Will a Tufnol in­su­la­tor washer pre­vent a Tri­umph’s hot start­ing prob­lems?

Classic Bike (UK) - - Workshop -

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.


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.

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