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Rating: 3
New BSA owner-|Carb question #734633
05/09/18 3:52 pm
05/09/18 3:52 pm
Joined: May 2018
Posts: 7
belleville
S
sdearman Offline OP
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sdearman  Offline OP
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belleville
Tks for allowing a new member! Certainly not new to bikes and lots of gray hair to prove it, but new to the world of BSA and AMAL carbs! Just got a 1965 Royal Star that was in really good shape but sitting a while....working through a few things and have it running but won't idle.....Bike has the AMAL Monobloc single carb....have adjusted the idle air mixture adj to the baseline 1 1/2 out and bike will run decent as long as I am holding throttle open about 3/8 inch....but if I back it off it dies. Have played with the throttle idle adj (one on an angle) but moving it all the way out or all the way in does nothing to the idle speed nor has playing with cable adjusters. My past exp was mostly harleys and SS carbs with a simple external cam/bolt adjuster and can't wrap my head around how this carb works yet despite going through manual and carb manual I got with it.....realize its likely something simple that will have me feeling like an idiot but might as well throw it out there and gain some quick knowledge from those that know......
Again, looks like a great forum and thanks for the invite.....


shawn dearman
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Re: New BSA owner-|Carb question [Re: sdearman] #734657
05/09/18 6:57 pm
05/09/18 6:57 pm
Joined: May 2013
Posts: 5,004
Rotherham - S. Yorkshire
Allan Gill Offline

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Allan Gill  Offline

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Rotherham - S. Yorkshire
Try setting the idle mixture screw to between 1 and 1.25 turns out, then go for a good run, at least 10 miles to get the engine nicely warm, then with the bike running screw the idle Mixture screw in or out to obtain the fastest idle speed (indicates good Mixture), the use the diagnal slide screw to regulate the idle speed. You should then check the idle Mixture screw again to see If the idle speed can not be increased any further (sometimes it can) and if it does, regulate again with the slide adjustment screw.

Also double check the ignition timing as this will effect things


beerchug
Re: New BSA owner-|Carb question [Re: Allan Gill] #734671
05/09/18 10:19 pm
05/09/18 10:19 pm
Joined: May 2018
Posts: 7
belleville
S
sdearman Offline OP
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sdearman  Offline OP
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Posts: 7
belleville
Thanks for the reply and ideas.....when I got it the idle mixture screw was out 3 1/2 turns! And the slide screw was almost all the way in......will try your settings and see if it will go around the block a few times....also need to deal with float level, thought I had it but have trumpet dripping fuel if it sits overnight


shawn dearman
Re: New BSA owner-|Carb question [Re: sdearman] #734680
05/10/18 12:48 am
05/10/18 12:48 am
Joined: Sep 2014
Posts: 209
Ohio
A
Andrew Dunham Offline
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A

Joined: Sep 2014
Posts: 209
Ohio
You must be turning the wrong screw for adjusting the slide height. I can't imagine it or the adjusters in the cable going fully either way and NOTHING happening.

The idea of it is extremely simple. The slide moves up and down in the carb body to allow more/less air in. The "throttle stop" screw is simply pushing against the bottom of the slide; so the more you turn in, the higher the slide goes, the more air in, and the higher your revs. The only thing that could make sense is if the screw that is in there is too short to actually contact the slide.

Here is a picture, although I'm sure you've already researched:

https://burtonbikebits.net/bbb/wp-content/uploads/2016/09/monobloc-exploded-5.jpg

Last edited by Andrew Dunham; 05/10/18 12:49 am.

1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: New BSA owner-|Carb question [Re: sdearman] #734719
05/10/18 11:42 am
05/10/18 11:42 am
Joined: May 2018
Posts: 7
belleville
S
sdearman Offline OP
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sdearman  Offline OP
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Posts: 7
belleville
Thanks Andrew and yes thats exactly what the throttle stop screw looks like...I cant figure it either...I would think that even a 1/4 turn either way would have an immediate affect but I can literally remove it and nothing changes or tighten it and nothing?.......


shawn dearman
Re: New BSA owner-|Carb question [Re: sdearman] #734723
05/10/18 12:03 pm
05/10/18 12:03 pm
Joined: Aug 2001
Posts: 4,114
argyll. scotland, uk
gavin eisler Online content
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gavin eisler  Online Content
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Posts: 4,114
argyll. scotland, uk
Remove the air filter and observe the throttle slide, it should visibly move when the throttle stop is adjusted, same goes for throttle cable. You may have the wrong throttle cable fitted, the slide may be damaged or the stop screw is too short, something is fr wrong , th slightest turn of the stop screw should have an obvious affect.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: New BSA owner-|Carb question [Re: sdearman] #734730
05/10/18 12:31 pm
05/10/18 12:31 pm
Joined: May 2018
Posts: 7
belleville
S
sdearman Offline OP
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sdearman  Offline OP
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Posts: 7
belleville
Thanks Gavin, will work through your suggestions.....the cable is a possiblity as it had wrong length clutch cable and throttle cable was routed wrong causing it to go to WOT when bars turned full left! Tks again for all the help guys!


shawn dearman
Re: New BSA owner-|Carb question [Re: sdearman] #734774
05/10/18 7:26 pm
05/10/18 7:26 pm
Joined: Aug 2001
Posts: 4,114
argyll. scotland, uk
gavin eisler Online content
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gavin eisler  Online Content
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argyll. scotland, uk
I have been thinking about this a bit more, new to monoblocs, there are some critical points any of which may be making things worse.
The float bowl banjo union hex where the fuel comes in, on old monos there should NOT be a fiber washer between the hex and the float bowl body, new ggeneration monos have this , not old ones it raises the fuel level too much. An easy external check, .
looking further inside, remove the float bowl cover screws, you can observe the float, check it isnt full of fuel, V important make sure the small tubular spacer is present on the end of the float bowl spindle, this is easy to lose and plays merry hell with the float level if missing. Typical symptoms will be fuel pissing out of the tickler on occasions.
Have a good look at the carb top, the threaded collar in particular, make sure its threaded on straight and true, if the choke slide is deleted , make sure the cable hole has been suitably plugged.
Any of these faults will be impossible to tune out.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: New BSA owner-|Carb question [Re: sdearman] #734815
05/10/18 11:37 pm
05/10/18 11:37 pm
Joined: May 2018
Posts: 7
belleville
S
sdearman Offline OP
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Posts: 7
belleville
Thanks Gavin! I actually noticed the fiber washer was between the hex and body and removed it which DID fix the fuel coming out of tickler when it was sitting....float seems solid and spacer is there, doesnt seem to be hanging up anywhere, but I did clean spindle to make sure it wasnt hanging up on sides as it seems pretty cruddy. It did have the beveled tip and it seemed good. Will double check the threaded collar, hadnt done that yet. Did check the ignition and corrected a slight gap variance. Progress between all of the things suggested as it no longer seeping oil from tickler or stack, starts pretty easily with no choke(choke stalls it immediately if used) with just using tickler, idles now with throttle closed but running rough so still some work to do.......getting there thanks to all of the help so far!


shawn dearman
Re: New BSA owner-|Carb question [Re: sdearman] #734821
05/11/18 12:16 am
05/11/18 12:16 am
Joined: Aug 2001
Posts: 4,552
Owego, NY, USA
Mark Z Offline
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Mark Z  Offline
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Posts: 4,552
Owego, NY, USA
You may also have a clogged pilot jet, especially if the bike has been sitting for a long period of time with old gas in the floatbowl. Fortunately, it's easy to remove the pilot jet on a Monobloc - it's under that little cap with a hex head.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: New BSA owner-|Carb question [Re: sdearman] #734869
05/11/18 11:37 am
05/11/18 11:37 am
Joined: May 2018
Posts: 7
belleville
S
sdearman Offline OP
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Posts: 7
belleville
Tks Mark, will give it a look today!


shawn dearman
Re: New BSA owner-|Carb question [Re: sdearman] #735068
05/13/18 3:05 am
05/13/18 3:05 am
Joined: Aug 2001
Posts: 4,552
Owego, NY, USA
Mark Z Offline
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Mark Z  Offline
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Joined: Aug 2001
Posts: 4,552
Owego, NY, USA
Is that Belleville, NJ? If so, I rowed there once, in high school.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: New BSA owner-|Carb question [Re: sdearman] #735145
05/13/18 6:34 pm
05/13/18 6:34 pm
Joined: May 2018
Posts: 7
belleville
S
sdearman Offline OP
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sdearman  Offline OP
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Joined: May 2018
Posts: 7
belleville
No :-) Belleville Ontario Canada...


shawn dearman
Re: New BSA owner-|Carb question [Re: sdearman] #735160
05/13/18 9:08 pm
05/13/18 9:08 pm
Joined: Aug 2001
Posts: 4,114
argyll. scotland, uk
gavin eisler Online content
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gavin eisler  Online Content
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Joined: Aug 2001
Posts: 4,114
argyll. scotland, uk
!starts pretty easily with no choke(choke stalls it immediately if used) with just using tickler, idles now with throttle closed but running rough so still some work to do.......getting there thanks to all of the help so far!!

This suggests that the pilot circuit is still too rich, from cold your bike should need the choke to run cleanly, tickling produces initial start up enrichment but after a few seconds running the choke would normally be needed . You have checked the float and needle, so other possibilities are.
1
The pilot jet is too big or the mixture screw is not turned out far enough.
If the jet hasnt been poked oversize the pilot screw should be somewhere in the 1/2 turn out to 2 turns out range, for a quick experiment screw it out a 1/2 turn more than the current setting and restart, see if things clean up, ideally the pilot mix screw should be set to give max idle speed, then the throttle stop is lowered to suit, this MUST be done when up to operating temp, if you do this cold the bike will be way too rich when warm.

2, The air passage to the pilot mix chamber may be partly blocked, blow through with an air line nozzle or carb cleaner.

3, the air filter may be dirty/blocked.
HTH

Last edited by gavin eisler; 05/13/18 9:14 pm.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod

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