The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Amal, Carburation => Topic started by: Stu on 06.03. 2023 15:09
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Guys, time to do the basic explaining for me, please.
I got the 61 A10 gf set up with electronic ignition, no magneto so using a battery for power. I get a good spark on both plugs but not a single beat, I'd even be happy with a misfire. I took the plugs out and kicked her over. I don't think I can smell any petrol at all from the plug holes. I stripped the carb and followed amal instructions. I had already replaced the float and needle etc with a carb kit. It looks like I bought a new style needle but I have old style jets. I'm also missing the pilot jet, must have been taken out years ago.
I have attached pictures, can you please advise what I must change. I live in Zambia so it barely gets below 20c unless mid winter so I'm not sure ill need a choke, my cable is buggered, thinking of just removing it because of other posts I've read on here.
Thanks in advance
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After reading anything I can find, I see some carbs had the pilot taken off and replaced with a bush jet. Mine might be that type, I'll check.
One thing I just realised, the choke cable is buggered and doesn't fit into the top of the carb, meaning a load of air can pass down through the top of the carb. I forgot the carb must be air tight, dumbass me.
Still looking for any advice.
Cheers
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All Mk1 Concentrics have the threaded hole, but only very early ones and two-stroke versions had a jet in place there.
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G'day Stu.
Yes later in life of the Mk 1 concentrics the pilot jet was replaced with a bush. Take the air (pilot) screw out and look in the hole. You should see a brass bush deep inside. The hole in the jet is equivalent to a #20 pilot jet and I think about 0.016". There a real bugga to clean, soak in carb clean for a day or ten. Find someone with an ultrasonic cleaner and with the right solution it'll be done in 30 minutes. My carbs get a bath every time they come off.
As for the choke just plug the hole. Never had one on the A7 plunger down at sea level. Now up the hill 3000ft she needs a longer tickle in winter!
I'm a big fan of the new premium concentrics, better material, removable pilot, adjustable stay up float (which you can put in an old concentric), anodized slide. Not cheap but the old girl has never run better.
Cheers
TT beat me.
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After reading anything I can find, I see some carbs had the pilot taken off and replaced with a bush jet. Mine might be that type, I'll check.
One thing I just realised, the choke cable is buggered and doesn't fit into the top of the carb, meaning a load of air can pass down through the top of the carb. I forgot the carb must be air tight, dumbass me.
Still looking for any advice.
Cheers
You can see where the air and petrol travel enter the idle jet circuit from looking at the base of the carb inside the float bowl (air enters from a passage way that is on the air filter side of the carb). The two passages untersect at 90 degrees at the brass mixing chamber (as per yr pic).
As muskie says cleaning the idle jet is not easy, I use a piece of wire from an old wire brush, then remove the idle adjustment screw and insert the wire through the threaded hole and through the idle jet itself, buried deep in the car body. The “secret” is to know when the wire has actually passed through the idle jet, as opposed to stopping on the step at the entrance to the jet, from memory the wire has to travel 32mm inside.
Using a wire will unblock the jet but may leave particles of dirt still in the air passage way to the jet, which compressed air may blow out.
Be prepared to unblock the jet a few times before it stays unblocked *sad2*
The burlen web site has sime good diagrams of the idle circuit…
https://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter
PS the plug leads are the right way around?
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I find it strange that people think that the top of the carburettors must be sealed to prevent air being sucked in.
Wouldn't air be sucked in around the cable end if in place?
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I find it strange that people think that the top of the carburettors must be sealed to prevent air being sucked in.
Wouldn't air be sucked in around the cable end if in place?
When resleeving became popular, overheating from running rich became a common problem along with sooty plugs and slow acceleration.
Reaon ?
Amal compensated for the air that leaks in around the top of the slide
Those tight fitting resleeved carbs had substantially less air bleeding in so the jets became too big .
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Ok,I found a small piece of debris in the main jet, cleaned out the carb as you all described and seems ok now as I can smell fuel from the plug hole when I kick it over with the plugs out.
Next problem....
When I put my hand over the back of the carb to choke it and kick it over,I get huge pressure blowing back through the carb.
I'm no expert but that's gotta be the inlet valves not closing properly eh?
Off with her head?
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One more thing, I ordered a fibre timing cog but it's the same as already on the auto advance except the hole in the middle is too big so I welded the auto unit closed. Is it possible I set the timing with the auto unit open, and now have sealed it closed so the timing has gone out? When I get the pressure blowing back it doesn't seem like it's sparked, more just like the inlet valve is stuck open and the pressure blows everything back through the carb. I've read somewhere that there will be some reverse pressure if you block the air filter, when I did this even petrol flew out of the tickler, caught me in the eye. Seems more than normal or am I wrong, again?
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I find it strange that people think that the top of the carburettors must be sealed to prevent air being sucked in.
Wouldn't air be sucked in around the cable end if in place?
Even though the throttle cable is never going to be hermetically sealed, I have found that a very loose fit of the outer cable in the carb top has a bad effect on low speed throttle response.
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Presume you set the timing fully advanced with the ATD held open, and simply tacked it closed? ATD in the closed position is the setting for starting. So it should fire up and tickover OK. Any attempt to increase the revs will give the symptoms of retarded ignition, typically lack of response, stalling, lack of power and ridden like this, overheating.
Blocking the inlet tract means any blowback through the carb will vent as it can, the tickler being the least restricted route to atmosphere. Probably gave the maggy a good wash as well.....
Swarfy.
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Ok, so I double checked the timing and valves. The spark was happening while the inlet valve was still open so I opened the valves, had them too tight, and moved the timing,I had that wrong too. It was firing too early and the valve was staying open too late. I sprayed a little wd40 down the hole and got a few cough so the timing is close or closer. Looks like I'm getting no fuel from the carb so carb cleaner and the little wire, plus a few days I guess. Thanks guys, you're help is getting me there in baby steps.
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The timing could also be a little out, gotta be to be honest. I'll try adjusting that in little increments and see if it helps before I strip the carb.
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I gave in and ordered new plugs and caps from U.K. Today. It's not the money, just gotta wait either two weeks for them to here. There's no way those plugs are sold in Zambia, that's the problem with being the only one doing this stuff in your country.
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While you're waiting you could set the timing up by the book....?
It's not really a "little increments" type of adjustment.
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So you've welded the ATD 'closed'. If you now set the timing where it is supposed to be, how you gonna start it? It'll kick back and maybe bust your ankle. Possibly set fire to the bike as well. It needs a little retard for starting, but not for running or, as described above, engine will lack power and overheat.
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So you've welded the ATD 'closed'. If you now set the timing where it is supposed to be, how you gonna start it? It'll kick back and maybe bust your ankle. Possibly set fire to the bike as well. It needs a little retard for starting, but not for running or, as described above, engine will lack power and overheat.
Hi RDfella, he has a Vape electronic ignition
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G'day Stu.
Sounds like a combination of carb and timing. With elec ignition you can get it close but it's not until you get it running and use a degree wheel and timing light to get it spot on. Double/triple check your static timing. I'm assuming the ignition uses a wasted spark where both plugs fire at the same time but only one side fires. Where you think it's firing with valves open.
Cheers
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Hi Muskrat.
Yeah, both plugs fire at the same time.I have two weeks before the plugs get here so ill keep trying to fine tune it. I keep noticing things I missed before so ill keep looking.
I'll keep spraying the carb with the cleaner.
One question, the long main jet needle fell off the half moon clamp at one time and I'm not sure I put it back on the correct slot. Where should it be? Which slot?
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While you're waiting you could set the timing up by the book....?
It's not really a "little increments" type of adjustment.
Yeah you're right, I'll keep trying to get it closer, I do have time.
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G'day Stu.
Sounds like a combination of carb and timing. With elec ignition you can get it close but it's not until you get it running and use a degree wheel and timing light to get it spot on. Double/triple check your static timing. I'm assuming the ignition uses a wasted spark where both plugs fire at the same time but only one side fires. Where you think it's firing with valves open.
Cheers
I think I had the timing set so far forward and the valves were staying open so long from the gap being so tight, it looked like it was firing on the compression side while the inlet valve was still open, almost closed. The other side inlet valve was completely closed so must have been on exhaust stroke I guess? I had everything wrong. I figured that out and I have had some cough and farts from it today so I'm getting closer.
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G'day Stu.
Needle position 3 from top. https://draganfly.co.uk/bsa-carburetter-jet-settings/
Cheers
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Hey Stu! There are a few of us on this group riding A10’s a few thousands km north of you in Kenya … I do occasionally and sometimes have to buy spares from the UK, although generally I find most of what I need locally and I’d recommend not getting too fixated on getting everything from the UK.. I’ve use NGK BP6E plugs and they have been super reliable and available in Kenya .. I can’t remember when I last changed them..I just clean them on a regular basis and they keep going.
From what you’re describing and others have eluded to it, it sounds like you have a number of combined issues going on… If you have a spark and fuel in the cylinders you should get a result.. so in the absence of anything, check the static timing, tappets etc first. The easiest way is to put the bike on the centre stand, remove the plugs then rotate the rear wheel in a forward direction until you find TDC on the compression stroke.. A chop stick or something else that’s soft but won’t break down the plug hole will tell you exactly where TDC is… if your static timing is correct and the valves are set, back the rear wheel up so whatever you have in the plug hole drops by about 11mm / 1/3 of in inch (someone here will have the exact measurement) then check your mag timing.
Its easy to the make the mistake and time the mag after TDC rather than before..I’ve done and it ate my head for days… once you know all that is set correctly, you should get it firing.. and you can move onto sorting the carb.
The main reason my A10 runs are the guys on this forum. There’s always someone awake somewhere in the world who’s there to help. I knew very little about my bike when I started and the generosity of information on this group is invaluable.. just keep asking and your bike will be running before you know it,
Guy
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Hey Stu! There are a few of us on this group riding A10’s a few thousands km north of you in Kenya … I do occasionally and sometimes have to buy spares from the UK, although generally I find most of what I need locally and I’d recommend not getting too fixated on getting everything from the UK.. I’ve use NGK BP6E plugs and they have been super reliable and available in Kenya .. I can’t remember when I last changed them..I just clean them on a regular basis and they keep going.
From what you’re describing and others have eluded to it, it sounds like you have a number of combined issues going on… If you have a spark and fuel in the cylinders you should get a result.. so in the absence of anything, check the static timing, tappets etc first. The easiest way is to put the bike on the centre stand, remove the plugs then rotate the rear wheel in a forward direction until you find TDC on the compression stroke.. A chop stick or something else that’s soft but won’t break down the plug hole will tell you exactly where TDC is… if your static timing is correct and the valves are set, back the rear wheel up so whatever you have in the plug hole drops by about 11mm / 1/3 of in inch (someone here will have the exact measurement) then check your mag timing.
Its easy to the make the mistake and time the mag after TDC rather than before..I’ve done and it ate my head for days… once you know all that is set correctly, you should get it firing.. and you can move onto sorting the carb.
The main reason my A10 runs are the guys on this forum. There’s always someone awake somewhere in the world who’s there to help. I knew very little about my bike when I started and the generosity of information on this group is invaluable.. just keep asking and your bike will be running before you know it,
Guy
Hi Guy.
That's great to hear I have compadres in Africa, they used to race these bikes in Zambia in the 70s and I bought a bunch of bikes that has been standing 20 years so I'm building mine from scratch.
I have been working on 8mm btdc to set the timing, let me try 11 as you say.
I love puzzles and this is just a big one for me.
I had and rebuilt a 65 a65 42 years ago when I was a lad in Cannock, staffs but had hundreds of guys local to me plus so many shops still selling NOS within a few miles so I'm feeling a little stranded here.
I'll keep on keeping on.
Thanks mate
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https://www.a7a10.net/forum/index.php?topic=947.msg6561#msg6561
as above...the timing setting isn't an exact science..
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G'day Stu.
Needle position 3 from top. https://draganfly.co.uk/bsa-carburetter-jet-settings/
Cheers
Thanks Muskrat, let me check that.
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G'day Stu.
Needle position 3 from top. https://draganfly.co.uk/bsa-carburetter-jet-settings/
Cheers
Have I got the right needle?
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https://www.vintagebikebuilder.com/mikuni-tuning-and-jetting-guide.html
this is for a Mikuni carb although pretty universal to all carbs.. it explains pilot, slide, needle, main jet, functions etc in relation to the engine speed and power.. the pilot and slide settings are what you need initially, then needle and main jet.. (although you said you don't have a pilot jet?)
Guy
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G'day Stu.
That looks like a concentric needle with the 3 rings at the top and for a two stroke. https://tinyurl.com/mr463m8b
What carb do you have? You should have a monobloc 389/18
Cheers
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Check the pic, amal concentric I think. I did order this needle but obviously got the carb wrong. I don't know what I did with the old needle, I'll have to dig around for it.
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G'day Stu.
That looks like a concentric needle with the 3 rings at the top and for a two stroke. https://tinyurl.com/mr463m8b
What carb do you have? You should have a monobloc 389/18
Cheers
Carb in earlier pic is 626 Concentric musky.
Bike presumably has run in the past, it looks well-used anyway, so I'd stick the clip in the middle of the three for starters - using the older needle if you can find it again.
However, sounds as if the #1 thing is to get the ignition timing close to where it needs to be for a kick off . . .
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Could we change the title of this thread to Jet Pilot Missing in Action 🙏
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More like"clueless in Lusaka" *eek*
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G'day Stu.
Sorry M8 it's a Mk1 concentric. From memory (not good these days) it should have 5 lip positions and two rings at top.
I "used to have" lots of them. I'll pull the one out of the plunger carb later.
Cheers
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If I can find out exactly what to get, I'll buy and send to my mum, she's coming over in a couple of weeks, unless I can find the old one. I know I haven't seen it since I got the bike or long after though. Mum lands 28th March so I can wait until then.
Cheers
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Hi guys, just an update.
With Swarfy' s help I found the camshaft cog to be almost 180 degrees out,I had set to the wrong mark. Spun it around and managed to get a few seconds of firing with engine start. It's not firing from the carb yet so ill work on that. The plugs, caps and even carb O ring are over 20 years old so I have new ones coming month end with my mum from UK. I'll keep adjusting the valves to get them exact, fix the wiring etc.
Thanks for your help guys, cheers