The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: mike667 on 21.07. 2011 15:28
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Hey Gang - sorry for long time no talky - moved from boston to sunny california for job reasons. Year around ridins - my A10 seems to love it so far - big ride this weekend on it up the pacific coast highway - yippy!
anyway a question about a friends bastard A10. He just redid the motor - started 2nd kick, though the timing does seem a bit advanced (will kickback unless one does the short-kick - kicker 1/2 way through stroke method.) The problem encountered is it seems to hesitate slightly when going at steady state cruise - accelerates great, starts typical 1st kick (but will kickback if trying to kick though the entire kick cycle), doesn't seem to ping under load. Plugs look great, and have tried dropping and raising the needles just to see what happens (has double carb head on it) with no discernible change in hesitation. Would one blame the slightly advanced timing on this - or others areas to look too
thx
Mike
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Expand on "Hesitation" what are the symptoms *conf*
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almost like it's a bit jerky - but to a very small degree, hard to explain, but it feels like the motor isn't happy running at a constant unchanged rpm - crank the throttle and it accelerates very well, but hold rpm's again for cruising and feels sluggish/jerky/hesitant again (not sure range since no tach - but some where in 2500-2500 i'd guess) - might be my imagination but exhaust report sounds a bit off too
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G'day Mike,
to start I'd back the timing off a tad to improve starting. It might help but it also sounds a bit lean on the slide, hence needle alterations not helping. Are the slides worn or is there an air leak at the flange ?
Cheers
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I agree, check the timing. Then if it still does it, do a plug chop, that is take the bike for a run and hold it at the speed where it's hesitating for at least a mile or two, then pull in the clutch, hit the kill button and stop, take out the plugs to check to colour. You could also try rubbing some grease or spraying WD40 around the carb flanges to either stop of look for air leaks. The flange on the amal carb is prone to bending if over tightened, but can be sorted by draw filing.
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Which magneto end ?
Auto or manual advance ?
A worn Aa unit will"bounce" around at constant speeds while under acceleration the bob weights will be pushed hard out.
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Hi Guys - OK - yes brand new carby- ( 389s), don't think its a leak at manifolds (did the spray thing w/ no results) - had rebuilt magneto (auto) - i'll try to retard a bit and see what happens from there. I'll report back
thanks as always!
MIke
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Not saying it's the answer, but Trevor's comment is very interesting. If you're timing with the timing cover off (I assume you will be unless you have slotted mag mounting holes and manual advance), then this is a good time to be sure the auto-advance springs provide a nice, positive, snap-back.
Richard L.
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Actually, the AA unit doesn't need to snap closed, it just needs to be free. The force of the engine turning the mag will close it providing its free.
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My recently rebuilt A10 was doing something similar and there were two causes:
First it was running too weak on the pilot jet (concentric MK1) which turning the pilot jet screw in certainly helped. Secondly, I had a fuel starvtion problem due to muck in the tap/carb. It ran fine given a big hand full but on continual cruise, it would hesitte and stutter. I initially 'solved' the problem by turning on both petrol taps!
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At the risk of wasting time on a point that may not solve the oiginal issue and, also, at the risk of being flogged for missing the point, I am inclined to disagree with Andy about the bob weights. Constant RPM centrifugal force will keep the weights at a given, let's say "radius", which is held against the force of the springs trying to return them to the at-rest, minimum-advance position. On acceleration or deceleration, they go on the move until a new constant RPM is held. As I understand it, maximum advance occurs well before redline, but this should describe the behavior up until said maximum advance.
Richard L.
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You would think so, but in reality, the AA unit is quite crude, its more of an on/off switch than a calibrated device which provides an increasing advance at increasing revs. Start the engine and at anything above tick over or thereabouts, it will be fully advanced, stop the engine and even if its still open when the engine is switched off, it will be retarded by the action of turning the mag as soon as the kick starter is moved. In other words, all it really does is give some retard at start up.
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OK, if you say so. Nevertheless, seems dumb. Do you think they did much testing to determine if a variable auto advance would be better? Do those of you who have manual advance use it as an on/off swtch? I suppose stronger springs result in more variation with changing RPM.
Richard L.
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OK, if you say so. Nevertheless, seems dumb
Sorry if I have caused offence, that wasn't my intention. *conf*
I dont think it's "dumb" at all. I have had several bikes with Manual advances, in fact my current AJS CSR has a manual mag, the lever is really only used to give retard at start up, but once its running you can advance it and leave it there. The only time I use any [slight amount of] retard is when running in traffic or slow journeys around town.
I dont imagine BSA even thought of variable timing on the cooking A10, most makes used a similar device at that time so it probably wasn't an issue. You only have to look at the puny springs compared to a japanese bike from the 70's to see that it was very crude. If they thought any bike needed variable timing, they put a manual mag on it.
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Wow. No offense taken whatsoever while reading your post. Enjoy the exchange, as always. The "dumb" was addressed to original designers, but I'm really not the one who should criticize them.
Richard L.
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they did a variable advance , it was a cable and lever, folk I know with rockets and Shooting Stars say they do use a bit of retard on hills, probably stops pinking as well and that might be the reason sports models have the manual type.
Thinking cost wise it would surely have been cheaper for BSA to fit a cable and lever than an AA unit?, and really it's no big thing to pull a lever back.
Of course there is also the haggle factor from providers, maybe Lucas did an all in one price for the maggie and the AA unit.
I recall in the Sixties Massey Ferguson fitted two fuel filters to their 35 tractor, Crossland had a contract with MF to supply fuel filters but CAV would not supply fuel pumps unless MF fitted CAV filters so two filters *doh*
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Lumpy running at road speed on light throttle makes me think rich mixture from worn needle jet or wrong needle clip position or retarded ignition timing.
If it's more of an even judder at half engine speed frequency, suspect throttles out of synch.
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Oh sure. Go ahead and get back on topic if you must. *smiley4*
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I commented on this because I didnt want people to think that their AA units should snap back, most don't and people would think they were faulty when they aren't. I mean, we have enough to worry about without that.. *smile*
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well men see we've strayed a bit- haha
still trying to get it right - retarded the timing and problem still exist. Geezer up the street who lost a foot racing his triumph back in the day (mentioned something about an illegal run from cop's - but know how tales go) swears we need slightly bigger pilot's so awaiting that. we'll see
thx
m
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Stumbling during no load is usually richness in my world. try dropping the needl a notch or two. If it's your slide then you'll have to find a friend with a slide with a leaner cutaway to experiment with.
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Hi All,
I'm presuming that the bike is running a Monobloc carb??
Check the carb needle jet?
If the jet has a T on it then it doesnt have the air bleed holes drilled across the jet *conf*
I had a bike with the same symptoms, and it turned out that it had a 106T needle jet fitted
HTH
John O R
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As shocking as it may seem - the larger pilot jets completely cleared up the problem - i am in disbelief but glad it did it - one-footed geezer up the street who suggested it is of course proud as can be - say's happy that these "kids" (i am 46 today) still like the old bikes and take advice from there elder's - haha - have to buy him a 12 pack of bud-lite in thx!
anyways thanks all for suggestion as per usual
mike
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Great. Glad to hear it is worked out. Hope Bud-Lite is his favorite, otherwise, c'mon, you could do better than that!
Now, I'm no carburetor expert, but I thought the pilots were out of service once fuel was flowing past the needle with the throttle open. I assume that bigger pilots means richer mixture, which goes against the popular choice of solutions. I hope to come to understand what was going on here. It's been an interesting quest.
Richard L.
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ManoS
yes actual bud-lite is his usual "strolling about the hood" brand of choice -
i hear you about the pilots - it goes against all that i thought i knew about carbs - new pilots probably masking some other carb problem - but friend has been tearing up the streets w/ his A10 and is loving it...
well till the mount on his custom oil tank cracked about an hr after getting the carbs dialed in that is....
gotta love british bikes!
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Do you guys know what Bud Lite and making love in a canoe got in common?
They're both f***ing close to water! *grins* *beer*