New Rover 12 owner

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Rosber
Posts: 1
Joined: Tue Aug 03, 2021 2:49 pm

New Rover 12 owner

Post by Rosber » Mon Aug 16, 2021 2:28 pm

I have recently acquired a 1947 Rover 12. It was running rough, difficult to start, no power when out on the road and would not start at all when hot. I am in the process of trying to get it running smoothly. I have cleaned out and "refurbished" the mechanical fuel pump, similarly the carb. I have also fitted an in-line fuel filter to try and keep the fuel pump and carb clean, as both were choked with rust debris - presumably from the tank. On the ignition side I have fitted new points (set t0 0.012" giving 47 degrees dwell), plugs (gapped to 0.025"), plug leads and reset the timing (points just opening at 11 Deg BTDC). The Condensor seemed okay, but I will swap it when I can locate a big enough soldering iron! The engine now starts well - and will settle down to a stable tickover. Afterwards I was able to take it out for a 20-mile shake down test run and, for the first time since I've had it, I did not breakdown, or suffer fuel starvation through apparent vapour locking in the fuel pipe and an associated glide to the side of the road until things cooled down. The failure to start when hot also seems to have been solved. I switched off after the run to let it heat-soak for several minutes and it restarted with no hesitation. So I think I have a car that is almost useable. Just one question. The acceleration seemed very poor - even for a 70 year old car and I am not sure whether the timing needs adjusting further - but I can find no information other than the initial static set up. What sort of acceleration can I expect? It gets to 40 MPH eventually and seems quite happy to cruise at between 40 -45 MPH on straight level roads. However, on roads with corners the lack of acceleration becomes readily apparent - as the long queue behind me will testify! The carb is not original and is an SU unit from a mini apparently. I have obtained a refurbished replacement Solex unit which I will fit in due course - it requires mods to the heatshield that has been fitted over the manifolds so that it will clear the linkage. Does anybody know whether this will improve things, or was there a good reason to swap from the original Solex unit? Many thanks in anticipation.

SHyslop
Posts: 50
Joined: Thu Dec 30, 2021 4:17 pm

Re: New Rover 12 owner

Post by SHyslop » Thu Aug 25, 2022 3:46 pm

Regarding your Rover and its acceleration. In writing the following I am the current owner of a 1947 Rover 12 with a Solex carburettor and I used to have a 1939 12 with an SU carburettor. I also have various other Rovers with a mixture of SUs and Solexes so what I'm going to write is based on how they've all been. That doesn't mean it's going to help your car but it is intended as being factually useful.

Firstly, make up a replacement condenser using any spare one you can get your hands on. There is no need to unsolder the one on the metal baseplate, leave it where it is and find a spare condenser off any vehicle but preferably one with a piece of wire coming out of the insulated end and a metal clip you can attach another piece of wire to. Connect one wire off the condenser to an earth and the other to the low tension wire going between the coil and the distributor, it won't matter at which end it goes to. Does the car now run any better? If yes, the condenser was at fault; if not - it's ok.

Without knowing exactly which Mini carburettor is fitted to your car, it's a bit hard to say how close or far off it will be. The easy answer is to say "well, it must be wrong" but if it's an H2 or HS2 (or similar), that might not be too far away in terms of choke size and only a question of having an appropriate needle. The original type of Triumph 1500 was fitted with a single SU but an HS4 and at 1493cc was a close match to your 1496cc engine.

The reason I've mentioned that Triumph is partly because I have one, although it's a TC, and to be honest, compared with modern cars, both it and the Rover feel lacking in power. Some years ago, I had a Rover 14 which was a really good one and I left it with my father to play with and go places in. Every time I went to see him, I asked how the car was and each time, he had another fault. The brakes were poor, the steering was poor, the power was poor. However, I had not adequately taken into account the difference between how he perceived them at the age of 22 and then at the age of 72 with a Ford Fiesta capable of 100 mph as his regular driver. If you consider that a Rover 10 has 1389cc , the 12 at 1496 is only 107cc more which is precious little for the added weight of a longer chassis and bodywork, also for the greater expectation of the owner !

I found both the Solex and SU carburettored cars start to run out of steam at about the same places in the speed/load range whereas the 14s with another 450 cc and the dual choke Solexes have a lot more go. However, I was severely puzzled by a 14 that ran out of puff at about 45 uphill in top whereas the other was trouble free. The problem was that the one car, which ran well, had been fitted with a rear mounted pusher type SU pump and the other had a front mounted puller type SU pump. Fitting a rear mounted pump solved its problem. Considering the same type of pump is fitted to a 2 1/2 litre RM Riley , it shouldn't in theory have made a difference but it did.

Another puzzle I had with the Solex fitted 12 was uneven running and this I traced to something rather strange. It was that on fitting the bakelite plug lead cover, the car ran poorly and on taking it off the car ran much better. Clearly, the cover was pulling a lead and I am going to replace it all when time allows as I plan to fit a side entry cap where the leads are screwed internally into the cap rather than the top entry cap with acorns.

If your car had been fitted with a D3 SU, as fitted up to 1940, it would have had an AUD1104CN needle. There will be a corresponding spring loaded needle for the later SU carbs but I have (temporarily I Hop) mislaid my Burlen needle dimensions book so I can't look it up but I am sure a call to Burlen would reveal which one it is. You could then check and see if that is what is fitted to your car.

As to the differences between the Solex and the SU, as the old saying goes, some people swear by them and some people swear at them. The jets on a Solex need to be kept clear of debris. That means the jets and all their passageways blown through with an air line and checked. I've found that particles in these jets can act like a flap valve, you blow through them and they seem ok but the dirt is hinged and is still sticking there. It needs an air line with full pressure applied to clean some of them. Leaving petrol in them will result in a fine powder of debris drying out in the carburettor.
Provided the fuel level in the bowl is right, they should then work in a satisfactory manner. Just make sure it is the right Solex model for the car.
The downdraught SU can have problems too but I have two at present, both recently overhauled by Burlen, and both are working properly just as I write this.

According to the Rover manual, the 1940-47 12 was fitted with a Solex 30FAI and Newnes Motor Repair says a 30AIP was fitted for 1936/37. This wouldn't, I think, be a standard fitting but an alternative to having an SU. I saw a car so fitted many years ago. The 30 FAI was also fitted to Standards and Hillmans and the 30 AIP was fitted to quite a number of vehicles so it would do to check and see that the unit you have is the right one for your Rover. It wants a main jet of 115, pilot of 45 and a choke tube of 23. The particular number that should be on one for a 1940-47 12 is S1369. S1368 is for a 10.

Two final points. Concerning the timing setting, too little advance will give a loss of acceleration but if the engine pinks or sounds rough is difficult to start (the wuw---wuw---wuw of a starter going laboriously over the hump) then there's too much. It is also worth checking that the points are correctly set. Some modern points have plastic cams that wear immediately and are useless. Also, when off the cam, are the points properly and fully shut, a check with a meter should show all this quite readily. Has the rotor arm got a rivet fixing the brass strip? If so, throw it away and fit one without a rivet. Is the centrifugal advance and retard working all right ? If the car had been laid up for some time, this can be a problem for acceleration as if the automatic mechanism is stuck, it will not give you the extra advance you need. This may require you to take the baseplate off, check the weights are free and oil the mechanism - the pivots and springs checking for free movement. You didn't mention plugs, new ones can be a problem. I don't think there's an easy answer to this question but it does seem right enough that when modern made plugs become "glazed" with an over rich mixture, it's hard if not impossible to return them to good order. I've been finding better results recently with Denso plugs. I used to always use NGK to solve problems but somehow they seem to have gone off a bit, maybe my bad luck?

Check for any leaks in the inlet manifold between the carburettor and the manifold. You know someone has played about with this and if there is a gap (usually accompanied by a whistle) this will result in a weak mixture also leading to loss of power.

A lot of this nearly takes more time to write than check so don't be put off. Finally, do remember that probably the number one failing of older cars when they were a few years old was the need for a decoke and valve grinding. Given that these cars don't have that much spare power, a compression test may be worthwhile and the valves seen to thereafter. Someone may have been hoping it's a job the next owner will undertake for a long time !

Now whether any of this is a help, I don't know, but if improvement is possible, it probably lies somewhere within these components, or the wires joining them.

Do advise how you get on as we all learn more that way.

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