Anglian carburation

[David Muir]

Hi, Got an Anglian fitted with a 26mm concentric. On the road the bike 4 strokes/8 strokes and I'm guessing that carburation is the problem. Anyone got ideas of jets/slides etc I should use to start with before fine tuning?
Thanks,
David

[Keith Beach]

Well David I am sure that others more knowledgeable than I will offer advice and have certainly been of great help to me. But here is my view.

My Anglian has always four stroked on the road when held at steady throttle around eighth to bit over quarter throttle (anyway unfortunately somewhere between end of pilot jet, slide cut away and needle position/jet) and whatever fettling I've done to date has not altered that. Its fine at low speed and when opened up and pulls fine too. I think book settings are 140 main jet, 106 needle jet, 25 pilot and a 2.5 or 3 slide. Initially because it was four stroking I expected to find on plug chops that the plug showed it was running too rich but it never did, if anything looking a bit on the weak side. Ive tried a multitude of combinations. A 105 needle jet and the needle in all positions on that and the 106 jet but it had no impact. Ive changed to various different slides. I've also played with the ignition timing a fair bit too suspecting that the four stroking was due to poor scavenging and that I therefore needed to retard the ignition but Ive currently got it at 3.2 mm BTDC and it still four strokes. Members that know about these things have suggested it is do with the porting of the Anglian barrel (though in my case I think I may well have a Challenger barrel fitted which might not help).

I just put up with it now. Id be interested to know how you get on.

Keith

[riflegreen]

The Anglian Concentric should have a 106T needle jet ,which has no bleed hole in the side .

A scrambles barrel won't make any difference , many of the Works bikes had MX barrels , just depended what barrels were available at the time .

The first thing we did was cut of that damn silly tube extension on the manifold and then alter the down draft of the manifold , also the copper asbestos washer seal between manifold and barreldistorted the manifold flange when tightened , far better using a Villiers manifold gasket .

Chris

[David Muir]

Anglian carburation

Riflegreen,
My concentric doesn't have a Pilot needle jet fitted.......it only has a pilot screw! Can I modify mine or were there different concentric bodies ( I think my carb. came from a Triumph Trident)?
David

[riflegreen]

David ,

If your carb is off a Trident then it is for four stroke use and not two stroke .

The main difference is the spray tube , seen through the carb inlet , a two stroke has a chamfered top , the chamfer facing the engine . A four stroke is flat topped plus you need the 105T needle jet , that has no bleed hole at the side .

There is no way of telling what the pilot jet is , it is under a small plate above the float chamber & is not easily cleaned out .

Your best bet is a new carb or a carb from a BSA Bantam .

Chris

[Rob]

Having just spent quite a while sorting out a concentric for my Anglian, I can add a few comments here.

Beware a carb from a Trident T160, it is worse than just a 4 stroke carb!

For a start the needle is different. The T160 needle has 5 rings above the fixing clip grooves. A 600 series 2 stroke needle has a single ring only.

David, you say your carb doesn't have a 'pilot needle jet fitted'. I assume you mean pilot jet. Post 1973 4 stroke carbs did away with the separate pilot jet fitted above the float and used a 'fixed pilot bush' situated beyond the pilot air screw. This was because Amal found that some bikes, eg. the Triumph T100, did not generate enough manifold depression to work properly with the jet up the far end away from the venturi. As a result, they moved it up front.

It could be that your carb has a fixed bush. There are 2 easy ways of testing if this is the case. The first is to poke a piece of wire of the correct length into the hole that the pilot adjusting screw sits in. The difference between carbs with/without bushes is immediately apparent. My test piece is outside in the workshop so I can't give you the exact length at the moment.

The 2nd way is to remove the air screw and pilot jet if fitted and fit the flexible pipe from a can of carb cleaner to the the pilot jet hole. This is tapped 5 BA and I have made up an adaptor but it would probably work without. Give it a blast and if a neatly vapourised jet emerges from the pilot adjusting screw hole, then a bush is fitted and it is clear. If a volcanic eruption of carb cleaner gushes out of the hole, then it is fairly safe to assume a bush is not fitted.

As Chris says, the spray tube of a 2 stroke carb slopes at the front. With the '2 stroke' carb I fitted, it had the right spray tube but some helpful soul had fitted a pilot jet obviously unaware it also had a pilot bush fitted. It also had a 4 stroke needle fitted.

The moral of this story is that you really need to check every detail of the carb to ensure it has the right bits to start with and that all the various orifices are clear before you worry about fine tuning. There have been so many different parts and changes over the years that it is a bit of a nightmare.

One further point. The main jet holder is available in 2 sizes. In original Amal documentation, the 2 stroke version is about 1/8" shorter than the 4 stroke. Originally, they were all the shorter type but Amal found that 4 strokes went better if the main jet was situated lower into the fuel in the float bowl. It also says that the short types are brass and the long types are plated but I have a plated short type in my box of bits so don't believe everything you read! Not only that, I have just received a 2 stroke carb from Burlen's and that has the longer type fitted so maybe the short type is no longer available, forgotten about or not important.

Hope this helps. Sorry for the ramble but the local Co-op is doing a special offer on Hobgoblin ale and it would have been churlish not to take advantage!!

Rob

PS - Chris - I would add some strong caveats to going for a new carb - I speak from (very recent) experience!!

[David Muir]

Anglian carb.etc

It seems my memory was failing me-the carb was bought new from Wassell many moons ago! [Trident carbs. are,in fact, 27mm]
Have looked in the air intake and the spray tube does indeed have a chamfer facing the engine, so it is indeed a 2 stroke concentric.
Will now investigate the points made by Rob.
Thanks.

David

[druid]

Anglian carb

David,
Having converted carbs to fit a Trident I can confirm that they a) need boring to 27mm and b) unlike all the 4 stroke carbs I have seen they had chamfered spray tubes.

Druid

[riflegreen]

David ,

John put me right on Concentrics , the Trident does indeed have a chamfered spray tube but just a chamfered spray tube doesn't make it a two stroke carb .

Chris

[Rob]

Chris, 4 parts make the difference, chamfered spray tube, needle, needle jet and main jet holder. Plus, by rights, should have a pilot jet and not a pilot bush (and certainly not both as I can verify!)

Cheers, Rob

[Terry Sewell]

Anglian Carb

David,
I have an Anglian that I have ridden for a number of years with a little bit of success. But I could never get an amal conc to run as well as a villiers carb. That is what I run at present.
It is very hard to say what you need for your carb as the settings you get in books are usually factory settings for brand new engines. I find trying to get carburation correct is a little hit and miss.

Here goes. This is what I would do.
Firstly make sure your electrics are ok. ie check plug, i use champion L82 ( dont like NGK to wide a heat range) check plug cap and that it has a good connection to the HT lead. I still use points with an outside coil. Set points to 12 thou and ign timing to 2.5 mm BTDC. When you are happy with the electrics move on to the carb.
As you say it 4 strokes on the road, i would think your primary circuit is ok as this operates up to 1/8th throttle opening. Try a No3 slide with a short two stroke needle and a 107 needle jet with no side drillings. Also fit the short mainjet holder, this has already been mentioned. If you were running in trials I would recomend a 120 main jet, but for the road perhaps a 140. I would also fit a new ajustable float so you can play with the float bowl fuel height.
What air filter have you got, is it blocked or too small, this would choke the engine. Go for a ride with no filter on see if it improves.
Another trick is when out riding and it starts to 4 stroke, turn the fuel off, see if it improves.

All the very best Terry Sewell

[Rob]

Here's something else to ponder!

When the Concentric was first introduced on the THS, the settings were:

Pilot: 20
Slide: No.3
Needle Jet: .105
Main Jet: 110

From frame number 24THS213 this changed to:

Pilot: 25
Slide: No.2 1/2
Needle Jet: .106
Main Jet: 140

This is more exciting than the inlet manifold saga and definitely better than discussing moorland Blue!

Certainly beats riding the bikes anyway!

Wonder if Bert did a recall for a factory re-fit to the new settings?

Anyway, I'm running a Wal Phillips Fuel Injector on my Anglian and it runs underwater!

[David Muir]

Carb.spec

Thanks Rob,
Looked inside carb. and its exactly as the later THS specification!
However, discovered Pilot jet blocked!
All back together and started first kick.

David

[Rob]

Well done David, glad that little speel helped! Just need to find out the story behind the change at 213.

I could always set up 2 carbs of course.................!!!!!!!!!!