did the job in the absence of the proper ‘D’ shaped seals. I had trouble with one ball valve, which was resolved with a careful clean with a small soft dremel brush twisted by hand.
Sorry, much longer rambling than intended, hopefully some useful info.
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