Amal needles and poor running (2014)

I've recently converted my race bike to be my road bike, and I'm having a couple of hassles getting it to run well low down. It has a pair of 36mm Mk2 Amals ( big I know ) and when I open it up it goes really well, but stuck in traffic it's terrible. The plugs get sooty , so it's obviously too rich but I can't seem to get it leaner.

I have 320 mains, 106 needle jet 20 pilots ( I took these down from 25 which didn't seem to help much). The slides are number 4 so they are the leanest you can get.

The problem is right down low, around 1/8 to 1/4 throttle. Above half throttle it takes off really well.

My question is about the needles. They seem to be marked 2A1 but the 1 is either badly stamped, or is not a 1 but some other mark.

They have 5 grooves fro the circlip, but I thought a 2A1 had 3 grooves. Have I got the right needles?
Does anyone recognise these needles?

Definitely a 2A- something



But is it a 2A1 ?



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pommie john said:

I have 320 mains, 106 needle jet 20 pilots ( I took these down from 25 which didn't seem to help much). The slides are number 4 so they are the leanest you can get.

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Miks and Mk2's meter the petrol, not the air like the ole Mk1 Amals to make it idle.
If # 20 is too big an idle jet, maybe you need smaller still ?

I know about nothing else of Mk2 Amals (aren't they about the same as some Miks ?), but the slide cutaway can always be filed out to be a 5 or 6 even. ?
That would lean it out, although maybe for more of the range than you would want.
Once done, there is no going back.
But if you happen to have a pair of spare ones....

Neat looking cycle.

P.S. What petrol are you feeding it.
Not all the stuff that comes out of a pump is the same.

Rohan said:

pommie john said:

I have 320 mains, 106 needle jet 20 pilots ( I took these down from 25 which didn't seem to help much). The slides are number 4 so they are the leanest you can get.

Click to expand...

Miks and Mk2's meter the petrol, not the air like the ole Mk1 Amals to make it idle.
If # 20 is too big an idle jet, maybe you need smaller still ?

I know about nothing else of Mk2 Amals (aren't they about the same as some Miks ?), but the slide cutaway can always be filed out to be a 5 or 6 even. ?
That would lean it out, although maybe for more of the range than you would want.
Once done, there is no going back.
But if you happen to have a pair of spare ones....

Neat looking cycle.

Click to expand...

I do have a spare pair of #3 slides so I could try that. I had a look inside and it seems to me that they meter air not fuel, so turning the screw out leans the mixture. The books says that if best idle is at 1 - 1 1/2 turn out, the pilot jet is about right, and that's what I've got.


I used 98 RON unleaded. I have got a can of race fuel I could try.. good point.

It might be that you have the carbs too rigidly mounted and are getting flooding. I would have thought the slides would be No 3 cutaway already. Perhaps the chokes are staying slightly open (not seating properly when off), from memory they feed petrol ?

I've put new chokes in and checked with carb cleaner sprayed up the choke orifice. The spray gets through when the chokes are on, and doesn't when they are off.

The slides re #4 the leanest I can buy.

The carbs are rubber mounted but I see your point. I have not considered flooding though vibration. I'm not sure how to test, or fix that.

I know nothing about Mk 11s but is this any help to you

http://www.britbike.com/forums/ubbthrea ... Post523966

The guy John Healy is seriously good

johnm said:

I know nothing about Mk 11s but is this any help to you

http://www.britbike.com/forums/ubbthrea ... Post523966

The guy John Healy is seriously good

Click to expand...

That is very useful info thanks. I'll have a look at the choke bores over the weekend. This evening, being Valentine's Day, I am unable to play with the bike any more

I have read many posts and articles from John Healey (Healy?).

He is a Triumph guy but seems to have been in the Britiish bike industry in the US since the 1960s and I have been very impressed with his posts and articles. He has a good set of articles on Boyer trouble shooting

[quote="pommie john
Neat looking cycle.[/quote]

I used 98 RON unleaded. I have got a can of race fuel I could try.. good point.[/quote]

Use 95 for carbs and 98 for injectors. 98 is too dense for carbs and will give you sooty plugs

I tried a pair of 34mm Mk 2s on my bike a few years ago. I eventually admitted defeat. It always ran rich at idle whatever I did. One thing I tried that leaned it up in the range you are looking at, was a pair of 2C3 needles. These I believe were fitted to parallel port Bonnies with 30mm Mk 2s. Hope this helps & good luck.
Martyn.

Thanks for the info everyone.

I now plan to blank off the chokes, both the jet and the air orifice of the starter circuit to isolate whether it's a problem with either the starter jet or the plunger leaking .

If that doesn't help I will try a 2C3 needle, and the link above suggested that drilling out the cross drilling in the needle jet can lean it out in the 1/4 throttle range.

Brilliant forum.

1/8 to 1/4 throttle sounds like needle-jet terrritory.Anywhere between idle and 3/8 throttle,the parallel part of the needle is still in the needle jet,and going down to a 105 would lean it off below 3/8 throttle.

You'd need to raise the needle to keep the mixture the same above 3/8 throttle.
Have you measured the needle jet size,to make sure they are actually 0.106"?If they're worn to 0.1065",it will run rich below 3/8 throttle.That might explain how you can get away with such a lean slide.The slide is most effective at just below 1/4 throttle too.

On a Mark II the mixture screws meter air just like on a Mark I concentric. I have a set on my Triumph and it seems to like to run best with them at about two turns out. The Triumph shop manual calls for them to be set at 2 1/2 turns out on bikes with the Mark II's. One major difference on Mark II's is they have an enricher circuit instead of a tickler. It consists of a plunger with a rubber cap. When the plunger is up a passage is open allowing the more gas to flow to help starting and warm up. When down it seals the passage. First make sure the lever and linkage is working correctly and when in running mode the lever is up holding the plungers down. The plunger rubber also deteriorates over time and starts to leak.
This can lead to an over rich condition as the carb is essentially flooding the engine all the time. You can supposedly test for this by holding the plunger down with your finger while the bike is running and see if rpm picks up. However, if the plungers haven't been replaced in a long time it might be a good idea to just get some new ones.

The 2c3 needle is for the stainless steel .105 needle jet that was used on the "smog" late Bonnevilles. The 2a1 is the correct needle for the .106 jet. Most I've seen have 3 grooves. On my Bonneville, which has open peashooters and open air cleaner I'm running #15 pilot, #35 choke and 3 1/2 slide. That seems like a huge main jet size, I'm running 210's on the Bonneville. Can't see how it would be that much different on a Commando.

A faked drain plug with a tube , for a piece of 3/16 bore neoprene tube , should get the float level visual - as long as you dont set fire to anything .

always thought I shouldve put a steel joining bar between the carbs , on the two tapped holes in the back of each .

You could even go crazy & put long mounting rubber tubes , and mount the Carbs to the Frame , rather than the engine .

Really , flicking a Choke OFF , from say half on should give a distinct / observable alteration in beat . The olde stutter - miss for too lean & the brupp brupp burupp rythmic beat when veering rich . Not to mention the black smoke .
Of course its got the viton tipped needles & the float levels are checked . and the floats arnt out to lunch with the new wonder fuel . No air leaks in the top cap / covers either .

Most of the electronic ignitions come in fully advanced around there , 2000 / 2500 - which is a bit early really . Can make it a bit crankey / stuttery with the clutch fully engaged across the transition trailing to leading throttle .
the cures to give it grief and hold 25 to 3000 where the clutch is fully engaged . would blow out the cobwebs anyway . :twisted: If this doesnt work you really do have a problem . Bar dont let it idle on the sidestand ,
as the lefts downhill - so the excess oil & petrol has a excuse to migrate there , leant over . the old ' taps off ' stopped to - with the sidestand in use , for much the same reason - let alone a cylinder of petrol .
tecnically you can tell the differance between Oil & fuel BLACK on the plug - as oils shiney & petrols sooty .

If its all spiffing and new , it might just want a decent spin in the country to settle in , before you get around to ' fine tuneing ' , as theyre freer loosened of - engines that is , not to mention beded in .
Throw a Comp guage on warm , to see if both cylinders are dead even . :?

They were refered to as ' smooth Bores ' developed to out carburate the Mikunis . being British theres a step in the ' smooth bore ' where the castings mate . if it were real irregular or the air tubes there are not 1000% it could be awkward .

Smoothing matching and polishing the bellmouths / flared intakes to bore , wont slow it down . Check those holes for flash or dregs as some are the float chamber pressure vents . Typical concentric was sticking float , the rubber hoses are the
suckers thatd go to the carbon canister on a car - to clean the nasty petrol fumes . As in they should be unrestricted when blown into .

What PLUGS are you running / might just want warmer ones in Town , If your not holding it at Redline off the Lights . :mrgreen: 36 is probly the equivilant of a 38 mk 1 , so ' WE' are into the equivilant of the Goldie with the 1 1/2 Carb .
Id useually let the Cars get a length before letting in the clutch so as not to ram them letting it it , otherwise it was to low a rpm to carburate properly as its not set up for TRIALS rideing . Once underway it was stuttery below 2000 but would pull from 1100 , with SLOW Ign Adv , with 32 mk IIs on the 750 . So Im thinking your going to be virneir increments on the throttle below say 3000 , matching the position to the revs , just leading . should be right from 35000 .
maybe you need a Six speed . :lol: :lol: or move to the Country :mrgreen: There seemed to be some debate as to wether the Traffic lights were just ' advisory ' or otherwise . :wink:theyre not these damn self adjusting c.v. whizz bang carbs .

Rohan said:

Miks and Mk2's meter the petrol, not the air like the ole Mk1 Amals to make it idle.

Click to expand...

htown16 said:

On a Mark II the mixture screws meter air just like on a Mark I concentric.

Click to expand...

Also the usual Mikuni round slide "VM"carbs.

http://www.mikuni.com/pdf/vmmanual.pdf

htown16 said:

That seems like a huge main jet size, I'm running 210's on the Bonneville. Can't see how it would be that much different on a Commando.

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A 36 mm carb has 44% more area to let the air in,than a 30 mm carb.It will need a bigger main jet.Somewhere about 300 sounds right.

1/8 to 1/4 throttle doesn't sound like needle jet problem to me. If you can screw in the idle adjustment until the motor misses then back it off slightly to get good running, the other low range jets should be OK unless you have a blocked air jet. Are both plugs sooty ? If they are, the problem is affecting both carbs and is unlikely to be a blocked jet. Your main jets sound quite large. Because the carb is larger, it doesn't necessarily mean the mains should be. The venturi effect is different in a bigger carb. The main jets only affect the mixture when the throttle is past 3/4 open, i.e. the needle is well up the taper in the needle jet. It is possible that your setup is metering off the taper on the needle when it should be running on the mains. If you fit a larger main jet the bike should run rich on full throttle (do a plug chop), if it doesn't you know you have this problem, get a richer needle. Some Amal jets are recessed for a few mm so that the needles don't obstruct the mains at full throttle. I always use Mikuni needles - the No 6 type are probably the correct length for your carburetor. There is much more information available about the various tapers, and I feel that the Amal needles are much less precise. 6D are lean, 6F are rich, and the tapers are usually two stage on Mikuni needles.

https://www.google.com.au/search?q=miku ... 00&bih=636

Thanks for all the replies. I'll be working on it next week. I have to work this weekend so the bike will have to wait a little.
I'll get back with updates next week.


John

acotrel said:

1/8 to 1/4 throttle doesn't sound like needle jet problem to me.

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Drill out a needle jet 0.001" bigger,or use one that is worn 0.001" bigger,and you can get all the richness you can ever use (plus more) at anywhere between idle and 3/8 throttle.It's a fast way to foul plugs.

Above 3/8 throttle you will also have some richness,but it will be proportionally less as you open the throttle more until you get to about 3/4 throttle.

The needle jet IS a low-throttle jet ,while the parallel part of the needle is still in the needle jet.
When the tapered part of the needle starts coming out of the jet,the needle taper causes it to also be a high-throttle jet (from about 3/8 up to 3/4 throttle).