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#826111 10/10/20 8:58 am
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Howley Offline OP
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Hi all,

The bike is now registered and I can ride it on the road! I've got a few questions about what I'm seeing and feeling.

Settings were:
276 carb
No 4 throttle cutaway
160 main
New standard needle jet
New needle on position 3
B6HS plug
Unknown pilot air

The bike starts first time with the carb tickled until fuel comes out the top of the float.

The running was a bit heavy and it ended up carbon fouling the plug.
I realised the needle should be on 2,so I set that and attempted to set the pilot air. I ended up 1 3/4 turns out, but:

1. Generally the pilot air setting only seems to make a tiiiny, almost imperceptible difference to idling. Is this normal?

After this initial tune it seems to run a lot sprightlier. Full throttle at lower speeds is OK but:

2. At around 70km/h (40mph) after a few seconds at WOT it starts to miss like its choking, maybe fuel starved? What are causes of this?

After getting it home from probably 10 minutes of riding and 5 minutes of idling the plug was sooty black again. The exhaust is sooty too.

3. Is this caused by rich running or am I not running long and fast enough to warm up the plug?

I tried revving on the stand with the needle at its lowest and the plug was still sooty.

4. Is there something else causing the richness here? I'd doesn't seem to be the needle position.

I suspected that the float height was too high causing richness, but the missing at high speed seems to indicate its too low. From memory if I go any higher the float contacts the tickler and the fuel never stops.,and if I go lower the tickler won't reach the float.

5. Any comments on the influence of float height? What is the standard setting?


The bike came with no cross-drilling on the bottom fitting for the fuel line banjo, so I drilled it myself.

6. Is it possible I need larger cross drilling to improve fuel flow? As it is I'd say there's more cross sectional area in the cross drilling than the fuel line. Is it possible to go too big?

7. From my readings it seems I may need a hotter or longer plug, a bp6hs or b5hs. With modern fuel is this required?

Any advice would be much appreciated. This is my first real dive into tuning these old carbs.

Thanks,

Luke

Last edited by Howley; 10/10/20 9:06 am.
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maybe daft...... but a friend of mine had the same problem when he drives his empire star.....when i do drive his bike i do not have that problem....

Why? I pull the choke lever.... he did not 😉

Just a suggestion, because i do not see anything mentioned regarding choke..../ enrichment

And.... do you use an airfilter?

Last edited by Motolab; 10/10/20 4:59 pm.

Harold / Motolab.nl
BSA: WM20 '40 M21,B31 '54 B33 '55 ZB34GS '49, DBD34GS '58
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Howley Offline OP
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I never use the choke, ie no enrichment.

I'm not using an air filter, just a small bellmouth.

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Never use it, or is it not fitted?

If it is fitted, and you do not use it, it is in use.... you have to pull the lever to disengage the choke..

For a 276 on a M21

Data is:

Size 1 1/16
Slide 6/4 (not 4 that is)
Main 160
Needle pos 2
Needle jet 106

Grade Plug has nothing to do with your problem.....

Is your float leaky? Weight? Correct float needle? Float needle undamaged? Float needle seat?


Harold / Motolab.nl
BSA: WM20 '40 M21,B31 '54 B33 '55 ZB34GS '49, DBD34GS '58
Triumph 5T '49 + T100 + speedkit
Sunbeam S7 '48
Moto Guzzi LeMans '79
BMW R51/3 '51, R100GS '89
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Howley Offline OP
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The choke is fitted and always pulled ie disengaged.

Your data on the throttle slide is different from what I've read elsewhere. My understanding was that 4 is standard for the m21.
http://amalcarb.co.uk/carburettor-for-a-bsa-m21.html
https://www.draganfly.co.uk/index.php/bsa/bsa/category/998-carburetter-and-air-filters

The float is metal and not leaking. The needle and seat are old but seal well. The carb won't overfill even if the fuel is on overnight.
The top of the float needle is a bit right but still seems to retain its setting.

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How's the mag?

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FWIW
I am in Sydney
run BP5 HS plugs for general running around , that would be a ride of 100 Km or less.
On longer rides like the 450 km Walla Walla to Newsted for the All British I run the colder BP6HS

If I run anything else then I have to starve the engine off because if not the plugs will foul then not firing and it will be a bugger to start

As for the pilot air screw ,the maximum you should be able to move it without causing the engine to stall is 1 turn, or 1/2 turn each way if you preffer .
SO your pilot passage ways are not clean or you have the slide stop up too high & you are idleing on the cut away and not the pilot passagways .
BEcayse the cylinder is so squat on he M series bikes they are prone to boiling he fuel in the float bowl.
That is why on a genuine M series v=carb, the float bowl sicks ou to the right side of the engine to get some cold air ( not easy in WA at this time of year ).
Also it should have a long inlet tract about 1.5"
Mine runs a 626 and needs 2" of space between the barrel & carb to prevent the carb overheating.


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Howley Offline OP
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Nick the mag is fine as far as I know. In my gloomy shed it makes a very fat bluish white spark.

I pulled the carb and checked all the pilot passages, and cleared them all completely by passing a fine wire through them. Everything, jet block included, is clear.

I'm idling with about half advance and dropping the throttle stop until it starts faltering. It seems to respond a little more to the pilot air than before but it's still very minor.

It seems to vary naturally in its idling rpm by a wider range than I can create with the pilot air.

Does the 626 differ in its pilot screw behaviour?

Is it always going to have sooty plugs if it's only idling from cold for a long period?
How long would a plug take to come to temperature at idle?

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The problem is the mixture of volatile waste solvents sold down here as "fuel" .
Normally I could not stop the engine with the decompresor and expect the bike to restart reliably if there was less than 1 hours running .
ANd that is with a BP5
The direct equivalent of the std 1945 plug is a BP8 but they are way too cool to stay clean with the stuff we have to run on these days.
The Concentric idle works the same way as the 276 idle .
Try setting your idle with the timimg fully advanced
If you are always getting sooty plugs then you may be too far retarded to start with.
For the purpose of diagnosing the engine have a fiddle with the points gap
Increasing the gap advances the timing and decreasing the gap retards it.
If the bike runs substantially better with the points set wrong the you know the timing is off
This is a good test because you can do a dozen runs along the same road wih different gaps in a relatively short time .


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Originally Posted by Howley
The choke is fitted and always pulled ie disengaged.

Your data on the throttle slide is different from what I've read elsewhere. My understanding was that 4 is standard for the m21.

IMHO,

If you have a problem, go to the BSA specs as published by the factory.
They use the data i wrote down above...

As i do not know if you use the correct old one, or a new one or a assembled one, i did give you what BSA use to deliver..

6/4 is the trottle designation they used back in the day for M21 276 carb..

Later on monoblock the designation for slides was just 3 or 4 or 5 depending on the bike...

Burlen, now also uses the designation 4 i see in my AMAL stock... but still, you want something resolved.... then you have to know exactly what is needed (and not a 376 slide no 4 converted to 275 use) so double check make sense to me

Last edited by Motolab; 10/11/20 2:07 pm.

Harold / Motolab.nl
BSA: WM20 '40 M21,B31 '54 B33 '55 ZB34GS '49, DBD34GS '58
Triumph 5T '49 + T100 + speedkit
Sunbeam S7 '48
Moto Guzzi LeMans '79
BMW R51/3 '51, R100GS '89
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G'day Luke,
I'm wondering if you have a mismatch of parts. There are two types of 276 carbs the early one with the four holes around the body above the large mixing chamber nut and the later one without these holes, the jet blocks for each type are not interchangeable.
On the early carb there should be a hole on the opposite side of the pilot air screw where you can see the point of the screw when it is fitted, some times people plug this orifice up and it upsets the pilot circuit. The later carb without the four holes has this orifice filled in.
Post a photo of your carb and lets see what you have.

Last edited by MattL; 10/12/20 6:43 am.
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Howley Offline OP
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Matt,

https://flic.kr/p/2jSNE8S
https://flic.kr/p/2jSSi4c
https://flic.kr/p/2jSNEVJ
https://flic.kr/p/2jSNDvV
https://flic.kr/p/2jST8VS

Looks like the hole just inside the intake has no mate in the jet block. Is it supposed to?
https://flic.kr/p/2jSP31j

Edit, it appears its supposed to. Can this be drilled? Are there other holes I'm missing?

I had been wondering how the heck air gets in to the pilot circuit.

Last edited by Howley; 10/12/20 12:24 pm.
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Hi Howley,
You have the prewar jet block , it will not work with the carb body you have
It looks as though the jet block has been attacked with a hammer????
The je tblock needs to be airtight as well as a tight fit in the body or air / mixture will be affected
There are dents and marks on the jet block where it should fit tight in the alloy, if the alloy body is scored or damaged you nee to find another
It might be just easier to get another carb altogether??

John

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Howley Offline OP
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Well that explains a lot. Yeah the jet block sure has had a hard life, God knows how it ended up looking like it does, probably was sitting on a bench in London during the bombings.

The four radial holes are obviously redundant and the intake hole is missing, is there a chance that it could work if that intake hole was drilled?
It's not that bad where it fits with the body, it's probably airtight there.

I'm having a look at jet blocks. Is the bore measurement the diameter of the through hole (ie the intake diameter)?

Last edited by Howley; 10/12/20 9:29 pm.
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Luke,

The jet block dia and the intake dia need to match. 1" dia for M20 and 1 1/16" for M21.

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Howley Offline OP
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Thanks Matt. I've got a bead on one in Australia.

I drilled the old jet block and gained a small amount of control of the pilot circuit, but not enough.

I swapped the plug for a bp5hs and it's coming out sooty, but clean at the electrodes. I'm happy with that.

There's still a choke at higher speed at (I'd guess) mid to high throttle opening, could this be related to the jet block or is it something else?
I'm not experienced enough to know if it's a rich choke or a lean choke.

It feels like it feels when you whack open the throttle at too high a gear, but given how it rides in lower gears I don't feel it should do what it's doing.

Any ideas?

Edit. Aah bugger, I've got a 1" intake diameter. Looks like I'm in for a replacement body too.

Last edited by Howley; 10/13/20 12:10 pm.
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Hi Howley,
If I had your M21 I would look for an intake extension and a suitable Monobloc carb as fitted to the later M21's

John

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John,

I appreciate that that would be easier to live with, but I love the remote float carb and I want to keep the bike true to the period as much as I can.
Maybe I'll regret that later, but for now there's no way I'm upgrading to a new carb.

Thanks for the info regardless.

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I feel the need to be a little more straightforward in my language, but meant as advice...sorry for that to start with..

You are looking for help, but i have to say... nobody can help you with a crap carb... unmatched parts
Drilled and “opened up” by somebody who says about himself quote” I'm not experienced enough to know if it's a rich choke or a lean choke.“
And then.... Looking for a solution in the grade of plugs..

Sorry, again... it is not going to work as it can and should work...

Buy somewere a new carb or a really and proper refurbished one... jetted as BSA meant them to be jetted and you will have a good runner (if... the rest of your bike is better than its carb) Plug grades are details for later on, tested on loooong runs, not short trips...

all of my classics do their job on their normal and standard plugs.....


Harold / Motolab.nl
BSA: WM20 '40 M21,B31 '54 B33 '55 ZB34GS '49, DBD34GS '58
Triumph 5T '49 + T100 + speedkit
Sunbeam S7 '48
Moto Guzzi LeMans '79
BMW R51/3 '51, R100GS '89
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AMAL sells all the bits for a 276 rebuild.

http://amalcarb.co.uk/generic-type-276.html

maybe you can rejuvenate this one?

or go all the way

https://www.eBay.com/itm/276-1-1-16-AMAL-Premonobloc-Carb-BSA-M21-1946-54/323513641066?hash=item4b52ea686a%3Ag%3A43YAAOSwrGlbzyiD&LH_ItemCondition=3

Last edited by kevin; 10/14/20 11:25 pm.

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Luke.
It might pay to place a WTB listing for a good used carb body in the sales and wanted section of the WD Motorcycle forum.
John Parker here in Melbourne sells new components for AMAL carbs, he's also a member of that forum,

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Hi motolab.

Thanks for your honesty. You're right, and I was ready for the fact I'd have to buy new parts.
I am two things:
1. Practical
2. Not well off.

I knew my jet block was junk, and drilling it out was free and gave me more insight into the working of the carb. I couldn't lose in trying it out.

I'm taking information from all of you here. I've accepted the Australian guys' info on the plugs because I'm using the same fuel as them.
I also completely agree with your assertion that there's no point asking for tuning tips if I have the wrong carb. Until Matt's comment I thought I had the correct carb!

I've since found and ordered the correct NOS body and NOS jet block. All the rest of my parts are new or in good condition so I'm hopeful this will sort the fuelling issues.

Again thanks for all the information and honesty. I'll be back with an update once the new bits are in.

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So how many days do you get above 30 C inthe Netherlands ?
Do you buy Australian fuel in the Netherlands ?

When we went from leaded to unleaded fuel the standard serice information was to go up one grade hotter plug and reatard the timing 5 %
This is because unleaded fuel burns colder and slower than leaded does .
On high performance engines you also needd to go up to jets around 10% larger to make up for the lower energy content of unleaded fuels.
When we went from unleaded to ethanol similar tuning information was made available from most fuel companies.

What is written in BSA's service sheets is only correct if you are buring 1954 petrol in 1954 air at sea level.
Otherwise it is nothing more than starting point for proper tuning.


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Yeah you are right... we have still oldfashioned fuel in the Netherlands and the whole of europe.
We use still leaded fuel and there is no alcohol in our fuel. Also it is very cold here.... all year around even in the summer and most important we do not drive our british bikes, we have them only to look at.....

So i think am proposed to only give input, regarding the outside shiny bits of bikes...



On the otherhand... my M20 from ‘40 was designed for pool petrol, very low octane and low energy fuel, there was no lead in it.. we did only did get lead in our fuel in the end op the sixties... in europe that is.... but what do i know...

Last edited by Motolab; 10/15/20 4:58 pm.

Harold / Motolab.nl
BSA: WM20 '40 M21,B31 '54 B33 '55 ZB34GS '49, DBD34GS '58
Triumph 5T '49 + T100 + speedkit
Sunbeam S7 '48
Moto Guzzi LeMans '79
BMW R51/3 '51, R100GS '89
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Originally Posted by Howley
Again thanks for all the information and honesty. I'll be back with an update once the new bits are in.

do that.

it's a good looking machine, and its come a long, long way


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Australia has only 2 oil refineries that between them make less than 40% of the petrol consumed locally.
This is because our crude is better suited for lubricating oils than fuel .
Most of the petrol consummed here is imported and is nothing like the petrol you get in Europe.
There is no standard for what has to be in Australian petrol, just pollution laws about what can not be in there and the maximum amout of various fractions.
Thus what comes out of pumps down here is a mix of every flamiable solvent or scrap liquid that can be bought bulk & cheap blended with what ever is available .
Thus one day it smells like a boot shop ( excessive solvent benzine ) and the next day it stinks like paint stripper ( excessive tolluene )
When I was running the 932 on the M20 it became very sensitive to WHERE I got fuel from .
Back then Burma oil had retail outlets and they imported refined petrol , sorry fuel ( not the same stuff ) directly from their refinery .
I tried to use it all the time because it did not change day to day week to week & month to month like the local stuff did.

Now yes the bike was over carbed but it really forced home fuel quality on yours truly to the point that it would idle nicely , if a little fast on a tank of Burma but if there was any more then 50% of any other fuel in there it either raced or would not idle at all .
I do not know where West Australia gets it's fuel from .
Both of the local refineries are on the east coast so I doubt that that WA would be getting fuel from Melbourne or Brisbane as local costal shipping is near twice the price of international shipping .

Then there is weather
Perth has an average winter temp of 20 C , go a bit inland and it gets closer to 30 C and the tar roads are oft better than 40 C .
In summer you can add anothe 10 C to those + some more .
Nothing odd about a day where even the M20 can not be parked on a bitumen surface because it has become so hot the stand sinks in to the point that the rear wheel touches the road & the bike falls over .

These sorts of days boil fuel in the carb very easily .
Even in winter when running hard I have needed to let the bike sit for over an hour to cool off because it would not start due to overheating.
And this is even after a 3/4" insulating block between the engine & the carb .

BSA recommended carb tuning was correct for the time it was printed in the place it was printed and an engine that was fresh off the production line.
None of these apply to Howleys bike.
After that is is no more than a starting point where the bike should at least start so that it can be tuned properly.

Howley's bike starts & runs so there is no reason for him to go back to the starting line .
His description matched an overheated carb .
Now from further posts it might be also a miss matched set of carb parts .

On the web every one's opinion is equal
We are just electrons floating about in cyber space .
I am happy that you have found thigs that work well for you in The Netherlands
And there is a chane that they might work for Howley but every person I know in Australia is running a plug at least one grade hotter for Champions and 2 grade hotter for NGK's where the heat ranges are smaller .


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@ BSA_WM20

Thbh, i am rather speechless...

Impressed what you know..... even about the weather in The Netherlands.... (we don’t have summers with 38 deg celcius right? And if so, we do not drive old bikes in that weather right?)

What is in the BSA service sheets is written regarding WM20 and M21 is based on POOL petrol....( commercial 68 octane, No. 1 grade 75 octane) lead introduced in Europe only after 1968 as far as i know... Not much better than the shitty petrol we have today in both europe and Australia i suppose, but... then Again, Australia may be very different


I am sure your help is meant and done with the same intentions as mine..


Harold / Motolab.nl
BSA: WM20 '40 M21,B31 '54 B33 '55 ZB34GS '49, DBD34GS '58
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I am sure your intentions were just as well meant as mine .
People in Europe tend to have very little understanding about riding condiions down here .
It just need to be remembered that what works in one location might not work in another and no tuning secifications are a hard law written in stone.
What works for me in Sydney does not work for others in Melbourne which is only 1000 km away.
When rifding down there I have to be very careful not to allow the bike on over run for extended times or the plug which never fouls here will foul down there.
I found that out the hard way twice ( cause I am a slow learner ) .

As for riding distances , most of the locals and the USA riders who were with us considerd the rides at the Halls Gap BSA International to be a bit on the short side. All of the write ups in the various BSA newsletters from overseals complained that they were too long.
It is just what prople are used to doing .

If Covid restrictions werenot in place the M20 would be hauling my fat backside up to Brisse for the opening of the Motorcycle , Art & Design exhibition in November , a 2400 km rounf trip + 300 km diversion to check the rides for the 2022 BSA National on the way back


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Are you really writing that?? Without knowing me? “People in Europe”. Really?

Sorry i am out..


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Having attended the Aussie rally the other year (and being from the UK) I like to think I have a good idea of the riding in Halls Gap and having toured Western Europe I have a reasonable idea there as well as riding around Petaluma. (There’s a lot of Europeans who have ridden further and have a broader knowledge) I tends to be that those within Europe travel more internationally than many of the countries which have a much larger land mass.

Although I was lucky, I borrowed Shane’s bike in Aus which was set up perfectly for the fuel that the bike was being used with. Also in Petaluma I was fortunate to borrow Rusty’s bike which was also set up to work with local environment and fuel.

It’s also a valid point that in Europe we tend to have the best pump fuel on the market. Although this does vary. The Dutch fuel is on par with the UK and the available fuel in Germany tends to be better still with RON Octanes around 101 for super grades.

Ps. I liked the runs in Halls Gap, it was good to be on the road and enjoying the breeze

Last edited by Allan G; 10/18/20 12:49 pm.

Now let’s all have a beer beerchug

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Yuppp, “we drive” from Norway, till Rome Italy, where +40 degrees celcius is quite normal. Crossing the Alps also that is... all on the same (standard grade plug..)
As i live on the german border, i buy often fuel for my M21 of 91 octane, still available in Germany, at least last year.. very cheap, rather low quality fuel. and far better than the Pool petrol in the UK back in The day...
That 91 octane contains even E10 (partial alcohol that is) .... good fuel for a M20 / M21 and even the B31 and B33... with their low compression..
Ohw sorry, i was out..

Last edited by Motolab; 10/18/20 3:56 pm.

Harold / Motolab.nl
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I thought the whole idea of military service vehicles of the WW2 era was that they could get by on pretty much any fuel they could get hold of in the field (as well as being repaired crudely by non-experts).

I would imagine North African desert service was as tough as modern Australia.

Ted Simon (of Jupiter’s Travels) on his T100 crossed the equator several times (including the above very hot/dry region) as well as across Australia, without mentioning any difficulties with fuel or plugs, though of course experiencing many other issues which he does detail.

It is too easy to assume that owners of classic bikes in small European countries only ride locally, while those in large countries ride enormous distances routinely.
There is no such obvious relationship.

Bikers are individuals who derive pleasure in different ways from their enjoyment of riding motorcycles. For myself, I’m happy with local forays for the most part (50 or so miles on a small island is enough not to feel like a stylus on a record), occasional jaunts to a festival (so up to maybe 500 miles on the mainland), or once in a blue moon a 2000 mile whistlestop trip of Europe or a 4000 mile odyssey to Morocco.
On that last journey I encountered many other Europeans, Aussies, NZ doing similar things on bikes, sadly only one was a classic Brit bike (an Aussie couple on a Commando). When we crossed paths at a campsite near Tetouan he jokingly asked if I was Ted Simon (I was with my same old Triton).

Is petrol in Australia truly as poorly controlled as Trevor suggests? Do others experience the need for plug/jetting changes when going from region to region?
Could it be just an M20 with borderline A/F ratio (rather than mid-way ratio) that makes it sensitive to minor changes in fuel composition and environment?

Just thoughts.

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Standard fuel here is 91 RON Premium is 95 Super is 98 some E10 is 94 although normally sold as 91.
You can buy E85 which is over 100 but it's rare really.

The super fuels vary quite a lot over the course of a year and are best bought from a station with a high
turnover.

I have not really had any problems with our fuel on any of my bikes, i normally use BP98 which was always
a good benchmark test fuel anyway. A long time ago mixing leaded super with BP98 would give a better
result but all leaded has gone now. Just now set the bikes up to run on what's available so a little richer and
a degree or two back on timing. Above 6000 you don't notice anyway..........................

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OK everyone the parts are here.
The pilot circuit is now working, however the throttle slide (new) is slightly sticky in the carb body (NOS).
It slides down when the throttle is released, but slowly.

Any suggestions on how to free it up?

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Brasso


Bike Beesa
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Measure the carb body for roundness. You don't need actual measurements--just use internal calipers to see if there is a variation around the bore.
With time, heat cycles and mechanicking it may have gone out of round slightly.
If so it should be capable of being rerounded (if there is such a word) by gently squeezing it in a vice.
Also Brasso as suggested or Solvol to polish the bore.
HTH

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wait

is this while its running? or stopped?

if the mixture is somewhat lean a blip on the throttle will return to idle slowly

if your slide is descending slowly with the engine not running i suspect a stronger slide spring is necessary.

if it moves by itself you are very close to being correct in any event


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BSA_WM20 said:

"When we went from leaded to unleaded fuel the standard serice information was to go up one grade hotter plug and reatard the timing 5 %
This is because unleaded fuel burns colder and slower than leaded does ."

If the fuel burns slower, why would you retard the ignition?

How does that work?

kevin #828144 Yesterday at 10:46 AM
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Originally Posted by kevin
wait

is this while its running? or stopped?

if it moves by itself you are very close to being correct in any event

Running, the slide was descending slowly.
As it turns out it was so close that all it needed was to be worked up and down 50 times. It's perfect now.

I've managed to tune the idle and it's starting brilliantly with no tickle and no throttle. Crazy!

I'll get out for a ride this weekend and report back!

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ive had similar issues with the choke slides in AMAL Concentrics. a bit of assistance for a few ups and downs and tge smoothed their engagement.

good to hear that you have a working 276.


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