Solex carb choke reassembled wrong? (with pics)

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AdrianO
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Solex carb choke reassembled wrong? (with pics)

Post by AdrianO » Sat Sep 15, 2018 6:00 pm

My beloved (but of course!) BX Meteor, with 99k on the clock, has a cold start issue. The engine fires up first time, but then stalls after 1-2 seconds. After deflooding with the pedal full down, it will restart on no pedal without too much hassle, but I do need to apply some pedal to keep the revs above 1000 or so to prevent further stalling in the first minute or so of running. After that, all is lightness and joy. I deduce the fast idle regime of cold starting is inoperative.

Reading thru all the Forum posts relevant to the Solex carb, and studying the Haynes docs (I have the blue cover Haynes BX manual, and some JPGs from their Carbs manual that I found on the Forum), I am having difficulty seeing how the supposed fast idle screw on my carb as it is configured now could be doing anything useful at all. See what you think.
throttle up.jpg
No throttle
The first pic is of the cold carburettor with no throttle being applied. Behind the lock-nuts just to the right of image centre there are visible two cams -- a brass one and a steel one behind it. Passing thru the steel cam on its forward facing extension is a screw with a clip over it -- I understand this to be the fast idle setting screw. The screw abuts nothing at all on either end. Curious, methinks.
throttle down.jpg
Full throttle
The second pic is the cold carb with the throttle cable being pulled on fully to simulate the accelerator pedal down condition. Again the brass and steel cam are evident in the image. But look under the steel cam and part of a third cam is visible, under the steel cam and extending to left and right behind the brass cam. The tip of this third cam can be seen contacting the screw secured in the middle cam, but laterally, not end-on. This does not comply with my documentation. Curiouser, methinks. (Non-compliance with the documentation is not unknown in the software world; rather, it is quite usual).

So the situation appears to be this. The fast idle screw is in contact with fresh air over most of the throttle cable travel, and is pushed on (by the innermost cam) only when the throttle is effectively 90% down. Which seems nuts.

Yes, the nuts. The obvious thing occurs to me -- undo the lock nuts, extract the cams, and see if the third cam behind can be remounted in a way to contact the fast idle screw end on, as it strongly appears to me God intended it to. Unfortunately my assorted spanners are all too fat, and my assorted needle nose pliers all too thin, so my obvious is temporarily deferred. On the other hand, my obvious thing may not be someone else's obvious thing, particularly one more knowledgeable about Soleces than I, so I could be wrong in my deduction that the absence of high idle revs when starting is due to the configuration of the auto-choke mechanism.

I had the carb cleaned a few weeks ago, after which the cold starting issue has manifest. I am reluctant to blame my local man, since he diagnosed the carb problem I brought him straight away just from my telling him the symptoms (blocked 2nd throttle jet), and fix it he did. Also, the auto-choke appears not to have been worked on at that time, since my cleaning and lubricating of the mechanism since have made the movements a whole lot less sticky. Neither do I recall having had work on the auto-choke or the carb done in the past (I've owned the car since 16k miles). So either I have a bad memory and the auto-choke was in fact reassembled in the past and wrongly, or my surmise on the fast idle adjustment screw is wrong.

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Kitch
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Re: Solex carb choke reassembled wrong? (with pics)

Post by Kitch » Wed Sep 19, 2018 12:01 pm

If it's been in bits recently, it's BOUND to be related to that. Not definitely, but likely.

I'm actually having this problem too. I dismantled the Z1 on my dad's 19GT, and upon rebuilding it have similar cold-start issues. I've found that the secondary flap on the top of the carb (there is only one, on the 'rear' choke) needs to be open slightly to allow it to run sweetly on the choke. If I hold it open at the 'right' angle, it runs beautifully, and once the choke is 'off', it stays open by itself, at which point the car runs fine.
The flap is connected to that spring (top right in your pics), so it's naturally being pulled shut, and only opened by forced by a cam or something. However, the mounting position of the blades and cams is fixed, as they're either keyed, or the hole in the centre is slotted, so they can only fit on the shaft one way.

It's bugging the hell out of me! Sounds like a similar issue to yours too. Shame it doesn't have the manual choke, as I did one of those a couple of years back, and absolutely nailed it!

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xantia_v6
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Re: Solex carb choke reassembled wrong? (with pics)

Post by xantia_v6 » Wed Sep 19, 2018 2:01 pm

If you look at the pictures in this document: http://xrms.free.fr/divers/405/tout_sav ... _rev_B.pdf it seems that there is a part missing (or mis-fitted) on your carburettor that the fast idle screw should act against.

In both of these pictures it is labelled as the "Came de commande du ralenti accéléré / denoyage" :

Image

Image

AdrianO
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Re: Solex carb choke reassembled wrong? (with pics)

Post by AdrianO » Thu Sep 27, 2018 4:35 pm

xantia_v6 wrote:
Wed Sep 19, 2018 2:01 pm
If you look at the pictures in this document: http://xrms.free.fr/divers/405/tout_sav ... _rev_B.pdf it seems that there is a part missing (or mis-fitted) on your carburettor that the fast idle screw should act against.
Many thanks for this! An exploded parts view of the auto-choke was what I was sorely missing. It seems to confirm that part 26 has been refitted wrongly.

BTW that's a great link c/w further source links in it also. Perhaps it should be sticky'd somewhere in the Forum?
Kitch wrote:
Wed Sep 19, 2018 12:01 pm
I've found that the secondary flap on the top of the carb (there is only one, on the 'rear' choke) needs to be open slightly to allow it to run sweetly on the choke. If I hold it open at the 'right' angle, it runs beautifully, and once the choke is 'off', it stays open by itself, at which point the car runs fine.
The flap is connected to that spring (top right in your pics), so it's naturally being pulled shut, and only opened by forced by a cam or something.
My first finding was that my choke flap was stuck in the vertical position even when the engine was cold (and the carb was supposed to be cleaned???). Flushing the spindles with lots of WD40 and lubricating them with oil has persuaded the flap to close correctly as the engine cools. The action of the spring is clearly critical here (I wondered if mine had lost tension through aging), but observe that it is attached at both ends to cams which move, so those need to be doing their thing correctly. One complication affecting starting is the presence (on some versions) of a choke pull-down mechanism, which, as I understand it, acts in the first second or two of starting to establish a more favourable fuel/air for continued running of the engine. I don't know whether the failure of the pull-down mechanism by itself is enough to prevent correct starting, but this whole sub-mechanism is predicated on the choke flap moving freely. I'm probably not being terribly helpful here, but if the problem is due to spindle bearings being worn, there is at least the possibility of having them renewed.

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Re: Solex carb choke reassembled wrong? (with pics)

Post by Kitch » Mon Oct 01, 2018 4:31 pm

It's weird, because the problem I've got (I didn't clarify) is that the engine won't run cold until I force the upper flap open slightly. With it shut, it runs ridiculously rich, but slowly as it warms up and that upper flap opens, normal running is resumed.

Really odd.

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xantia_v6
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Re: Solex carb choke reassembled wrong? (with pics)

Post by xantia_v6 » Mon Oct 01, 2018 8:22 pm

AdrianO wrote:
Thu Sep 27, 2018 4:35 pm
xantia_v6 wrote:
Wed Sep 19, 2018 2:01 pm
If you look at the pictures in this document: http://xrms.free.fr/divers/405/tout_sav ... _rev_B.pdf it seems that there is a part missing (or mis-fitted) on your carburettor that the fast idle screw should act against.
Many thanks for this! An exploded parts view of the auto-choke was what I was sorely missing. It seems to confirm that part 26 has been refitted wrongly.

I just read your response more carefully, and I think you are looking at the wrong part. The part I was referring to is the smaller one which in the upper picture is un-numbered, but the caption box is just above the caption for part 26. In the lower picture it is near the bottom left.

Note that it appears to be the only part that is keyed onto that end of the shaft, the other levers are a sloppy fit on the shaft.

AdrianO
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Re: Solex carb choke reassembled wrong? (with pics)

Post by AdrianO » Tue Oct 02, 2018 12:13 pm

My bad. As you pointed out in your first reply, it's the "Came de commande du ralenti accéléré / denoyage" part that's wrong.