1958 Dominator 88 losing power when hot

Hi,

If you're happy that your ignition & carb are set up correctly, it might be worth checking your valve clearences, if they're a bit tight, when the engine gets hot, the valves may be held slightly open, this would result in a loss of compression & give the symptoms you describe.

Regards, Tim

Previously jones_jones wrote:

Hi I have a norton dominator 88 1959,standard spec still running 6 volt points & coil ignition,the bike runs and starts great,but after it warms up about 5 miles it's starts to lose power,you can stop it and it starts up again no probs,but it doesn't pull properly you have to really open the throttle and it stutters,if I leave it over night it's fine again,until it gets hot then the same happens !! It has champion n5 plugs in,I've checked the points they are fine not burnt or pitted,and the gap is correct,the carb has all the standard jets in,& the pilot is 1 & half turns out,any help would be very much apprcieated cheers rob

Sounds like your running rich, turn the pilot to 1 1/4 out and try again. I have had similar problems and it was the carb settings.

Is the bike new to you? Is this a recent occurrence? Could even be the choke being left closed. Gordon.

When this happened to me it turned out one of the two carb needles was set too low. It was too lean, so too hot, nipping up, wrecked the piston and scored the bore. Hope yours is OK - David

I had the same problem with my '54 88. In my case it was due to a previous owner fitting alloy pushrods in a motor with an iron head. When the engine got hot, the pushrods expanded, losing clearance (and compression) on the exhaust valves. I have seen incorrect valve clearances listed in a reproduction owner's manual. In my case, increasing the valve clearances to 6 thou inlet & 8 thou exhaust solved the problem (these are the clearances listed for an 88ss). John.

A bit suspicious of thechoke being fully open even for starting. Have come across a similar problem wherew the chole cable inner was too long - although the choke lever appeared fully open, it was hardly liftingthe air slide. As David says, verify that the air slide is really fully open. Gordon.

Hi I have a norton dominator 88 1959,standard spec still running 6 volt points & coil ignition,the bike runs and starts great,but after it warms up about 5 miles it's starts to lose power,you can stop it and it starts up again no probs,but it doesn't pull properly you have to really open the throttle and it stutters,if I leave it over night it's fine again,until it gets hot then the same happens !! It has champion n5 plugs in,I've checked the points they are fine not burnt or pitted,and the gap is correct,the carb has all the standard jets in,& the pilot is 1 & half turns out,any help would be very much apprcieated cheers rob

Hello This Machine as all the trates of fuel starvation your bike runs 5 mile and then runs out of puff , this sound like a sticking float needle in its housing not letting fuel into the float chamber or there is a obstruction some were in line with the carburettor float chamber .also try Bosch W7DTC you find your bike starts Better, So then you need to check the Fuel Petrol tap and fillers in the tap and carburettor And Please take Note That with Ethanol You may need to size up the main jet, as ethanol tends to dry out quickly when a engine is Hot Even Modern bikes have the same problem from time to time , Hope this may help

Previously jones_jones wrote:

Hi I have a norton dominator 88 1959,standard spec still running 6 volt points & coil ignition,the bike runs and starts great,but after it warms up about 5 miles it's starts to lose power,you can stop it and it starts up again no probs,but it doesn't pull properly you have to really open the throttle and it stutters,if I leave it over night it's fine again,until it gets hot then the same happens !! It has champion n5 plugs in,I've checked the points they are fine not burnt or pitted,and the gap is correct,the carb has all the standard jets in,& the pilot is 1 & half turns out,any help would be very much apprcieated cheers rob

Hi, another component to check isthe condenser on the points plate - I had a 1960 dommie 99 (208JHY are you still out there?) and had similar problems -couldn't find anything wrong but a new condensor got it going again for a few months -eventually sorted by replacing it with a mag off an old ariel twin from a local scrapyard - cost 2shilling and 6pence!! does sound suspicious if it starts from cold with no choke easily as if it is getting too much fuel. have you checked the float level in the carb?

good luck - Terry

Could even be a blocked petrol cap breather hole. Worth a check.

Previously Gordon Johnston wrote:

Could even be a blocked petrol cap breather hole. Worth a check.

Just to concur with Gordon's suggestion, I had exactly this problem on my Dommie 99 after fitting a new cork gasket to the filler cap to cure a leaky tank over fill, but obviously now making the tankmore air tight.

I had poked the outer and inner vent holes in the cap to check that they werent't blocked but it was only upon dismantling the sprung Ceandess ventmechanism that I realised there was a third vent hole inside the domed chamber. This was well and truly blocked - what a difference once cleared !

I thought initially it was heat associated but discoveredthe reasonby doing a petrol flow test. With the pipe disconnected from the carb petrol flowed normally into a container until about half a pint, upon which it reduced to a trickle and then stopped. Releasing the filler cap restored the flow, clearing the internal vent blockage likewise.

Hello So then am I in the right ball park with this one, !! yours Anna J

Choke on an Amal is easy, Slacken the cable and you have choke a tight cable (full tension) is choke off. (No choke) I agree that lack of a petrol tank breather will eventually restrict, if not stop fuel flow. The N5 Champion plugs are correct for the 88. Finally, keep off the Ethanol, unless you have no choice, like an empty tank outside Tesco's!!!!!!!!!

Incidentally, the mixture screw on the side of the carb (Not the tick over screw at an angle) has much more influence on carburation than what many people think. I only make very small adjustments at a time.

Previously neil_wyatt wrote:

Choke on an Amal is easy, Slacken the cable and you have choke a tight cable (full tension) is choke off. (No choke) I agree that lack of a petrol tank breather will eventually restrict, if not stop fuel flow. The N5 Champion plugs are correct for the 88. Finally, keep off the Ethanol, unless you have no choice, like an empty tank outside Tesco's!!!!!!!!!

Incidentally, the mixture screw on the side of the carb (Not the tick over screw at an angle) has much more influence on carburation than what many people think. I only make very small adjustments at a time.

Hi everyone Thankyou very much for all your help,an up date I took off the the fuel pipe and checked the filter on the carb banjo,it was it was pretty much clogged up,so was the end of the pipe,In fact when you turned the tap on it was just dripping out ! I took the tank off drained it cleaned out the tap filter and tank and it flows freely now,waiting for the rain to stop now so I can try it so watch this space ! This club message service is superb by the way,especially for a beginner like me thanks again,ps the next issue I have is the crankcase breather,mine just goes on to the chain but quite a bit of oil comes out of it so I end up with quite a bit on the garage floor after a ride any suggestions ?

Hello So I was Right then with this one as well , it was in the Fuel line IE tape filter Anyway For your other problem now run your pipe into a Catch tank and then have small pipe for a drip feed the chain, yours Anna J

Hard to come by now but if you can find a late oil tank with an intake on the top it would cure your problem, well the problem of oil on the floor after start up after a few days + anyway.

Of course it depends how much oil is coming out as it might be hiding a problem. This works well on my sick 650 and I don't believe any oil gets up into the oil tank anywaybut better still, there is none on the floor.

If you want to take the breather apart then I know there are better people than me who can guide you through that. Just remember that if your bike has wet sumped a bit you will get more than theusual amount of oilout of the breather. The long pipe, complete with reducer works well.

Agree completely with Neil. I fitted a later oil tank which has the breather from the engine leading up to an oil separator tower in the oil tank. No more oil puddles on the floor. Some think that this is a Bad Thing To Do on thegrounds of possible oil contamination but seeing that it became the standard Norton setup it can't be that bad. It works for me. Gordon.

It's a long time ago,but i had a BSA Road Rocket,which exhibited a serious loss of power after a few miles,which magically cured itself when it cooled down.I changed the plugs to a harder grade -N3 i think and the problem disappeared.I'm sure it had N5's in it which were obviously getting too hot ,and would have eventually holed a piston.I've not checked which plugs your bike requires,but it's worth a thought.

Previously jones_jones wrote:

Hi I have a norton dominator 88 1959,standard spec still running 6 volt points & coil ignition,the bike runs and starts great,but after it warms up about 5 miles it's starts to lose power,you can stop it and it starts up again no probs,but it doesn't pull properly you have to really open the throttle and it stutters,if I leave it over night it's fine again,until it gets hot then the same happens !! It has champion n5 plugs in,I've checked the points they are fine not burnt or pitted,and the gap is correct,the carb has all the standard jets in,& the pilot is 1 & half turns out,any help would be very much apprcieated cheers rob

It's a long time ago,but i had a BSA Road Rocket,which exhibited a serious loss of power after a few miles,which magically cured itself when it cooled down.I changed the plugs to a harder grade -N3 i think and the problem disappeared.I'm sure it had N5's in it which were obviously getting too hot ,and would have eventually holed a piston.I've not checked which plugs your bike requires,but it's worth a thought.

Previously jones_jones wrote:

Hi I have a norton dominator 88 1959,standard spec still running 6 volt points & coil ignition,the bike runs and starts great,but after it warms up about 5 miles it's starts to lose power,you can stop it and it starts up again no probs,but it doesn't pull properly you have to really open the throttle and it stutters,if I leave it over night it's fine again,until it gets hot then the same happens !! It has champion n5 plugs in,I've checked the points they are fine not burnt or pitted,and the gap is correct,the carb has all the standard jets in,& the pilot is 1 & half turns out,any help would be very much apprcieated cheers rob

with weak mixture and over advanced timing , yours anna j

I still suspect it is nipping up. Eiher because the bores are too tight or beause the carb needle(s) are a notch too low and it's too lean and overheating. Same symptoms as I had. Then it needed a rebore...

Have you checked the valve clearences yet ? If they're a bit tight, they will give exactly the symptoms you describe. Simple thing to check & at least you can eliminate it as a possibility.

Regards, Tim

Hi Rob,

it has been suggested to you that maybe the breather in the tank fuel cap is blocked,!.... have you checked this out?... Easily done while riding when the engine starts to lose power, simply release the cap momentarily to let some air in, you will feelthe enginepick up straight away, (pushing down the tickler will do nothing if the fuel wont flow)

Ãlso, I recently fixed a coil ignition Triumph twin with a similar problem. Would start easily when cold, then after a few miles it would start tolose power to the point of being unridable. I put the coil on my tester and it was OK, then I did a pre heat on itand the spark all but dissappeared.Dud coil breaking down when warm,replaced itand no more problems.

Let us know how you get on.

Paul

You are running out of things to check, that means you are getting closer to a solution!...

What about checking the condenser in the distributor? ...just could be!

The misfire and difference in exhaust pipe colour suggest to me that the problem is not fuel based. I do not think it is a manifold problem either.

Change both of your plugs and see if this makes a difference. In my experience, Champion plugs are not the best choice for a Norton and I would be changing them for NGKs. I have come across quite a few Champion plugs that were poorly manufactured with internal problems causing the kind of misfire you suggest.

If changing the plugs does not help then I would be checking out the valves and guides next. When your bike loses forward motion do you still have good compression? If not, then a valve may be sticking open. Somewhere in the depths of this website is a similar mystery to yours. In this case it turned out that this Dommie owner had refurbished his cylinder head but fitted guides with clearances that were too small. The bike would fire up, run down the road and then the warming valves would sticking partially open until thumped closed by the pistons.

Finally, as mentioned above, the Achiles heal of the distibutor ignition system is the condenser/capacitor. So after changing the plugs check this bit out as well.

The misfire and difference in exhaust pipe colour suggest to me that the problem is not fuel based. I do not think it is a manifold problem either.

Change both of your plugs and see if this makes a difference. In my experience, Champion plugs are not the best choice for a Norton and I would be changing them for NGKs. I have come across quite a few Champion plugs that were poorly manufactured with internal problems causing the kind of misfire you suggest.

If changing the plugs does not help then I would be checking out the valves and guides next. When your bike loses forward motion do you still have good compression? If not, then a valve may be sticking open. Somewhere in the depths of this website is a similar mystery to yours. In this case it turned out that this Dommie owner had refurbished his cylinder head but fitted guides with clearances that were too small. The bike would fire up, run down the road and then the warming valves would sticking partially open until thumped closed by the pistons.

Finally, as mentioned above, the Achilles heal of the distributor ignition system is the condenser/capacitor. So after changing the plugs check this bit out as well.

Now Phil I just done some selling corrections for you. And having tried NKG and Champion , for some years I find that Bosch are Better by far , So see Green-Spark-plug-co Do have a word with Tim Green he will direct you to the right spark plugs But I do find that these 3 point electrodes are far easier to start a cold engine and more reliable too but this is my experience you can take it or leave it. yours Anna J

Rob,

FWIW I run NGK B7ES plugs in my '58 99 with no problems. I use a wired car type condenser (anything around 25?f will do as far as I know) cable-tied to the frame close to the coil. If you go this route it saves taking a chance on the many crap aftermarket condensers out there that are supposed to fit 18D2 distributors but don't. I have the condenser body attached to earth and the wire to the positive pole on the coil, and have binned the original condenser. Bear in mind that if you do manage to find a NOS condenser, it will most likely be old and degraded and of no use anyway. I got this advice from Mick Hemmings years ago, and it works well for me.

Martin......Totally agree with you regarding plugs and condensers.

The problem with Bosc stuff is it aint always made in Germany anymore. The NGK plugs either work or don't. Whereas I have found both Champion and Bosch plugs will sometimes get you from A to B but not back again.

Condensers for Norton Dizzies are available but the mounting place is rather hit or miss. Like you I used to generally do an exterior fix using a car type item with a chunky wire and solid mounting plate to take some proper screws or bolts. Then I got hooked on electronic ignition and haven't looked back.

Martin......Totally agree with you regarding plugs and condensers.

The problem with Bosch stuff is it aint always made in Germany anymore. The NGK plugs either work or don't. Whereas I have found both Champion and Bosch plugs will sometimes get you from A to B but not back again.

Condensers for Norton Dizzies are available but the mounting place is rather hit or miss. Like you I used to generally do an exterior fix using a car type item with a chunky wire and solid mounting plate to take some proper screws or bolts. Then I got hooked on electronic ignition and haven't looked back.

We in my experience over the last 38 years Champion and Bosch have always been no trouble were As NGK have be the pits even in the cars I had too , my Suzuki GT550 I had use to eat NGK every week it just would not run on them I must have 50 dead sets of NGK plugs. But when I fitted a set of Bosch plug they were no bother and did not miss a beat , My Norton Manxman has had Bosch W7DTC now for the last 4 years and Starts easy and runs very nice, it never missed a beat yet, So they cannot be all that bad, and Green spark plug Co recommended them so you pay you money and take your choice your anna j

I don't need to go Green to know what works best on my bikes.

Below is hot off the NOC Spares Scheme pages for twins. I could not find any other make of plug for sale.........and I would have thought that they are a good authority.

SS02 C2_B8ES

I have just had a similar problem with my Dommi 99. The new pipes got blued, left more than right, a misfire developed, and the engine slowed eventually. I have a concentric carb which I'd just reconditioned with a Burlen kit. Examination of the replacement needle showed it to be five thou oversize throughout its length, so I replaced all the old bits and the bike is OK now. Your description sounds like lean mixture, which combined with modern fuel will cause gross overheating. Dous anyone have experience of the Colourtune plug?

Previously tom_mcewen wrote:

I have just had a similar problem with my Dommi 99. The new pipes got blued, left more than right, a misfire developed, and the engine slowed eventually. I have a concentric carb which I'd just reconditioned with a Burlen kit. Examination of the replacement needle showed it to be five thou oversize throughout its length, so I replaced all the old bits and the bike is OK now. Your description sounds like lean mixture, which combined with modern fuel will cause gross overheating. Dous anyone have experience of the Colourtune plug?

I have and use a Gunsen colourtune on my norton 650 and (sorry!!) t120 and find it ideal for setting up for tickover settings but resort to the trial and error method for other throttle openings.Terry

I have a colourtune plug somewhere at the back of a drawer. OKish for tickover only but the step by step method in the old Pitmans handbooks works best.

HI.

A long shot (because this was such a long time ago I canât remember how bad the symptoms were) but worth a try. I had a problem with my (twin carb) Dommi running badly when hot. It turned out to be worn throttle needles (and probably needle jets)allowing the mixture to be way too rich at mid openings. The needles, I seem to remember, had a definite âridgeâ on them. Hard to tell whether the needle jets where worn too but I replaced them anyway. It would explain why you have to âreally open the throttleâ to get it going so taking it past the point where the needleâs taper haseffect. I'm assuming you've checked the needle and needle jet are thecorrect ones and the needle clip is in the right position. Worth a go?!?!?

Ian.

It must be running too lean. I had the same problem after rebuilding the carb, due to not noticing the replacement needle in the kit being 0.005" oversize throughout its length. Nice new pipes blued, engine could have been wrecked. Give-away was amount of choke needed and popping on the over-run. Replaced old needle, problem went.

Jones x2 mentioned the following at the beginning of this thread:-

Hi everyone I've changed the coil now and the problem is still there, I've noticed that the exhaust on the left cylinder where it comes out of the manifold is not colouring like the right one(brown) I've done a compression test and got 140 psi both sides,could it be a distributer problem ?

While not discounting a possible carb problem, I would think that both pipes would be going blue if the mixture was weak enough to be an issue. His engine is a single carb job.

Hi Jones Jones,

I understood the initial problem was a loss of power when hot, but you later mention a misfire, when hot I presume. Could you please clarify the symptoms. Was the compression test performed hot or cold and is the misfire on both cylinders?

I don't need to go Green to know what works best on my bikes.

Below is hot off the NOC Spares Scheme pages for twins. I could not find any other make of plug for sale.........and I would have thought that they are a good authority.

SS02 C2_B8ES

Spark plug - NGK Twin Carb & SSNew £ 2.00Members OnlySS02 C2_HW/OSKOil seal kit - Heavyweight Twins engine and gearboxNew £ 6.50Members OnlySS02 C2_B7ESSpark plug - NGK Single carb TwinsNew £ 2.00Members OnlySS02 C2_B6ESSpark plug - NGK 650/750 1966 onNew £ 2.00Members OnlySS02 C2_B5HSSpark plug - NGK Cast iron head TwinsNew £ 2.00Members Only

Hello the most favorable spark plugs that Norton found was KLG FE100 3 point electrodes And Now the Modern equivalent is Bosch W7DTC And its works very well price £2.50p to anyone via Green spark-plug .co I have tried and tested these plugs so I do know there good plugs and do not over heat the engine they run cleaner too as there self shielding, you do not get this with NGK witch are made in Japan so you think but a lot are made in china , Bosch are made in the EU many Germany. Over heating is many down to lean fuel mixture and over advanced timing IE see Triumph engine run over advanced thats why you see the exhaust pipe blue on Triumph's and this is also the reason that Triumph's have a over heating problem . I found that a model 99 runs better timed at 31.1/2 degrees instead of 32 degrees. The 650 will run nice at 32 degrees as it as a longer stroke than the model 99 And As for colour tuning my Great uncle Freddie Dixon he use to take off the exhaust pipes and run the bike on the bench to see the colours of the exhaust flames he could tell if the engine was running right by this, and tune the carburettors or change spark plugs so he get the right mixture . yours anna j

Previously phil_hannam wrote:

I don't need to go Green to know what works best on my bikes.

Below is hot off the NOC Spares Scheme pages for twins. I could not find any other make of plug for sale.........and I would have thought that they are a good authority.

SS02 C2_B8ES

Spark plug - NGK Twin Carb & SSNew £ 2.00Members OnlySS02 C2_HW/OSKOil seal kit - Heavyweight Twins engine and gearboxNew £ 6.50Members OnlySS02 C2_B7ESSpark plug - NGK Single carb TwinsNew £ 2.00Members OnlySS02 C2_B6ESSpark plug - NGK 650/750 1966 onNew £ 2.00Members OnlySS02 C2_B5HSSpark plug - NGK Cast iron head TwinsNew £ 2.00Members Only

Hello the most favorable spark plugs that Norton found was KLG FE100 3 point electrodes And Now the Modern equivalent is Bosch W7DTC And its works very well price £2.50p to anyone via Green spark-plug .co I have tried and tested these plugs so I do know there good plugs and do not over heat the engine they run cleaner too as there self shielding, you do not get this with NGK witch are made in Japan so you think but a lot are made in china , Bosch are made in the EU many Germany. Over heating is many down to lean fuel mixture and over advanced timing IE see Triumph engine run over advanced thats why you see the exhaust pipe blue on Triumph's and this is also the reason that Triumph's have a over heating problem . I found that a model 99 runs better timed at 31.1/2 degrees instead of 32 degrees. The 650 will run nice at 32 degrees as it as a longer stroke than the model 99 And As for colour tuning my Great uncle Freddie Dixon he use to take off the exhaust pipes and run the bike on the bench to see the colours of the exhaust flames he could tell if the engine was running right by this, and tune the carburettors or change spark plugs so he get the right mixture . yours anna j

Hello Update On Spark plugs Now at Green Spark plugs co Bosch W6DTC and W7DTC are £1.75 and NGK B7NT triple electrode .£2.90

then there is Champion N9BYC triple electrode the Triple Electrode plug give you easy starting cleaner exhaust and better running reliability, good fuel economy, And more suited to Ethanol in the fuels as new cars and motorcycles are now using this type of spark plug . and there self shelfing this is the benefit of this type of spark plug all you need to do is try them out. and see for your selfs . see Green spark plug co Tim Green will give you all the information you need on Spark plugs and he dose all items in the ignition side of your motorcycle as well as bulbs too ,also take a good look at his web page, for other items , Yours Anna J Dixon

I don't need to go Green to know what works best on my bikes.

Below is hot off the NOC Spares Scheme pages for twins. I could not find any other make of plug for sale.........and I would have thought that they are a good authority.

SS02 C2_B8ES

Spark plug - NGK Twin Carb & SSNew £ 2.00Members OnlySS02 C2_HW/OSKOil seal kit - Heavyweight Twins engine and gearboxNew £ 6.50Members OnlySS02 C2_B7ESSpark plug - NGK Single carb TwinsNew £ 2.00Members OnlySS02 C2_B6ESSpark plug - NGK 650/750 1966 onNew £ 2.00Members OnlySS02 C2_B5HSSpark plug - NGK Cast iron head TwinsNew £ 2.00Members Only

Hello Tim Green is a Ignition specialist and is backed by the VMCC. and FBHVC as well.! The Norton owners club spare part department only sells a very limited stock of spark plug there not Specialists in ignition parts yours Anna j Dixon

31 1/2 degrees BTDC. Golly gosh. Personally I think 31 degrees is more suitable. Perhaps we should compromise at 31 1/4 degrees. Better check my timing. Fetch me a fag paper, the old one has worn out.

Seriously I had a similar problem with a bike with a pre monobloc. It started fine and when opened up it had no power and bogged down, it was gutless and jerky just like it was missing. I found I had the wrong slide number fitted and that was causing the engine to choke by not getting enough air. Playing with the choke lever made no difference which is a good indication that it's not lean.

i filed out the slide to go from a /3 to a /4 which is a 1/16 inch if I remember correctly. Worked a treat so I recommend to check you have the correct slide. Mine started fine every time but as I say bogged down and bucked when trying to accelerate. I also changed the needles and pilot jets as they were worn as part of the process but it was the slide.

Could also be your slide carb is worn, borrow a carb off another bike and try that, could save you a lot of time.

Mark

Sorry one other thing, when all this was going on the bike ran fine then started missing. My theory is the ethanol fuel ( because running rich) was killing the spark plugs I changed for new and didn't miss for a while until I knackered the plugs again, (about 50 miles). Cleaning the plugs does not work they are scrap so I don't think they like rich running as designed for F inj.

I use champ N 5's and since I corrected the slide I have not scrapped any more plugs.

Markk

Sorry one other thing, when all this was going on the bike ran fine then started missing. My theory is the ethanol fuel ( because running rich) was killing the spark plugs I changed for new and didn't miss for a while until I knackered the plugs again, (about 50 miles). Cleaning the plugs does not work they are scrap so I don't think they like rich running as designed for F inj.

I use champ N 5's and since I corrected the slide I have not scrapped any more plugs.

Markk

Have you tried Bosch W7DTC are about the same as N5 Champion Heat range there more suited to Ethanol they work fine in my bikes 1954 Dominator and 1960 650 manxman yours Anna J

A good point here - yes - I have experience with Colortune; it's so precious I keep it indoors in a cupboard. It has served me well with bikes and cars, including my lovely Jaguars (Many more cars than bikes - sorry guys!). When you are trying to sort out a 4.2 litre engine with three carbs it is worth its weight in gold! Mind you, after a while I was able to tune them by ear - just listen to the intake hisses.

Two main things strike me here. 1) starting cold with no choke implies that it's running too rich. 2) Have you checked the points gap for BOTH cylinders?

Re: Champion plugs; I thought the higher number (say N4) was a 'colder' plug for sustained fast running? e.g. motorway. In other words a 'hard' plug more able to sustain hot/fast running.

Cheers, Lionel

Previously tom_mcewen wrote:

I have just had a similar problem with my Dommi 99. The new pipes got blued, left more than right, a misfire developed, and the engine slowed eventually. I have a concentric carb which I'd just reconditioned with a Burlen kit. Examination of the replacement needle showed it to be five thou oversize throughout its length, so I replaced all the old bits and the bike is OK now. Your description sounds like lean mixture, which combined with modern fuel will cause gross overheating. Dous anyone have experience of the Colourtune plug?