DIRTY STUFF
MITCH AND JOANNA HAD BUILT A CLONE OF HOLDEN’S FAMOUS TORANA XU-1. BUT AFTER CRANKING THEIR INLINE SIX INTO LIFE, THEY COULD SEE IT WAS BELCHING BLACK SMOKE OUT OF THE EXHAUST
SOMETIMES, it’s really difficult to find stuff to fit into old cars. Even with a huge aftermarket supply operating all over the world, often these specialist businesses are hard to find, and a lot of good gear simply isn’t made anymore.
There was a case I got involved in a few weeks ago, where a bloke, Mitch, and his missus Joanna had built up a clone of Holden’s famous and desirable Torana XU-1. Made a great job of this project over 18 months, sourced a good 179 HP block, which was bored to 192, added a lot of good go-faster stuff and mated that to a steel-case Celica five-cog ’box. Of course, all XU-1S breathed through triple CD Stromberg carbs, so Joanna found a good set of these on Gumtree, along with an aftermarket intake manifold, and that was about the last piece they had to add to the venerable engine.
After cranking their inline six into life, the mill settled down but they could see it was belching black fuel smoke out of the shiny new exhaust. So they figured that after a few run-in kays, their shiny toy would need a session at a local dyno shop.
So they booked it in, and on the rollers, the operator fiddled with the ignition timing and the adjustable carburettor settings, finally deciding that the tapered fuel flow-controlling needles locked into the diaphragm-attached sliding pistons were all wrong, and that was why the mill was running so rich on the leanest settings he could get. And he didn’t own a range of the rare Stromberg carby needles.
Stromberg CDS are very similar to the slidingpiston English SUS, which were made in their millions, except that the shanks of the graduated tapered needles of the latter are smaller than the shorter needles of the Strombergs. The bloke had a small pile of different-spec SU needles, so he looked through his stock and his needle charts, picking a set of three that he reckoned would work in the 192, then had to carefully cut three very thin brass shims to wrap around the SU shanks, and finally lock these into place in the alloy pistons.
It worked like a treat; the exhaust-gas analyser said the fuel/air mix was a tiny bit rich, but that was a whole heap better than what they had in the beginning. Got great rear-wheel horsepower figures, until they bolted the period air cleaners back on, ran the test one more time and found they had dropped a big heap of horsepower. Air cleaners can do that, if they don’t have the capacity to pass the huge quantities of air an engine on full song will demand. So they ripped the cleaners off again, back came the right reading of what they had before, and Mitch and Joanna went away happy.
Until three weeks and one day later. They were out enjoying a private cruise one Sunday, drifting along in the XU-1 and thinking about stopping for a counter lunch somewhere, when something spat the dummy and the red six went onto four cylinders. With just enough power to shortcut the cruise and get them home, Mitch rang me and asked if I could come around and have a quick look, in case it was something disastrous. I wasn’t doing much, so I threw in my travelling toolbox and I was there just on 10 minutes later.
They had lost cylinders five and six and the 192 was running real rough for almost no reason. Mitch dropped the air cleaners so I could check to see if the linkage to the CD throttle shafts had slipped, closing off the intake draught in the rear carburettor. I was about to poke a piece of fuel line hose into the throat, when I noticed a small roll of brass shim floating around inside the hole. Funny, I thought. I had better lift the top off this CD Stromberg, as that bit of shim should not be in there.
Got the top off the carb, being careful not to split the tissue-thin diaphragm, and discovered the simple reality that the foreign SU needle with its shim had come loose, dropped out of the base of the piston, and blocked off the main jet!
You would reckon that this would be a simple fix to refit the shim with the needle to the same shoulder height I had checked with another piston – in case the dyno man had varied the normal installed height, where the shoulder should be flush with the piston base. He hadn’t done that, but with my arthritic fingers that I have now, I stuffed up the tiny thin shim so I couldn’t refit it, and didn’t have anything like that with me.
No way would the piston’s needle locking screw hold the SU needle central without a shim. But then Joanna had a flash of neargenius while I was trying to figure out an escape from this situation. “Would a small piece of my kitchen Alfoil work?” she asked. I almost kissed her, so she got the stuff and I got her to make a new shim with her nimble and younger fingers, slid the needle back into place and locked this in with the screw.
Worked real well and solid too, so now all they need is a new set of air cleaners!