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+--- Thread: Solex MOV idle and mixture (/showthread.php?tid=3719)
Solex MOV idle and mixture - Tom Coates - 04-01-2020
I'm having trouble getting my 30MOV solex to work properly, i can either have a decent idle and huge flat spot or reasonably progressive pick up but an idle so rick it fouls the plugs at every traffic light.
I have had to solder up the hole in the throttle butterfly and unscrew the idle speed control all the way out to get the idle down to a normal level, have other people had this problem? I think that it may indicate that there is leak somewhere in the inlet tract, this would probably upset the slow running mixture. I also wonder how vacuum tight the modern exhaust/inlet gasket materials are?
I find it works much better with a 4/5 jet cap than the later n°12 assembly, possibly the fatter earlier type holds more around it to richen the mixture when you open the throttle, I can't think of any other difference. What are other people using?
I have the standard set up otherwise, 50 slow/110main/23mm choke.
RE: Solex MOV idle and mixture - Erich - 05-01-2020
Tom, the Solex 30MOV is a good carb, but it does, in my limited experience, tend to soot up a bit at idle. You might contact Robert Foreman as he is an expert with the Solex carbs.
Erich in Seattle
RE: Solex MOV idle and mixture - Damian GT - 06-01-2020
Hi Tom,
My experience with Solexes taught me that you struggle to get rid of the flat spot.
I would be a bit suspicious that you have an air leak somewhere in the inlet tract if the hole in the butterfly needs to be soldered up. Robert is obviously the 'man' when it comes to calibrating jets/choke/etc. I expect he'll be able to help.
As you'll remember I used to have a 30 MV (rather than MOV) on my car. The 'O' signifies the air bleed screw. Getting the screw bleed right helps I'm sure. The MV never ridded itself of the flat spot however hard I tried and I had to get used to feathering the throttle from idle to main. That worked after a fashion but if you ever booted the throttle it spluttered awfully and died. They really need an accelerator pump I reckon. (I messed with the idea of trying to make one).
When I fitted the supercharged engine I stuck with a Solex and fitted a 35MOH. It took me forever to work out why it didn't work properly across the range and in the end discovered that we'd lost one of the three screws holding the air inlet to the blower - so I was bleeding air into the blower through the cross-sectional area of a 1/4 BSF thread. Once plugged it worked and I got the idle right down. When it came to tuning that carb I needed Jeremy Brewster's help. Any amount of messing around myself failed to get it right - even with a Lambda sensor and a box full of jets that Charles P and I sourced on French ebay!
With the blown engine a snap throttle closure (think about approaching Sawbench at Wiscombe and hitting the brakes) kills the engine. My solution was to set the hand throttle open and not allow the main to die. I also think there is some fuel surge going on in Solexes as the problem is worse on right handed bends and the float chamber is on the left side. All of this relates to competition of course - that's when you really notice what doesn't work.
Forgive my ramblings, and see you about soon I hope..
(and for what it's worth the blown engine only worked when the original progression holes in the jet were soldered and new ones drilled lower down in the jet). I am afraid that I think that Austin 7s with Solexes may need bespoke jet refinements - at least those with blown engines..). And there are different float weights too, of course. I can't remember all the weights off by heart but you might have an unduly light float too I guess. Compromise between float weight, fuel SG and position of progression jet holes are likely behind this issue when you think about the science..
RE: Solex MOV idle and mixture - Malcolm Parker - 07-01-2020
When I had the GE Brooklands it had the Solex 30MOV and was jetted as per the 200 Mile Race Cars. It had a huge flat spot and you needed to open the throttle gently, otherwise the engine would falter. Once the revs had built up it went well and cruising on a main road was very good. I took the view that if the carb is jetted for flat out running at Brooklands, you can't expect good low down flexibility.
If you consult the Beattrice Canning A7 Competion History you will see that the Solex on the Brooklands was fitted with a smaller main jet for road use, as it gave much better pick up.
The weight of the float is critical, from memory it needs to be 42 grams. Robert Foreman is the man when it comes to the Solex 30 MOV.
From what I have read my engine worked very well on the Solex.
RE: Solex MOV idle and mixture - Tom Coates - 08-01-2020
Thanks for your contributions. Robert Foreman re-bushed the throttle spindle for me and i have discussed the subject with him at length. The problem seems to be that different people get very different results with ostensibly the same set up .
Given the problems other people have had maybe I'm not doing too badly after all. In my limited experience the key to good pick up is the size of the well in the jet carrier assembly which fills up with fuel at idle speed and lets it out in a big splurge when you blip the throttle - a sort of jet pump effect. There are various different sized assemblies, the details of which do not all of which appear in the solex literature. After a bit of fiddling I have now got it set up reasonably satisfactorily and will possibly need to make a new jet cap to replace the one on loan from my brother which is the bigger size and seems impossible to find.
Part of the trouble is city driving, on the open road the pick-up and idle mixture are less crucial, but now i have my car in Paris i spenf a lot of time at traffic lights and driving on part throttle which magnifies these problems. I am thinking of getting a lambda sensor to try and make the tuning process a bit more scientific...
RE: Solex MOV idle and mixture - Charles P - 08-01-2020
(08-01-2020, 09:36 AM)Tom Coates Wrote: Thanks for your contributions. Robert Foreman re-bushed the throttle spindle for me and i have discussed the subject with him at length. The problem seems to be that different people get very different results with ostensibly the same set up .
Given the problems other people have had maybe I'm not doing too badly after all. In my limited experience the key to good pick up is the size of the well in the jet carrier assembly which fills up with fuel at idle speed and lets it out in a big splurge when you blip the throttle - a sort of jet pump effect. There are various different sized assemblies, the details of which do not all of which appear in the solex literature. After a bit of fiddling I have now got it set up reasonably satisfactorily and will possibly need to make a new jet cap to replace the one on loan from my brother which is the bigger size and seems impossible to find.
Part of the trouble is city driving, on the open road the pick-up and idle mixture are less crucial, but now i have my car in Paris i spenf a lot of time at traffic lights and driving on part throttle which magnifies these problems. I am thinking of getting a lambda sensor to try and make the tuning process a bit more scientific...
I think you're right about the "well". John Howell in his article on carbs for vintage racing cars highlights this. Later carbs, with the bigger main jets have more scope here than the earlier ones, where the casting in the carb may not accommodate the later, bigger jet carrier. Narrowing the OD of the jet may help.
Like Damian I found that on the 35MH I got a reasonable balance of mixture across the range only by soldering up and redrilling the bleed holes (another Howell tip) in the jet but it's a painful trial and error approach with a lambda. Still not perfect and the main jet is bigger than the Solex "ready reckoner" would suggest.
Charles