Bushmans Idle mod.

AussieCombat · Sep 6, 2011

Hey guys, and girls.
Does any one have the Bushmans idle modification fitted to their carbs. Mk 1 932. Concentric.
That is.... The fitting of a removeable screw for cleaning, and the enlargement of the Idle/Pilot
passage, plus the fitting of a removeable/replaceable brass Idle jet.
I do, however, I need to replace the #30 jet with a smaller size, but can't find what brand they are.
Do late model Amals have a small brass jet with a round head and one slot.
The Mk 2s I have do not.
They are not Mik or Kiehin.
Hopefully someone out there has some info, as I am waiting, waiting, for a reply from Bushmans.
NB.... I have a print out and exploded view and price list from Surrey cycles for a Mk1 Concentric
clearly showing a removeable Idle jet, PART #14, and "state size" when ordering.????
There is no info on removeable jets (mods) that I can find on their site. Awaiting reply there too.
AC.

ando · Sep 6, 2011

I have modified a couple of concentrics by drilling and tapping (2BA from memory) the body and fitting a filed off blanking plug to enable cleaning of the .016 pilot jet in the body. I believe however you are referring to the replacable pilot jet that is screwed into the base of the main body. I know these are available in 20, 25 and 30 and probably more. there is a guy called Amal Jeff that gets around a lot of swap meets in NSW and Vic that has good stocks of pilot jets. Apart from that Draganfly motorcycles (http://www.draganfly.co.uk/index.html) in the UK (Ariel and BSA specialists) keeps good stocks of amal jets including pilot jets and i have always received deliveries within 7 - 10 days from placing an order. Most concentrics do not need the pilot jet to be fitted as metering is mostly by the .016" jet that is fixed in the body behind the pilot air screw.
That said I purchased a couple of second hand concentrics that had been modified for alcohol. The seller did not mention the carbs were set for alcohol when I purchased them. the give away was when I stripped them and found alcohol needles and 600 main jets. the mods also include enlarging the .016 jet in the body. I have subsequently tried fitting 20 pilot jets (the smallest I have been able to buy) but they are still too large to get the bike to idle. Be careful with any probing you do through the pilot air screw not to enlarge that .016"jet.
regards
ando

john robert bould · Sep 6, 2011

ando said:
I have modified a couple of concentrics by drilling and tapping (2BA from memory) the body and fitting a filed off blanking plug to enable cleaning of the .016 pilot jet in the body. I believe however you are referring to the replacable pilot jet that is screwed into the base of the main body. I know these are available in 20, 25 and 30 and probably more. there is a guy called Amal Jeff that gets around a lot of swap meets in NSW and Vic that has good stocks of pilot jets. Apart from that Draganfly motorcycles (http://www.draganfly.co.uk/index.html) in the UK (Ariel and BSA specialists) keeps good stocks of amal jets including pilot jets and i have always received deliveries within 7 - 10 days from placing an order. Most concentrics do not need the pilot jet to be fitted as metering is mostly by the .016" jet that is fixed in the body behind the pilot air screw.
That said I purchased a couple of second hand concentrics that had been modified for alcohol. The seller did not mention the carbs were set for alcohol when I purchased them. the give away was when I stripped them and found alcohol needles and 600 main jets. the mods also include enlarging the .016 jet in the body. I have subsequently tried fitting 20 pilot jets (the smallest I have been able to buy) but they are still too large to get the bike to idle. Be careful with any probing you do through the pilot air screw not to enlarge that .016"jet.
regards
ando

Yes that .016 hole is a real pain to clean, I found the following "Tool" worked well; saw a piece of 3mm brass bar 3in long, into the lathe and drill a 1mm hole up the end approx 1/2in deep, next strip out a single wire strand from a control cable approx 1. 1/4 long and flat the end with a hammer,[cutting edge] insert the wire into your pre-drilled bar and glue it in with thread lock. You now have a good strong "pilot Hole de-cruster" Air screw out and rotate the "tool" up the blind hole, with care ! A few spins between finger and thumb does the trick...bowden cable strands are quite strong....

mw21837 · Sep 6, 2011

The original concentrics used a screw in pilot jet untill about 1969 when the press in .016" jet was fitted. The later models still had the threads for the screw in jet, but were not used. If the press in jet has been reamed out oversized, you can drill it out, and then use the screw in style. AMR of Tuscon has some good tips on Amal Concentrics and addresses this topic. http://www.amr-of-tucson.com/ According to my workshop manual that I bought in 1973, the Pilot jet size should be .025. This would be for a 930, I don't know if a 932 would be different.

Since my press in jets had been oversized by a Previous owner, I drilled them out with a 1/16" drill and then fitted the bodies with .020 screw in pilot jets (that is what size I had on hand) . I run the pilot air screws at approximately 1 1/4 turns out. It idles solid as a rock and usually starts on the 1st kick. As a side note, I had my carb bodys repaired by AMR. They were bored oversized, and fitted with heavier, chrome plated, brass slides. The air slides (chokes) were eliminated and I don't miss them. I could not be more satisfied with their work!

Mike Wolf

swooshdave · Sep 6, 2011

Rumor has it that Amal will offer new carbs with this option.

Jeandr · Sep 6, 2011

swooshdave said:
Rumor has it that Amal will offer new carbs with this option.

When :!: :!: :!: in 1970 or 1971, they are always promising but never delivering.

Jean

pete.v · Sep 6, 2011

AussieCombat said:
Hey guys, and girls.
I need to replace the #30 jet with a smaller size, but can't find what brand they are.
Do late model Amals have a small brass jet with a round head and one slot.
The Mk 2s I have do not.
They are not Mik or Kiehin.
Hopefully someone out there has some info, as I am waiting, waiting, for a reply from Bushmans.
NB.... I have a print out and exploded view and price list from Surrey cycles for a Mk1 Concentric
clearly showing a removeable Idle jet, PART #14, and "state size" when ordering.????
There is no info on removeable jets (mods) that I can find on their site. Awaiting reply there too.
AC.

Amal pilot jets 124/026-15, 124/026-20, 124/026-22, 124/026-25, etc. $3.20 us each

Edited. The mk1 bodies underside, old and new, have always had the little threaded hole to screw in a pilot jet.

swooshdave · Sep 6, 2011

Jeandr said:
swooshdave said:

Rumor has it that Amal will offer new carbs with this option.

Click to expand...

When :!: :!: :!: in 1970 or 1971, they are always promising but never delivering.

Jean

It hasn't been publicly announced so it seems more of a beta or testing market viability.

They have came through with the hard anodized slides. And the stay up adjustable floats. So never is a bit of a stretch.

AussieCombat · Sep 6, 2011

Thanks for all the in put.
Dragonfly and AMR Site is worth a look for all those State side.
Sorry I wasn't aware that early model Concentrics had screw in jets.
Swoosh and Jean, Surrey cycles in England are offering Carbs with the mod now.
http://www.surreycycles.com
Complete carb... 104.00 Pounds. (Quid, to us poms and convicts)
With optional chrome brass slide... 129.00 Pounds.
Am on the trail here in Oz for Amal jets.
None in Adelaide, none in Brisbane, waiting for call from Melbourne, Sydney to go then Perth.
Ah well summer is coming.
Edit.... I don't know if I've done a bad thing, but I found some jets at a Triumph dealer.
Union Jack Motorcycles,... Melbourne.

ando · Sep 7, 2011

further to my first post I just found a business card for amal Jeff Skillon. his phone no is Aust 02 49323231. apart from a good range of jets for concentric, monobloc and 289 type he also sells stainless BA replacement screws for concentrics extended idle and throttle stop screws with knurled ends for finger adjustment rather than screwdriver, slides and rebuilt concentrics.
ando

ebsbury · Sep 7, 2011

swooshdave said:
Rumor has it that Amal will offer new carbs with this option.

There's a post about new Amal carbs with a new pilot jet on Britbike here:
http://www.britbike.com/forums/ubbthrea ... Post385058

There's an article here that explains the change from pilot jet to bush:

http://www.amalcarb.co.uk/TechnicalDetail.aspx?id=11

The relevant section is:

"Pilot Jets

When first introduced all carburetters were fitted with a detachable pilot jet screwed into a threaded hole in the bottom of the carburetter body. This arrangement is retained for 2 strokes but from 1968 was replaced for 4 strokes by a bush pressed into the gallery behind the pilot air screw.
The detachable pilot jet caused problems with some 4 Stroke engines. The remoteness of the jet from the two pilot circuit outlet holes caused starting and idling problems on bikes with lower manifold vacuums, and could cause stalling during deceleration due to a weak mixture. The introduction of the pilot bush moved the pilot jet nearer to the outlet holes to overcome these problems. The bush has a flow rate of equivalent to 20cc/min. Carburetters fitted with a bush retain the threads originally used to fit the removable pilot jet."

stockie2 · Sep 7, 2011

Bugger the post above stole my thunder. Now just to contradict this location of the pilot jet, a mate has some new carbs from Surrey that have the pilots screwed in thread in the float bowl area, on the body. His Bonnie does not suffer from starting, idling or stalling after pulling up to a stop sign. As a side bar though, I noticed a huge difference in the way my commando pulls up fuel from cold, once I fitted Total Seal piston rings in a new engine build. So I guess that means a stonger manifold vacuum when kicking over. Only down side is she takes an even more hefty kick to turn her over. You can stand on the kicker with all your weight and it will hold you up, amazing!

Cheers Richard

Bushmans Idle mod.

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