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Amal 626 concentric settings

I ve been advised by Burlen that if I go for a concentric, a 26mm Concentric carburetter is a good replacement with a 200 Main Jet, 106" Needle Jet and a No 4 Throttle Slide. Any experience by anyone with these settings? What are your thoughts?

Re: Amal 626 concentric settings

Assuming you are taking about M20 fitment follow the settings and jet sizes for the Monobloc carb used on later M20s as a baseline set up...It should run OK on those settings with only minor adjustments at most...Ian

email (option): ian@wright52.plus.com

Re: Amal 626 concentric settings

Hi, my experience with the 626 concentric is that, with the no 5 slide, the engine is jerking at low speed. Alsof the bike is not "picking up". The no.3 is working Just fine. Maybe I try the no.4 as adviced by Burlen.
Main jet is 230 (with airfilter).
John 🏍️

email (option): john.kater@chello.nl

Re: Amal 626 concentric settings

I am using a 3 or 3.5 currently.
The trick to smoothing it out is a long induction tube the longer the better.
The spacer off a WD B40 works really well
even better with a 1/2" wide tufnol gasket

Re: Amal 626 concentric settings


Trevor, I have a 40 mm. tube because you adviced me that a few years back. Also I have a no.3,5 and a no. 4 slide that I can use.

John

email (option): john.kater@chello.nl

Re: Amal 626 concentric settings

Amal 626 premier on WM20 motor
Pilot = 19
Needle = 106
Needle set to position 3 (highest position)
Cut-out = No 4
No air filter, 25 mm spacer.
New valve guides. No air leaks.
Put 300 miles on the bike with the 626 on.
The last 15 miles was putting around town before the head was removed.







Spark-plug-color

Bore-damage

email (option): zola.industries@bigpond.com

Re: Amal 626 concentric settings

Judging by the plug colour, running way too lean
Judging by the scoring that starts right up at the top of the bore also suffering from rock injestion.
Really need to see the piston and in particular the inside of the piston crown
The oil has gotten way too thin ( because it was too hot ) so has bypassed the rings and caused the coking on the head.

Hopefully the bore is not as bad it looks.
FWIW I am running a projected tip spark plug, BP6HS around town & BP7HS on long trips.
The electrode really needs to be in the combustion chamber not hiding 1/2 way up the plug hole because you end up with red hot glowing sections of the thread which because it is a side valve can ignite the incoming charge way too early.
A 16 pilot seems a touch on the small side as well
I think mine is a 24 and I am running an air filter .

Re: Amal 626 concentric settings

Thanks for the spark plug tip wm20. Please find a picture of the piston below.
I’m running a premier 19 pilot which I think is equivalent to a 30 in Pre-Premier carbs.
Main Jet is 200
No4 Cut Away
106 Needle
Premier 19 pilot
These are the same settings from Burlen that were given to Piero at the start of the thread.

If you have a look at the piston failure thread there is a story there. Pretty sure I cooked it very early as it did run very hot in needle position 1 and 2. Needle position 3 seems fine.
I thought the coloration does look lean for just putting around town. Thanks for verifying this line of thought.
It ran very well even with the piston in this state. Only the metal in the oil prompted me to look further.
None the less will get it sorted and go again. With some changes.

Cheers

Brian

Found this table on the internet:
1 Ring - 622/502-15 (Equivalent to 20 Pilot Jet in pre-Premier carbs.)
2 Rings - 622/502-17 (Equivalent to 25 Pilot Jet in pre-Premier carbs.)
3 Rings - 622/502-19 (Equivalent to 30 Pilot Jet in pre-Premier carbs.)
4 Rings - 622/502-21 (Equivalent to 35 Pilot Jet in pre-Premier carbs.)
5 Rings - 622/502-23 (Equivalent to 40 Pilot Jet in pre-Premier carbs.)

Piston

email (option): zola.industries@bigpond.com

Re: Amal 626 concentric settings

I'd also be tempted to look at the conrod alignment. This can also be the result of a hand reamed small end bush done in situ.

email (option): pes.sales@btconnect.com

Re: Amal 626 concentric settings

Problem with lean running is the engine always seems to running good, till it dosen't.
Good thing is that piston looks like it will clean up so with a little luck some new rings & a hone & you will be ready for another try.
What I really wanted to see is inside the piston.
The under side of the piston crown tells a lot
As does the little end of the conrod
Both will show tell tale signs that will confirm lean running & overheating .
When running in a new engine you need to keep an eye on the pipe ( if it is chromed ) and the oil tank
You should be able to hold your hand against the side of the oil tank and water ( or spit ) should not bubble on it .
Ideally the oil will be around 80 C or if you like the temperature of off peak hot water .

The other tell tale is the sound.
A lean engine will have a hard sharp exhaust note to the point of being painful.
A rich engine will have a softer muffledd sort of fluffy exhaust note

You may have even been sucking in air around the spark plug

Gunsons make a wonderful tool called a COLORTUNE which is basically a spark plug with a window in it
Wonderful tool for people who are not proficient engine tuners.
I use mine a lot, mainly for diagnosing small 2 stroke engines with weird running .
If you get one then just be careful not to cook the engine because it is easy to sit there fiddleing for a long time with the bike sitting there not getting any cool breeze .

Re: Amal 626 concentric settings

BW

What make piston are you using?

Bob

Re: Amal 626 concentric settings


I don't know Bob. Bought the piston with the barrel off a chap that were surplus to his requirements.

Thought I would freshen up the top end before putting the bike on the road.

Some pictures on the way.

email (option): zola.industries@bigpond.com

Re: Amal 626 concentric settings


Yes, WM20 you are spot on with the sound the bike was making.

The small end measured correctly when I put it back together.

Thanks for taking the time to look at these.


Wrist-pin

20211123-233329

20211123-233412


Looking at the information on this site the big end needs to be replaced.

So.... will be pulling the motor down.

cheers

Brian

email (option): zola.industries@bigpond.com

Re: Amal 626 concentric settings

Just a observation, but shouldn't the oil grooves in the small bush be at the top of the conrod?

email (option): pes.sales@btconnect.com

Re: Amal 626 concentric settings

There are two intersecting spiral oil grooves machined into the small end bush with an oil hole at the top where the grooves intersect...The hole should line up with the slot machined into the conrod...

The gudgeon pin to small end bush fit should not be too close or overheating will be the result...When fitted the piston should fall either way under its own weight with no resistance to movement, yet at the same time there should be absolutely minimal perceptible play between the bush and pin...The bush normally would protrude from either side of the conrod and I see yours doesn't...

If you are going to fit a new big end that would be the time to check the conrod is both straight and not twisted...If handled roughly they are prone to damage when the crank is out of the engine or when the top end is not fitted...Too much force applied when removing a tight gudgeon pin can cause problems as well...Ian

email (option): ian@wright52.plus.com

Re: Amal 626 concentric settings


Thanks for taking the time to respond Mark.

As Ian mentioned. See picture. Mind you, it was clean the last time I saw it.....


20211124-073201

email (option): zola.industries@bigpond.com

Re: Amal 626 concentric settings


The bush protrudes either side. Looked like it did not due to the camera angle.


On assembly the gudgeon pin measured .750 now measures .750

On assembly the small end bush measured .7505 now measures .7515


For installation and removal of the gudgeon, the top part of the piston was inserted into the barrel with rings.

I made up some spacers so I could place the barrel with piston onto the top of the crank case leaving enough room to install the pin.

This seemed to work quite well.

Cheers
Brian




20210805-132229

email (option): zola.industries@bigpond.com

Re: Amal 626 concentric settings

Ian Wright
Assuming you are taking about M20 fitment follow the settings and jet sizes for the Monobloc carb used on later M20s as a baseline set up...It should run OK on those settings with only minor adjustments at most...Ian

This is what I have on my M21, works fine.
I mounted a bakelite manifold spacer in order to make the floatbowl go clear of the dynamo drive housing. Think it was specified as for AJS/Matchless, bought a smaller diameter and bored it out to proper size. Might have gotten it from Feked, can't seem to remember.

/Simon

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