A great article from Robin Dunk

I set the advance up as per recommendations and off up the road I went. It sounded a wee bit meatier but there was never the urge or the rolling sound that I expected. To be honest, it was flat in the critical 2000-3500 band. It briefly cam alive around 3500 but below that, nothing.

It was suggested the standard HS2 pair wasn’t feeding the beast it’s new dietary needs. That made sense to me. After a fair bit of searching various online markets I found a pair of HS4 off a 67 MGB and pair from a 79/80 Spitfire (or a 79 Midget), plus a few random strays of different sizes (need a pair of H1 for your Mk1 Sprite – I know someone who has a set he will gladly sell!). Note, the MGB ones I knew came off a working car so logically, I didn’t tackle them first. I rebuilt the late model HS4 with the ball bearing pistons. Mistake #2. 

I’ll come to Mistake #1 later.

That said, the lessons I learned from re-bushing the first pair carbs, the additional tools I’ve acquired etc has been invaluable.

Mistake #3 was my not pushing back against Moss for a major part that they sold me. HS4 needs a different manifold as the stud pattern is different. The suggestions I had was (a) cut and shut an MGB manifold (technically challenging), buy a Maniflow manifold (issue – availability) or Moss had a very neat manifold available on their website from Mangelosti, a known manufacturer of high quality racing intakes. The answer seemed logical. When it arrived, I read a warning on the packaging that didn’t appear on the Moss website. It stated that ‘some modification to body work may be required’. I should have sent it back immediately but I hung my hope on the words ‘may be’. I should have sent it back! The carburettors hit the inner guard and the car lay immobile for another month as I found and bought (and then had fixed) Option 2, the Maniflow manifold.

If you haven’t heard of Maniflow they make some of the best intake and exhaust manifolds in the business. The business grew out of Downton Engineering and, for A and B series engines, they have a great reputation. However …. they were heavily effective by COVID19 with their manufacturing program being at a very reduced capacity. And, there is one chap in the company who makes the Midget one. Anyway, the new, very sexy manifold duly arrived via SU Midel and I quickly switched everything across and, very excitedly, fitted the manifold. I was like a kid in a toy shop who had been looking through the windows for years. Mistake #4. In my haste to turn fuel and air into wonderful noise, I didn’t put a straight edge over the manifold. I trusted that, as the manufacturer of perhaps the best A Series intake manifolds anywhere, that it would be right. It wasn’t. The head faces where not flat and the faces were not parallel. Once it finally started (with three full turns on the jets and the chokes all the way down) it went to 4000+ revs on start-up and died. The air leaks were massive. I thought it was just air leaks…

By now the carbs have been removed four times and it just got worse. I went through everything trying to close the manifold leaks. New stepped washers, different gasket, gasket goop (we are up to six times on and off now, in case someone is counting). Out of frustration, I ring my brother and bounce ideas off him. Put a straight edge across it and shine a light up and see if its flat he suggests. Sure enough … a call to SU Midel, supplied them photos and they offered me to wait for the guy at Maniflow to get back off leave (and sea freight) or have it repaired. They quickly arranged for the manifold to go around to a local race mechanic and he agreed with my call on the manufacturing (phew) and resurfaced it. Back it came and, like that kid in the toy shop again, I rapidly re-assembled the manifold and installed it all.

Side note – by the 7^th re-fit I can now install a set of SUs pretty quickly by now.

Everything was set and ready to go and it all should work right? Yeah …… no. Yes, it idled, kind of, but it wouldn’t drop under 1500 rpm. Mistake #2 was coming back to haunt me. The carburettors where off a Midget 1500 or a Trumpy Spitfire Mk5 (FZX1122). Why did I chose these to rebuild? Mainly because of the low profile ‘HIF’ style vacuum chambers were never going to hit the bonnet – Midgets have a severe lack of room under the bonnet! What I didn’t know was that the 1500 Triumph engine also uses a very different cam profile on the choke cams and the throttle quadrants. Now, in my defence, I wrote to SU Carbs (Burlen Fuels) in the UK to make sure my rebuild parts list was correct before ordering and I think they missed the part where I said it was for a conversion to a 1275 A Series. As a result, it was never, ever, going to idle under 1500 rpm as the cams hold the throttle discs too far open, even with no idle adjustment and no fast idle screws. 

Oh – the carbs have now come of another two times as I’ve been trying to resolve this and the used gasket count has been spiralling, but at least I’m not destroying exhaust gaskets, only the SU ones at $2 a pop (x6). Don’t do the maths, its depressing!

So, as I stood, beer in hand, contemplating giving up and refitting the original HS2s and going back on the road with my tail between my legs I remembered the early MGB ones. Has to be worth a shot I thought? The throttle shafts were heavily worn but by now my tool chest includes a neat oversize throttle spindle reamer from Joe Curto at British Superior and one set of his oversized (and over priced) shafts. Within 30 minutes and no more than a hand drill I had installed two brand new shafts, perfectly aligned the both carbies where finished. I refitted the low profile ‘HIF Style’ vacuum chambers, and in doing so made Mistake #5. The engine started, it idled, it behaved and using a pair of Colortunes I kind of got the mixture right and I rejoiced. Finally, off out onto the open road and up the old road to Belair, my favourite road for tuning the car. It was absolutely gutless and totally gut wrenching. Terrible doesn’t begin to describe it. The rockers where clattering like they were about to explode, there was some sort of fumes coming from the bonnet at the lights and the temperature was off the scale. 

Mistake #2 was still plaguing me and now Mistake #1 really kicked in. So I headed onto every Australian A Series forum I could find. It had to be the damned cam shaft and I was already devising ways to get the cam out without pulling the engine.  At about 9 o’clock on Sunday night I struck gold. Someone could identify the camshaft and gave me the cam grinders name and email address. So, I wrote to him. Checked my emails all Monday and was getting pretty frustrated when, at 5.30, the phone rang. It was Graham Russell, the chap who ground the cam. A quick chat over the phone and he basically sorted out my issues, corrected the last part of Mistake #2 and, most importantly, resolved Mistake #1 in about 30 seconds. 

The last part of #2 was the use of the HIF style vacuum chambers. They use the SU ‘B’ style spring for which the softest is the Red (4.5 oz tension) spring. I needed the lighter Blue (2.5 oz) as the vacuum wasn’t strong enough to lift the pistons. So, the MGB vacuum chambers where fitted and miracle, they clear the bonnet – just. Voila, I’m getting full movement in both pistons.

Which brings me to Mistake #1. The root cause of everything. When the cam came, the shop I bought it from gave me the advice to ‘set it as per the book for a standard cam’. So, I grabbed the book, got the timing details and set it all up. Here’s the rub. I have three versions of the workshop manual. A large folder of photocopy sheets of a 1971 British Leyland workshop manual, one of the first editions of the Haymes manual that I picked up for free in an op shop and the current version of the Haymes manual. The new one was on the top of the pile so I used that. It said use 13 degrees before top dead centre at 1000 rpm, vacuum disconnected. I couldn’t get it to run at 13 as every time I turned it off it ran on, but at 12 degrees it ran. I’ve been using that setting for exactly 12 months. Well, the book has a misprint – the timing should be 4-8 degrees BTDC. I backed if off on the vernier the full way (5 degrees) back to somewhere in the 7-8 region and the car cam alive. The engine note deepened, the power came on early, the engine ran cooler. Up the road to Belair it was pulling out of corners in 3^rd where previously I felt I needed to get out an push in second. For 12 months its run like a woolly goat and it may well have run ok on the original HS2, but I’ll never know. 

Somewhere along the line, Haymes have attempted to make the manual look a bit tidier and easier to read and in doing so they’ve printed the wrong data. Six degrees of separation? I’ll take five degrees of ignition retardation any day!