26 VA carb experts?

[JonE]

Just reading up on the sidedraft. If the stock engine is running well and the jets are "as specified", is there any adjustment to set via the plug colour (which seem a little blacker than I'd like if using a SU)? 

There is a good vintage Tuning article in the PWA7C Digest that talks about swapping out the 80 for a 60 slow running jet to try for optimum running (and coincidentally removing a slight flatspot). Does anyone know the variables that brought that spec change in in the first place?

[Bob Culver]

For tuning plug colour was taken after full throttle.
From my experience with other makes the idle colur is closely related to oil consumption. Wirh modern lead fee fuel and low oil consumption stay much as new. devouring perhaps a pint in 300 miles light grey

[Ivor Hawkins]

Bob’s correct Jon, to do an accurate plug cut you need to crack along at full throttle for a mile or two then when you see somewhere safe to pull in cut the motor and pull up.

Pull the plug and with luck it should be the colour of a digestive biscuit...not the one with chocolate on it!

[JonE]

OK will try! Still unanswered question on the change in spec of slow running jets.
Might this be at the same time as the bowls/physical changes to the 22VA happened? I suppose the only thing to do is see if the recommended change elicits any effect, perhaps.

[Bob Culver]

I was given Vol 1 and 2 of Modern Motor Repair and Building , Newnes, about 1933.
A table in Vol 1 gives the A7 carb as 26VEGH. Based on an A10 carb I have these are the same as VA but dismantle into more separate parts. Slow run given as 60
in Vol 2 they did a road test of an RP? without rear body seams. Tinkered with the carb and timing and on successive short runs got up to 45 mpg (altho improveemnt probably due warming up) The carb has slow run screw at an angle. They changed the slow jet 80 to 60 and claimed it removed a flat spot.

In the late 1940s my father meticulously checked mpg. In the manner of the time we used to go for a Sunday sfternoon run , tootling along the very quiet backroads at just 25 mph or so (sometimes following cut down Model Ts with all the rugged up family and dog on the tray). My father reckoned the petrol consumption then was poor altho he regualrly got 50 mpg on long trips.

The Newnes book interesting as gives section dwgs of other 2 brg engines sv Minor, Singer 9, BSA 10 and 9, latter with 2 rolling bearings, crank single end fed without circular ducts!?

The book also gave braking distances from 30 mph 46 ft, 63% one up..... from memory our 40 to 68 ton trucks are only required to meet 50% but other do not dawdle in their path.

[JonE]

that's the same article as I'm reading, Bob! So interesting that in 1933, it WAS 60.
When he refers to earlier models for the 80 spec, it must be the pre-sidedraft carb, as the 26VEGH was surely the earliest incarnation?

[Ian Williams]

Jon personally I find that most std A7 on 26VA side draft carbs seem run rich on todays fuels, all my notes are still is storage from the move so In cant tell you which combinations of jetting I have experimented with at present.

[Bob Culver]

Hi Jon E
If a 26VA on your car, it will differ from the photos in Vol 2 notably the vertical slow run screw. May be the basis of the two different float chambers.
Uncertiin jets can be gauged using the taper of a needle or safety pin. Check from both ends.
On other makes it is more common to eliminate flat spots by increasing the slow run jet.

[dickie65]

You can always try the fuse wire trick in the jet orfice !! 3 amp and 5 amp size, put two bits of 3 amp wire in the jet and go for a drive, the other old trick is to flash solder into the jet to reduce and watch makers reamer to open out. Failing that fun just buy an assortment iof jets to try.

[AustinWood]

The level of petrol in the float chamber affects mixture. Assuming everything is correct with the carburetor, if the level's too high the engine will run rich, weak if too low.