The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Amal, Carburation => Topic started by: barry2 on 30.01. 2019 07:30
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Hi mates
my R/R has sooty exhausts , The carby is a 376/286 Amal mono' 1 1/16" the pilot was right but the main jet was 250, should be I think 240, would that cause it to be that rich, the needle was at No2 groove so dropped it to leanest just to see what happens, any thoughts?
Barry
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Exhausts will always be sooty on a carb fed bike. The colour of the plugs will tell you more about what’s happening in the combustion chambers. A colourtune may also be a wise investment for setting up your carb
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G'day Barry.
Dropping the needle (raising the clip) should help but the needle jet and needle wear. it would only take half a thou" to give the same result as the next size up jet. I'd replace both.
As morris said plug colour is the best way to tune with plug chops. I have a spare Colour Tune you could borrow. Their good for getting pilot and slide right. Plug chops for needle and main.
Cheers
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Hi Mates
My ex' pipes are thick w/ soot after I cleaned them after about a week
Thanks for the help and offer, but I'm in WA, I have a colour tune hven't used it for years , will dig it out , I think maybe the fuel level is too high, when I took the pilot jet cap off petrol took ages to stop flowing ( after a very hot day and night, will let you know how I get on
Barry
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G'day Barry.
Put a piece of clear tube (fish tank air line) over the pilot and bring it up p[ast the float bowl. Turn fuel tap on and see where the fuel level is. Should be a pip in the middle of the bowl cover.
Cheers
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Lowering the needle to compensate for a worn needle jet will make the mixture weak at typical highway speed throttle openings. That can be dangerous to your engine.
Get a new needle jet.
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Hi Mates
I got a new needle jet, it was about .004 dia' smaller than the old ("chrome plated ") Amal jet I took off, I have a feeling that was a Indian? copy,, but now it dosen't tick over too well and when I take off from start it misses and cuts out , still goes well at speed though ,, the exhaust pipes still getting sooty just after a short ride I don't get it on to main jet ( flat out ) much, will be putting new plugs in today,, I checked the fuel level , that was spot on
all the best Barry
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G'day Barry.
4 thou is a long way in needle jets. For example going from a 109 to 105 *ex* or are you meaning the needle? Always best to replace both the jet and needle.
A 55 RR should have a 1,1/16 TT9 carb. A 376 with 1,1/16" is a 57-59 SR carb should have 250 main, 25 pilot, 3,1/2 slide, 106 needle jet, clip 4 from top, pilot screw between 1,1/2 to 2,1/2 turns out.
Cheers
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Hi Mates
Just remembered it has a later SR engine fitted , when it was cold was missing a bit when pulling away , did about 50 ks went fine when warm, will put the colour-tune on this PM
Barry
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G'day Barry.
Colourtune is your friend for up to 1/4 throttle unless you have a set of starter rollers then it's up to flat out. From 1/4 on it's seat of your pants and plug chops.
Their all different depending on comp, timing, temp and if you got any recently *smile*.
Are you within 100 miles of Richard (orobanda)?
Cheers
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Hi Mates
put the colour tune on , it was spot on at tick-over but the engine was still missing at tickover , it has high compression ( I have to get it over compression before kicking ) and sound like a lumpy tuned up motor,, I didn't C/tune above idle didn't think that would mean anything, will do Monday
Barry
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G'day Barry.
Have you ever used a timing light on her to check the timing exactly whilst running? You'd be surprised how far out the old pencil down the plug hole can be. Especially with a high comp motor timing needs to be a tad retarded.
Cheers
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The engines with the 357 cam do have a lopey , cammy idle when warm, or at least mine sure does.
Ive no prior experience with these bikes and at first thought the idle needed improvement, although its actually a strong idle, no dieing.
Then I listened carefully to half a dozen or so YouTube videos of running post 61 Super Rockets.
Every bike had the same idle as mine.
Now I like the sound, it's a signature BSA 357 idle.
These are HHC bikes afterall.
I haven't given a good listen to the earlier HHC engines with a bit lower compression and 356 cam. I suspect they may have a similar idle.
I've also noticed that the idle of this SR is dead smooth when cold. I think this is because I lift the slide ever so little to maintain running when cold.
Later on when the engine is warm and the slide is dropped onto the idle stop, the brup brup idle comes in.
So the cammy sounding idle may be down to air /fuel mixture idiosyncrasies of the BSA A10 inlet tract, not the cams and compression.
Edit- here is an early HHC in a 57 Road Rocket. The idle sounds very much like my 63 SR.
https://m.youtube.com/watch?v=oQIoP_iNDwQ
Glen
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Hi Mates
Hi Torn--thanks for that, took it on a 200Ks run yesterday ran well only "missed once slightly" but is harder to start now , have to give good hard kicks usually on the center-stand , then when it starts it's usually one one the then other comes in , will test the quality/strength of the park today
Barry
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hi Mates
should have been strength of "spark"
Hey Muskrat-- how do test w/ timing light on the magneto?
Barry
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Sounding more and more like spark. Modern fuel will fog plugs but leave them just working. Might also be worth running a clean cloth around the slip ring incase there is a conductive carbon line causing grief. Take the points out first otherwise it will surprise you!
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G'day Barry.
Attach + & - leads to a 12v battery (doesn't have to be the bike battery) and the pickup lead to the sparkplug lead.
Drop the primary cover off and put a timing disc under the cush nut. Rig up a pointer off one of the screw holes. Find TDC using a dial gauge down the plug hole and mark the disc. Mark the disc at 25, 30 & 35 degrees BTDC. A high comp SR on 98 octane should spark at about 32 degrees BTDC.
You can also swap the pickup to the other lead and check that the timing is the same both sides.
It all sounds harder than it actually is.
Cheers
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Hi Mates
Checked the spark, jumping 5mm, I though I'd check the brushes , to my surprise the bottom bush holder never had a brush on it, it was under the slip-ring ( manage to get it out w/- tweezers and a mirror ), it had never been on ( years ?) , no wear marks, it is very hard to get the bottom brush holder on as mine has a oil filter on the r/h side , my first attempt failed , wouldn't run on that cylinder, next time put a new holder / brush on that I had in stock, goes well well now,
thanks for all the replies and help ,
Barry
this all started with sooty exhaust , well they are still sooty, I'm leaving it for now