The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Amal, Carburation, Fuel => Topic started by: Gerry on 09.09. 2014 05:00
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OK Guys...its me again...Still having problems with the Flash since last November when I first registered it. As said before, I have had three mags and a boyer fitted with no change in the missing. Had one mag fully overhauled and tested and still got the problem so got two 376's off a mate who assured me they ran on the bikes they came off.....no joy. Fitted a 930 I had lying around and all came good except when she got hot the throttle slide stuck (brakes to slow me down and cut the engine!!). Tried another 930 (haven't got a 928 unfortunately) and the same thing happened, sticking throttle when hot. Bought a secondhand 356 off Feebay and did a lot of cleaning and heating to get the throttle stop and pilot jet out and faced the flange. All jets correct, needle also. Fitted it and tick over good but cuts out or misses on left hand (near side) cyl' when throttle opened a bit quick. Fitted a #30 pilot jet...same problem. Raised the needle a notch #3...still a problem. OK not the best thing to do but put the slide out of the 1st 930 in the lathe and took a couple of thou' off the high spot. Then took a 1/16" of the bottom of the slide to give the same effect as a smaller cutaway.......still got the problem!!! Took both petcocks out of the tank...no crud, good flow. Replaced both the fuel lines and fitted new carb screen at the float bowl. Fitted neoprene float valve. Oh forgot to mention, before fitting the 930 I borrowed a completely overhauled 376 carb, off a mate and it still misses at slightly open throttle!!! So all the carbs' I have tried seem to miss or cut out as soon as the throttle is blipped and yet the 930 didn't do this the first time I tried it, just stuck throttle when hot. Where do I go from here. Got a feeling in me water there's a problem elsewhere. :-( Cheers. Gerry.
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Hi Gerry
Watching this one as my Flash chokes on a swift handfull, never thought of it as a problem though as you'd never stay on the seat if the engine responded in synch with your wrist.
My RGF on the other hand does keep up with the twsit grip better, maybe just a performance thing
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The thing that I wonder about is why 2 apparently good carbs both stick when they have been working well . Was the carb really hot to touch when you'd brought the beast to a stop? Incidently have you a manifold spacer fitted behind the drip tray ? I was told this was there to stop the carb getting to hot if you have whats it made of could be tufnell or some form of plastic . It's the only thing I can think of but would check and also check your throttle cable with all this messing about it would be a shame to have a frayed cable stop you again when you do sort this out ,best of luck, BobH.
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And next, just how tight are you dong up the carbs?
They should be just a bit over finger tight.
When done up properly you should be able to grab the bady and wiggle it on the studs, if you can not then it is too tight.
Next is the O ring.
Must be a nice new soft one, not an old hard one which just acts as a fulcrum to bend the carb flange when over tightened.
Instant response is controlled by the slide cut away up to about 1/2 - 2/3 throttle
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Instant response is controlled by the slide cut away up to about 1/2 - 2/3 throttle
scuse me jumping in Gerry
So Trevor if you leave the choke down the response should be better ?? (yes/no)
Those four simple steps Amal give for tuning a monoblock never quite stuck in my old brain (even when it was young)
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OK, 'O' ring is good, used a smear of silicone grease to hold it in place while fitting the carb. Flange nuts definately not over tight (been there, done that), don't have an insulation block between the carb' and manifold, only the bias alloy spacer. So..manifold, gasket, bias spacer, gasket, drip tray, carb' with 'O' ring. Latest update is I took it for a ride today and at a certain throttle opening it was running on the off side cylinder only and if opened up from there continued to miss as if starved until with the throttle opened up further it came good. Didn't have the presence of mind to close the choke though, maybe I should have but the bloody choke is down on the frame in front of the oil tank and not easy to find with gloves on (should have left it on the bars but got the frame one later and fitted it) Am I going the wrong way fellas? Should I be looking at increasing the air and reducing the gas??? Doesn't seem right to me though somehow. It is bad enough so as not to want to take it on a good long run. Some times while ticking over it misses on the left hand cyl' and some times just cuts out altogether. If its not the mag and not the carb' what else could it be, timing? I haven't strobed it. But can't think of that as a problem as it pulls like a train when going on both cyls' IT HAS BEEN TEN MONTHS OF F^~K*#G HEADACHES My wife says "why don't you give up, you have the patience of Jobe" The lttle C15 Trials Pastoral took me 7 years to complete with bits quite rare to find and yet when finished and after 6 kicks it never looked back!!! Think I'll go out the shed and look at it and have a smoke! Thanks Guys Gerry
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Gerry,
I typically stay away from trying to comment about obscure carburation issues because I know very little about jet sizes, needle settings, cutaway profiles, etc. Nevertheless, it seems to me that chronic failure to fire on one cylinder is probably not carb related. As far as I have ever heard or read regarding bias, it does not cause a dead hole. Some other possibilities that haven't been named: sticking or floating valve, spark plug, plug wire and end fittings (quality and terminations), mag pickup (check for hairline cracks along which spark can travel), points symmetry between lobes, leakage in plug wire (spark jump) to nearby metal, other? (Please take no offense if any or all of these thoughts are rudementary to you.)
Looking forward to being chastised for naiveté an finally finding out what the problem was.
Richard L.
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Hi Richard, Thanks for some other things I should maybe looking at. I have new plugs (changed numerous times NGK) new leads and NGK plug caps, also new, mag overhauled with new slip ring brushes and new points cam ring, new mag' pick ups and new capacitor/condenser which fits under the points, old one inside armature end cover removed. Plus as said before had numerous mags' and carbs' on it. Ends of plug leads soldered into washer that fits into pick ups. Maybe check these ends for contamination with oil or petrol? What I cannot understand is why does the 930 carb' miss fire same as all the other carbs' I have fitted when it didn't do that in the first place. I think you have pointed to a few things other than carb and mag that need looking into. I don't think its a sticking valve either as it ticks over with only an occasional "hickup" and if I open the throttle slowly it picks up fine (when in neutral on the centre stand, it is far worse under load of course). I have had the head off numerous times and re lapped the valves and checked valve stem to guide clearance and can find no problem there either. I am missing something but can't think what. I shall have a bloody party when I get it right but I bet it will be just as the registration runs out!!! Cheers and thanks again. Gerry
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From what I can see in their advertising, NGK plug caps all include resistors, which should not be used with magnetos (as I understand it).
Richard L.
Edit: Adding to that, different value resistors are available. Are you sure the caps are matching? Have you tried swapping plug wires and pickups to see if the problem moves to the other cylinder?
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Gerry, just a couple of things I thought of... maybe you can check..
are you running Suppression plug leads or caps?
to me it really sounds like it's getting too much fuel & not enough air when opened quickly..
does the fault go or improve if you remove / replace your air filter?
as I was typing this Richard had the same idea... ( GREAT minds think alike ) *computer*
best of luck with it...
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Richard had the same idea... ( GREAT minds think alike )
...and sometimes I jump in too.
Richard L.
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Had exactly the same symptoms on the '58 SA. When opening the throttle to quickly it choked, and some time later it wouldn't fire on the right cylinder. Since I got the bike the right cylinder also never fired regularly at tickover. Fiddled a lot with the carb (brandnew Amal, trying 3 different sizes of pilot jets, and 3 different slides) in an attempt to solve it. Finally, when checking the magneto I found a carbon trace all around the slipring (it was really hard deposit, had to take the magneto apart to get it off). Also replaced the pick up brushes. After that it ran fine for a couple of weeks until the story started all over again and the slipring had this carbon trace again. Getting tired of it, I replaced the magneto by a Pazon ignition. The ignition is on for about 6 months now. Since then no more problems. Pulls like a train through the revs without hesitation, fires equally on both cylinders at tickover and always starts first kick.
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NGK also make non resistor plug caps.
Trev.
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Thanks, Trev. I've now found them and stand corrected. Stand back so that the egg dripping from my face doesn't stain your shoes.
Richard L.
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Hi All
Gerry,
A lot of carb problems with throttle responce etc can occur if there is a step in the inlet tract especially at the bottom
Having a too big a carb will cause a step and also lag in throttle responce
There was a link to an article on this some time ago but cannot remember where ????
HTH
John
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Good points there (no pun intended *smile*), and did you experiment with plug heat range, or types..?
I had a 'not so similar' thing, and was running BP7ES, and went back to B7ES, and it made an immediate difference...so far, so good... still a touch rich, might try 6's...??
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Hi Richard, You may have a point there as the first plug caps I used fell apart when pulling them off the plugs so bought the NGK to fit when I fitted the Boyer so I think if I remember right that they are resistor caps. OK will see what I can replace them with. Hi WazzA, No there is no difference with the filter on or off. I'll check the slip ring, but haven't done more than 10 miles on it since fitting the overhauled mag'. Hi Morris, I did fit a Boyer system to it as a desperate attempt to solve the weak near side cylinder problem, but that didn't make any difference either although at that time I didn't have the missing with quick throttle response with either the Boyer or the various mags I tried. Hi John, When I first tried the 930 after many attempts with 356's it was the first time it ran well other than the weak left cylinder, open the throttle and immediate response, just stuck slide when hot. Hi Dutch I am using NGK BP7ES, wanted BP6ES but couldn't get hold of any locally. But I have been using them since I first got her running after the build and the problem I have now wasn't there earlier with the 930 carb. Will keep you all posted as I progress. Thanks again fellas. Much appreciate all the help. Gerry
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Hi John, I got it wrong!!! The last carb' I fitted was a 928 which is the same bore as the manifold. Just replaced it with the 930 and still have the problem. I also got the plugs wrong..they are BP6ES I couldn't get BK7ES but the 6's were also recommended somewhere but can't remember where. Next job is to find a set of non-resistor plug caps and check the mag' slip ring. Then if all else fails, strobe the timing. Cheers. Gerry ps getting pretty close to strip and rebuild blindfolded.
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Just a thought with regard to resistor caps- I've read that the spark goes 'TO' the plug on one side and 'FROM' the pug on the other side (if yea kenow whut I Mean...?), sooo, would that mean a resistor cap on the side where the current goes TO the plug, the risistor would mess it up..??....but on the side where the current flows FROM the plug, and then through the resistor cap, it would be less affected by the resistor...??
But then just as I finished, that little theory, I remembered that is in the case of a magneto, but you had the problem also with the Boyer....??
Maybe move over and make room on the bench, offer up the green cone Richard.... *fight* *beer*
uhoh...
I thought about specifying 'head cone', but am probably already in deep enough... *ex*
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Two good links about resistors in plug caps.
http://www.a7a10.net/forum/index.php?topic=5576.msg37955#msg37955
Make the noted selections after going to:
http://www.brightsparkmagnetos.com/faqs/
FAQ about magnetos generally
Are suppressors and resistor sparking
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HI Gerry,
Then took a 1/16" of the bottom of the slide to give the same effect as a smaller cutaway
This also has the consequences of lowereing the needle and making it leaner
to make it work you also need to bore the same amount away where the needle clip seats
I cant remember who had similar problems some time ago??? (was it you?)
As you have tried several ignition systems, ruling out ignition problems
check with a strobe on each side anyway its easy to see misfires with the strobe light
If one cylinder is lean to the point it misfires then that side is drawing air??? worn or loose valve guide??
I had a bike in with a miss on one side (after trying everything) it turned out to be a collapsed valve spring
HTH
John
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A lot of carb problems with throttle responce etc can occur if there is a step in the inlet tract
There was a link to an article on this some time ago but cannot remember where ???
Here it is again;
http://www.braigasen.com/Induction_port_obstructions__%28by_George_Templin%29.pdf
You got us all puzzled here Gerry. With the danger of being put on a stake and get burned by the international women's league, don't listen to the wife this time. Keep on looking. When you've found the solution, the reward will be great!
John might be on to something when suggesting an air leak. Hairline crack in the left side inlet tract maybe? If I'm not mistaking up until now you haven't tried another head yet?
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Hi Dutch, Richard, John and Morris, OK I just checked the Brightspark website as suggested by Richard, very interesting that a resistor might eventually breakdown the armature winding insulation and showing the fact that it does interfere with the spark in a minor negative way. So resistor caps are a No No!! Things have changed since I first had the non-firing near side cyl'. That side is now firing much better and besides that the other problem was the sticking slide when hot. Now I have the severe missing when blipping the throttle or on the road at about 1/4 throttle opening only the right side is combusting. If I open her up further she comes good after a lag of a second or so. What has changed? Only the magneto. I think I am going to remove the cast head and fit the alloy twin carb' head with manifold and see if that improves things, will also check porting alignment prior to fitting as suggested in the site John added (thanks John very interesting). Remember I have also tried a 376 that had been bored and resleeved with brass which was the right port size. So air finding its way around the slide wouldn't be a problem I don't think. Cheers and thanks again all. Gerry
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I am with "Morris", check your slip rings for carbon deposits. Had it on my Brother in law's A10. The pickup carbons can be too soft and they leave a track on the slip ring.
Try cleaning the slip ring If ok for a while get new quality pick up brushes, there are a lot of pattern pickups that are way too soft.
930 concentric carbs are renowned for distorting either when hot or when tightened. Strange some carbs never do it. other always do no matter how you prepare them, flat flange and stub etc. Took mine off and went to Mikuni, not everybodies cup of tea but good starting, idling and running, what more do you want? and you can always revert back if you become a rivet counter.
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OK Guys, Took the plug caps off and wired the lead ends direct to the plugs....seemed to improve the idle but that could be wishful thinking. Checked the slip ring of the mag and absolutely clean and bright brass strip. So off came the tank.....again... and removed the rocker inspection covers and checked the tappet clearance WHATTHA!!!!! I set these with a lot of care and patience and now the right hand inlet is 0.024" should be 0.010" the exhaust is 0.020" should be 0.013" the left hand side all over the place as well....what happened here? So bugger it, took rockerbox off removed the pushrods (straight as), removed the head and placed my palm over the right hand barrel and using my other hand cranked the engine. Couldn't push the kick start too far as the suction on my hand was too much. Did the same on the left hand barrel and could turn the crank over even though there was suction on my palm it was not as much as on the right cyl'. Took the barrel off (difficult) and checked the rings and all seems good. Good clean bore in the barrels, no scoring, no visible problems with the pistons and rings are free and shiny. Looks like I shall be investing in another set of new rings and the alloy head with single casb' manifold bolted on. Looks like a quick hone to give me the cross hatch pattern to bed in new rings. Would all these problems give me the results I have been getting? Cheers. Geriatric. I have now copied this to the engine section.
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HI Gerry,
How do the cam and followers look?
Tappet clearance increasing can be due to wear on the cam and followers
caused by lack of oil pressure bypassing the PRV *sad2*
Usual cause is worn timing side bush, or bad pump *sad2* *sad2* *sad2* *sad2*
The current A10 in for refurb arrived with the owner saying "its not charging"
Timing cover off to reveal a v belt dyno drive full of oil and loads of up/down play on the main bush *eek*
John
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Hi John, See my post in engines. Cheers. Gerry
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OK Time to go back to first principles.
Get yourself 1 ( 2 is better ) colortunes .
They are soft plugs with a window in them so you can see what is happening inside the cylinder.
This will take a lot of guess work out of your problems and save thousands of hours fixing problems you never had.
The absolute fastest way of isolating ignition problems from fuel problems particularly to the untrained ear.
You really have to go back & stop look & listen otherwisw we will happily tell you our pet problems ( the one that had us foxed forever ) and you will work through each one of our problems till one of them lines up with your particular one.
Now for starters you must have a tuffnol gasket in the inlet train and better still would be two. The thicker the better.
BSA did not fit them for the fun of it , fashion or to drive the price up
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Well fellas we now know what the problem was as said in another post, the bloody crankshaft timing pinion was off an A7 and one tooth out with the valve timing. Cheers. Gerry