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TT carb.. today's lesson


Slowly I learn. 

Lesson 1: if the bike won't start in one or two kicks, don't waste energy but feed it with a fresh plug. Keep a plug and spanner in your jacket pocket. You know it makes sense! Don't give up and buy a Mikuni.

Lesson 2: if you want a TT to tickover steadily, don't butcher the slide  but add a set screw on top of the jet block. You will have the most inaccessible possible throttle stop, but it works perfectly and it totally unaffected by handlebar movements (unlike hanging the slide off the cable).


My TT carburettor came with a purpose-made cable which prevented the slide from bottoming out.  It also led to a situation where if you turned the handlebars once it had started it would cut out or the revs would increase depending in which direction you had turned the handlebars.  My learning curve [roughly equivalent to a 1-in-3] was that the carb is designed for that area between 4,000 and 6,000 rpm.  The supplied 5 cutaway and 350 main jet led to very brisk acceleration.  

A late friend spent two years trying to get his single to work with the TT carburettor.  His results were that he could get his machine to start easily but it would run atrociously, or it would hardly ever start but ran fantastically.  He had the patience of a saint [and a fair amount more] but eventually fitted a suitable Mk.1 concentric and it ran superbly.  When he sold the machine the TT went with it and the new owner fitted it back onto the machine and then complained that it wouldn't start!

Good Luck! 


I run an Italian machine with a Dellorto SSI which is the same design as the TT , The only way to start is to flood till fuel drips,catch it on the throttle and hold a quarter open till the excess fuel is used ,then keep rolling the throttle . No use in traffic. When stationry keep the bike leaned over to the right .Not easy with a right side gearchange.


They are both lever taps thanks Robert. Just 2 days before we were all imprisoned I nearly filled the tank, so I'm not keen on draining such a large amount of fuel. Although if it leaks enough it might be worth it!

PO fitted a cable stop but, as Colin says, tickover would change as I moved the bars, and it was always unreliable.

I keep blaming my starting problem on the carb  but actually it is solved by a fresh clean plug. I keep worrying about the oil control piston ring. It smokes when at tickover and pulling away from traffic lights when it is hot. It doesn't seem to leave a smoke trail on the road. Could it be the rather generous valve guide lubrication system? I've never seen direct oil injection into the valve guides before.


Although I know some singles I've not had a Norton , but that sounds very likely .if the plug is not oily then it could be the exhaust guide.


Is the "TT" carb really suitable for the "New" normal road use as it's name suggests,  spirited riding and bump starts?




Its really only for racing,but some do make it work well enough for a  classic ride away from traffic.  The main problem is it turns you into a hooligan, I once tried to ride the Mayday run from Locksbottom to Hastings.The journey was frought with a thousand Jap crotch Rockets and police traps,I can't  do Traffic with that bike so made myself unpopular by overtaking all and sundry in all the wrong places ,"sorry can't stop"  get out of the way!. A bit like the pioneer LB run. Lucky not to get pinched. Better off with an Amal 289.


It seems to be fine on the road. Not found any flat spots. They have numerous settings to play with and they are probably pretty hopeless if worn out. The air slide acts over the whole range so you can effectively change the main jet size on the road. Sounds a good way to burn holes in pistons...allegedly they tuned the race bikes to run fully open (maximum air), but closed the air inlet  a bit for the first few miles to enrich the mixture before the engine was fully hot. (I've been doing lots of reading in lockdown). Amal claimed the TT had to be flexible because "there's always a Governor's Bridge".

I suspect the main  drawback is the huge choke size, so low speed torque is probably not as good as with a smaller size. That makes the bike thirstier as well. The Inter has bags of torque and isn't as heavy as my Dommie 88SS, so even though in theory the Inter isn't as quick it certainly feels like it is.  I don't think the TT would suit the 16H.


I run a 1957 Model 30 with a 10TT.9 and I would really like it to start easier without popping and kicking back!

My bike is an ex-road racer so the carb is probably right for racing as once she's running she runs great.

My carb has the following components: 320 Jet, No. 5 Throttle Valve, 109 Choke Jet, Jet Needle appears to be a porely stamped No.5 (or possibly a 6) and is clipped 2nd notch down out of 7 notches and looks to have always been there with the wear, and my Pilot Needle is 10 notches out (about a 1/4 turn) but my Plug comes out quite black as though its running too rich. 

I have a Champion OE068-N3C plug but I've gone hotter with an N4C and might even go up to an N5C to see how it works?

I am open to trying any ideas in the quest to find easier starting, even changing any carb settings or components, and I will resist swapping the TT for a concentric for as long as I can.  If I have to change the Carb, what model and settings do I need for an easy life?

I'm not looking for her to tick over without using the throttle screw just consistant easy starting.



I'm check my settings later today. But my pilot screw is a lot further out than that.

I seem to have got over my starting issues at present. Maybe it's just the warm weather. But I now have a very fixed routine.

My advance lever is marked at 42deg BTDC. I back it off just under 1/4". Fuel on, close the air lever, tickle the carb, fuel off again so it won't flood too much. Then usual up and just over compression, almost no throttle, and give it a go. As soon as it catches  advance the ignition immediately, open the throttle very slowly, and remember to reopen the fuel tap. As long as the bike knows there is a spare plug immediate to hand, it starts straight away. If it doesn't, then don't continue kicking for too long...change the plug. It seems to tun best with the air lever about half open, but I ought to do some proper checks. Not east to do plug chops etc on the ridiculously busy roads. Any hints would be welcome.

I found it worth playing with the pilot..since it is richer when screwed out, I adjusted the tickover to get the best it will do  but erred on the side of further out. I can't be sure but I think it's nearly 2 turns out.

On the road it's just like any other carb. Apart from fuel leaks  which are worse.

Good luck!

Hi David,

If you’ve had the opportunity to check your settings I’m very interested to know what they are?

I’ve also purchased Amal’s Parts and Settings book and await for it to arrive via snail mail.

Can you advise how you set the degrees on your advance lever?




Andrew...just looked up my settings. 1932 Inter. Comp ratio I think is 8.5.

Needle. 7 notches, set in middle notch (no. 3 from top).

Slide. Cut away no. 6 (3/8").

Main jet 320.

Needle jet 109.

Carb is marked 34/041.  10TT34.

Pilot needle is I think about 2 turns out. I played with it a few weeks ago and I opened it up quite a lot from the 1.5 turns I started with. It made quite a big difference to tickover speed, unlike the 276 on my 16H where the pilot screw has almost no effect.

Plug is NGK B6ES.

Differences between yours and mine aren't much apart from pilot screw. You probably know slides are very expensive, and if the carb has been resleeved then a standard sleeve probably won't fit anyway.

I did have starting issues but they seem to have receded. Partly I think because of opening the pilot, partly because I now know exactly where to set the ignition.

I usually start with the air slide down, but open it to mid way to run. Otherwise it bogs down.


Timing is 41deg BTDC on full advance. I've put a thin paint line across the lever and disc to make it clear. I back off by about 3/16 inch (4 to 5mm) to start. Any less and there's a risk of savage kick back. Much more and it becomes more reluctant.

Actually I timed it with about 1mm left to pull on the lever, hence the line. (Measured at the edge of the middle disc on top of the lever)

With my jet block top screw, tickover is too fast on full advance, at about 2000rpm. But it drops to well under 1000 when I retarded the lever. I want to slow it a bit to make it easier to engage first gear from a stop without retarding it quite so far. The TT of course wasn't intended to be used at a standstill.

Hope this helps. I've stopped worrying about stopping and starting it now. (If course it might just be the warm weather...)

In reply to by david_cooper


Taank you David for all the information.

All being well the weather will be better in Inverness and I'll be able to play!

II obviously have a note of my settings, but I'll reset the carb as you've detailed and see what happens, and all being well she'll burts into life very quickly.

Another question though, or more an observation... I have noticed that the underneath of my fuel tank gets quite wet above the open bell mouth, is this to be expected with the amount of fuel that must pass through the TT?

Have a good weekend. Andy


Thats blowback from valve timing more suitable for the race track. Sometimes it can be reduced by  a different exhaust  ,but the cure is to either rev it more (race!) ,or  change the cam/ or cam  timing. The bike will also be easier to start with  milder valve overlap. And be more powerfull at the revs used for road riding.I have the same issue on a 250 OHC ex race bike I use on the road. I will swap the wild overlap low lift ultra revvy cam for a high lift road cam.Can't do much about the 40mm inlet valve and 29mm carb.


I have an annoying amount of fuel leaking onto the oil tank, usually stops once it fires up. I've not looked upwards! I now turn the fuel off again after turning it on, and flooding it a bit. Then turn it on when it fires up. It's better now since I flatted the sides of the banjo which were not quite parallel.

An air filter is of course a good idea. It not only preserves engines but saves fuel because any that spits back is re-breathed. I've never seen one on an Inter, but long bell mouth should have a similar effect on reducing spit back.


The other issue with blowback is the fueled up air goes back in the  carb and picks up yet  another charge of fuel , so at that rev range the mixture will be very rich  and any attempt to tune out the issue by weakening the carb will produce a weak spot  somewhere else. Not nice for pootling around the lanes. No issue at all at 110 mph down Bray Hill.------Why only 110 ?, I now have the attention span of a gnat ,so have to set personal limits!.



I’m still playing trying to find better starting settings with my 10TT9 carb and don’t seem to be getting anywhere fast using David’s settings as a starting point and may have to resort to changing for a 289 carb?

Please excuse my ignorance (as basically I’ve been a 2 stroke person until I got my Inter), but I’ve been reading various threads and If I’m reading correctly the Cams and exhaust type can majorly effect the carb settings.... in what way are the settings affected?

My exhaust is a Goldie style with a stubby tail/outlet, but how do I determine what Cams I have without stripping the head down (is this even possible)?




I can't help with cams, but I'm fairly sure the exhaust won't affect running until the revs start to rise.

My starting problems seem to have gone away. After a couple of turns with the decompressor just released enough to get it over TDC it started yesterday on first kick following my usual routine. I never blip the throttle. I think timing is more critical than anything. The old adage...most carb probablems are caused by timing. How is your ignition timing?


Just with playing with the pilot screw (coming gradually out) I have been starting from hot and cool but only time will tell and the proof will be the next time she comes out if she starts!!

Come the end of the day she was sitting ticking over nicely high prompted me to get my helmet but not managing to leave the drive as the clutch plates had stuck together with lack of use, the clutch has also now been stripped, cleaned and hopefully now ready for when the dry weather returns to the Highlands. 

yes, I use the decompressor to pass just over TDC but I do find that I need to flood the carb to be able to start.

I haven’t played with the timing, all I’ve done is check my plug gap and I’m a great believer with my Inter that if it’s not broke I won’t fiddle with it but to be honest I am nervous about when I do need to touch the timing as it’s totally alien to me compared to the Japanese 2 strokes of my youth.


I am running a pair of  1.5/16" GP2 carbies on an Atlas. It starts first kick and idles and runs 100mph in 13 seconds over the quarter. BUT the slides are brand new SS I made myself and hang off the cables. I have a friend with a 500 DBD Goldie that also starts first kick and runs very well with the GP fitted but burns petrol at a prodigious rate. A friend now deceased told me years ago to run monoblocks on the Atlas as they smash the fuel up better than the GP does and are better for acceleration, but that the GP's would be better down the Clady straight! Now a TT is halfway between the two SO a TT in good order should run nicely around the street and as fast as we are likely to use a road bike these days. I will know as soon as I get my Inter back on the road.


David, I had many a long hour trialing different fixes for the incalcitrant starting of my 37 inter ms. With fuel spills,  lack of spare slides and sheer exhaustion from formerly bumping and latterly kicking the machine into life I opted for a carb change.  A similar fate with a shiny Velocete left me with a spare 930 concentric jetted for a 500 but much lower sized jets.  I bought the appropriate jets as advise and she runs. Now with a stable base it was easy to work out that it was far to rich.  I ended up with the velo 280 main 106 needle and no3.5 slide.  What the concentric gave me was an easy starting baseline where I could get it running and make the necessary measurements and adjustments to make it a reliable starter/ runner. (colour tune, timing light, gas analyser).  Now I’m working on the TT carb , bringing it in line with concentric settings.  Knowing all other settings are good gives greater confidence in proceeding with  the TT.  

I note the comment previously on cam timing re: spitting back, and would be interested to know which part of the overlap you adjust? I understand exhaust opening to be one of the critical points for this type of engine so guess I would alter the inlet cam timing for less overlap. Any advise welcome.

Best regards and seasons greetings to all...




I understand the inlet timings seem to be: racing, 57BTDC to 60 ABDC. Road (silencer) 47 and 70. I think mine is 47/70 or close. Ignition 37 I think.

Starting problems seem to have gone away. I don't quite know why! I now make sure I do not flood it. Retard a bit under 1/4" on the lever disc, turn over a couple of times, usual push just over TDC, and kick. A reliable tickover helps me a lot.

I've had the top off, and the bores looked like glass. So I used fine wet and dry in spiral directions and washed and scrubbed it clean. I've not yet needed to remove a plug again, but the smoke seems to have gone. Although the only ride I have had, it rained most of the time...

Anyway, fingers crossed...all we want for Christmas is to have our lives back.

Happy Christmas!


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