276 Pre-Monobloc Amal

[sprangerny]

Am having a devil of a time getting my 'new', Amal 276 carb to run more lean - on my '48 Triumph Speed Twin. Damned thing runs seriously rich, even though the Needle is set down 1 notch for from the top (i.e. lowered nearly all the way). NeedlePosition.jpg

That combination is running 'rich' through most of the operating range. QUESTION: WOULD GOING DOWN TO A 106 OR 105 NEEDLE JET yield a much leaner condition? While still being able to go back to the center notch on the needle itself? Don't fully understand the relationship between the Needle & Jet . . . .

Am using the correct, and Amal-supplied, 3.5 cutaway slide, #6 needle (which is supposed to be the middle notch), 107 needle jet and a 140 main jet. I read somewhere that the 107 jet is 'rich', while the 106 jet is 'standard' and the 105 jet is 'lean'. But Amal supplied it with a 107, so that's where I'm at. Rode the first 2,500 miles without an issue - using a more modern carb from the 60's. But wanted to go the period-correct direction . . . .

THANKS for any input or prior experience with this much-too-complex carb.

48-Triumph-LoRes2-Fla.jpg

[kitabel]

Yes, .106 is a big change.
I wrote this for the 1955-67 Monobloc, but the component function is very similar.
http://victorylibrary.com/MONO.htm

[Rubone]

Which "276" did you get? There are many different throat (venturi) sizes. The needle jet and the needle are very simple. The jet has a fixed size hole, the needle a taper. The richness is determined by where that taper is in relation to the jet. Lower is leaner, higher richer. So if all the way down is still too rich go to a smaller jet size, start again in the middle and work up or down as needed. What elevation are you? All base adjustments are set at sea level. The higher you are, the leaner you need to be. The slide cutaway affects things as well. Have you talked to Amal tech?

[sprangerny]

Kitabel: thanks, have ordered your Amal tuning booklet. These Pre-Monobloc's seem to confound more than the monobloc's I'm using on a few other bikes. But have ordered both the 105 and 106 needle jets to give them a try. Not quite sure why the 276 comes standard from Amal with a 107 ('rich') jet.

[sprangerny]

Rubone: Amal (Burlen) showed a specific 276 for my '48 Speed Twin [276AX/IAT: 3.5 cutaway, #6 needle, 107 needle jet, 140 main jet] I'm confident it's correct, but just not sure why they recommend the 107 Needle Jet (rich) when the 106 (standard) and 105 (lean) are also in the range. Guess they figured you can always lower the needle to cure a bit of richness. After screwing with this Pre-Monobloc 276 for the better part of a week, fiddling with the needle settings, test running with new plugs, etc. I have come to the conclusion that ONLY a smaller Needle JET orifice is my best option. So have those on order. Reached out to Amal/Burlen but have yet to hear back.

BTW: at sea level here in Daytona, Florida.
FOOTNOTE: In taking the carb on & off (and on & off) a bunch of times, I now have a knack for draining fuel and wrenching the myriad of temperamental and prone-to-leakage connections.

[PRG]

Howdy sir,

As an aside, carbs actually compensate quite well to even extreme elevation changes as they follow IGL (ideal gas law) where air density/pressure dictates fuel drawn into the venturi from the bowl. Where you can get into problems are enrichment assistant devices like accelerator pumps or their primitive predecessors, modified fuel nozzles in old Linkerts. Don’t overlook your ignition system’s influence. Vincents run a 50 degree mag and thus one pot can suffer from lack of coil saturation and weaker spark if the original Lucas is not perfect and with original spec points fitted. Thus many will run different jets on each cylinder. At 274ft above sea level and with my recently restored the Rap in my avatar (Amal 276,s) having already proven finicky and aware of IGL I jetted down from 170’s to 150’s to get it to run cleanly around Steam Boat Springs at up to 9000ft. Fast forward 20 years, now older fatter and less motivated, we spent a week around Black Hawk, Co up to 12000 ft on my 229/289 Amal equipped Shadow and the only thing I touched were the idle screws. The difference, a capacitive discharge based BTH mag with electronic advance. Standard issue 180 mains not changed or needles moved.

[T. Cotten]

Howdy sir,

..Where you can get into problems are enrichment assistant devices like accelerator pumps or their primitive predecessors, modified fuel nozzles in old Linkerts. ....

Golly Peter...

I can see some follies with pumps easily.

But please explain the problem with the incredible DLX/Linkert nozzle design that was successful for over a half of a century?
(From the early glory days, all the way through the golden, and then some,.)

Only when it comes to elevation? Or only the 'modified'?

...Cotten
PS: I think I've got some 'modified'!

[sprangerny]

PRG, et. al: thanks for the additional info. Think I might have the overly-rich running resolved. Scrounged an older 106 Needle Jet (while waiting for new one's to arrive) to replace the 107. First 20 mile test ride is promising. Solid performance in all rpm ranges. Plug looks only a tiny bit lean. Can now move the needle UP to the middle groove - then take another 20+ mile run. Thanks to all who responded!T5-RtSide-LRG.jpg

PS: anyone know of a place to source a 'proper' Pillon seat?

[sprangerny]

Rubone: finally have the combination (106 needle jet, needle in center notch) that's giving me great throttle response throughout all ranges, idles quite well and plugs are the perfect color. BUT, IT'S VERY HARD STARTING!! Need to hand choke while kicking a bunch of times. Now have the valve tappet/lash set at approx. .002 Intake and .004 Exhaust.

QUESTION: should I be opening UP the valve lash for easier starting? How far? Used to be a 1 kick bike with a newer 1960's carb . . . . many thanks. Doug

www.youtube.com/watch?v=CIC3qh1XUto