Amal mk11 carb

Hi All.
I have a question for those that know. Mallory for JS2 was a mixed affair, the main problem being carburettor set up. I now use
an Amal mk11 as opposed to the concentric John used and I'm confused with the chock layout. With the lever pressed down the
motor runs well, lift the lever the motor dies but, in the paddock with lever up motor runs well and picks up from low revs, under
load motor dies, so can anyone who uses the mk11 enlighten me.

The last session for us went very well JS2 came to life with the lever down,but should it have been up. I have contatced Amal but
they are so busy it's taking too long I need to know.

Thank you in anticipation.
Regards to all.
Confused Les.

Hi Les,
Glad to here the test day went well for those who went.
With regards to choke lever on the MK 2 lever down lifts the plunger giving full choke.
As to set up you can pm me for my set up on last seasons settings. Got the carburation spot on by mid season and the bike was fast and reliable .
All the best Nick

I was on mk2's for 25 years so lever up means the plunger is down closing off the secondary choke tube turning off the choke
if it dont work without this closed somthing wrong if its changing you had some crap/dirt in it, always a posibility.

if it does not run without this you have a simple cause or causes
1) ther is a tiny hole inside the front side of motor check this is not blocked ofted easy to do this.
2) ask the question and ED has a copy of the amal original setup from me Ido not have it to hand but may be he can help her.

Ihave to say sounds like a blocked pilot jet or the wrong blanking jet in the float bowel, there should be 2 one with one with out its not uncommen to have two blanking screws in both locations so hey no Btm end encouraglment to themain system.

sure Brian white will know this straight a way he is still on amal were as Ihave gone much more sophisticated after my return and loads of issues with sticking throttles, frittened the life out of me.

two other things tell me the bore carb/main jet and needle jet and needle

Bore 28 to 30mm should be 107/106 needle jet about 280/300 main 2d1 needle the air jet Ithink should be 2.5 or 25?
bore 32 to 34mm be 107 needle jet about 280/340 main 2d1 needle air (25)
Bore 34 to 36mm 108 neddle jet about 320 to 360 main 2d1 needle (35)
bore 38 to 40mm 109/110 needle about 360 to 400 not sure on air jet (50)and

if its got a small float get rid of it use std larger item even though there is less fule in float bowel it dont work at all,

also check the air/screw 1.5 to 2 out from in / if its old remove the base check no one has overtightened it,
and the air restrictor that is located inside the Bell mouth its a tiny alloy plug with a 3.5/4.5mm hole NOW Idea what it does ask Brian but Im sure it should be in, o yes is the belmoth on correctly not blocking the holes at the rear, I have a 38 with a home made coper! trumpet will bring it to the bash if you whant we can strip it get Brian white to remind us all who / what jets do what. take just 5 mints to strip a carb.

hope this is helpful, sure must be others on here.

glad it whet ok for you and the bike looks "the taggems" great to see it out.

I love the idea on the rear sub frame triangular fabrication please explain looks very technical.

very best regards Derek

Hi Les

Nick is definitely right if he is reffering to the mk2 Amal on my bike (previously Nick's bike). The choke is on when the lever is down. I believe it is a relatively new carb as it is made in Spain. I don't know if they changed the design at all. I think Derek is about right with all the settings. If you are interested in my carb settings just ask. I think I have got my bike running alright but I'm sure you realise they could only be used as a guide.

Rob

hello les ,
i have an amal mk2 on mine, it has a 108 needle jet , 320 main and 2d1 needle set in the third groove, also the pilot jet in the bowl s a 30 ,

the carb you have , is it a new one or second hand old one? only i read a while ago that the choke plunger has been changed on the end rubber seal , mine is an old one , and as i managed to start the bike with no choke needed (i.e lever down) i took the lever off, i heard that the rubber seal , when worn and let air through and give erratic running so i sealed it down .

Hi guys.
First I thank all those who sent a reply to my question and as a result I thought I would strip the carb.The carb is a new one
so I didn't expect to find a problem, the chap from Surrey Cycles ( where I bought it ) did ask if it was for a 2 stroke or a 4 as it
would have to be setup, he set the carb for 2 stroke. I mentioned the carb angle,12 degrees max was the reply but Amal state the carb will work up to 40 degrees but the pilot jet will have to be relocated to the main body. Surrey Cycles were most helpful suggesting I would need a deep float as the angle of the carb is set at approx 30 degrees and change over pilot and blank positions
so I did that, motor still ran better on full choke.Now, I found a small jet at the bottom of the bowl where the long brass tube
location is and this is a number 50 and clear, needle jet 106 clear,pilot jet 30 clear, pilot screw, tried half turn out,one turn.one and half still no joy. I've checked every orifice within the main body, all clear, the only thing I've not done is to change the deep
float for the standard one.
Thanks again guys for your interest and advice. By the way Nick B, did you get my first attempt at a PM?

Regards still confused.
Les.

Hi les

Could you be having any trouble with the petrol level in your carb. The float is not adjustable in that carb and if you are mounting the carb at an angle it could affect this and also the gas velocsity/pressure required through the carb to vaporise the fuel correctly.

Rob

the float level is adjustable, you have to remove the fuel inlet and filter from the underside then heat the bowl with boiling water and use a 3mm pin to tap the the brass cupped seat up or hit it from the top to lower it , its a real cruddy idea , the float should be protruding in a level manner when viewed from the side

Hi All on the angles of AMAL carb, and how it affected the running

Brian white borrowed me his spare Engine at Pembrey, after I did a big end in, in about 1990/1 ish I think, the problem was my bike tilted the engine forwards more than his "OK" it fired up ok and reved fine without load, but I have horrendouse problems in the race and getting it off the line, but under way it was supper from 3/4 to full throttle, but once I did allow it to drop out of this region it took a fit a coffing spluttering to get it back up again, I'm I eventually was second behind Peter so Brian was prity happy as it was his new motor, anyway, he identified the problem in the ppadddock or Tom did it was down to the fact the carb was tilted forwards by about 25 deg or more. The other story was how he got the exhaust to fit what an amazing bit of engineering that was, with a little bit of help from John sawer with a anti vibration bracket. a story for another day though,
on riding other bikes, I always believed this engine had a wankle inside it as it was so smooth, I think this was down to the way brian built and balanced his cranks "good times".

anyway getting back to the issue at hand, the carb it ran ok part throttle but wollowed part throttle to 3/4 range but from 3/4 to full it was a missile, he won the championship with this engine the following season or was it the one after!. Anyway I dont feel the float level will affect just the pilot system on its own, sure it would affect the whole range to full open, but for sure it may well cause problems with starting if the level is incorrect.

I would not adjust the factory set float level, I would leave it well alone, just a few thou out, and !- also if this is move this too often it could affect the seat/location, or come lose and the thing will vibrate and could move when underway, could not imagine the consiquences with a bit of look "just a flooded the motor", but the other way "ouch".

great topic! we need more like this.

Derek

A friend of mine ran a MK11 on his motor and experienced endless , niggly carb problems , he also had a fair amount of inclination
to the carb . At the suggestion of some one in the team , an angled plate was made to reduce the incline substantially , end of problem !
The thinking was that the pilot system was swamped with fuel at the original inclination by the effects of raised fuel height .
Don`t know if it`s applicable in your case , but it is another piece of advice , won the hard way !

All the best in your endeavours , we run just such a carb on Mark`s machine with no problems , apart from the odd main jet change .

Cheers for now , Trevor

Good Evening All,

This is a good subject for us, we are going to run a mk2 34mm, does anyone have any base settings to work from?


Regards


Eddie & Malcolm

Hi Ed ,
Main Jet 320
Needle Jet 107
Needle Pos 3
Cutaway 3
Pilot Jet 25
Air Jet 2.5

These are settings we have used , no garantees , but worked for us so it may form a basis for experimentation !
Nice to be able to assist you both in this small way .


Cheers for now , Trevor

hello trevor , whats a" cutaway3" ? do you mean the spray tube? i.e angled 2 stroke style

Hi ,
Sorry , should have made that clearer ,

Throttle slide with a number 3 cutaway


Hope that helps , Trevor

Good Afternoon Trevor,

Thank you for the carb information, i will have a look through the spares box tonight.


Kind Regards


Eddie