my 65 a65 single carb is running a mk1 Concentric carb ,carb is a later type & not worn out,the bike has not done many miles since being rebuilt,bike seems to be getting richer at idle the more miles i put on it.i have dropped the needle & it has lightened the plugs colour slightly plus improved mid range response ,however at idle the bike is rich ,mixture screw only changes the idle a small amount.what sort of base jet sizes should i be starting from .bike is not running hi comp pistons etc just downpipes without silencers with baffle fitted inside them.i have cleaned the carb loads of times no effect ,even altered ignition timing to reduce some low rpm piston slap or pinking .i can get a smooth idle when the timing is slightly advanced however the engine knocks badly under load at low speeds.the bike is running the wassall electronic ignition system.power seems good & fuel consumption is fine.any ideas
mixture screw is 1.5 turns out ,i dropped the needle because there was some slight 8 stroking at part throttle ,above idle the bike runs great ,i have no silencers to try on the bike .there is no heat insulator block fitted however there is not the room to fit one & have an airfilter ,it is pressing right up to oiltank mounting bracketry.i am going to try one of the stay up floats because when i shut the fuel taps after only a few seconds the idle smooths out & the mixture screw seems to affect the idle quality.just been experimenting & discovered the effect shutting the taps make ,must be flooding very slightly or float height a bit high.
i am going to try one of the stay up floats because when i shut the fuel taps after only a few seconds the idle smooths out & the mixture screw seems to affect the idle quality.just been experimenting & discovered the effect shutting the taps make ,must be flooding very slightly or float height a bit high.
I wouldn't be in a hurry to use a "stay-up" float.It may take you days and much modification (including float weighting) to get the fuel level correct with a stay-up float.Far easier to check the float level of the existing float and adjust if necessary. If you have a brass float needle,replace it with an aluminium needle.
Most of the richness is likely to be caused by a worn needle jet. 0.0005" wear will make it rich,especially from idle up to 1/3 throttle.Needle jets wear out in 10,000 miles.
Above 1/3 throttle,you can adjust the needle clip position to lean it off.
Does this carb have screw-in pilot jet or pressed-in pilot jet?
As peter has just said, needle jets wear oval in a short amount of time particularly if you idle the engine a lot. Contray to popular belief they are a standard tune up item and when the bikes were new got replaced with the points, condenser & plugs. Next if you can turn the mixture screw more than 1/2 turn in either direction without the engine cutting out then the pilot jet is blocked and you are idleing on the slide. About 90% of the A 65's I have come into contact with were doing this and many ran quite reasonably with the jet fully blocked if you exclude an idle speed 50% to 100 % higher than what it should be. Last get the carb sorted out now, before you start changing things, once you have it running right, then fit the new float otherwise you will have too many variables to sort out. A good rule is only ever change 1 thing at a time.
thanks for all the tips ,carb is a 920 type ,it looks to be the float needle at fault ,its a plastic type .mixture screw only works correctly when i turn the fuel off.as soon as i turn fuel on engine runs rich but does not flood out off tickler etc .you can leave the bike stood with the fuel on & it does not leak.bike is a bitsa & i think carb was used just because it fitted & was not set up correctly.i have had the head off ,the carbon was very soft which directed me to the rich mixture .looks like its a few more hours workshop time to iron it all out
because the bike has virtually straight thru pipes & setting it up in the garage really impresses the neigbours, i decided to fit a set of old triumph pipes i have,removed the baffles from the downpipes fitted the silencers & whoopee bike runs way better, idle better ,no hunting so for now bike is back in daily use ,time will tell if its a cure ,i think the baffles i fitted were the culprits
my carb richness problems have reappeared with a vengance ,i have replaced the float & float valve with an adjustable float,also added an extra pilot jet incase the built in jet had been drilled out or similar.the problem seemed to correct itself when i added silencers to the bike .i think i have found the culprit.bike has a replacement chrome pancake airfilter with a paper element .the bike is used in all weather & when it gets damp the mixture gets rich ,dry the element out & all is fine till it rains.i seem to remember that the old type filters on my bike years ago had a wire gauze filter .is there a substitute element available for these filters,i have seen k& n elements up for sale but are they worth the cost ,or should i just cut some paper from the element to reduce its restriction.
#463747 - 11/18/1212:07 amRe: 65 a65 carb settings. problem back
I recently had carb setup problems to which the filters were making a very large contribution. I went through the same replacement strategy pretty much as you did because I was tearing my hair out. I had been running the gauze filters made by Copper Asbestos (Something) which were OEM suppliers. John Healy has discussed these here recently in a thread possibly started by Allan Gill if you care to search. I sourced these from EAW m/cycles (www.eawmc.co.uk) who should be convenient for you. You can proably get them anywhere though.
I found the filters were loaded up with an 'oily residue' and I'm not sure where that came from. I did at one stage have a minor dribble fron the tappet oil supply at the head or it could be from reversion? Anyway, washed them with petrol but this did not completely cure the problem. I replaced these with fresh gauze filters from the local brit bike shop (brand unknown as they change supplier like I change undies, could be EMGO, but they looked a lot like the copper asbestos ones) This cured the bulk of my problems, then I could go systematically through the proper carb setup routine.
Just try it without the filter and start from there. Change one thing at a time (even if only for your satisfaction that you know where the problem was). Consider that when you put a filter back on it will slightly more rich.
From here on I'll be considering filters another 'standard tune up item' (to quote Trev) and changing at regular intervals.
I'd recommend using the original style filters. Elements are cheap. In future I wont be using anything other than a 'gauze' filter. I hunted the Copper and Asbestos ones down because I was dissatisfied with the paper elements the local shop had sold me at a previous time (seems I need to keep my own stock of 'proved parts these days what with carb spares being somewhat unreliable also depending on who the local guys bought from last week. My mistake was not to consider the need to ever replace them (i'm still learning about this stuff). Original style filters are a known quantity for these bikes and obviously work. You might be able to find a housing cheap on evilbay?
For the carb parts I wouldnt use anything other than sealed plastic packed genuine AMAL and hope its recent production. There is some junk available.
One approach might be to get it sorted without a filter first because you can start there right away. And then optimise with your filter of choice.
BSA 1969 A65F BSA 1966 A65H Triumph 1968 T120 Kawasaki A1R & too many projects!
thanks ,thought i was being daft as every british bike i see localy has these paper elements but the bikes are show & weekend bikes .i have located a washable gauze filter & its on its way .hopefully happy days are here again
#463787 - 11/18/129:00 amRe: 65 a65 carb settings. problem back
I'm not disagreeing with anyone, but I've used the paper elements in pancake filters in all weathers without them getting soaked, except once, when I was using a very short Manx front mudguard. The front wheel threw water right over the top of the engine, in very wet weather conditions. It never happened with the normal sensible front mudguard, which I've used ever since.
I must say, I've always found Amals easier to tune with no filter fitted.