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SU for a Pembleton


Philip Hardcastle

I have a confession to make: between November and February I put the Pembleton on SORN. If there were commandments for Pembletoneers then I'm quite confident that 'Thou shall not take thy car off the road' would be one.

There was good reason for this; Every time I returned home I smelt like the Esso forecourt. I'll be honest and say I'd not really done much about it, but then I lost the oil pipe over summer and since then it didn't start very well anyway and I shelved fixing her under the 'I'll have a look at winter' heading.

SU carb installation

At some point in late autumn I'd taken a trip round the village 'sans bonnet' and could see vapour pouring from the carbs on full throttle. A quick message on the forum was replied to by Ken who explained this was 'fuel standoff'. More research on Google give a little more info, explaining that standoff occurred due to the length of inlet/vibration of the engine reaching a certain frequency. It wasn't helped by the fact that the Keihins were running with no air filter due to the proximity of the gear lever. A solution was a little beyond me but I'd already decided I wanted rid of the twin Keihin carbs because I didn't fully understand them and would rather have something simple to deal with when I breakdown in the middle of nowhere.

I'd looked at using a SU carb before and even got so far as to buying a HS2 (1.24”) with an A-series manifold. I couldn't work out how to fit this under the bonnet and gave up. This winter I had a little more time and found that I could make a mounting plate coming from the lamp bar. Manifold wise, I'd planned to use the Minor unit connected to 28mm steel with rubber hose. At the other end I'd braise it to custom inlet flanges. I'd long since sold the actual carb though, so invested in another HS2 from eBay.

SU carb installation

Step one was to make a plate to sit between the carb and manifold. This would act as my throttle connection plate, and luckily I had plenty of aluminium spare from the build. I ordered a bicycle brake cable fitting and then a 90 degree bend from a Lambretta to ensure the cable cleared the bonnet without getting snagged.

Once I'd mounted the manifold to the lamp bar using metal strips from Wickes, it was time to look at the connections. My dad turned up some beautiful inlet flanges from a single piece of aluminium, which the steel tube fitted into beautifully. I spent my Christmas money on a blow lamp and brazing rods and (naively) assumed that I'd be able to connect the pipe to alu inlet flanges. Sadly this was not the case as I just couldn't get anything hot enough. I'm quite sure the issue was the cheap blow lamp. Buy cheap, buy twice.

With that idea out the window I turned my thoughts back to copper (I had used 28mm pipe for the previous manifold). I thought that the 28mm might have been restrictive so called past my local plumbing merchant and bought some 35mm pipe, along with some 45 degree bends (ebay as they were a quarter of the price than from the merchant!).

SU carb installation

Luckily, my neighbour is a plumber and soldered my pipe and elbows beautifully. Some 35mm ID silicone connected either end to the chopped Minor manifold at one end and the original inlet flanges at the other.

The final task was to source some inner cables as mine had seen better days. Wilko sell universal bike cable for only £1.25 – which in my mind was a bargain.

SU carb installation

The only task remaining was to get the car started and have a test run. It hadn't started very well before the change, and although I'd hoped that this was because of my previous carb set up, there was still no joy. Jumping the car from Chloe's Jeep got it spinning fast enough to fire, and with some throttle adjustments it ran beautifully, but still wouldn't start when required.

I ordered new points and condenser, and when the time came to fit them the problem was obvious – some of the oil from the summer blow off had somehow made it into the points box and put a small film of oil over the points. I did have a look at the crank seal but all seemed dry from there. Once fitted it struck up beautifully. If only I'd done this earlier!

My only concern was the lack of throttle spring-back. I'd used a strong spring already on the carb end, and thought that anything stronger would cause too much wear on the throttle spindles. The answer was another piece of Wilko cable taken from the second throttle mounting on the throttle pedal, through the bulk head to a strong spring connected to the chassis.

So what are the results? To be honest I've not done enough miles to be sure, but it's really changed the characteristics of the car. Acceleration appears much slower, but top speed it greatly improved. I'm not sure why – and do wonder if this could be because the old carbs were not opening fully, but either way the new top speed is quite a difference – It has moved from an indicated 65-70 to 80mph!

The finished product:

SU carb installation

I've added some pictures of the modifications. Unfortunately most were done in my single garage over winter and the lighting isn't ideal.

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