Carburettor choices

Anyone who's wondering about AMAL MK II carbs. They are only making the generic ones (300/301) so you specify the desired jetting. Today:

2928/300 coming but they don't have a date, 301 available.
2930/300 and 301 available
2932/300 available, 301 is 3-4 weeks out
2934/300 available, 301 is 4-5 weeks out

They no longer make any other MK IIs.

AFAIK, they are not available on the web site, only to dealers (could be wrong if you contact them). I don't have them in stock but will be placing an order in the future.

marshg246 said:

Anyone who's wondering about AMAL MK II carbs. They are only making the generic ones (300/301) so you specify the desired jetting. Today:

2928/300 coming but they don't have a date, 301 available.
2930/300 and 301 available
2932/300 available, 301 is 3-4 weeks out
2934/300 available, 301 is 4-5 weeks out

They no longer make any other MK IIs.

AFAIK, they are not available on the web site, only to dealers (could be wrong if you contact them). I don't have them in stock but will be placing an order in the future.

Click to expand...

That’s the problem tho Greg, they don’t make big ‘uns.

Schwany said:

I thought pumpers were not legal for vintage racing.

Click to expand...

When I was racing my featherbed/Commando in AHRMA, accelerator pumps were not legal, so I removed them from the carbs. AHRMA was fine with that. With proper jetting, the Dellortos worked fine without them.

Ken

marshg246 said:

Not knowledgeable and certainly not an expert, just wondering.

Shouldn't you, in effect, replace the crossmember by putting one behind the tubes. I would think that would maintain the rigidity of the frame and still give you clearance. It probably would not need to be as "tall" as the original if it gets in the way of the air cleaners.

Click to expand...

I did consider adding some additional bracing, but decided against it. There is still some of the original gusset left to provide stiffness at the juncture of the tubes, and it didn't look to me like the design needed any more. I doubt very much that the change is enough to produce any noticeable change in the handling, particularly on a street bike. But that's just my "looks ok to me" sort of assessment.

Ken

Fast Eddie said:

That’s the problem tho Greg, they don’t make big ‘uns.

Click to expand...

Understood - that was half the point of my post - I listed all they make in the MK II carbs today. I should have been clearer to not expect any others. They probably only make the ones they do to support the later vintage Triumphs. At least the MK I carbs were heavily used so they can say in business for now.

These folks are developing a 4 stroke carb, which should be pretty interesting…

Mine on a Seeley Mk3

lcrken said:

When I was racing my featherbed/Commando in AHRMA, accelerator pumps were not legal, so I removed them from the carbs. AHRMA was fine with that. With proper jetting, the Dellortos worked fine without them.

Ken

Click to expand...

Are pumpers still illegal, or do they put an old Norton in another classification if used?

I had a heck of a time making a big Dellorto pumper work on a ATK 604. The Rotax was actually quicker with a 36mm TM bored out to 39mm by Harry Lillie. Much quicker. Yeah I know way off topic.

The 35mm FCR pumpers work well on a street Norton 750 with some compression and a JS2 cam. I know people like to disable the pump, but I can't find anything negative about leaving it active.

Have you disabled the accelerator pump on the FCRs on your hot rod build?

To throw the cat amongst the pideons , or down the intake , or a rat . A mouse'd go . Anyway ! .

LOOK where the CARBS ARE AIMING . Strewth , youse blokes . The silly cross brace , un butchered
( Shoulda taken to it , took 3/4 off the lower edge maybe , across . ) The Mk II , originally up'n back with the 14 inch vave head to jet ,
The Silly chokes hadtabe removed , as the brazer had shifted the fittings for the rubbermount Fwd. And the choke levers coincided with
the lower edge . the MANIFOLDS were ex. 32 bore Pipe Bends . The Good uncrushed ends . Matched . So from TWO ' U ' Bends .

NOW , if yer lookit the Head . Theres a mounting face - SQUARE to the intake port bore , which CURVES away Down .
So , we get that curve . Theres a THING called continuity .

The STOCK hideous intakes - the lower run is way shorter than the top run - in the bore - of the factory intake ( Mk1 concentric ) manifolds .
Therefore , if a bloke walked along the top , he'd arive at the head some time afdter the bloke walking along the bottom - if they were evenly matched .
If they got there at the same time , theyed obviously be missmatched . So you can see where THIS is going . A bit of a MIX UP .

THEREFORE , if we get good clean open bends flowwing with no irregularity into the head intake port bore , as one , as it were . Were way ahead.

Which it was . !

AS the woiks wons were firty free bore , on the 750 , cluding P.W.s I.o.M. monococque , we assume the 32 Mk IIs match or better the flow . So There .

As for Carbs . They got shifted forward , more into the curve . From That . So the Intakes were then upat the frame brace . AND the chokes were fitted
as the factory STILL haddent ( and never did ? ) come out with the promised cable choke set up . Therfore they were more downdraft on the toobs
with the back cutoff . As thats a full description , you can layout the assembly as it were . And fi a Weber or DHLA toit . Or BRACE the Dual Mk IIs
across , as theyre supposed to be .

If youve fitted a rev cut out , you could fit 36s , Remember Tach Lagg , if its the orrible cable magnetic wotsit .



If you can gettit working thatwell , your getting somewhere .

Looking at the 250 , youd be better to put the cylinder head on backwards , on the inclined engine , and it'd all line up better . Off Course , it'd be easier with a Triumph .


WHAT the POINTIS , is to get CONTINUITY . They go to all that bother with the PORT FLOWING
then chuck a ELBOW on the darn thing . Comeoffit . Least I useda BEND .

KINKY ONE .



THOITY DEGREES IN 40 m.m. . O.M. G.

Gethe pitcher , wottle go throughit .


figure this out , for each
\\\\\\\\\\\\\\\\\\\\\\\\\\\\
Think they were the 8 inch U bends . Very Carefully square cut , on the curve . asin at a exact radiun . exiting tothe clean transition ( uncrushed )
unless you look at it the other way . Which was how it was going . IN not out , as it were . the Radius matched the corve of the intake port .

WHAT you blokes THERE have , is virtually a sectioned elbow .


WhereAS , weve got a REAL BEND .


Which flows twice as much . But MORE IMPORTANTLY ,
the Pulse Wave can run bore center . Its less inclined to Hit the Roof or wall , get impeeded , distracted or reflected prematurely , say what .
. When you throw a cat down it .

CAT 3406B Intake Manifold OEM# 4N9007​

https://www.google.com/url?sa=i&url=https://www.heavytruckparts.net/item/Cat/3406b/Intake-Manifold/5146584/1/59498?oemnum=4N9007&psig=AOvVaw0CTjtxiJ9pPzMsNthJ7X6D&ust=1720760563984000&source=images&cd=vfe&opi=89978449&ved=0CBIQjhxqFwoTCKDUg-aanocDFQAAAAAdAAAAABAE
IF you LOOK at the Max Pressure ( say a ball ) it can Run a fluid motion . As it has PROGRESSIVE TRANSITION .
notta abrupt counter shock . PREGRESSION illustrated below . More or Less .

Now THIS is a Intake Manifold !

lcrken said:

When I was racing my featherbed/Commando in AHRMA, accelerator pumps were not legal, so I removed them from the carbs. AHRMA was fine with that. With proper jetting, the Dellortos worked fine without them.

Ken

Click to expand...

I raced bikes on methanol for years, and it is much more forgiving of tuning errors - I think because of it's latent heat causing air to be much more dense, the jets flow almost twice as much. I used to get good power. However I never suspected how much more power I could get by running as lean as possible right down the needles. With my 34mm Amal Mk2 carbs I make my own needle jets in increments of 0.5 thou of an inch of ID. In doing that, the bike became much faster, and it went even quicker when I fitted the leanest Mikuni needles. With petrol, doing that might be a real battle - you would need needle jets in 0.25 thou of an inch increments of ID.
I doubted my own work, so I asked Steve Oszko about what he use to do with his race-winning Manx. - He confirmed 'as lean as possible right down the needle'. Steve was a qualified motor mechanic and had all the tuning instruments at his disposal.

One of the things I regret about getting older, is most of the people I need to talk to are now dead. In the old days, many experienced riders did not say much about how to go faster to other riders. I am not like that. If I know anything, I don't worry about other riders beating me by knowing it. If they go faster, it is all part of the fun. My ego is not fed by racing motorcycles.

Now you mention it , a FLOW CHECK out of the tank fitting / hoses , is a prerequisite .

With the 2S cam , I could get the jetting o.k. , at a set throttle setting - and then it'd vary with speed . or VcV , Drove ya nuts . To Distraction .
So watch out for blind brows into ' T 's or ' L's on unriden roads , establishing jetting . On a Trip - so ' opperating conditions ' stabilised .

Figured intheend , it was the groty snoty wois than useless 6 Volt Coils , and just thought " WITH THE 2MC " as it had no battery .

The BLUE & WHITE SPARK , if you establish these things refining the jetting should be easy . Think it was o.k. with the later fitted stock cam .
Differant , B M E P , whichis WHAT the intake tirade is about !

The Entire insides where WHITE , from the plug tip to the tailpipe end , at 5.000+ continuous , High alt. desert road .

Any flow impediment woulda bin catastrophic . Pumps & presurised fuel tanks & the like . tecnically , big tank , gravity pressure head would vary 6 inch , full to low . Over a one foot run !

so 18 , down to 12 inch ' head ! .

Lotta the V8s go to 1/2 bore from tank , drag racing . A ' fuel header tank ' forward of the motor too. So as Fuel Pressure to carb is increased under acceleration . NOT decreased .

Matt Spencer said:

Now you mention it , a FLOW CHECK out of the tank fitting / hoses , is a prerequisite .

Click to expand...

A good point.
I found that even with a stock 850 on the motorway I needed both taps open.

B+Bogus said:

A good point.
I found that even with a stock 850 on the motorway I needed both taps open.

Click to expand...

Never had that problem, but then again I make my own taps out of Ball Valves.

cash said:

Never had that problem, but then again I make my own taps out of Ball Valves.

Click to expand...

Picture would be nice..
I like ball valves..

Where is the tank breather on a Commando ?

I found this video interesting,

MichaelB said:

Picture would be nice..
I like ball valves..

Click to expand...

Can't post pictures on here. I use standard stainless steel 1/4" BSP male one end female the other, fitted with Viton seals. And 1/4" Brass nipples to solder in the reserve tube and filter mesh. The brass nipples screw into the female end of the valve. Chromed brass ball valves cost less. They last for ever, the pair on my Commando have been in service for over 25years. I fitted them to my Grandson's GM speedway bikes and boy do they guzzle Methanol.
Send me your email if you want a picture.

cash said:

Can't post pictures on here.

Click to expand...

PM sent