I think the recommended oil for Strombergs is actually very thin, roughly sewing machine oil viscosity.
I’ve heard this before, but its not recommended according to my literature, or any of the carby specialists that I have dealt with. Maybe its OK for fast-road or race, or cold weather, or maybe even for SU's, but for normal conditions it should be engine oil in Strombergs.
I've spent many years fiddling with twin strombergs, although I admit not on Alpines as yet. Difficult to get perfect, but will give good performance if you get it close. On performance Imp engines, a good set of Stromberg 150’s will give more power than a single weber 28/36, and can even give twin 40’s a run for their money, but a bad set will always give trouble.
A common problem with strommies that don't seem to want to synch is that there may be a leak around the brass spindle that holds the throttle butterfly. Sometimes this causes slight petrol leaks from the side of the carb, but it also creates an air leak on suction, particularly idle. Can be fixed using new spindles, but if the carb body itself is worn then its difficult to fix (unless you insert bushes). If you end up removing the carbs then check for wear in the throttle rods. It’s the main reason for having to throw Stombergs away. Most other parts are available for easy overhaul.
I find that the best way to set up, without using vacuum gauges, gas analysers or spark colour tools is to :
- disconnect the linkage (ie so they are independent) and remove air filters
- unscrew the throttle stop (idle) screws on both until they no longer contact the carb body.
- Wiggle the throttle a little on each and allow to rest in the closed position (to make sure they are both closed, but not forced shut)
- screw each idle screw until it just touches the carb body, then screw each one in by an equal amount, say 1 ¼ turns
- re-tighten the throttle linkage – from now on, only ever move both screws by equal amounts if you need to adjust the idle.
- Remove plunger from dashpot (where the oil goes in).
- Stick finger through each air intake and lift the piston. It should rise and fall easily. If it doesn’t, then the jet needs to be centralised. Not difficult, but I won’t go into it here.
- Screw each jet adjuster (mixture) up until it just contacts the jet. It will continue to screw upwards at this point, so it is important to see/feel carefully when it makes contact. I like to get an old pencil with an eraser on the end, insert it (eraser down) where the plunger thing goes, so that you can see it move upwards slightly when the jet adjuster starts lifting the jet. Alternatively, look through the air intake to see when it starts to move.
- Unscrew each jet adjuster by equal amounts (this is usually 3 full turns, but may vary for the Alpine? Need to check). This will be the starting point for mixture adjustment, but should be close.
- Start the car and warm up. It will be a bit rough, but set idle so that it will run.
- Once warm, carefully stick your finger through the air intake of each carb and lift the piston very slightly (should really be lifted by something the thickness of a bicycle spoke only, or small-size drill if you have one, but don’t let go!!)
- If engine speed drops, then mixture is lean, so unscrew jet adjuster slightly and try again. If engine speed increases, then mixture is rich, so screw-in the adjuster slightly. When correct, the engine speed should rise very slightly and then perhaps return. Repeat for second carb. YOU SHOULD NOT HAVE TO ADJUST EACH JET ADJUSTER BY MORE THAN HALF A TURN EACH WAY. Repeat process for other carb and then recheck.
- Once set, reset engine idle by adjusting each idle screw equally.
Better still, use a vacuum gauge to balance the suck from each carb, or a Gunsons Colortune to set mixture, but be careful not to fiddle too much as the baseline settings described above should be pretty good. If it differs too much then you have other problems, eg air leaks, fuel starvation etc.
Good luck!
. There are many people running the Stromberg carbies with no problems and with routine maintenance are more than adequate to help push our beloved Alpine's along. There are books around on these carburettors Johnny to help service them, but if you are a bit unsure it may be better to take your car to a carby specialist for balancing/tuning.