Carburettor settings vs modern fuels in classic motorcycles.

[@michaelpopelka1483]

I needed this info in 1967😄

[@mv4ago]

Another great video Paul👍. I'd never run an old bike on E10, it's worth finding your nearest garage with E5 and filling up a few jerry cans with it. I run my bikes on a 50/50 mixture of Avgas and E5.

[@peterhodes6708]

Try Shell E5 or Esso E5, they,re 99 octane , other brands are 97 . I use petrol stabiliser as well. No fuelling probs for my old strokers!!😃

[@iandaniels8386]

E10 rots petrol lines on old bikes i use super unleaded bit more better long run sadly less and less sell it

[@peterhodes6708]

true. A friend of mine fitted an in-line filter (made of plastic) within a year he experienced a blockage, turned out it was plastic from the filter!🙃 (Yes , he was using E10!

[@daniellyne9420]

Very interesting! I have an Indian built bullet 500 which has a PWK carb that someone put on it prior to my ownership, tweaking jets has been very interesting to say the least.it does run very well now, although it still blackens plugs slowly over time!

[@johnwilcox4078]

Thank you for pointing out that the needle jet is a wear item. The original needle jets on my T140V were worn and causing noticeable mid-range acceleration problems at 6000 miles. The holes were clearly oval shaped from the needle vibrating in there, resulting in an over- rich mixture. At about the same amount of miles, the slides on all Amal carbs (except the new Premiers) wear to the point that it causes a seriously annoying stumble just off idle due to air leaking past and causing a lean mix. When both these conditions exist at the same time, a lot of cussing takes place until things get repaired! Also, here in Wisconsin, we are lucky to have non-ethanol gas readily available in 87,89, and 91 octane. I use 87 non-ethanol with Seafoam gas treatment for all my bikes, no troubles.

[@teej710]

As usual an interesting topic. Unfortunately, I've found that the vast majority of people, have very little understanding of how a carburettor works. As a consequence, they only modify the main jet, to resolve any fuelling issues. The main jet only comes into play fully, when the throttle is held wide open. Otherwise, it's usually a combination of pilot, needle and main jets, which determine the correct air/fuel ratio, at other throttle positions Most people potter around at quarter to half throttle, so the main jet has very little influence on the fuelling. Therefore, many bikes continue to run lean at these throttle positions, even though a larger main jet has been fitted. Unless the engine is under load, then pinking may not be so obvious and the modern fuels don't work well for spotting fuelling issues, via the spark plug colour. More attention should be paid to the pilot and needle jets, as well as the air screw setting and not just the main jet.

[@paulhenshaw4514]

Thanks, I concur.

[@philhawley1219]

Don't forget about the slide cutaway.

[@teej710]

@philhawley1219 agreed the slide cutway can have an affect on the mixture, as can the float height. However, if these are the factory specification, for that particular carburettor, then these shouldn't really need any alteration, unless a poor idle or pickup is experienced, after all avenues have been exhausted. In my experience, poor low speed running and response, will be an air leak, a blocked airway, blocked or incorrect pilot/needle jets. Tuning carbs is a science and without the use of AFR meter, can be very difficult to get right easily. However, by starting with the originally intended carburettor and jets for the make/model of motorbike, then trial and error will get you somewhere near. It's always safer to start rich and lean off, as necessary.

[@norsehall309]

G'day Paul, very interesting 🤔 l put a new Carburettor on my BSA Super Rocket 🚀 with the right settings from the factory and the engine ran lean and the plugs where white, had to move the needle from central notch to next notch down, now plugs are perfect, thanks for this video, cheers mate, Neil 🤠.

[@neilmcintosh1200]

'Back in the day' there were 2 obsessions which required alterations to carb settings. One was higher comp pistons and high lift/different duration and overlap cam timing. The other was noise: An open pipe made them run rich. A mega made for weakness. Goldie pattern were the most severe for weakness as far as I could make out. All meggas were used with reverse cones or 'tulips', as the racket from an open mega was just too much like inviting trouble.

[@gregcampbell8888]

Great video Paul. I had many travails sorting out the jetting on the non-standard 36mm Concentric fitted to my DBD34 (cue the chorus of « you should have gone back to the GP »!) Suffice it to say I had to change every jet plus the slide cutaway to get it right. One thing I learned was not to trust the number stamped on needle jets - they can vary by several thou and you need to measure them before installing!

[@cedley1969]

I agree, my W650 was always on the lean side, needed a lot of choke from cold, i increased the main jet from 118 to 125 which helped at the top end but two 2mm shims under the needles transformed the mid range and part throttle response far more.

[@simont1108]

That's a good observation. The petrol now has less octane so jetting up makes sense. I've done plug chops at 30 50 and 70 with Amal carbs and it helps to set the needle which I've always found the hardest part of resetting a carb.

[@mickandpathardy8239]

Oh the mysteries of carburation! Very well discussed & explained Paul. Thank you.

[@hermangibbs8163]

Thanks Paul.

[@garryhorton9105]

Valuable knowledge to know thanks Paul 👍🏻

[@grantbaker3336]

Hi Paul, It would make perfect sense to have to lift the needle or increase the size of the needle jet if it is found a larger main jet is necessary. I think one of the issues with modern day petrol is the ethanol contents propensity to absorb water this in itself will lead to a weakening of the mixture. I fully agree with you on not messing about with ignition timings, in my past life when I was building and modifying engines timing was always the first thing to be set and always and only on very rare occasions the very last thing to be adjusted.

[@joetocchio9666]

Very interesting. Thanks

[@MrFigFisher]

Top class information there paul.

[@twostroke350]

Trouble is the fuel quality is very variable. My 612 bullet can go from running like a dream to pinking badly between fill-ups. Doesn't seem to be any real consistency between normal and super too, it'll run well or pink on either from one tank to another depending on where I filled up and apparently wind direction. If it was consitant, I'd set it up to run well on what I can get but no, I spend ages getting it all set up, then get a tank of "bad" fuel and spend the next 150 miles nursing the throttle.

[@bsa_brummie7775]

Interesting results, thanks for sharing 👍

[@barryjones5194]

Hi Paul when I was racing grass track bsa bike running on methanol we had to increase the main jet drastically now using E10 fuel (Ethanol similar to methanol) the mixture has to be increased in my opinion way to go !!

[@bobrogers7004]

I always found a colourtune plug useful as you can see whats happening.

[@alexbowey2760]

My Cub run's a 140 main jet on my mikuni vm22, works fine

[@williamnethercott4364]

An excellent addition to your technical files, very informative, thanks for posting! Carburettor woes with my previous bike did not respond to my uninformed fiddling with jets and slides, mainly because the carburettors I was using were clapped out and the only replacement parts I could get in those days were not made accurately enough. My current bike (AJS) is jetted by the book, although it uses a Wassell "concentric" rather than an Amal Monobloc but I've learnt two key things about it. The first is that I was underestimating the time it takes for the engine to warm up thoroughly (it takes about 5 miles minimum), The second is that it runs/starts much better on BP E5 than it did on BP E10. I think I have the carburettor about right now but I want to look at the auto advance/retard soon.

[@RD-650]

Nice one paul 👍

[@paulhenshaw4514]

Thanks 👍

[@shug831]

This was built at the time of good old 4 ⭐. Modern fuel injection systems can compensate to a point for fuel differences.

[@peterturnham5134]

Hi Paul, are you using a lead substitute (liquid) or the lead tablets you drop in the fuel tank? This may increase octain. If you have just replaced valve seats and are using lead free fuel mixture could be affected. All my tuning/jetting/timing work was on 750 Nortons back in the 1970s. They were all high compression, high lift cams, flowed. Ignition was backed 2° and the books all said up the jetting but the 750 allways ran best on completely stock concentric settings.

[@paulhenshaw4514]

Hi Peter, I never use any additives or potions and have never had any problems, and all the valves and seats in my machines are as original and they have all been fine.

[@MONTY-YTNOM]

I do miss my Tiger Cub

[@dogpaw775]

no mention of slide cutaways, a motor is run much more in the range where the cutaway has more influence not at full chat where the main jet comes into play, thoughts?.

[@paulhenshaw4514]

Agreed, but the problem on this Cub was nearer full throttle, when pulling hard and the raised needle and much larger main jet fixed it completely.

[@bobtidy7164]

Hi Paul, I was just wondering what slide this buke das compared to yours, very good and useful video thank you

[@paulhenshaw4514]

Thanks, this one has a 3.5 cutaway, the trials Cub will be either the same, or a 3, from memory.

[@750triton]

Do you set ignition timing with a some sort of rod through the spark plug hole? I ask because a high topped piston would on the mark before a lower CR piston, so timing would be advanced. Correct?

[@paulhenshaw4514]

I often set the timing using a measuring tool through the plug hole, but a domed piston will still give readings btdc just the same as a flat one - after finding tdc, going back by a given amount would give the full advance timing, just the same.

[@750triton]

@@paulhenshaw4514 😁I was playing devils advocate there Paul. Sorry.

[@paulhenshaw4514]

Careful - you might bring out a whole army of armchair experts doing that!

[@750triton]

@@paulhenshaw4514 🤣

[@marshalmercer594]

In 1964, my T20-S used a 140 main jet in its Monoblock carb. It had a wide-lobed cam, with greater duration than either my T20-Cs or T20s. The 9.5 compression ratio piston required at least 95 octane, leaded fuel. Are the owner's valves hard-faced, to resist wear from unleaded fuel?

[@paulhenshaw4514]

Hi - I have no idea about the valves or seats in that Cub, but none of my own machines have 'unleaded' valve seats. I have always thought it to be a big con.

[@nickaxe771]

Apart from carbs....I found my old BSA needs slightly retarding with the ignition timing. My engine just felt harsh with ethanol all it took was 1 deg.

[@TornadoCAN99]

On my 500cc Velocette MSS with a Amal Premier 928 concentric, I find it runs fine except at wide open throttle....where there is a noticeable drop/bog down in power. According to the Amal carb guide booklet, that is a sign of too lean a main jet, so I changed it from the 220 in there to a 280. Still had the bogging at WOT and later found the plug fouling more. Should I try a main jet smaller/leaner than the 220 or something else?

[@paulhenshaw4514]

Perhaps your exhaust and / or air filter are too restrictive?

[@TornadoCAN99]

@@paulhenshaw4514 Actually, intake is a velocity stack with a wire screen flame arrestor. Bike does have a stock oem metal mesh type filter box I may try re-fitting. Exhaust is the stock fishtail used on all the post war Velocettes.

[@paulhenshaw4514]

Ah - those gauzes on the bellmouths are actually quite restrictive - that could well be your problem!

[@cbrider726]

Hi Paul . Now thats food for thought . Great thinking Paul. I have been having problems starting my 350 Bullet . The engine was fully rebuilt . The carb was replaced in India so i am going to try to get another carb and give it a try . Do you have the correct carb in stock?? Great stream 👍👍👍

[@paulhenshaw4514]

Hi, and thanks. Sorry, but I doubt I would have a carb, but they are probably easy to find on the internet, I would think.

[@cbrider726]

@@paulhenshaw4514 Thanks for getting back to me 👍👍👍

[@adammedyna2365]

Very interesting observation Paul, why not to try 106 needle jet on this engine?

[@paulhenshaw4514]

Thanks, it seems happy with the needle raised and the 140 main jet to be honest.

[@callmeanythingbutlatefordinner]

The internal parts, materials, fuel-air delivery systems, and ignition and inlet- exhaust timing controls in modern bikes are designed to compensate for gasohol and other lower grade fuels. I NEVER use gasohol, or any alcohol blend, in my old Bullet 350. Only a pure 95 octane benzine-gasoline blend. That's what these old bikes were designed to run on.

[@AmitUP-tp2kw]

How to increase the performance of bullet 350 year 2008 indian made. I am not about heavy modification to the engine.

[@rogerlishman2532]

An interesting discussion Paul. Since the removal of tetraethyl lead, I don't think we have replicated its excellent anti-knock qualities. I've read that the addition of ethanol has raised the octane rating, and some other chemical has also been added to help. I've noticed that modern motorcycles tend to have shorter strokes and higher RPM, which help to prevent knock. Would the slightly longer stroke of the Cub need a richer mixture to prevent the onset of detonation, compared to the 50-55 mm stroke of a Japanese superbike, taking into account modern fuels?

[@paulhenshaw4514]

Hi Roger, the Tiger Cub is not really very long stroke at all, being 'square' at 63 x 64 mm.

[@69woodburner]

I suspect it has something to do with ethanol in modern fuel. It carries oxygen along with the carbon and hydrogen, so it will make a difference to the required mixture.

[@allenjames515]

Pinking does tend to increase at very weak mixture but that is rare on old English motorbikes. BSA were usually the ones with light grey exhaust after fully hot running. Cars with SU often produced grey exhaust, that was using leaded petrol, unleaded won't replicate it. Pinking is always worse at low rpm and open throttle, so can be minimised by lower gear and greater inlet vacuum. Now "Modern petrol". Throughout the last 100 years the stuff varied, from different wells and additives. Shell and The Distillers Company sold Cleveland Discol for 40 years, no lead. Distillers provided ethyl alcohol. It was used in everything just as the leaded petrol or Benzole Mixture was. No magazine fussed about it. Unleaded petrol often has butane as octane number improver, it boils at 4 degrees C, so if left vented will disappear to atmosphere, after which pinking is more likely. Cars put tanks underneath, cool and no sunshine. Bike tanks shroud hot engine and receive sun. The shape of combustion chamber matters and high compression from short strokes is difficult but careful design helps - i have two Guzzis, the softer pinks worse than the faster, larger over square version. I dont think flooding a poor combustion chamber with petrol is the best solution. If it were mine i would use a flatter top piston.

[@paulhenshaw4514]

I am not flooding it with petrol, merely using the jet size Triumph specified for the high compression piston.

[@allenjames515]

Case 1: level road, 30mph, 2% open throttle, sweet running top gear. Case 2: uphill 1 in 15, 30mph, 20% open throttle, pinking, top gear. Case 3: as case 2 but this time 3rd gear and 30% open throttle, no pinking. Why? Nothing to do with main jet. The higher speed and heavier inlet charge carries more energy and turbulence in combustion chamber, where flame front moves rapidly to consume all petrol in shorter time during which unburned mixture failed to explode. Case 2 pinking not too destructive because not huge quantities of exploding fuel but if it had been at full throttle and best torque speed it probably would have been, to minimise that the rich mixture. But that is not a good method. Better octane rating or more turbulence in compressed mixture is wanted, so squish areas usual in water cooled cars. Triumph not very good. The high domed head worked well with flat piston crown in long stroke Riley from which copied. See also Jaguar 2.4 or Chrysler hemi. Both of which demonstrated the disadvantages of short strokes and big domes.

[@PeterTaylor-p4s]

Hiya Paul I take it you use E5 fuel ?

[@paulhenshaw4514]

The stuff I use from down the road is labelled as E10.

[@PeterTaylor-p4s]

@paulhenshaw4514 umm interesting

[@michaelking7499]

Thanks for the information, my T140 was pinking a bit under load last year, so I retarded the ignition a bit, but I think I will raise the needles as well now 👍

[@daveco1270]

Is pinking a chirping sound...or is like someone's tapping on the engine with a wrench or something? I'm not sure I've heard it before, and I haven't found a good written description of it. .

[@michaelking7499]

Yes it’s definitely sounds like a light rapid tapping sound 👍

[@DrRobert7898]

Back in the 60s you could get 100 octane fuel quite easily, this E5 and E10 is terrible