Setting Up an Amal MkII

Hi,

I'm fettling my Combat and purchased an Amal MkII from RGM. I advised the spec of the bike so assume the guys at RGM have set the carb up correctly jet wise.

Today was 'start the bike' day and joy of joys after about 3 years of sitting the bike started fine but the plugs are getting very black - too rich I guess. I'm not riding the bike just letting it sit and giving it a blip as I check things over, ensure good oil circulation etc.

Could anyone offer any advice about setting this carb up?

cheers

d

You can't tell much about the jetting until you're out riding it, or you put it on a dyno. You need to operate the bike across the throttle range and under load to see if the mixture is correct, not on a stand in a garage.

All you can do in the garage is set the tickover speed and mixture, as Dr H says you need to take it out and do some runs up a long hill at various throttle openings and do plug chops to see what the mixture is. Mark your thottle with 1/4 1/2 and 3/4 points (a wrap of masking tape marked with felt tip) so you know at what opening you are.

Amal has a pretty good manual (little fold-out pamphlet) that comes with their carbs, and explains how each part of the carburettor works at different throttle positions. All you can do in the garage is set idle speed and idle air mixture. On initial start-up, you're better off running rich than lean. A lean motor or cylinder can get real hot, REAL fast.
If you are running twin Amal 932s, the factory setting for the Combat would be: 230 main jet, 106 needle, needle set in middle groove, and a throttle valve with a number 3 cutaway. Label on the carb box should be marked with this information.

Some experienced tuners may have a different initial set-up, based on your particulars, but should mark the box label with their settings.

I've not had any experience with MkII's, but have tuned a few Monoblocks, Concentrics and one particular GP. In general, I try to get the 'wide open' mixture correct first by changing main. Next is mid-range by changing the needle and/or needle position. After the wide-open and mid-range are adjusted, I adjust the idle using the idle mixture screw.

The idea is that the main jet affects the carb mixture at all settings, the needle at intermediate settings. The idle settings affect just that, the idle only.

I think the following is a pretty good guide to tuning carbs:

http://www.jba.bc.ca/Bushmans Carb Tuning.html

Another good guide to tuning Amals is:

broken link removed

Hope this helps.

SteveMinning said:

The idea is that the main jet affects the carb mixture at all settings

Click to expand...

only if it is miles to small or blocked :| :|

I'm running twin 34mm Mk2's and been through a lot of changes setting them up and still fine tuning them.
What size is it and what settings do RGM supply the carb with? Re you running a filter?

In general terms tuning is pretty much as the Mk1 as far as jets are concerned but there are a couple of things that don't get mentioned too much that I've found help.

1. Fit the large floats Amal p/n 622/196. The carb can bounce around more on the rubbers than a Mk1 which can make it flood at idle and screw up the mixture. The bigger float helps control this.
2. Remove the air jet. It's held in place by the bellmouth. Remove the bellmouth and It'll drop out.

My set up is: Twin 34mm + K&N
pilot 25
slide 4
needle jet 107
needle 2nd top
main 280
no air jet
deep floats
Still playing with needle/slide combinations.

Rich

splatt said:

SteveMinning said:

The idea is that the main jet affects the carb mixture at all settings

Click to expand...

only if it is miles to small or blocked :| :|

Click to expand...

I should have said that the main will affect the mixture from half to full throttle.

Richj:

What effect does removing the air jet have?

Your slide seems really lean, I had to go from a 3 1/2 to a 3 to get good crisp throttle response on my 34mm Mk2's. Also the 107 needle jet seems pretty rich. How's that working for you?

Anyone have issues with the vent lines pouring fuel if you turn on the petcocks before you start the engine? I checked the floats and they're not hung up. Float needle seats look clean. Doesn't do it when the engine is running.

FWIW: My set up is: Twin 34mm w/ factory velocity stacks
pilots 25
slides 3
needle jets 106
needle position 2nd top
mains 260

Removing the air jet will reduce the depression in the primary mixing chamber causing the needle and main jet to run very lean.

I run my twin 34s to book, though the pilots might be 20 and the choke jets 35, they perform faultlessly over the 40k they've been fitted.

Cash

This subject has come at the right time. I have an RGM mk 2 on my 850 Mk 3 and the initial pull away from idle is not good, with the engine ready to stall (sometimes does or it seems to choke unless I give it more revs. The plugs are also sooty and I have put 750+ miles on it since.

I was going to look at the pilot jet are some advice from an enging shop (A Norton one).

I'll post the results and keep an eye on here.

cash said:

Removing the air jet will reduce the depression in the primary mixing chamber causing the needle and main jet to run very lean.

I run my twin 34s to book, though the pilots might be 20 and the choke jets 35, they perform faultlessly over the 40k they've been fitted.

Cash

Click to expand...

There is no "book" setting for Mk2's on a Commando. All you can do is follow where the tuning route takes you, what's right is what works for your machine, you get what you get.

I've got two sets of Mk2's with different spray tubes there are also about 4 different 4 stroke needles available as far as I know any idea what you've got?

Dr_Hiller said:

Richj:

What effect does removing the air jet have?

Your slide seems really lean, I had to go from a 3 1/2 to a 3 to get good crisp throttle response on my 34mm Mk2's. Also the 107 needle jet seems pretty rich. How's that working for you?

Anyone have issues with the vent lines pouring fuel if you turn on the petcocks before you start the engine? I checked the floats and they're not hung up. Float needle seats look clean. Doesn't do it when the engine is running.

FWIW: My set up is: Twin 34mm w/ factory velocity stacks
pilots 25
slides 3
needle jets 106
needle position 2nd top
mains 260

Click to expand...

This explanation was posted elsewhere while I was having set up problems
"The 'Air Jet', more correctly called the 'Air Correction Jet' is used in one form or another on all AMAL and Mikuni carburators.
Physically, it's the horizontal air passage parallel to and centered underneath the large main air passage through the carburator. When looking into the throat of the carbie, there are three drillings below that throat, and this is the central one.
The purpose is to admit and meter air to the small chamber surrounding the top of the needle jet and below the fuel discharge nozzle in the main bore. Earlier and smaller carbs offered no adjustment to this air correction passage, but the MKII included a replaceable bushing retained by the bolted on 'air horn'. This bush was offered by AMAL in different sizes in order to refine the mixture at the top of the needle jet, It may have been added to meet Federal emission standards by allowing finer mixture adjustment.
The principle involved is that it's much easier to adjust air than it is to adjust fuel to reach a correct mixture, due to the vast differences in the volume of each. This principle is the same as is used in the pilot circuit of Monobloc, Concentric, and MK II AMALs "

I found taking out the air jet helped a lot. Its one of the simplest things to try and you can always put it back in if you find it makes no difference.

As I said I'm still trying to improve the transition from pilot to needle so may go back to a 106 needle. I may go even leaner on the slide if that doesn't work.

I had a single Mk1 years ago which ran really nice, to get that to work I started at 3.5 slide and filed the cutaway it until the it ran right, ended up with more cutaway than number 4 then as well, maybe my bikes just odd?

Thanks for the info. Still dialing mine in as well, so every bit helps.

While I'm hijacking the thread, I've got another issue... carb balancing. I've done the drill bit shank thing for basic setup and tried to balance from there by ear, but I'd rather use my carb stick. Anyone got a best approach to putting vacuum ports on the stub manifolds?

Dr_Hiller said:

Thanks for the info. Still dialing mine in as well, so every bit helps.

While I'm hijacking the thread, I've got another issue... carb balancing. I've done the drill bit shank thing for basic setup and tried to balance from there by ear, but I'd rather use my carb stick. Anyone got a best approach to putting vacuum ports on the stub manifolds?

Click to expand...

Can you use the balance tubes on the manifolds?

There aren't any balance tubes or vacuum takeoffs on the spigot manifolds I got with the carbs. They're like these: broken link removed

So, what are folks doing to balance spigoted carbs?

You can buy some 10-32 brass fittings from Thunder Products. They can be installed as seen in this photo.
To the left of the carb body just before the rubber connecting hose.
The aluminum keyway shaped stock has a short shoulder bolt at the center line this allows the carbs to be hung from rubber bands. Without this mod and many others, some talked about you are going to struggle.

There is no "book" setting for Mk2's on a Commando.

Click to expand...

The settings are from Amal's booklet and are not specific to any model. Apart from the pilot and choke jets the rest are to Amal's book. What I have found, if the motor is over advanced plugs can look very weak.
Cash

The carb RGM sent is a 34mm Mk2.
Main - 270
Needle 2 A 1
Needle jet 106
Slide chrome 3
Pilot 15

Meantime I've been introduced to a 'guru' and I'm putting the bike to him for setup - each to his own and all that

I'll report back when he's done his stuff. Just now the bike kicks back when starting but once running seems fine although it seems to get hot very quickly.....

d

RedEvo said:

The carb RGM sent is a 34mm Mk2.
Main - 270
Needle 2 A 1
Needle jet 106
Slide chrome 3
Pilot 15

Meantime I've been introduced to a 'guru' and I'm putting the bike to him for setup - each to his own and all that

I'll report back when he's done his stuff. Just now the bike kicks back when starting but once running seems fine although it seems to get hot very quickly.....

d

Click to expand...

I've found the chrome slides to be a problem in a twin carb setup. One of the two, and I can't remember which, can hang up on the adjuster. Screwing in the adjuster jams the slide unless you lift it every time you want to adjust, anyone else found this issue?