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A Quantum of Solex Part 2

Simeon

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blog-0965307001455541467.jpegFollowing on from my blog entry on fitting these carbs and the various things I had to work around (mainly related to the Cannon inlet manifolds) I thought I would post a separate entry on rebuilding them and a third for tuning and adjustment. There is so little information available on these carbs, I am hoping that someone else may find it useful.

Resources

The FAQ of course but specifically a few diagrams posted by CD and JGerock. The Haynes manual has some information on the PHH, strangely given the TI was never sold in the UK but TII, which were, does not get a look in as far as adjusting the K-fish is concerned.

Before we start...

I started off by examining the jets and other calibrated parts that are fitted. It may seem obvious but I will say it anyway, twin carbs can only work properly if they are truely a matched set. This includes all of the calibrated parts like jets, chokes etc but also things like the transition holes and the knife edge angles on the throttle plates. My pair of carbs look physically different to each other as the casting seems to be stained to different shade and minor differences such to some of the fasteners show that they are different ages. The guy that I bought them off supposedly ran them on on a Targa rally car but obviously not that successfully since he apparently wanted to change to Webers. I actually intend to rejet the carbs to match my car since I have a number of different variables to the original TI, so while I want to check what is installed, I only really care about making sure it is a matched set between both carbs at this stage since it will only form a baseline for future tuning.

When I looked closely down the throats of my carbs I could see 'Solex' and '40-30' peering back from the chokes. Oh-o these carbs have 30mm chokes and have therefore come off a 1600. Apart from being an item of rarity, they would be no use for my 2 litre. I also noted from a quick check of the jets on both carbs that the idle jets on the front carb are smaller than those on the rear. Not a great testament to their previous life. I had better pull them apart and see what else I can find. The following is the detailed disassembly procedure I followed on the rear carb. I have also included some pictures of the front carb where different.

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Top plate removed to reveal air correction jets (155) at the top of the emulsion tubes.

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Idle jets (52.5)

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Top cover removed including float and emulsion tubes. These are fixed into the carb and don't appear to be easily replaceable (I didn't want to force them out of position and break them). Both carbs are fitted with the same tubes.

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Needle valve assembly removed from the top cover. The inner section is removed by unscrewing from the outer section before the outer section can be unscrewed from the body. Crush washer in place between the inner and outer sections.

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Needle valve assembly showing constituent parts.

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One of the float pivot posts fell out from where it was swaged into the top cover.

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Staking it back into position with a centre punch.

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Removing the accelerator pump jet tube. Undo the banjo bolt, crush washers either side, I had to pick the lower one out with a sharp point.

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Undo the screws on the choke plates. These may be tight and peened into position. I usually try and unscrew first with a sharp screwdriver and steady pressure. Be prepared to mangle and have to drill out.

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The choke plates wiggle out of the shaft but remember to push in the poppet valve on the plate as this wraps around the shaft.

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The throttle plate screws could not be moved, so I had to grind off the peened threads from the inside and drill and use an EZ-out to remove the screws having mangled the slots.

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Screws came out quite easily with a satisfying crack as they loosened.

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[Genius / Bastard] linkage that allows you to balance individual cylinders. This is held in place on the ends of the two throttle shafts by pinch bolts.

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I undid the bolts to allow the shafts to be wiggled free of the housing in an outwards direction. The outer linkages could actually be left on the shafts if desired, though you will probably want them off for cleaning.

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The auxiliary venturi (or pre-atomiser as Solex like to call it) in position.

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These are clamped into position by conical shaped screws through the carb body. Mine were very tight and held in with locktite (I think they should have lock nuts on them). I will add new nuts when reassembling.

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Shot of the venturi showing the fuel port and an anti-rotation dowel. This needed to be lightly gripped with needle nose pliers and pulled away from its mating hole in the carb body. When reinstalling, the screw needs to be fairly tight to jack the exposed section of tube into the body of the carb.

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Choke showing how it had been bored out. Chokes are a good tight fit in the carb, no air leaks.

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Measurement puts the choke bores at 33.89mm and 33.88mm respectively so 34 is what we are shooting for.

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Unscrewing the main jets.

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130 main jets fitted, screwed in to the main jet carrier and sealed with a crush washer.

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Pump jet cover removed by undoing screws. Pump jet rod disconnected by undoing the lock nut and then removing the adjusting barrel nut.

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Solex branded diaphragm - when were they last made? To be fair, it still felt pretty pliable.

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Pump jet block removed. More Solex branded parts.

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Unscrewing the pump jet ball valve. Clean until it rattles and add a new crush washer.

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Organisation. Quite a lot of parts for one carb.

The body was scrubbed with a small wire brush and carb cleaner. All passage ways were flushed with carb cleaner with a straw fitted to the can and then blown clear with an airline. Watch your eyes! All of the individual parts were cleaned with wire brush, scotchbrite and carb cleaner before reassembly. Reassembly, as they say, is the reverse of removal but care was taken to work cleanly, replacing seals and crush washers as you go. The only tricky part is to ensure that the throttle plates are centred in the throats properly and are covering the progression holes.

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Detail of plate / progression hole interface.

For some reason both of my carbs have one throttle plate with a small hand filed dip on the edge, just where the progression hole appears. Not sure why that is there and only on one throat in each carb. This may be an attempt to dial out a slight misalignment due to the split throttle shafts and some lost movement in the [genius / bastard] linkage. Time will tell if it is noticeable when trying to tune and get the carbs to idle. I elected to flip the plates around (making sure I get the knife edge on the edge right) to move this to the other side of the carb. Playing with the carbs off the car, I had no problem using the [genius / bastard] linkage to dial the plates so that the progression holes were equally covered and opened in tandem.

After shopping around for new throttle plate screws, I determined that the thread was the same for both Solex and Weber (M4 X 0.7). Weber screws, which are easily available, have a pan-head Phillips design as opposed to the countersunk Solex screws, they also have a massively variable price up to $4.95 AUD each! Since I was resigned to not matching the countersunk design, I elected to buy 100 button Allen headed screws from eBay in the appropriate size. At least they are slightly more streamlined than the Weber equivalent.

The front carb was stripped and cleaned in the same way. Here are some of the highlights / differences to the rear carb.

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The idle jets in the front carb are different to the rear carb 47.5 vs 52.5. That can't have done anything for driveability. I did wonder if they had been drilled but after checking with the shank of a 0.5mm jet drill, they obviously hadn't. All the other jets were the same and were tested for size using the shank of appropriate jet drills to 'go / no-go' the jets so someone was obviously aiming for stock TI jetting. Seems like an obvious issue for someone running a rally car. I bought a new pair of 52.5s and 4 X 55s for tuning if I need to richen the idle circuit. The rest of the jets I will drill initially prior to buying replacements in the ball park.

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The linkage on the front carb.

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Here is the rebuild kit bought from Alfa1750. There is an address and contact details on the front in case you want to cut out the middleman. Ruddies of Berlin are also another good source of parts.

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A few weird things about the kit. The accelerator pump diaphragms are double skinned. The rubber, while pretty tough, is notably thinner than the original. It also seems to be missing the crush washers for the accelerator pump jet delivery tube. Be prepared to save yours or try and find generic ones locally.

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The off centre hole in the pump block gasket was too small and in the wrong position.

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I had to enlarge this with a scalpel.

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Replacement throttle plate screws - when installed crush the exposed thread end with needle nose vice grips to prevent them backing out. Don't use locktite as they are bathed in fuel. The traditional method of staking the ends is also OK but risks bending the throttle shafts, needs a long punch and must be done before assembling the auxiliary venturis and chokes.

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What you are NOT looking for. The plates actually can move around slightly in the slot in the throttle rods until pinched into position by the rod when the screws are tightened. Play with this and the rotation of the shaft at the [Genius / Bastard] linkage until the plate snaps shut cleanly and very little, equally distributed, light is visible when shining a light in from the rear. If it feels 'woolly' then it is not quite right. Make sure that the [Genius / Bastard] linkage is in the middle of its adjustment when doing this. This way, centre is both plates closed fully. Unwinding the screw from the centre position opens one plate and screwing in from centre opens the other. Play with it off the car and you will get the principle.

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The throttle shaft (and choke shaft) end nuts are then tightened. These are only nipped up tight, no leaning on them with a breaker bar. As you tighten, then keep flipping the throttle (or choke) open and closed. You will feel when it is too tight as you will lose the crisp snap as it shuts and it will move into woolly again. When you have them as tight as you can but retaining the snap, then stop. At this point, the anti-rotation washers are folded tightly over opposing flats of the nuts. This shot also shows the new lock nuts on the auxiliary venturi securing screws.

Before reassembling the choke plates, check the direction and aim of the pump jets as they are tricky to reach once the choke plates are installed. One of the diagrams that CD is famous for posting shows the spray direction in two different planes. Basically the stream of petrol should be aimed at the lower side of the throttle shaft at the outermost side of the bores. After reinstalling the main jets and accelerator pump valve, fill the float chamber with petrol and operate the throttle until it squirts. If aimed correctly this should actually pass cleanly through the open throttle as the stream continues for a short time after the throttle is fully open. Don't worry too much about quantity at this stage, I reset the adjusting nut on the pump arm so that the same number of threads are exposed as the untouched front carb. This will serve as a baseline for tuning.

That's it, they are relatively straight forward to rebuild if you are well organised, work cleanly and do one at a time so that you can refer to the other. Take lots of pictures of the linkages as well as this will aid reassembly. My carbs may not have a bling rebuild with all new / replated parts but I am certainly a lot more confident in them now and have learnt a lot about them along the way.

Any questions, let me know. Thanks for reading.



6 Comments


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As you said, not much info on those Solex

Can't wait for part 3

Pierre

69ti owner with original and troublesome Solexes

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Thank you for this write up. I am rebuilding a pair of Solex carbs now and have found this extremely helpful. I do have a few questions though and was hoping you might be able to assist me.  The carbs I'm rebuilding are original to the car so I am being extremely careful. 

 

First, I cannot get some of the gaskets to break. I haven't done anything crazy/forceful out of fear of damaging them. Any suggestions on how I can get them apart?

 

Second, when I took the top cover off one of the carbs I noticed that the emulsion tubes were not straight (in the other carb the holes in the tubes appeared to be lined up perfectly front to back and left to right). It looks like one of the pictures you posted of the tubes show the holes are not perfectly aligned as well. Does anyone know if the direction/alignment of the holes matters? If so, is there a way of reositioning the tubes out without damaging them? They are extremely tight and do not seem to twist at all. I don't know of its safe to use heat or something like PB or WD40 (I'll definitely be cleaning the carb before reassembly). Maybe that's a noob question but candidly I am a noob when it comes to carbs. 

 

Thank you for taking the time to share this information. I'm sure there will be plenty of Solex owners who will come across this and be thankful for it.... I know I am. 

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Good stuff here - thanks for posting!  My accelerator pump diaphragms were similar to yours.  Will have to go back and see if I made the same notch/cut you did.  The new ones were a slightly different shape as well.

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On 06/07/2017 at 9:31 AM, TG2k2 said:

Thank you for this write up. I am rebuilding a pair of Solex carbs now and have found this extremely helpful. I do have a few questions though and was hoping you might be able to assist me.  The carbs I'm rebuilding are original to the car so I am being extremely careful. 

 

First, I cannot get some of the gaskets to break. I haven't done anything crazy/forceful out of fear of damaging them. Any suggestions on how I can get them apart?

 

Second, when I took the top cover off one of the carbs I noticed that the emulsion tubes were not straight (in the other carb the holes in the tubes appeared to be lined up perfectly front to back and left to right). It looks like one of the pictures you posted of the tubes show the holes are not perfectly aligned as well. Does anyone know if the direction/alignment of the holes matters? If so, is there a way of reositioning the tubes out without damaging them? They are extremely tight and do not seem to twist at all. I don't know of its safe to use heat or something like PB or WD40 (I'll definitely be cleaning the carb before reassembly). Maybe that's a noob question but candidly I am a noob when it comes to carbs. 

 

Thank you for taking the time to share this information. I'm sure there will be plenty of Solex owners who will come across this and be thankful for it.... I know I am. 

 

With regard to the gaskets, obviously time and fuel additives may stick them together. Rather than pry them loose and damage a sealing edge, try striking them sideways with something non marking like a piece of wood. 

 

You might need to post post photos of yours to make sure I am not confused. As long as the number of holes, size of holes and height up the tube are the same then you will be OK.

 

The tubes see the world from inside a small chamber filled with petrol where the depth of the fuel varies depending upon the amount of vacuum across the choke / venturi of the carb. This rises up, covering the holes as the vacuum rises and change the ratio of air to fuel in the 'emulsion' that is drawn in via the mains into the venturi. Low vac, lots of holes exposed, lots of air. High vac, fuel is higher in chamber, less holes exposed, less air. The small chamber means that any difference in fuel height due to forces like braking, acceleration etc should be limited in effect on the tube with the 'turned around' hole pattern. 

 

What they are are sensitive to is the spill over height of the carb set by the float depth. I have a (completely unverified) theory that that is why the Solex design has fixed emulsion tubes but the unusual external float chamber adjustment. I think that when we are really tuning these carbs we need to use float height to get the right result on the mains (within reason). 

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One set of carbs I have had old intake gaskets and isolators that were a real PITA to remove. Small strikes with a chisel and Dremel grinding got them off.

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Thank you @simeon and @jgerock for the suggestions on the gaskets and for the detailed info on the tubes. It's amazing how much goes in to making these carbs work despite the simple principal behind them. All of this info is amazing and if I can add anything to it over time I will. 

 

I took a small break from the rebuild (those gaskets got me fired up and rather than doing something that would damage them I decided to take a T/O, haha) but I'll post some pics when I get back to it... sounds like they are okay as is though (phew!!!)

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