The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: bsapete on 15.12. 2018 06:26

Title: Misfire under load again
Post by: bsapete on 15.12. 2018 06:26
Hi gents,
This misfire and lack of power occurred previously (on my first ride of the bike) when the advance/retard outer cable had come out of its sleeve on the lever therefore retarding the timing. Once this was put right it seemed to run well. I’ve just fitted new handlebars and when I refitted the A/R lever and checked it’s operation it became stuck in the retard position and the lever and cable wouldn’t return to the full advance position. I removed the magneto end cover (venturing into new territory here) to see what was happening. I removed the cam ring and put it back and the lever was operational again with the cam ring rotating freely.
I then took it out for a quick ride to check the new handlebars and it’s running poorly again - missing under load and lacking power. It starts easily, usually first kick and idles well once warm. I replaced the plugs with NGK BP7ES gapped at 18 thou but no difference. Odd that I had a moment of smooth running earlier and now the problem has returned. What should I be looking at next - points?
Bloody difficult magneto access too with the high level exhausts.
PS when blipping the throttle I noticed a puff of smoke coming from between the head and barrel on the timing side. I’ve also noticed the exhaust ring on that side isn’t hard up against the head as it is on the left side so maybe it’s not sealing the pipe properly. Hopefully the smoke is coming from there and not the head gasket? Don’t really fancy pulling the head after a month of ownership!
Any suggestions welcomed.

Cheers,
Pete
Title: Re: Misfire under load again
Post by: Servodyne on 15.12. 2018 09:53
Hi there.
It may seem a daft question, but do you have a spring fitted to the A/R plunger at the mag end of the cable. This ensures that the slip ring returns to it's fully advanced position and stop it 'fluttering'. This may give the misfiring and lack of power symptoms that you are experiencing.
I leave my A/R lever at the full advance position at all times and just give it a hefty kick when starting.
Cheers
Jim
Title: Re: Misfire under load again
Post by: groily on 15.12. 2018 10:48
You obviousy need to verify the head gasket hasn't gone walkabout, and then maybe look at the plunger and the camring to see if the two stay in engagement through repeated applications of A & R at the lever. Wear on either or both can cause slipping out of engagement as you discovered initially. A poorly-cut or slightly off-position notch in the camring can also be the culprit.
Sometimes it's possible to limit the cable movement to prevent disengagement using the cable adjuster - but you do want to be quite sure you're getting full advance.

As Jim implies, you can always leave (or jam) the camring at full advance and it will be fine if you are blessed with a good right foot for starting. I've been running two of my other bikes (with much higher compression ratios than my A) on fixed advance for years now, without any problems.
Title: Re: Misfire under load again
Post by: mugwump on 15.12. 2018 13:43
Ht tracking  can also  be a problem under load too.
Title: Re: Misfire under load again
Post by: berger on 15.12. 2018 14:35
bsapete this is a long shot but I once found that a cam ring was working itself out a bit and losing its plungy thingy contact with the ring even with the outer cover on---- just a thought
Title: Re: Misfire under load again
Post by: Klaus on 15.12. 2018 20:03
Hi Pete,

the hight level pipes are strait throu, or do you fit a silencer?
My first test was with only the pipes, it was horryble loud, but great performance and ascelleration.
than I fit the silencers I have ordered from Amours, no way teh bike did nt run popper. No Power and stall by full throttle.
She drive me crazy...with silencers off, great again. I ordered a cheap taiwan pair with no baffels, easy running bike.

Cheers Klaus



Title: Re: Misfire under load again
Post by: duTch on 15.12. 2018 22:16

 Something makes me think this problem may be symptomatic of a condenser starting to fail....but I'm sure groily would have mentioned that... *dunno*  Just I had similar happen in my Tilly a while ago

 
Title: Re: Misfire under load again
Post by: bsapete on 16.12. 2018 03:13
Thanks as usual gents for the suggestions, I will do some more investigation.
I do leave the A/R lever in the fully advanced position and give it a good kick and never a problem starting although it will kit back if you’re too gentle!
I’ve disconnected the cable from the lever to make sure it was getting full advance (ie if the cable wasn’t allowing the camring to fully rotate. Klaus, I do have a pair of baffles and it makes no difference whether they are in or out apart from the noise of course! As suggested I’ll try jamming the camring fully advanced. Should it be lubricated at all and what with?

Cheers,
Pete
Title: Re: Misfire under load again
Post by: groily on 16.12. 2018 08:30
DuTch could well be right of course, depending on the state of the thing, when last looked at, etc.
If the camring is wedged at full advance, lube isn't really an issue, but a smear of grease wouldn't hurt so it couldn't get corroded in position over a long winter! Generally, I use a light lithium grease, but I don't think it matters hugely as long as it doesn't get all over the points. I've used marine anti-corrosion grease on one bike for years, as it's out in the shite more than most and the camring has got stuck after coming back from wet days out on salty winter roads.
But I'm sure you wouldn't abuse a pretty machine like that!
Title: Re: Misfire under load again
Post by: bsapete on 16.12. 2018 10:33
Took the end cover off the mag and operated the lever back and forth a few times and I guess it’s operating properly. The cam ring doesn’t jam at all and doesn’t rotate any further even with the cable disconnected from the lever so I suspect it’s as it should be.
I’ve just remembered that when I got it running properly after the first issue with the A/R cable I adjusted the carb when I got home as it was idling too fast. Now, looking at my new manual I’m sure I’ve inadvertently adjusted the air screw to lower the idle. Presumably I should’ve instead adjusted the throttle stop screw?
Lesson learned: don’t screw with things (literally) when you’re not sure what you’re doing. Could this be causing my running issue?
Title: Re: Misfire under load again
Post by: groily on 16.12. 2018 11:58
Hmm  . . . pilot air setting affects mixture across the whole range, but if you richened it to slow the idle down (?) by screwing it IN, then I'd have thought it would burble at you at low revs, or even '8 stroke',  and make the plugs a bit black up the range. But not maybe cause a misfire. If you UNdid it to weaken the mixture until the thing slowed down - tho usually revs will rise a bit, not drop off, as you start to weaken - then it could have affected the thing I s'pose? But it would probably have been spitting and coughing on the throttle at all settings if you'd unscrewed it that far, and maybe become a pig to start as well?
Too many variables! I'd start with going back to maker's on the air screw - turn and half out from fully in maybe, depending on what carb? - set the idle by the other screw like you said, and then see if things are better, worse, no change.
Thinking more about what DuTch suggested, if you have a dark corner in the shed, you might just be able to see any stray arcing from an HT pick-up, if there is any. Usually it'll be the one on the front, cylinder side, of the mag, and any sparks will show up quite well in the dark! But then again, if it needs a heavy load to make it misbehave, it's harder!
Title: Re: Misfire under load again
Post by: Triton Thrasher on 16.12. 2018 13:01
If a rich idle mixture soots up the plugs, it can miss under load.
Title: Re: Misfire under load again
Post by: bsapete on 16.12. 2018 19:24
After I fitted new plugs hoping it would cure things it was running just the same immediately so wouldn’t have had a chance to foul the plugs presumably. Won’t hurt to re-adjust carb. I’m fairly sure I turned the air screw ant-clockwise and only a little to slow the revs down. Perhaps a ride in the dark would show up any arcing from pick-ups or HT leads.
PO said petrol was new but new from petrol station or old can in the shed? I’ll drain the tank and add fresh petrol too.

Cheers
Title: Re: Misfire under load again
Post by: lawnmowerman on 16.12. 2018 21:36
Maybe a shot in the dark but fairly easy to check.
My A10SR never did run right ever since I bought it and I suspected a dodgy mag so had it rewound and a new condensor and it seemed to improve things but slowly got worse again - difficult to start, running on one, misfires under load.
Following a post a while back regarding dodgy brushes with the carbon too soft, I cleaned up the slip ring and replaced the brushes and the brush holders with quality items from Brightspark. (The old brushes could write on paper and the brush holders were the "universal" type with the hexagon ends). I also needed new acorn nuts as they were a different thread to the ones fitted.
This totally transformed the bike and it runs perfectly now and starts first or second kick so I assume that the spark was tracking around the slipring and taking the easier path to the other plug which was not under compression, or to earth through the holders, or perhaps both.

Hope you get it sorted

Jim

You may find this topic interesting https://www.a7a10.net/forum/index.php?topic=13258.msg106664#msg106664
Title: Re: Misfire under load again
Post by: bsapete on 16.12. 2018 23:08
Thanks Jim, I read recently a post somewhere regarding cleaning the slipring using a cloth wrapped blunt end of a pencil if I remember correctly.
Any tips here would be useful as this is all new territory for me as I’ve never played with a magneto before.

Cheers,
Pete
Title: Re: Misfire under load again
Post by: lawnmowerman on 17.12. 2018 10:13
It's worth a try Pete - just use a piece of fluff-free white cotton cloth dampened with some switch cleaner and you can see if black carbon is coming off. I used my finger to press it on the slip ring while slowly turning the engine with the rear wheel in top gear with the plugs out but be prepared for a few shocks  *countdown*. Perhaps a piece of dowel would be safer - remember that a pencil has a graphite rod through the middle so may still give you a belt if you are touching the end.
If the rag is showing a lot of carbon then I would change the brushes.

Jim
Title: Re: Misfire under load again
Post by: Klaus on 17.12. 2018 11:33
Just remember me, wonderfull idle and it starts first kick. But on load,one pot misfire.
Guilty was a pick up with hair crack.

cheers Klaus
Title: Re: Misfire under load again
Post by: RichardL on 17.12. 2018 12:59
Jim,

I think ust holding down the kill button while cleaning the slip ring will avoid shocks. Good job for the wife. No wife? Tape or gentle clamp.

Richard L.
Title: Re: Misfire under load again
Post by: Rex on 17.12. 2018 15:36
Just put a small piece of cardboard or some similar non-conducting material between the points before turning it over. Just don't forget to remove it....!
Title: Re: Misfire under load again
Post by: lawnmowerman on 17.12. 2018 16:41
Jim,

I think ust holding down the kill button while cleaning the slip ring will avoid shocks. Good job for the wife. No wife? Tape or gentle clamp.

Richard L.

Good idea Richard - never thought of that. I guess a test lead with a croc clip on each end could be used to earth the terminal on the end cover if working single handed. Not sure if I would trust the wife to keep the button down  *whistle*

Jim
Title: Re: Misfire under load again
Post by: RichardL on 17.12. 2018 19:41
Jim,

I think ust holding down the kill button while cleaning the slip ring will avoid shocks. Good job for the wife. No wife? Tape or gentle clamp.

Richard L.

Good idea Richard - never thought of that. I guess a test lead with a croc clip on each end could be used to earth the terminal on the end cover if working single handed. Not sure if I would trust the wife to keep the button down  *whistle*

Jim

ROTFLMAO. *lol* *lol* 
Title: Re: Misfire under load again
Post by: bsapete on 17.12. 2018 23:58
I wouldn’t want to the wife to know it’s a “kill” switch! *eek*

Just when I had a brief moment this morning I warmed the bike up with a quick lap around the block then while idling I screwed the air screw in a turn which lifted the idle. (I had mistakenly used the air screw to adjust the idle down previously). I then lowered the idle back with the throttle stop screw to where I thought the idle speed should be. Took it for another ride around the block and it definitely had better power and pulled pretty well without misfire but is now pinging badly. Too lean or timing to far advanced?

Cheers
Pete
Title: Re: Misfire under load again
Post by: Klaus on 18.12. 2018 00:04
its to lean, lift the needle, this would be my first try, its much easyer.
cheers klaus
Title: Re: Misfire under load again
Post by: bsapete on 18.12. 2018 03:49
Ok, pulled the carb off. The needle was in the top groove. Lifted it one groove so now in the 2nd from top. Cleaned the inlet filter which was a little dirty but not too bad. Screwed air screw all the way in then out
1 1/2 turns. Tickled the carb and gave it a kick. Bingo! started first kick. Went for a test ride (neighbours haven’t objected to the open pipes yet) and very much improved power and pulling pretty well. Just a little flat on initial acceleration but then she pulls hard. Perhaps just a little more fine tuning to get it spot on.
Thanks everyone for your advise. What a brilliant forum. I hope at some point I can offer some advice from my experiences too. I will continue with my magneto maintenance even though my problem seems to be fuel rather than electrical.

Cheers,
Pete
Title: Re: Misfire under load again
Post by: cyclobutch on 18.12. 2018 09:21
... even though my problem seems to be fuel rather than electrical.


And ain't that ever so?
Title: Re: Misfire under load again
Post by: Klaus on 18.12. 2018 09:57
Hi Pete,

lift the needle one groove more, and see what happend.
This engines love to run one the rich side, it is better for the internal cooling.
You have openpipes and no, or weak, reflection wave form the exhaust.

Amal chart says 1959-63 Roadrocket and Spitfire (Export) 1 5/32 bore Pilot 25 Cutaway 3 Main 290 Jet 106 needle Pos 2
Title: Re: Misfire under load again
Post by: Rex on 18.12. 2018 12:54
In another thread I recently asked for ideas for my '51 A7 that would tick-over just fine but break up badly under an accelerative load. The Amal Premier carb came "jetted for your bike", but clearly wasn't as the pilot jet needed increasing in size, the slide went from a 3 1/2 down to a 3 and the 140 main jet was increased to a 200.
That improved things a lot but still far from perfect, so the mag was stripped, the various components cleaned (including the HT spike) and one of Groily's Easy Caps fitted.

First proper run today so I couldn't go far or fast on wet roads, but the bike is transformed. Smooth and powerful.
A good blast to see if the 200 jet is correct will have to wait for drier weather, but so far, I'm very satisfied.
Title: Re: Misfire under load again
Post by: muskrat on 18.12. 2018 19:08
G'day Rex.
Most carb problems are ignition and vise versa *ex*
Cheers
Title: Re: Misfire under load again
Post by: Rex on 18.12. 2018 21:17
Ah well, I was being greedy and had both. Only teething troubles and to be expected on a bike rebuild. ;)
Title: Re: Misfire under load again
Post by: bsapete on 19.12. 2018 07:16
Klaus, I’ll see how it goes with fresh 98 octane plus some booster before I lift the needle further. I sell octane booster so I can get it at the right price 😉
I contacted the PO and he told me the mag was fully rebuilt by a specialist when the bike was restored albeit 10 years ago. It’s done only a handful of miles (70) since then (just started and ridden around the block
occasionally) and I don’t think it’s ever been fettled properly. I’m enjoying this process particularly when I get positive results. Thanks to all.
Title: Re: Misfire under load again
Post by: Rex on 19.12. 2018 09:31
My mag had been overhauled (rewound and new capacitor) relatively recently too, but the capacitor had still degraded enough over time to cause problems. Probably depends on who did the rebuild and what capacitor they used as to whether it's still good or not.
Title: Re: Misfire under load again
Post by: duTch on 19.12. 2018 10:20

 I don't want to flog the horse to death, but like Rex, I had my maggie overhauled mid-90's but then it was fairly much idle until 2013 when I got the rig back on the road....was ok for 3 years, but then I a winding burned and the condensers (little modern pillow shaped orange ones), blew out....ol' mate said it'd outlast me- musta thought I looked a bit ragged.. *conf2*...Having said that, time will tell and I hope for your sake pete, that you're close to a win...(and not on a dead 'orse)  *beer*
Title: Re: Misfire under load again
Post by: bsapete on 19.12. 2018 11:57
I guess time’ll tell won’t it.
If it ain’t broke don’t fix it I say. *beer* to you all lads.
Title: Re: Misfire under load again
Post by: Black Sheep on 19.12. 2018 17:18
So much depends on who rebuilt your magneto. The ones on the A7 and A10 were rebuilt by the same person about 40 years ago and are still going strong. Another rebuilt one has developed massive bearing play after only 10,000 miles. I spent ages fiddling with carburation trying to sort the misfire under load before noticing the bearing play. As you say, most carb problems are the mag and vice versa.       
Title: Re: Misfire under load again
Post by: bsapete on 02.01. 2019 07:21
Update: I drained the tank and ended up with a leaking tap (another story) but have sorted that. Added fresh 98 octane and test rode today. With gradual acceleration it pulls ok then when opening it up a bit it has a big flat spot then picks up. If you crank the throttle open quickly it responds better - ie less hesitation. Also still pinging unless on a light throttle. I assume it’s pinging anyway. Doesn’t go away though if you retard the timing with the lever. Revving it up when stationary the engine is fairly quiet albeit a little tappety. I’m kinda struggling a bit here but I’d like to try and sort it myself. No doubt an experienced person would be able to read the symptoms better than me.
Any advise welcome.

Cheers and Happy New Year,
Pete
Title: Re: Misfire under load again
Post by: muskrat on 02.01. 2019 07:55
G'day Pete.
Put a mark on the twist grip and a corresponding mark on the housing, now twist it full on and mark the twist grip. Now mark the grip 1/2 way and 1/2 again. So now you can hold in the problem area and know which jet to change.
Timing is still too advanced.
Cheers
Title: Re: Misfire under load again
Post by: bsapete on 08.02. 2019 05:24
Hi chaps,
Been a bit preoccupied with pulling the supercharger off my Jag to replace heater hose. Yuk.
Back to the Beeza - Musky, I did as you suggested. With markings on the throttle housing and grip, it seems to be breaking down in the mid-throttle position. I’ve just pulled the carb off to get some numbers etc.
It’s stamped 389/228 and 065 (from a 1965 A65 Lightening & Hornet according to porklips) should be 389/047.

Pilot jet is stamped 25 (correct?)

Cutaway is stamped 389 .4 should be 3?

Pilot jet is stamped 106

Main jet is stamped 400 should be 290?

Needle looks like D to my old eyes and should be in position 2.
Was originally in position 1(top groove) ran better in position 2, ran worse in position 3

Suggestions/thoughts?

Cheers,
Pete

Title: Re: Misfire under load again
Post by: Klaus on 08.02. 2019 08:08
Hi Pete,

yes your are right with your suggestions and the correkt set up is for the 389/047

The cutaway you have fit is to big, so the mixture is to weak.


cheers Klaus
Title: Re: Misfire under load again
Post by: orabanda on 08.02. 2019 08:28
The slide (cutaway) is richer as the number reduces. The next size down is a 3 1/2, then a 3.
Try the 3 1/2
Title: Re: Misfire under load again
Post by: duTch on 08.02. 2019 09:32

 
Quote
Been a bit preoccupied with pulling the supercharger off my Jag to replace heater hose. Yuk. .....


  *bright idea*

 Try it on the Beeza while you can.... *smile* *bash*
Title: Re: Misfire under load again
Post by: bsapete on 08.02. 2019 10:26
Did cross my mind duTch. Gives the Jag an extra 100hp. Now where would I run the belt drive from...

I’ll track down the correct size jet and slide and see what gives.

Cheers
Pete
Title: Re: Misfire under load again
Post by: muskrat on 08.02. 2019 11:07
G'day Pete.
Definitely need a richer slide and a smaller main jet.
As orabanda suggests a 3 1/2 would be better.
You could turn the 4 into a 3 1/2 by taking 1/32" off the bottom of the slide but you'd need to raise the needle the same amount (lower the clip 1 notch).
Also check the fuel height in the bowl. Take off the pilot jet cover and put clear tube over the pilot and bring it up beside the bowl. The fuel height should be at the pip on the cover (just under the ma of Am.al).
Cheers
Title: Re: Misfire under load again
Post by: chaterlea25 on 08.02. 2019 21:26
Hi Pete,
Is the bike in question the one in your avatar ? with the twin high level open pipes?
If so you maybe check out the settings for a Spitfire Scrambler,  *????*
The second part of the number on the carb is only an indication of its original  fitment
Once the choke diameter matches the head it should work OK once properly set up

John
Title: Re: Misfire under load again
Post by: bsapete on 09.02. 2019 05:32
Thanks fellas, I’ve found a 290 main jet and slide with 3 1/2 cutaway locally so have ordered (don’t trust myself to modify the slide I have). John, the settings I listed above are for the 389 carb fitted to 59-63 Road Rocket and Spitfire Scrambler so fingers crossed when I fit the correct size main jet & slide I’ll get a good result.

Cheers,
Pete
Title: Re: Misfire under load again
Post by: bsapete on 15.02. 2019 05:49
Update: new slide and main jet arrived today. On reassembly I note the slide is tight in the bore to the point of not being able to be pushed all the way in. I have taken to it with some 1200 wet & dry and improved it somewhat, it slides but it’s still sticking open at full throttle position. Any suggestions? Keep on lightly sanding until it freely slides up and down? Perhaps a buff on the polishing wheel? The original slide moves up and down with no tight spots.
Title: Re: Misfire under load again
Post by: Greybeard on 15.02. 2019 09:30
I keep seeing this kind of reference:

I had the same problem with overrun on one of my bikes.  It turned out that I had slightly overtightened the carb mounting bolts and distorted the carb body, thus binding the slide from quickly returning to the idle position (also only when warm).  Try loosening the bolts and just tightening them enough to eliminate any air leaks.  Hopefully this will help!  I agree with A10gf on the float level being off on the stalling on the sidestand.

Seabee
Title: Re: Misfire under load again
Post by: bsapete on 15.02. 2019 11:06
Thanks but this is without the carb bolted up to the head so not a case of distortion and also the old slide was moving fine.
Title: Re: Misfire under load again
Post by: coater87 on 15.02. 2019 11:17
 I would buy a new carburator.

 Sanding is just making it easier for air to leak around the slide.

 Really the best you can hope for is the throttle does not stick open when your riding it.

 Lee
Title: Re: Misfire under load again
Post by: Greybeard on 15.02. 2019 12:02
...the old slide was moving fine.
That may only mean that slide and body are both distorted, or that the old slide was so slack that the distortion of the carb body didn't matter. If you put the old slide in are you able to rotate it freely? If not, that would indicate ovality in both parts.
Title: Re: Misfire under load again
Post by: bsapete on 15.02. 2019 22:52
Yes the old slide is a nice fit and will rotate through 360 degrees without binding. I’ve achieved the same with the new one with light sanding.
Title: Re: Misfire under load again
Post by: trevinoz on 16.02. 2019 01:41
Maybe you should have sent the carby away to have the body bored and the slide sleeved.
Probably wouldn't have cost much more than a new slide.
Title: Re: Misfire under load again
Post by: bsapete on 16.02. 2019 23:53
Maybe you should have sent the carby away to have the body bored and the slide sleeved.
Probably wouldn't have cost much more than a new slide.
[/quote]

It cost me $30 for the slide, I doubt I’d get much done for that
Carb is reassembled and back on the bike. Started second kick after a good tickle. Idle was high so screwed the idle screw out to settle it. Took it for a ride and once warmed up it pulls well. Certainly a marked difference with the correct 290
main jet and the 3 1/2 cutaway slide.
Title: Re: Misfire under load again
Post by: coater87 on 17.02. 2019 23:28
Maybe you should have sent the carby away to have the body bored and the slide sleeved.
Probably wouldn't have cost much more than a new slide.

 I had that done, I dont know if they did it wrong or if never being able to change slides is a side effect.

 They bored the body than sleaved the slide to fit the body.

 A new slide is much to small a diameter.

 Lee