I had bought a pair of Solex 40PHH carbs a number of years ago which did a great job of gathering dust on my garage shelf. As is typical with me, I often seem to do things the hard way. Not because I am some kind of perfectionist who looks for tricky solutions to easy problems but more because I am impulsive and optimistic about the effort involved when it comes to cars and parts.

Want to put side draft (or draught) carbs on your car? Sure. Going to buy a pair of Weber DCOE or even Dellortos? No, I will go with Solex carbs.

I don't think that the PHH is an inherently bad carb but given the scarcity of components and support there are definitely more obvious choices. I had been going cold on the idea of fitting them as I am actually quite happy with the performance of the car with the 32/36 and since most of my driving is quite slow, using only the primary choke, I figured what is the point? I had a long discussion with a guy at work who is an enthusiast of hot 70's Japanese cars and he convinced me to have another go with the Solex carbs and to look on it as a learning experience. Worst case would be that I would need a day to remove and go back to the downdraft carb. So here we go...

The carbs are in overall good condition, having been taken from a Targa rally car in Queensland. I have bought rebuild kits from the eBay seller Alfa1750, who I will ultimately buy new jets from as I go about tuning them. I will write a separate, detailed blog entry on rebuilding them as there is so little information available about the carbs. You are welcome, crazy Solex people!

The previous owner said he only pulled them as he wanted to go with 45 DCOEs ( but then what else would you say when you are trying to sell some carbs?). He also had the correct BMW manifolds but he hummed and hawed about keepin them so I ended up having to get my own. Again, I could have gone the easy way and bought a pair of BMW manifolds but I ended up with a pair of Cannon manifolds off eBay. These are ok but there were a number of minor issues with them that expanded the work required.

The first problem is that the carbs didn't actually fit the manifolds. Think that all sidedraft carbs are the same? Think again. The Cannon manifold runners actually have far too much material between the two bores and the Solex PHH has a small linkage that extends forward between the chokes to allow adjustment of the two part throttle shaft to balance flow between the two chokes. This feature is either brilliant or terrible, allowing (along with the individual idle mixture adjustment screws) each cylinder to be perfectly balanced / tuned regardless of compression OR... It just gives me another set of frustrating adjustment points to get wrong when tuning. We shall see...

First task was to clearance the manifolds to allow this centre linkage on each carb to swing with the throttle. This was completed by scribing the gasket outline on the flange (didn't want to remove too much) and then cutting a chunk from each flange with a hacksaw. A bit of clean up with a file and the carbs can finally slide down the studs fully and fit the manifolds.

Hacksaw cut - first vertical through the flange before horizontal.

A shot of the freshly clearanced manifold and the offending [genius / bastard] linkage.

The manifolds brought their own issues with regard to hardware. I could tell at first glance they were quirky enough that I decided to build the assembly offline on an old head as far as possible to avoid getting to a crucial part of the installation and find I am missing a part.

The studs in the manifold were not M8 as might be expected on a manifold for a German car, they are 5/16". OK, no problem, I will get some hardware from the local store. I remove one of the studs to take with me and then promptly lose it. No problem, I will find a replacement... Seems the stud is not that easy to find (in local stores here). The manifold end, with the short thread is 5/16" UNC and the free end, which passes through the carb is 5/16" UNF. Why? The fine thread would have worked on both ends (the coarse would be ok too) but instead we have a combo that complicates its replacement. Can I contact Cannon and a buy a spare? No, they seem to be like Keyser Söze and either don't actually exist or they are so well hidden underground the FBI couldn't track them down. I ended up having to buy a set of studs with nylon nuts from the Australian Weber carb specialist http://www.weberperformance.com.au . These studs actually came with a whitworth thread instead of UNC on the short thread but UNF on the long. Whitworth and UNC thread forms have exactly the same number of threads per inch but with a different angle of thread. With steel studs wound into aluminium manifolds this seems to have made little difference.

The next issue that I would love to have been able to contact Cannon about was the brake servo vacuum take off. The manifolds came with a bare threaded hole into one of the runners and after establishing that the studs were an imperial size, I fully expected to be finding an imperial pipe thread size to take a hose tail piece. After applying my vernier calipers and imperial thread gauge I was none the wiser as to what fractional size and thread it could be. While idly flipping through the Ireland Engineering website, I was reading their page on the Cannon double barrel downdraft manifold. This, I was advised, required the BMW vacuum take off from the factory single barrel carb manifold. Surely this won't be the case here that I would be reliant on an ancient BMW factory part with a parallel metric thread? I promptly ordered one from Blunt as my car with a factory double barrel manifold has a pressed in vacuum port so I can't remove it. When I got the part, it seems that my original idea was correct. The BMW part was too big, M22, so I was back looking at hose tails with a pipe thread. I ended up with a 3/8 BSP but I suspect that it is actually an NPT thread (less common in Australia) which means that the thread will not run all the way in. Since this is not under a lot of pressure, I will fit this with some Teflon tape and will call it a day.

When fitting up the manifold to my old head, I noted that the available clearance between the head studs and the manifold runners was limited and variable. This meant that standard M8 nuts that require a 13mm spanner, or even worse the current flanged style of manifold nut were out. I bought some smaller but still flanged nuts from BLUNT that still wouldn't quite fit the lower studs. I took my air belt sander and ground the flanges off from the lower 4 nuts to reduce their diameter. I also relieved the runners in rear of the lower studs with the belt sander. This made them a lot easier to install both on the bench and when bending over backwards to get them on in the engine compartment.

The next issue to be addressed is coolant, or more accurately the lack of coolant. The downdraft manifolds are heated with coolant returning from the heater to the back of the water pump. My 32/36 Weber also was fitted with a water choke so there was a large amount of hoses that needed to be addressed as part of the conversion. I ordered the E21 bypass pipe and reducing hose from Blunt. This connects between the returning heater hose and the back of the water pump. This includes an additional take-off which runs to an expansion tank but I just sealed this up with A short section of hose clamped on a bolt to seal.

The water neck, or divider, which provides the outlet from the cylinder head to the radiator, also needed to be addressed as this has an inconvenient take-off positioned to foul the nearest manifold. Some people treat this by cutting this off and welding this shut. I chose not to do this, mainly so that I would have the ability to revert back to the 32/36 if my experiment with sidedrafts was a failure. I tried to order a new E30 water neck from Blunt but BMW had just posted them as NLA so after trying local Adelaide scrap yards (don't know why I bother) I ended up buying one from Echappe off this board (Ernest). This has two sender ports (probably E21) so I will fit the temperature gauge sender to one and may fit a fan switch to the other.

I am fitting the carbs to the manifolds with some 9mm DCOE phenolic carb spacers and gaskets since Solex have a problem with being overheated and warping. As I have a RHD, there are no issues with clearance from the brake servos but I do need to relocate the dipstick bracket so that this will project through between the carbs.

For a linkage, I went with the replica TI linkage that LarsAlpina on this board sells. This is a beauty of hand fabrication and fits perfectly, apart from needing modification for the RHD linkage arrangement (which to be fair it was never designed for). Instead of having a linkage from the pedal which runs vertically on the same plane as the linkage lever arm, the RHD has a rod that extends horizontally across the bulkhead from a bell crank that comes through the pedal box on the other side of the engine bay. This horizontal rod passes underneath where the rod pivot is attached to the bulkhead. This means that the crank on the bulkhead end of the carb linkage rod was pointing in the wrong direction. After grinding off the welds I removed the crank from the rod with the idea of re-welding it at the correct angle but I noticed that an adjustable crank with a pinch collar from an old side draft rod linkage set fitted perfectly. This allows me to adjust its rotational position on the rod to make adjustment easier. The existing horizontal rod on the bulkhead has a threaded end to allow a threaded fitting to be positioned for attachment to the existing down draft linkage rod. Since the linkage rod is moved closer to the engine by about 80mm, the point where the horizontal rod and the crank intersect will move by the same amount, outside of the threaded length. The simple solution is to reduce the length of the horizontal rod and cut a new thread to use the same fitting. This doesn't fit with my ethos of a fully reversible swap since the RHD throttle linkage is getting hard to come by these days. I bought a 6mm male rod end and some shaft collars. Threading the collars and rod end along the shaft, I can secure the rod end exactly where I need to intersect with the linkage crank. A couple of nuts and washers and the linkage is complete and fully adjustable.

A further issue with using the Cannon manifolds but the stock (replica) linkage is that the throttle return spring has nowhere to go. Armed only with minuscule exploded diagrams and poor photographs it wasn't clear to me where this spring attached either to the carb linkage or at the 'other end'. JGerock from this board (who is building a beautiful TII tribute car) put me straight in that there is a small stud inserted into the flange of the front manifold which accepted the spring and the other end attached through a hole in the front carb linkage. This places the spring towards the front of the gap between the carbs and the drop rod for the linkage towards the rear. Since I don't have the factory manifold I had to fabricate a plate suspended between the top studs to secure the spring on the front side, directly opposite the carb linkage.

This will be painted and finished along with the rest of the linkage before figment.

I will wrap this entry up now at the point where I am able to move into fitting the carbs. Part 2 of this blog will cover rebuilding the carbs and part 3 will be actual fitment to the car and initial tuning. I will retrospectively add some pictures of the linkage when painted to complete.

Any questions, let me know.