Wheels, fuel leaks and squeaky clean emissions

Last issue I explained how I had freed off the brakes on the Skoda Favorit so that it could be pushed around on the drive when necessary – it would run (albeit a little roughly), but I prefer not to start engines up just for a few seconds of driveway shuffle. However, on one occasion when I did start the Skoda, I noticed fuel leaking from the back of the engine. I examined the fuel pipe and saw it was very badly deteriorated, but even after I’d replaced that with new R9 hose, fuel was still leaking. So I looked more closely and found that it was pouring out of the accelerator pump on the Pierburg fixed jet carburettor. Making room to access this, I also found that one of the vacuum hoses for the choke pulldown was completely rotten too, which couldn’t have helped with smooth running.

I took the pump off the carburettor – four screws on the pump lever, followed by the diaphragm. This looked OK, but holding a torch behind it showed that the rubber had split around most of its circumference. I bought a carburettor rebuild kit for £50, but was not keen on a total carburettor stripdown and rebuild as these are fiendishly complicated items. In the end I decided to fit just the new diaphragm first and see how it runs. If this cured the rough idle and the fuel leaks then I would have got lucky. If I then had to strip the carburettor further and replace more parts, then I wouldn’t have lost much time and the new diaphragm would still be fine.

The new pump in the kit was soft and flexible where the old one had been hard and brittle. While fitting it, I noticed that the pipe from the fuel pump to the gas bubble separator was cracked too so I replaced that as well. Then, with everything reassembled, I primed the float chamber – one of the practical touches on Skodas of this vintage is that they provide a manual pump lever on the fuel pump. The car then started up instantly, which was a great improvement. It settled down to a smoother tickover too, but low at 550rpm. My vague hope was that getting a little bit of use and some fresh fuel running through the system would improve matters, but right now I had another issue

to deal with.

I’d always known that the alloy wheels were very scabby, but now one of the tyres started to go flat overnight. When it came to pushing the car about on the drive, that did rather negate the progress I’d made previously on the brakes. But there was also a bigger problem. I do have rather a lot of cars about the place, and I try to minimise any negative impression this might give to the neighbours by making sure that anything parked on the drive is complete and presentable. If a car is being dismantled for more than a day, that invariably happens inside the garage and out of sight.

However, other and more pressing projects had bagged all the undercover spaces, and having a slightly ratty old Skoda with a flat tyre on the drive was not ideal. That is why I bit the bullet and had the wheels professionally restored and fitted with new tyres. It wasn’t cheap at £190 for a set of four new tyres and £288 to have the alloy wheels restored, but my reasoning was that I would have had to do this eventually anyway, so I might as well cough up the money now and smarten up the drive in the meantime.

Hall’s Garage removed the old tyres for me (the oldest of which dated back to 1996, making it a classic in its own right!), and I then took the bare rims to Wheelrite in Gosberton near Spalding ( www. wheelrite- online.co.uk, 01775 840180), who did a cracking job. First they span the wheels up on the balancing machine to make sure they were straight, then ran their fingers round the rims to feel for problems. The wheels looked in a bad way to me, but Wheelrite assured me that they had seen far worse. Only if the rim was so badly corroded that it had become too thin to be safe would they have had to say no, and that only becomes clear when you have removed any corrosion.

So first they removed the weights and valves, then put the wheels in a chemical tank to strip off all the paint. Then, to remove the alloy corrosion, the wheels went into an automatic blaster that rotated them and blasted in stainless steel shot from all angles. Each wheel took just three minutes to be cleaned back to sound metal. The guys then examined them carefully to see if there was any kerb damage – light

damage can be taken off in the lathe while more serious damage can be TIG welded up and then machined back, but all of my wheels were straight and true.

So then it was into the oven to de- gas the aluminium, then they were powder- coated in primer and put back in the oven to be part-baked so the paint went off but didn’t go totally solid. This process was then repeated with the silver top coat, then after a little cooling they were lacquered and finally given a full bake. And I have to say that with the wheels refinished, new tyres and a new set of Skoda wheel centres fitted, the Favorit looked good value for its spot on the drive.

Turning then to the TR7, you may recall that despite being classified as Historic and so exempt from needing an MoT, I did have it tested recently and although it passed, the emissions were borderline. We thought this was probably down to the fact that the SU carburettors were still running with their original waxstat jets. These were developed in period to fine-tune the mixture as the engine warmed up, but after 40 years or so they can be ineffective and actually upset the mixture. So I ordered up a conversion kit to replace the waxstat jets with plain ones, and took the easy option of booking it into Hall’s Garage and letting Danny do the spannering for me.

First job was to take off the airbox and filter – the filter had clearly been on there for a while because it was pretty stuck in position, but it came off eventually and looked as clean as a whistle. Danny noticed that one carburettor was missing its gasket to the airbox, and also that the clevis pin securing the accelerator cable to the carburettor mechanism was missing its split pin – that could have been nasty if the pin had dropped out and left me stranded.

After some consideration, Danny decided that it would be easier overall to remove the carbs and work on the bench. We did wonder if we’d made

the right call initially, especially as the lower two bolts securing each carb to the manifold were almost inaccessible. In the end Danny ground a spanner in half to make a special tool, but as it turned out we didn’t think we could have done the swap on the car anyway, certainly not without a great deal of faff.

With the first carb on the bench, Danny removed the link pipe from the float chamber, then the linkage rod from the jet to the choke mechanism. That released the waxstat jet, which could be pulled down and away. Danny then dug out the rubber seal from inside the float chamber. The other end of the link was trickier, though. There is a tab on the end and a keyway in the hole of the choke mechanism, but it was not possible to turn the rod enough for the two to line up. For that, we had to remove the throttle linkage and its integral return spring, then figure out how it all went back together again. Good job it is a twincarb arrangement, leaving us the other carburettor for reference! We did notice when emptying the float chamber that the fuel was very pink. Looking inside we found a lot of fine rust dust, so I made a mental note to fit an inline fuel filter when I got home.

The new kit came with the non-waxstat jet, a new rubber seal and washer for where the pipe goes into the float chamber, some clips for the link rod, a new link rod and a mystery clip which we did not need. The rod was easy enough to get into the hole because it did not use a keyway, but to compensate, the round securing clip was a real pain to fit. We got there in the end, but it needed more than one pair of hands to hold the linkage, the clip and the pliers.

With both carburettors converted, Danny set each one’s jet level with its bridge to get an even starting point, then started the engine. It was very lean initially, so he had to richen it up quite a bit before it would run, turning both jet adjusting nuts by the same amount to keep the balance. When it was sounding happier, he hooked up the gas analyser. This showed that the engine was still running very lean, so he continued with the richening process one flat at a time. That also raised the idle speed, but we could not get this down because the choke linkage was obstructing the throttle. Eventually we got everything adjusted so that the emissions were good, the idle was around 750rpm and the throttle response was good. Danny took it for a test run and seemed to be gone for quite a long time. He came back with a big grin and said how impressed he was with how the TR7 went and with its handling.

The only drawback I have since found is that the engine now takes a lot longer to run smoothly when started from cold, but at least I know it is running as cleanly as it can once warmed up.

“Danny took it for a test run and seemed to be gone for quite a long time. He came back with a big grin and said how impressed he was with it”

ABOVE: A vacuum pipe for the choke pulldown had also dissolved at one end, and Simon had to search out a suitable replacement – it came from a classic motorbike.

ABOVE: When new fuel hoses failed to effect a total cure for the leaking petrol, further investigation showed that this diaphragm in the carburettor was also perished.

ABOVE: At first sight, fuel leaking in the Skoda engine bay seemed down to that usual culprit: old and cracked pipes.

RIGHT: The tyres were ancient, but the wheels were even older and alloy corrosion made them unable to hold air.

ABOVE: With new tyres and some later Skoda wheel centres fitted, the Favorit was once again easily mobile and fit for public viewing on Simon’s driveway.

ABOVE: Specialists Wheelrite near Spalding blasted the wheels clean, then powder- coated them with light grey primer, followed by silver and then lacquer.

ABOVE: You have to love cars that were designed by practical people – the Skoda has a priming lever on the fuel pump.

ABOVE: After the wheels had been chemically stripped, the corrosion on the rims where the tyre beads sit was obvious.

ABOVE: The waxstat jet (top) seemed to be a good idea at the time, but they tend to suffer badly with age. The simpler plain jet (bottom) will be a long-term solution.

ABOVE: Unhappy with the emissions on his TR7, Simon asked Hall’s Garage to replace the waxstat jets on the carburettors. Danny Read drew the short straw...

ABOVE: Accessing the bottom nuts to remove the carbs was a nightmare, until Danny ‘modified’ a spanner on the grinder.

ABOVE: Danny spotted a missing split pin from the clevis pin that joins the throttle cable to the carburettor linkage.

ABOVE: This link rod has a tab that goes into a keyhole on the operating arm, but the entire linkage had to be removed from the carburettor before the rod could be released.

ABOVE: After richening the mixture to get the engine running, fine-tuning was carried out with help from the exhaust gas analyser to get the cleanest emissions.

ABOVE: When setting up the carburettors, Danny first balanced them by setting each one’s jet flush with the bridge, then adjusting them both in equal increments.

ABOVE: The new kit came with lock clips for the rod rather than the tab and keyway. It was still a fiddle to fit, though.