Hi Just thought id replace the over size AMALConcentric i was useing with correct size/ model AMALMonobloc on my 1955 BSA A10 to try and improve traffic light take off ,(the Concentric always coughed back and sometimes stalled on sharp take up from idle). Ive purchased a used correct AMALMonobloc 376 , with 1 1/16 bore , 240 main jet , 25 pilot , 3 1/2 slide , 106 needle jet and letter D 106 needle, set in position 3 from top. I have the air screw 2 turns out it has a bellmouth inlet at present which i will change for a K and N filter. This configuration is correct according to all the data i have for my bike . It works very well out on the road , pulls nice and clean , with only minor hesitation on fast take up off idle , which is where the problem is ?? The idle is blistering fast ?? even with throttle stop screw removed it wont slow down , and ive given ample free play in throttle cable , ive even put finger in carb to push slide down , which ive discovered rattles a bit . There are No air leaks ? could it be wear in the slide , makeing slide shake about with induction pulses , pulling extra fuel in ??.
Richy, I don't have an A10, but had exactly the same issue with an A65 and concentrics that had worn rattling slides. Could not turn down the idle. New carbs solved the problem. It is my belief that the worn slide lets extra air pass and you try to compensate with the idle mixture. Same was true on my b44 with a worn slide.
That is my experience. Good luck
Re: amal monobloc , very fast idle problem ?#28614 08/26/071:33 pm08/26/071:33 pm
Spot on , 10 points ive just discovered the nipple on throttle cable was hitting inside slide on top of the centre piece casting , which isnt in the concentrics . stopping the slide from fully bottoming . i just countersunk the middle piece around small hole to allow nipple to recess into it . Yippee it worked , slide fully closes now , even though it still rattles about a little ? . i read somewhere that the BSA A10 should snap open throttle instantly responding with no hesitation , spitting or coughing , ive still yet to get mine to work like that , maybe the magneto mechanical advance cant work that fast , or maybe its just a miff ???
Re: amal monobloc , very fast idle problem ?#28616 08/26/074:02 pm08/26/074:02 pm
any ideas how to get the carb to pick up quick off of idle with out that bloomin hesitation ?? its no better than the Concentric i had on before ?? I know modern carbs use a power jet that gives the engine a nice squirt of fuel ? is this why the amals are not so responsive ??
Re: amal monobloc , very fast idle problem ?#28617 08/26/074:15 pm08/26/074:15 pm
My T-Bolt was a slug at take off but during the card rebuild I noticed I had the wrong jet. Installing a larger jet improved the situtaion but still a cough. Finally moving the needle up a peg solved my problem.
In your case as the needle is at it's highest (third from the top) how about dropping it a ring just in case you're too rich.
1971 BSA Thunderbolt
Re: amal monobloc , very fast idle problem ?#28618 08/26/074:21 pm08/26/074:21 pm
it actually picks up better if i use the choke , but soon falters after , as i guess the plugs soot up ? Its as if it needs a shot of richness just to overcome the sudden throttle opening . richening the pilot doesnt do much ? i think i will have to ignore the standard factory setting and undertake a laborious , jetting and tinkering session , may even have to get my colourtune plugs out ???
Re: amal monobloc , very fast idle problem ?#28619 08/26/074:23 pm08/26/074:23 pm
hi Alex Idle jet ?? i guess you mean pilot jet . if im running the standard no25 jet which numbers are richer ?? higher or lower and in what increments . im a little unsure about the looks of my modern cone shaped K and N filter ? On the previous Concentric i used a chrom cylindrical fast flow type that looked smart , i dont want my pistons and bores wearing out with that huge open bellmouth , any ideas ?? thanks to the fuel inlets in the way on the Monobloc i cant flush fit a filter onto the back of the carb ? hence the stubby cone job .??
Re: amal monobloc , very fast idle problem ?#28621 08/26/074:52 pm08/26/074:52 pm
Higher numbers are richer. Try adjusting the air screw in first. IMHO, if going up one jet size (30) doesn't do it, the slide is too clapped out.
BTW are you using the fuel banjo that goes almost straight up? Those were made for monoblocs fro that very reason, so you could fit pancake filters...and what about a stock airbox? They're not that hard to find.
A smattering: '53 Gold Flash '67 Royal Star '71 Rickman Metisse '40 Silver Star '37 Rudge Special sixtyseventy Lightboltrocket road racer...and many more.
Re: amal monobloc , very fast idle problem ?#28622 08/26/077:39 pm08/26/077:39 pm
Hi Alex Yes vertical inlet banjo sounds good ? i will need one for twin taps though ??. Ive looked at all the AMAL website dealers but none show this item ? I will keep looking. due to haveing large battery @ box in way i cant fit in a airbox . I was hopeing people were going to tell me there isnt any BSA,s that are good off of idle ?? now im determined to get mine working right, i dont want no more revving it at traffic lights then cough , stop just as they turn green .
Re: amal monobloc , very fast idle problem ?#28623 08/28/071:16 pm08/28/071:16 pm
for a different perspective , and because 2 entirely different carbs are presenting the same symptom , I would have a look at the ignition timing . Since you have an A-10 ,I am gonna "assume" you are using a Lucas K2F or something similar . I would double check timing , if it is manual advance unit try different positions with the lever , if it is the auto advance type you may have worn springs or stuck mechanism .Points gap , plug gap , overall condition and health of the magneto/plug wires and quality of spark have to be up to snuff or no amount of carb tuning will get it in the zone . All of this has to work in sync with the carb or you might get the symptoms you describe.
Hi has 1500 mile from new K2f with new recon auto advance , ive tryed new NGK plugs .over the champions ? after hard run have noticed one plug is sooty to brown (right cyl) and left side plug had near white earth electrode , rest sooty ?? Possible some sort of bias going on ??? The engine has superb compression after a SRM complete rebuild approx 2000 miles ago. also if i turn the tickover right down to near stalling the bike falters to run on only one cylinder ? i guess the magnetism is dropping off with speed of rotation ?? i can only set the timming with my BTDC tool down plug hole and thin cigarette paper , i feel fairly confident its as close as can be considering what a tossy thing the K2f is to set timming ??
Re: amal monobloc , very fast idle problem ?#28626 09/11/0711:31 am09/11/0711:31 am
check the ignition timing on each lobe of the cam.I found the RGS was 12 degrees different side to side. use a dremel and a fine stone to alter the cam ring so they are within a couple of degrees.Slow process but worth it.
Re: amal monobloc , very fast idle problem ?#28627 09/11/076:41 pm09/11/076:41 pm
Check the ignition timing between the 2 cylinder by using a strobe light with an inductive pickup but put BOTH the leads thru the pickup. Use some white paint / etched line on the crankshaft pulley to make a temprorary timing mark for "one off" testing. It wouldn't surprise me if timing was different between the two cylinders
Try rotating the cam ring 180º. Has it got the correct cam ring and is it in the right way around? there are CW and ACW types. Make sure the points carriage is truly centred, if it was even a trace off center it would give you this problem
376 should have a type "C" needle.
Anyone got a diagram of a K2F, my memory is going and I would like a refresher.
~~~~If all else fails~~~~~~~
As RGS bob suggests, VERY carefully work with a fine oiled "slip" stone on the cam ring (a good quality ladies emery board used for thier nails) , shave away at the start the 1st mm of the "lifting ramp " on the advanced side in order to retard it to the same as the retarded side, then retime the motor and check for correct advance on both sides, you will be talking about shaving off microns, at most maybe 0.0002".
You AREN'T aiming to grind stuff off, you are polishing the ramp off the advanced lifter to make that lifter more retarded. ~~~~~Measure twice, cut once~~~~~~