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Spark plug colour

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Hi advice welcomed Here is the situation. 72 750 fettling to get back on the road.

1) Carbs replaced with new Amal 932s. Plrobem of intermittent misfire when cold and occasionally when accelerating from 2000 to 4000 rpm (seems ok over that but I dont ussually hold it at that for long)

2) Repalced the Champion N7YC with N6YC. Took four kicks not the usual one t or two to start. Same misfire symptoms as above. No difference really.

Checked plugs after a 20 minute run up and down the rev range. New plug's N6YC electrodes are now white Pic1. N7YC that were in the bike when bought a month ago Pic2

It seems that I am now running a weak mixture even though no changes have been made to the carbs. Any thoughts? Thanks Nick

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Nick,

I would put my money on carb your settings. You can phone or e mail Amal , with your engine spec and they will tell you exactly what needles, jets and slide you need for your engine. Apart from that I have used NGKs for decades and have never had a problem. Try BP7ES.

CheersHT

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As I understand the post he hasn't changed the carb settings just the plug temp? His last sentence refers? But a call to Amal wouldn't hurt!

Dan

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Hi Guys thanks for your suggestions. Just to be clear the only change has been the change of plugs from N7 to N6. Carbs have not been altered from when they came out of the box except when I have adjusted the pilot screw while sorting out tickover. (1 1/2 turns out from stop) The carbs are standard Amal concentric 932 from a trusted source, FDs in Great Dunmow. I will take up the advice to call Amal. Cheers N

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Perhaps your motor runs a bit hotter than usual and needs the cooler plug. Do your barrels have a powdercoat finish?.Have you changed to a fuel with eth from a non eth fuel. ?.

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The first paragraph, of this thread might provide a clue. "Carbs replaced with new Amal 932's" . It would appear that the problem started from this point, further, it was started that the carbs "have not been altered since they came out of the box". Presumably, therefore, no check has been made to find what size jets are actually fitted (white plugs being a symptom of weak mixture). Hans' advice, to check with Amal, is the best starting point. Changing the heat range of the plugs is no cure for incorrect fuel mixture.

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John Shorter plus 1, look at your old carbs and compare the jetting and needle position to your new carbs, bet you will find either a bigger main jet and/or a higher needle position. Even if the needle position is the same the old needle jet being worn would be running richer.

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Think a little more clarity would help. Did you change the carbs between changing the plugs. ?.Because if you did not (as you seem to say) then why would the the mixture change all by itself.

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Hi sorry if I am not being clear, this is the situation

1) I changed the carbs because the originals were worn and had bits of fibreglass sludge and tank liner. Of the old carbs it turned out that one had a main jet of 220 the other 230

2) The new carbs have 230 jets. I have run the bike succesfully with the N7 plugs for a few weeks up to 10 miles or so, but with the same intermittent occasional misfire when cold and in the 2-4K rev range

3) The only thing I did was to change the plugs from N7 to N6. I had the same misfire issues (intermittent etc), and just thought I would have a look at the plugs. They are absolutely white at the electrode. The old plug N7 has an OK looking tan colour electrode which seems OK.

I am genuinely confused as no adjustments were made to the carbs but I seem (according to the plugs) to have a very weak mixture. So Robert is right why would anything change so drastically all on its own? N

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That is the puzzle. I would not have expected a change of plug grade 7 to 6 to cause such a big change. Perhaps you are now running harder or looking at a different part of the throttle range as well.Certainly does not look healthy.Perhaps you have a flow problem and its just a coincidence,check fuel cap and tap filters A change of.fuel grade makes a big difference on one of my bikes . Its not very unusual to have different jet sizes on a twin.Look for bits of swarf in the carbs,used to happen in the past.

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I had a similar experience last year with a new pair of Amals 932 (not premiers) for my mk3 850 - set them up exactly as the old ones but the bike ran poorly - I checked all the jets and channels - eventually took them off and put the the new slides and float bowl assemblies back on the old carbs and put them back on - it ran as sweet as a nut (and still like that after 3K miles) - can only assume there was a bad batch of Amal castings.

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Just to make it clear,It was running reasonably but with a bit of missfire and the plugs looked a fair colour. A change of plugs (and nothing else) and we have some very omminous looking plugs.

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Hi Robert that is it in a nutshell. Is there any other reason for this plug colour you can think of? It has me flummoxed.

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I hadput new Amals on my commando, whenI got a misfire some time later, a strip down of the carbsI found the main jets were loose. It might the same in your case.

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This is one of the reasons I love these old fossils, I can toss and turn half the night worrying about health,finance,family etc ,OR I can immerse my brain in some Norton minutia and fall asleep safe with the thought that it does not really matter a jot and a solution will turn up sometime.

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Too right Robert! One good fossil deserves anothe I guess. There has to be a logical explanation or is it just a voodoo bike messing with my head?

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Think of it as a sort of therapy in a world where everything modern is too complicated to fix and costs a fortune for some half trained berk to practise at your expense.

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Sorry to return to earth. Try raising the needles a notch. The old needle jets were probably worn and would give a richer mixture than new, unworn ones. I swear by NGK B7ES plugs - not had much luck with Champion the wonder plug.

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Hi Gordon turns out my local Halfords has the NGK plugs will get a pair tomorrow. Also I will check the carbs and try raising the needles one notch and checking the jets. Does anyone know offhand if the Amal Premier pilot jet fits straight into a 932?

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The pilot jets are different in design but function the same way, an old pre premier 25 pilot jet is the same size as a new premier 17 jet, the 25 was a flow measurement, 17 is the size in thou and as you use a 16 thou drill to clean out a old 25 jet it means 25 = 17. Simples NOT

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Thanks John I am beginning to regret not waiting to get a couple of the Premier Amals but I was impatient to get going and thought better the devil you know.

I guess from the response to this conundrum none of us have come across this situation before. This means that we have cracked it we can definetly claim to have added to the sum of human knowledge..........

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I understood your post! ..... Before you alter any carb settings I would do the simple things first, I'd clean the old plugs and put them back in, run the bike see what the colour is, if it's black again you know the only thing is the different is the plug, you could then try the NGKs or a new set of champion N7YCs and see how they look. remember it's not the tip of the electrodes that indicates richness/weakness it's the colour around the edge of the plug and in the well which shows the colour of the burn. Don't confuse plug heat with mixture. There's loads of info about reading a plug if you google it. For what it's worth I doubt a misfire is a mixture or plug heat issue, lean engines hunt and rich ones go blubbery but in my experience don't misfire, unless they get super hot. I'd check plug caps, leads coils etc while I was at it.

Personally I,d go with the recommended plugs, I prefer NGK too, and then look at the jetting to get the colour right if . I would also look at adjusting the needle as that is where you will be riding most of the time unless you are fond of WOT! The main jet only really comes to play on the last 1/4 throttle opening.

What is weird in this case is the change from black to white with one plug changer hotter, one change usually results in a100c temp rise, yours looks much more than that.

Ps I don't own a commando so all of the above can be disregarded if you like!

Cheers dan

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Previously Dan Field wrote:

I understood your post! ..... Before you alter any carb settings I would do the simple things first, I'd clean the old plugs and put them back in, run the bike see what the colour is, if it's black again you know the only thing is the different is the plug, you could then try the NGKs or a new set of champion N7YCs and see how they look. remember it's not the tip of the electrodes that indicates richness/weakness it's the colour around the edge of the plug and in the well which shows the colour of the burn. Don't confuse plug heat with mixture. There's loads of info about reading a plug if you google it. For what it's worth I doubt a misfire is a mixture or plug heat issue, lean engines hunt and rich ones go blubbery but in my experience don't misfire, unless they get super hot. I'd check plug caps, leads coils etc while I was at it.

Personally I,d go with the recommended plugs, I prefer NGK too, and then look at the jetting to get the colour right if . I would also look at adjusting the needle as that is where you will be riding most of the time unless you are fond of WOT! The main jet only really comes to play on the last 1/4 throttle opening.

What is weird in this case is the change from black to white with one plug changer hotter, one change usually results in a100c temp rise, yours looks much more than that.

Ps I don't own a commando so all of the above can be disregarded if you like!

Cheers dan

If you check Champion charts lower number plugs are cold, this is the reverse of NGK plugs.

If the bike is running hotter with the N6Y I would suspect a bad plug. There are a lot of bad plugs being sold, possibly not manufactured by the name on them. I would only by plugs from a reputable dealer.

I sorted my neighbours missfiring Triumph Trident, out of six new Champion labeled plugs only one worked properly. I replaced the plugs with three Champion plugs obtained from The Green Spark Plug company. That was over a year ago and my neighbour has had no more problems and says the bike is running the best it ever has.

The plugs did however cost twice as much as the failing ones he got of a stall.

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Previously nick_ohare wrote:

Hi advice welcomed Here is the situation. 72 750 fettling to get back on the road.

1) Carbs replaced with new Amal 932s. Plrobem of intermittent misfire when cold and occasionally when accelerating from 2000 to 4000 rpm (seems ok over that but I dont ussually hold it at that for long)

2) Repalced the Champion N7YC with N6YC. Took four kicks not the usual one t or two to start. Same misfire symptoms as above. No difference really.

Checked plugs after a 20 minute run up and down the rev range. New plug's N6YC electrodes are now white Pic1. N7YC that were in the bike when bought a month ago Pic2

It seems that I am now running a weak mixture even though no changes have been made to the carbs. Any thoughts? Thanks Nick

Well Having read the nonsens your carburettor are fine, and are the right ones of the machine Now hear this its the fuel thats Changed and owners are going buy old information on things like Spark plugs were the Fuel has now E5 in it you need better spark plugs that are suited to E10 fuels like Bosch W6DTC I run my Norton Manxman 650 on W7DTC there mid range heat are as W6DTC are a bit cooler running for twin carb set up, so look some farther in to the Bosch range of spark plugs I have found there very good , only try them out , and see, More information At Tim Green spark plugs Co yours Anna J

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The reason I asked, at the beginning of your thread, about the source of the carbs is that I have had two instances of "new" carbs supplied by a dealer that I've struggled to get working properly. To the extent that both owners have gone down the single Mikuni route. If the carbs came in a Amal box with the jet sizes marked inside the box lid then they are probably the genuine article, otherwise you take your chance. I spent considerable time and effort swapping out carb components to try and get "new" carbs working properly and finally went down the Homer Simpson route, if at first you don't succeed, give up.

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"Having read the nonsens your carburettor are fine"

Well, that's the problem solved then. Just ignore every other suggestion. Don't know why the rest of us bother. Meanwhile, should you try NGKs and raising the needles a notch despite it being nonsense, I would quite like to know if it makes a difference. Transformed my Velo, which has rewarded my efforts by developing a leak in the petrol tank. Sigh.

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Anna I think you are missing the detail, in this case all said he changed was the plugs, - same fuel and same carbs. While what you say about fuel is correct I doubt it would cause a misfire. I Can't comment on Bosch plugs I always use NGK.

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Has no one bothered to read all the original post?

1. Carbs were replaced as part of the restoration.

2. There was a problem with miss-fireing.

3. Plugs were charged, as an attempted cure (didn't work!

Go back to basics. Using recommended plugs, check out carbs first, then ignition, a grade, or two, either way should make very little difference to performance.

No mention has been made, regarding performance (or lack of) prior to restoration. Have any adjustments, or alterations, been made to the ignition system? Retarded ignition will also cause overheating, and white plugs.

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Previously John Shorter wrote:

Has no one bothered to read all the original post?

1. Carbs were replaced as part of the restoration.

2. There was a problem with miss-fireing.

3. Plugs were charged, as an attempted cure (didn't work!

Go back to basics. Using recommended plugs, check out carbs first, then ignition, a grade, or two, either way should make very little difference to performance.

No mention has been made, regarding performance (or lack of) prior to restoration. Have any adjustments, or alterations, been made to the ignition system? Retarded ignition will also cause overheating, and white plugs.

I agree go back to new standard plugs and start from there.

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The proof is usually in the pudding..........or in my case road testing. I fitted a new single Amal Premier 32 Concentric to my 750 Commando in March of this year. I have now done over 1000 miles including the Irish International last week. I got it from Surrey M/Cs because Amal informed me they had a 6 week waiting list and also could not give me any info regarding a single carb set-up. The main jet was a 220. I was concerned that this was a bit low in view of running a Mercury with a 930 and 260 main. I was assured that this would be ok as the new carb was manufactured much better. However, an obvious alck of oomph and a plug check led to a 240 main jet plus K&N cone filter. This resulted in a light brown plug colour and 55 mpg at 70 mph.

I got a miss-fire while riding across Wales in the very heavy rain. Wet electrics being the cause. A clean up around all the major connections sorted this and I was able to paddle home.

I use either NGK BP7ES or Champion N7Y plugs with a Pazon. All ok. As the original posting mentioned a miss-fire in a specific rev range then I would recommend checking the parts of the carbs that cover that. I would also be checking the whole wiring loom for a wire shorting out on the frame.

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Previously Phil Hannam wrote:

The proof is usually in the pudding..........or in my case road testing. I fitted a new single Amal Premier 32 Concentric to my 750 Commando in March of this year. I have now done over 1000 miles including the Irish International last week. I got it from Surrey M/Cs because Amal informed me they had a 6 week waiting list and also could not give me any info regarding a single carb set-up. The main jet was a 220. I was concerned that this was a bit low in view of running a Mercury with a 930 and 260 main. I was assured that this would be ok as the new carb was manufactured much better. However, an obvious alck of oomph and a plug check led to a 240 main jet plus K&N cone filter. This resulted in a light brown plug colour and 55 mpg at 70 mph.

I got a miss-fire while riding across Wales in the very heavy rain. Wet electrics being the cause. A clean up around all the major connections sorted this and I was able to paddle home.

I use either NGK BP7ES or Champion N7Y plugs with a Pazon. All ok. As the original posting mentioned a miss-fire in a specific rev range then I would recommend checking the parts of the carbs that cover that. I would also be checking the whole wiring loom for a wire shorting out on the frame.

Hello Your all using the wrong type of spark plugs for E5 fuels Bosch are better than Nkg or any other make they where the first too make spark plugs anyway , there Three point Plug give a direcet spark to the fuel and are And shelded type of spark plug this mean it shelded from Fouling and glasing in the procilin witch then make a earth so the half the spark runs to gound under perssure, relsuiling in a miss fire, you need something like FR7DTC Check out the Bosch range but the heat range is from 6 to 7 on the chart find out more at www.boschsparkplugs.com yours anna j

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Hi All, first thank you for all of your input on this mystery.

FYI, Fuel BP Ultimate - 0 ethanol: Boyer Electronic Ignition: PW3 cam

Here is what I did:

1) Cleaned and replaced the Champion N7s (Halfords only had one NGK in stock ....)

2) Started OK but the same misfire when cold, more of a stutter as I go up the revs between 2000 to 3500. It seems as though it is about half throttle. Rode up and down the rev range until it cleared up and engine was warmed up. Pulled the plugs. Black around the outer ring, tan inner electrode, metal electrode lighter see pic1

3) Plugs back in went for about a five mile run up and down the rev range, now no misfire pulling cleanly up to 4500, slow running fine. Pulled plugs again and looked the same pic2

The issue of mixture seems to have been resolved by changing back to the old plugs

The misfire until properly warmed up seems to be at a particular throttle opening going past the 2000 and stopping misfire at 3500.

Unfortunately domestic duties precluded dealing with the needle or checking the other jets. I suspect it is a carb issue given the relationship to throttle opening? Any suggestions happily taken on board. Cheers Nick

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Dirty enough to cause a missfire and foul up your oil . You could take the bike in for a dyno run to check emissions at various throttle positions.Its also possible for an intermitent ignition fault to produce the same effect.In my case a dud distributor cap did this.

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Previously nick_ohare wrote:

Hi All, first thank you for all of your input on this mystery.

FYI, Fuel BP Ultimate - 0 ethanol: Boyer Electronic Ignition: PW3 cam

Here is what I did:

1) Cleaned and replaced the Champion N7s (Halfords only had one NGK in stock ....)

2) Started OK but the same misfire when cold, more of a stutter as I go up the revs between 2000 to 3500. It seems as though it is about half throttle. Rode up and down the rev range until it cleared up and engine was warmed up. Pulled the plugs. Black around the outer ring, tan inner electrode, metal electrode lighter see pic1

3) Plugs back in went for about a five mile run up and down the rev range, now no misfire pulling cleanly up to 4500, slow running fine. Pulled plugs again and looked the same pic2

The issue of mixture seems to have been resolved by changing back to the old plugs

The misfire until properly warmed up seems to be at a particular throttle opening going past the 2000 and stopping misfire at 3500.

Unfortunately domestic duties precluded dealing with the needle or checking the other jets. I suspect it is a carb issue given the relationship to throttle opening? Any suggestions happily taken on board. Cheers Nick

Hello is Glasing on the plug under pressure, that makes the spark run to gound , and misfire, you realy need to try triple point plugs there shealed from this Glasing of he porciling like in Photo 1

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BarryCarson wrote:"induction air leaks".... did you check? alsocompression levels? are they good and holding when hot? haveyou gotaleaky top end?

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Hi, yes I did check all the induction side, nice and tight. Plenty of compression but not checked numerically (just the right foot meter method)

The change back to N7 plugs has bypassed the white plug syndrome seen on the N6s so mixture seems OK (not perfect perhaps a tad rich now given the colour of the N7s). I did notice that the connectors are not a tight fit on the two coils so whe I have the tank off I will be able to clean the spades and crimp them better. I will need to get new plugs as well. Is it worth paying out for the fancy Iridium type or stick to the copper electrodes? As plugs are only a couple of quid each or so, I might want to do a back to back comparison of Champion, NGK and Bosch. Anyone know what the Bosch equivalent is for the Commando?

Anna's pic of the three extra bits on the plug looks intriguing but you have a 650 rather than a Commando?

Wednesday is a half day off so I will be digging in to this further then.

Cheers N

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Previously nick_ohare wrote:

Hi, yes I did check all the induction side, nice and tight. Plenty of compression but not checked numerically (just the right foot meter method)

The change back to N7 plugs has bypassed the white plug syndrome seen on the N6s so mixture seems OK (not perfect perhaps a tad rich now given the colour of the N7s). I did notice that the connectors are not a tight fit on the two coils so whe I have the tank off I will be able to clean the spades and crimp them better. I will need to get new plugs as well. Is it worth paying out for the fancy Iridium type or stick to the copper electrodes? As plugs are only a couple of quid each or so, I might want to do a back to back comparison of Champion, NGK and Bosch. Anyone know what the Bosch equivalent is for the Commando?

Anna's pic of the three extra bits on the plug looks intriguing but you have a 650 rather than a Commando?

Wednesday is a half day off so I will be digging in to this further then.

Cheers N

Hello well you where looking at one of the first Down draft twin caburettor Cylinder Heads , and was late to be developed for the Commando, Via the Norton Atlas Models there has been something like 5 vertions of this cylinder head made since this Norton manxman one, but with spark plugs you have to take in the atomsferic Compession raitos and air to fuel mixtures to find the right spark plug for your motorcycle engine , do not just go by what the chart data siad from years ago, because the fuel has changed alot since back then the chemical compasition of its makup has changed too the oils that the petrol is made from has a more surger base has most oils are parm oils and alot less in the good old black oil , your parm oil are more hydroshopic and contain sugers this is why you get some residue inside your carburettors when left for some time, and this also coats your spark plug too this is why they end up the fail, now the 3 point plugs are not something new , but the latest reseach have now found there better at handeling this new types of fuel in a better way, and are less prone to get fuel residue on them, that why most car makers have changed over to there manufacture in large numbers, and Bosch being the world leaders in Spark plug have now gone the hole hog , and have a large range of them , to suit all engines, so do try and do some reseach, for better spark plugs , and do not go by old data , yours anna j

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i would put good quality plugs in the best money can buy for the commando model you have and run it down to your local garage and let them run it on there exhaust gas analyser that will be more accurate than looking at spark plug colour and no i don't have a commando i don't have an ice cream van either but i know its function just thought it might help.

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Hi Barry, interesting idea I hadnt thought of. I will see what I have locally, any idea what to look for in the analysis?

Anna, thanks for your input. I have found a good site for plug equivalents

www.sparkplug-crossreference.com

the pain is that I cant find anywhere actually selling them so it will have to be mail order.Cheers all Nick

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Previously nick_ohare wrote:

Hi Barry, interesting idea I hadnt thought of. I will see what I have locally, any idea what to look for in the analysis?

Anna, thanks for your input. I have found a good site for plug equivalents

www.sparkplug-crossreference.com

the pain is that I cant find anywhere actually selling them so it will have to be mail order.Cheers all Nick

basically looking for a happy medium not to rich nor to weak mixture. i suppose the operator of said equipment will have a good idea as to what is an acceptable level either way.

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You need to put some draughting tape round the throttle and mark it up to correspond with the phases of the carbs .that way you can get the operator to take a reading at the tickover,cutaway needle jet and main jet.

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Hi Barry and Robert thanks for that, turns out my local MOT garage has the kit I will se if they will indulge an eccentric old codger in his quest for carburretion perfection. At least I will have some actual data to work with.

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Previously nick_ohare wrote:

Hi Barry and Robert thanks for that, turns out my local MOT garage has the kit I will se if they will indulge an eccentric old codger in his quest for carburretion perfection. At least I will have some actual data to work with.

Hello Nick well I am glad Us old Codgers come handy, have some fun in the Sun , Yours Anna J Dixon

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Isn't it the case that the colour of spark plugs has changed greatly since the removal of lead from petrol? This makes the reading of plugs that much more uncertain.Also modern plugs are alleged to have unglazed porcelain tips because modern fuel management systems keep them much cleaner. So when they do pick up deposits from our old engines they do not self-clean as well as they used to - and are more prone to arcing.Oh - and the inventor is a matter of dispute. Robert Bosch was one - but not the only one. It was (like many inventions) a necessary device whose time had come. The UK provided Oliver Lodge - etc. Bosch seemed to have invented the plug + magneto combination in 1902, but spark plugs were already in use in total loss systems at that time. My 1902 Quadrant doesn't have enough power to drive a mag...but it has a spark plug.
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It's back to the old, unscientific method. RIde the bike at the problem throttle opening. Partly close the choke. If it goes better, you are running too lean. Turn off the petrol. If it goes better just before the engine cuts out, you are running too rich. Simple methods for simple machines.

 

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