strange running A10

[mike667]

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 

[A10Boy]

Expand on "Hesitation"  what are the symptoms

[mike667]

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

[muskrat]

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

[A10Boy]

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.

[BSA_54A10]

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.

[mike667]

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

[RichardL]

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. 

[A10Boy]

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.

[t20racerman]

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!

[RichardL]

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.

[A10Boy]

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.

[RichardL]

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.

[A10Boy]

OK,  if you say so. Nevertheless, seems dumb

Sorry if I have caused offence, that wasn't my intention.  

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.

[RichardL]

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.