TUFNOL IT OUT
Will a Tufnol insulator washer prevent a Triumph’s hot starting problems?
Graeme Curtis writes to say that he’s been putting a few miles on his Triumph lately, but finds that he’s having trouble with hot starts. ‘It generally runs and starts easily apart from this and the problem seems to be fuel evaporation,’ he says. ‘The carb is too hot to touch and when I press the tickler button only vapour comes out! I’ve seen various Tufnol insulator washers available, is this the solution?’
I’d certainly think so. These fibre insulators were standard fitment on most bikes, but may have gone missing over the years. The problem is less apparent when riding, because evaporation has a cooling effect. Wh of petrol vaporising in t things cool – cool enoug icing in the right circum BSA A10 used to suffer icing that I removed all bolted the carb direct to after a fast 50-mile ride amazed to find the carb stone cold and on a dam the bike would splutter full choke. The only wa was to ride it until the e warm, then pull over an engine to allow the engine heat to warm the carb. After that, generally it would be OK. On the other side of the coin, my Martinsyde has one flange-fitting carb with an insulator and one stub-fitting without, and when you stop the engine you soon hear the fuel in the stub carb boiling alarmingly in the float bowl. Modern fuel burns hotter than the old days and the extra heat has to go somewhere. Anything that will break the metal-tometal thermal bridge is a help. A fibre insulator of any thickness at the carb flange will help. Norton rs came with 1/8in lators between manifold as well en manifold and ce insulators ally standard it e possible to fit he existing studs, ling that Graeme d be able to get er ones to suit are fairly generic ost British bikes.
rich running on his 1953 Triumph Speed Twin, despite having had the Amal 276 carb sleeved. “The jets are all correct,” he says, “I’m tempted to disconnect the air filter and try running a bellmouth to see if it’s better but am I expecting too much from an old carb?”
I’d check two things. The original carb should be stamped 276FE/1AT. It’s the slide cutaway and, most of all, the needle jet that affect most riding. The slide should be a 3½ – which means 3.5 sixteenths of an inch or 7/32in (5.5mm) at the highest point of the cutaway. The needle jet should be .107. It could be the wrong size – they’re not always marked – or it and the needle may be worn.
Incorrect float height is another possibility. Because the float chamber is separate, it’s important to make sure its position matches that of the carburettor needle jet. There are different depths of bottom nut which can confuse, and even incorrect thickness fibre washers will have an effect. Similarly, if the float has had a soldered repair, the extra weight can affect the level – which should be just below the top of the needle jet in the carb. These carbs have sometimes been built up from mismatched parts – check the jet block inside is stamped 39 by the way (I’m going through this with my Norvin at present). Persevere – having been reconditioned, it certainly should work. My mate Rick Bailey has got two Norton Commandos: one he’s owned forever, the other for just a few years. He rang me the other day to see if I had any ideas about a strange problem with the ‘new’ Commando. It seemed the bike had started dumping all of its oil as though it was wet sumping, yet the circulation appeared to be fine. “Any ideas?” he asked. “It’s driving me nuts!”
It rang a bell about a problem another friend had with a Norton that was an incurable smoker, so I rang him and he directed me to the Andover Norton website where the remedy can be found (andover-norton.co.uk/en/ si combat crank case ). The story goes that Norton changed the breather and scavenging systems for the 1972 Combat engine, picking up from the front of the crankcase and fitting a breather tower behind the cylinders. Evidently over 4500rpm or so, the oil doesn’t scavenge properly and frothing oil was more or less pumped out of this breather. A service bulletin was quietly issued suggesting relocating the pickup to the rear of the cases and breathing via the timing cover. The system was changed for the following year and by now most Commandos have been modified. Rick confirmed his engine is one of the affected models – but the immediate cause of his problem had turned out to be that the breather pipe had come loose on its connection to the oil tank. Evidently oil has been pumping merrily out of the breather all along but was nonetheless going back into the oil tank until the pipe came loose! For the time being Rick has made good the pipe connection but it looks like further work is on the cards.
POLARITY MIX UP
David Wilson’s 350cc Velocette Viper came with its original
Miller dynamo, but the magneto has been converted to a Boyer Bransden Mk3 electronic system. There was no battery on the bike, and having fitted one (negative earth, as standard) he finds the bike fires up for about ten seconds, then loses its spark. “What polarity is the Boyer?” he asks. “I know positive earth is more common on old bikes, so maybe the Boyer is too? Also, is the system voltageconscious, meaning I’d need to fit another one if I convert to 12v electrics later?” I had a word with Kevin at Boyer (boyerbransden.com) who explained that these systems can be run either positive or negative earth – but the wires from the box need to be connected correctly: red being positive and (usually) white negative. So by checking the wiring from the box, David will be able to see which battery polarity he needs; if he’s got it wrong that may have damaged the box. As to voltage, Kevin says there is a six-volt version fitted with an internal regulator and although these would work at 12v they will be overloaded and probably fail before long. The box label will reveal voltage – David may have a 12v box fitted, which could be the problem. A 6v system in good order should deliver about 7.5v, but the 12v system struggles below 8v. Otherwise
Nick Taylor has a Lucas voltage regulator box which he says is “in good condition, but is missing the points on the regulator coil. Any idea where I can get replacements?”
Well, Nick, I don’t know if you can. No doubt it’s the adjustable point that’s missing: a fine-threaded screw secured by a lock nut that can vibrate loose and fall out. When you remove the box lid to see why the bike is no longer charging, the screw slips unobtrusively out of your life into the long grass... but looking at my old Lucas books it appears that points weren’t actually supplied separately. I think Nick’s best option is to look for an old regulator at an autojumble and cannibalise it for parts. Old Lucas CVC units are pretty cheap to buy – especially if they don’t work.
Mismatched parts can cause problems on early Amals
The screw that got away as always with electronic ignition, good earths are essential for proper function, so a good clean up of earthing points might be the answer.