Amal 928 on gold flash 59 cutting out with quick throttle opening

[Gerry]

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.

[bsa-bill]

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

[Topdad]

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. 

[BSA_54A10]

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

[bsa-bill]

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)

[Gerry]

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

[RichardL]

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.

[Gerry]

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

[RichardL]

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?

[WozzA]

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 )   

best of luck with it...

[RichardL]

Richard had the same idea...  ( GREAT minds think alike )

...and sometimes I jump in too.

Richard L.

[morris]

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.

[trevinoz]

NGK also make non resistor plug caps.
Trev.

[RichardL]

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.

[chaterlea25]

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