The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: owain on 02.07. 2018 21:17
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My 1950 A10 plunger (with sidecar) is showing no signs of life at all. The bike has been running great until a few weeks ago when the exhaust rocker box gasket split and lots of oil came out. No big deal, I thought. So I when I got home, I took the rocker boxes off, fitted a new gasket and recalibrated the valve clearances and double checked them. Started the bike and away I went.
A couple of days later, I went for another bike ride and started to encounter problems. A few minutes into my journey the engine stopped when I was at the traffic lights. Then a few minutes later, it started to splutter. I remedied this by giving it some more throttle and started to make my way home. Then the real trouble happened. The engine started to only fire on one cylinder. I stopped. Tried to see if the cables from the magneto had came loose. Nope. Managed to get the engine going again after two dozen kicks. Still running on one cylinder. Instead of abandoning the bike by the side of the road, I decided to rough it out and make the 2 mile trip home running on one cylinder.
Now comes my diagnostics:
Carburettor has not been touched in months. I checked the carb nonetheless (Jets, float level). Everything appears to be fine.
Could the spark plugs have fouled? The spark plugs looked a little (but not very) black. So I placed new spark plugs in. Engine still wouldn't start.
Could the bike have wet sumped? Drained the crankcase of oil. Engine still wouldn't start.
Could the valve clearance be wrong? Triple checked valve clearance. All within spec. Engine still wouldn't start.
Could I have bad compression? Checked compression and found each cylinder to have 150psi. Plenty of pressure. Not that then.
So it must be the ignition!.My magneto was well overdue a restoration so I sent it to APL magnetos. Got it back a week later. Set the timing i.e. when the points just begin to separate at 11/32" before TDC on the compression stroke. Made sure that I tightened the double threaded nut back on with the auto-advance unit wedged in the fully advanced position....Engine didn't start!
Repeated this step five more times. Engine still won't start.
Finally, failing to see any other alternatives. I emptied the tanks petrol and filled it with a gallon of fresh petrol. Still no luck.
Does anyone else have any idea about what could possibly be preventing this motorcycle from starting/running? I'm all out of ideas. Cheers :)
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Presumably you have checked that there is a good spark. Have you tried switching the plug leads around, having re-fitted the mag and re-timed it. Are the ht leads and connections good and no chance of tracking. Can't think of anything more as you seem to have covered most other possibilities. Do update the form when sorted please.
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If any petrol engine has sucked in a mixture of air and petrol vapour, has a healthy spark at the plugs, occurring at the correct time and has cylinder compression it must at least fire, if not continue to run. So, check the basics again.
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My 1950 A10 plunger (with sidecar) is showing no signs of life at all. The bike has been running great until a few weeks ago when the exhaust rocker box gasket split and lots of oil came out. No big deal, I thought. So I when I got home, I took the rocker boxes off, fitted a new gasket and recalibrated the valve clearances and double checked them. Started the bike and away I went.
A couple of days later, I went for another bike ride and started to encounter problems. A few minutes into my journey the engine stopped when I was at the traffic lights. Then a few minutes later, it started to splutter. I remedied this by giving it some more throttle and started to make my way home. Then the real trouble happened. The engine started to only fire on one cylinder. I stopped. Tried to see if the cables from the magneto had came loose. Nope. Managed to get the engine going again after two dozen kicks. Still running on one cylinder. Instead of abandoning the bike by the side of the road, I decided to rough it out and make the 2 mile trip home running on one cylinder.
Now comes my diagnostics:
Carburettor has not been touched in months. I checked the carb nonetheless (Jets, float level). Everything appears to be fine.
Could the spark plugs have fouled? The spark plugs looked a little (but not very) black. So I placed new spark plugs in. Engine still wouldn't start.
Could the bike have wet sumped? Drained the crankcase of oil. Engine still wouldn't start.
Could the valve clearance be wrong? Triple checked valve clearance. All within spec. Engine still wouldn't start.
Could I have bad compression? Checked compression and found each cylinder to have 150psi. Plenty of pressure. Not that then.
So it must be the ignition!.My magneto was well overdue a restoration so I sent it to APL magnetos. Got it back a week later. Set the timing i.e. when the points just begin to separate at 11/32" before TDC on the compression stroke. Made sure that I tightened the double threaded nut back on with the auto-advance unit wedged in the fully advanced position....Engine didn't start!
Repeated this step five more times. Engine still won't start.
Finally, failing to see any other alternatives. I emptied the tanks petrol and filled it with a gallon of fresh petrol. Still no luck.
Does anyone else have any idea about what could possibly be preventing this motorcycle from starting/running? I'm all out of ideas. Cheers :)
Plug leads around wrong way is most likely, as a long shot check the tickler, which doubles as a breather for the float chamber, is not blocked. If you rule out ignition as the cause of the problem and you have a monobloc you can can check the float is working correctly using cling film and a rubber band.
If you have a concentric carb cleaning out the idle jet is NOT that easy to do properly, what carb do you have!
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I've checked whether I'm getting a spark with a spark tester (getting a strong flash from the light bulb). I also removed the spark plugs, connected the plug leads and saw a good spark. I know that compression makes it more difficult for a weak spark to jump the gap, I wouldn't expect there to be a weak spark from a newly reconditioned magneto though...
I'm running an amal concentric carb on the bike. Petrol squirts out of the tickler when tickling the carb, so I think that is clear. A new pilot jet was fitted to the carb last year but even so, I tend to start the bike with the throttle half open. :/
I'll swap the leads and give it a go and will try to fiddle with the timing again. After my previous attempts of setting the timing, I was getting the odd flame out of the carb. Then I changed the timing again and I got the occassional flame out of the exhaust pipe. After my last attempt of setting the timing at 11/32" before TDC the engine won't combust at all.
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Only the early 4 stroke and new premier concentrics had a removable pilot jet (Though in different places). But they still had a threaded hole to take one. The other models had a pressed in non removable difficult to clean one. This link to Amal details rebuilding a concentric and cleaning a pressed in jet;
http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter
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Only the early 4 stroke and new premier concentrics had a removable pilot jet (Though in different places). But they still had a threaded hole to take one. The other models had a pressed in non removable difficult to clean one. This link to Amal details rebuilding a concentric and cleaning a pressed in jet;
http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter
Great minds think alike eh! I was going to post that link but you beat me to it, also I noticed it does not mention cleaning the air way from the rear of the carb to the “mixing chamber” behind the pilot adjuster screw. I was trying to find a pic of the whole pilot circuit but haven’t yet.
At this stage I think it’s possible the idle jet is blocked, but more it’s likely an ignition issue.
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Owain, do you check that the timing has not moved after you have set it. And, are the points gap still at 13thou.
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Are the spark plugs getting wetted with fuel. Is the petrol tank vent clear.
Try disconnecting the kill lead on the mag.
A problem I experienced recenty was the needle was incorrectly fitted and was not rising with the slide, should be easy to check from the intake bellmouth.
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Only the early 4 stroke and new premier concentrics had a removable pilot jet (Though in different places). But they still had a threaded hole to take one. The other models had a pressed in non removable difficult to clean one. This link to Amal details rebuilding a concentric and cleaning a pressed in jet;
http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter
In case you have to clean a concentric's pilot jet, some folks use an 0.016 guitar string. My approach was to go with the #78 drill method, as described here:
https://www.a7a10.net/forum/index.php?topic=11619.msg89032#msg89032
Richard L.
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I'll swap the leads and give it a go and will try to fiddle with the timing again. After my previous attempts of setting the timing, I was getting the odd flame out of the carb. Then I changed the timing again and I got the occassional flame out of the exhaust pipe. After my last attempt of setting the timing at 11/32" before TDC the engine won't combust at all.
I recently got my plug leads reversed after timing and had some pops and bangs before I swapped the leads over.
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If you start on half throttle, there is something badly wrong with your carb setup. Sort out the pilot jet as mentioned above.
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Update:
Sprayed a little bit of starter spray through the carb. Started straight away! FFS!
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Update:
Sprayed a little bit of starter spray through the carb. Started straight away! FFS!
*smile*
I'm glad it fired up; shows there is nothing much wrong. Have you been able to start it normally since then?
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Ah well I may have spoken too soon actually. It seemed to run ok yesterday. It wasn't sounding very good today though. When I accelerate it sounds good. When I'm cruising it sounds like it's 'hiccuping'/ running a bit poorly. I thought that maybe this could be due to the timing being slightly off. If I didn't give it any throttle. It dies on idle. I had to twist the idle screw in the carb really far in to keep it alive at a fast idle.
I'm thinking of taking the carb apart checking all the jets e.g. blowing them out with compressed air. Then giving it a go again. If it is still running a bit off when cruising then I'll reset the timing again to see if that improves the situation *???*
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Some progress then *smile*
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G'day owain.
Sounds like the pilot circuit is blocked or too small jet. Is the pilot jet screwed into the body above the float chamber or pressed in opposite the air screw? Early concentrics had the screw in but later had a non adjustable jet pressed in. Hesitation at cruise could be needle jet and needle or slide (they wear).
Cheers
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Cheers everyone, the bike is back in the garage for this evening. I quickly removed the spark plugs though and they are already black and they were brand new. They were not wet or oily, just coated in black soot. So a problem with the carbs jets/ needle position seems like a logical place to look.
Oh and the concentric is the old type of concentric with a screw in pilot jet.
It seems a little odd though that the bike has been running fine with this carburettor and jets for the last few months and all of a sudden it's running so rich that spark plugs foul within a few minutes?
The other suspicion I have is that the valve sleeves are allowing oil to get past the valves and into the combustion chamber. Perhaps the oil leak from the rocker box could be an indicator of a cylinder head issue?
The carb is definitely the cheapest and quickest area to investigate first. Failing that, it's a little annoying if the valve sleeves do need replacing as a machinist checked out the cylinder last summer and told me everything was in good order *roll*
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Ah well I may have spoken too soon actually. It seemed to run ok yesterday. It wasn't sounding very good today though. When I accelerate it sounds good. When I'm cruising it sounds like it's 'hiccuping'/ running a bit poorly. I thought that maybe this could be due to the timing being slightly off. If I didn't give it any throttle. It dies on idle. I had to twist the idle screw in the carb really far in to keep it alive at a fast idle.
I'm thinking of taking the carb apart checking all the jets e.g. blowing them out with compressed air. Then giving it a go again. If it is still running a bit off when cruising then I'll reset the timing again to see if that improves the situation *???*
In my experience compressed air is not always enough to clear the idle circuit on the concentric, to clean the idle circuit properly you need to get an understanding on “how” the air and petrol gets to the adjuster screw, and thereafter to into the manifold. I’ll have another look for that diagram of the idle circuit.
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Yes I had one that was so blocked I had to remove the brass welsh plug to clean it out. Check the passage in the bowl that feeds the pilot jet, often overlooked.
Black sooty plugs is the other way so the air passage may be blocked. I had an XT that was giving similar problems. Found the aftermarket filter was blocking that passage.
The needle and needle jets wear, especially noticeable at cruising throttle opening and can upset pilot settings.
Cheers
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The other suspicion I have is that the valve sleeves are allowing oil to get past the valves and into the combustion chamber. Perhaps the oil leak from the rocker box could be an indicator of a cylinder head issue?
Oil in the combustion chamber will leave a trail of blue smoke behind you but won't make your engine run rough.
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One exception to that ^^^ morris. If the inlet guide is bad enough and on small throttle openings crankcase fumes/air can be drawn in upsetting the mixture.
Cheers
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Just too add...
I had an almost identical experience yesterday on my 53A10, coughing, spluttering, running on one cylinder under load, black plugs etc. There was a little bit of oil in the left hand pot, no real smoke though, but I assumed it an exhaust valve not bedding correctly or a valve seat.
I pulled the head off and it all looks pretty fine. Valves sealing perfectly..no sooting on the rocker side..
If only I'd read this yesterday.... thank you for sharing all this. It has an impact around the world and keeps bikes running,
Guy