Amal running rich?

[denill]

Recently acquired a '51 Triumph TR5 Trophy. Looks great (as you can see) but it is running extremely rich and does not clear even under acceleration. It is fitted with a 1 inch Amal 376 Monobloc.

Is there a float setting for this carb. It doesn't appear to offer any adjustment though. Main jet is 150.

Any ideas out there?

[Motu]

Surely there is a how to on Monoblocks on the internet somewhere, that'd be easier than me finding a book to look through in my library? Turn off the fuel and see if it cleans up as it runs out.

[denill]

Surely there is a how to on Monoblocks on the internet somewhere, that'd be easier than me finding a book to look through in my library? Turn off the fuel and see if it cleans up as it runs out.

Yes, it runs sweet when the carb is running dry. That's
Why I looked at the float level. I have googled to no avail..........

It surely is not a major and just hitting on the problem should not be hard. Thanks Motu.

[cs363]

Is this any help: http://www.britcycle.com/Manuals/MonoblocTuning.pdf

[Voltaire]

Personally I'd give the old carb an overhaul.
There is not much to a monobloc
The jets and needles wear out due to the vibration
How much slop is in the slide to bore.

Amal are still around'
http://amalcarb.co.uk/
or locally
http://www.britishspares.com/

Motu was working on these when I was at school
There is loads on the net about pre unit Triumph

Nice bike.

[buggerit]

Stay off the curry

[Grumph]

1" 276 std is the correct carb - not 376 Monobloc. Jetting for that is 150 main, 3.5 cutaway slide and a .107 needle jet.

If a 376 monobloc has been fitted, it'd take a 150 main, same 3.5 cutaway,.106 needle jet and a 30 pilot jet.

i'd start with a new needle jet - and check that when the float chamber end cover is fitted, the float will still have endfloat on the pivot pin. Not unknown for everything to clamp up solid when the cover goes on....The idle jet not screwed firmly home can give a too rich mixture also.

Nominally, there's no adjustment for float level. Test float needle to check it is shutting off by holding the float up against the needle.

[Banditbandit]

1" 276 std is the correct carb - not 376 Monobloc. Jetting for that is 150 main, 3.5 cutaway slide and a .107 needle jet.

If a 376 monobloc has been fitted, it'd take a 150 main, same 3.5 cutaway,.106 needle jet and a 30 pilot jet.

i'd start with a new needle jet - and check that when the float chamber end cover is fitted, the float will still have endfloat on the pivot pin. Not unknown for everything to clamp up solid when the cover goes on....The idle jet not screwed firmly home can give a too rich mixture also.

Nominally, there's no adjustment for float level. Test float needle to check it is shutting off by holding the float up against the needle.

Yeah - all of that ...

Apart from the bigger carb, checking that the float needle is sealing is a good idea - it may be the needle seat, which can pit and wear .. it may be the needle.

Check that the float is also sealed - in the past I have had a leaky float, which meant the needle was not hard up against the seat .. shake the float and see if it has liquid in it. It can be hard to find the leak if it has one, but it is relatively easy to solder the float once you've found the hole - just make sure it is dry and give it time for the fuel inside to drain and dry - the last thing you want is for the float to burst into flames as you try to solder it ..

[Paul in NZ]

Here we go....

First off - NICE BIKE mate and very very special - I'm horribly jealous...

This might help....

"AMAL" was formed from the 'amal'gamation of three companies in the years immediately following the First World War in order to manufacture and market carburettors and associated products. (Binks, Brown & Barlow + Amac). I think that it’s important to put this into historical perspective. Prior to the First World War motor vehicles could be rather, um, experimental devices and advances made during the war years would be better exploited by larger organisations providing better technologies.

At the close of the Second World War the AMAL dominated the domestic market and the type 76 & 276 Series ‘pre monoblock’ types were fitted to most road machines and the TT / GP series was standard fare on the racing / high performance models. Triumph did briefly fit SU carbs to Thunderbirds in the early / mid 50’s but these were undoubtedly more expensive than an AMAL and didn’t stay around long despite arguably better performance.

1954 was a pivotal year in Triumph specification with the appearance of coil ignition and the new AMAL Monoblock. This new unit with an integral floatbowl was made in types 363, 374, 375, 376 and 389. The intention was to lower production cost and complexity thus reducing places to leak and correcting fuel surge that could occur with the higher powered bikes coming onto the market.

On our TR6C we run a single concentric - different carb - different engine but similar problems once the switch to unleaded happened.

On the open road - no worries, ran like a top.

Around town it clagged up and sooted up the plugs pretty quick. After a new set of plugs it ran great but gradually sooted up.

Every adjustment point on an AMAL affects a portion of the carbs function at various throttle openings. Some adjustments such as slide cutaway seem to affect things dramatically - some not so much...

On a concentric (apart from the very early ones) the pilot jet is a fixed bush and the only idle mixture adjustment is the air screw.

What was happening (I think) is the new fuel runs cooler and the plugs are not getting hot enough to self clean at around town speeds due to the bush being too big. The answer is to set the idle mixture as lean as possible using the airscrew (so that the bike still idles) and go up one heat range in plugs AND move to an extended tip plug. This is OK in the unit 650 but I would advise caution in a pre unit 500... Triumph went to and ext tip plug with the later T140E (e for electronic ign)

With a monoblock you can change the pilot jet. The pilot actually affects the mixture more than most guides indicate and its not like a light switch. by that I mean at idle it has a huge impact BUT at 1/4 throttle it has a little impact.

SO - IF the bikes clagging up at town speeds but is OK (ish) on the open road, rather than mess with the plugs at this point OR change the float level I would lean out the pilot mixture on the original pilot jet. If no improvement drop the pilot jet a size or two. If no good go back to the original pilot jet and try dropping the needle (always start with a new needle and needle jet) If no good go back to the original settings and put in a hotter plug.

Eventually you should find a happy place. Be warned - in my experience, changing the slide cutaway affects the mixture a LOT! You may want to fit a new slide of known size anyway as people do cut them to get 1/4 size changes and do all sorts of daft things..

Before you do this though - pull the whole thing down and replace ALL the gaskets and make sure the idle by pass passages are all clean. From memory there is a gasket under the jet block?? If that's had it the carb will do weird things. I do have some munted monoblock munt and jets kicking about - sing out if you get desperate.

[denill]

All good stuff there and thanks for taking the time.

Dismantled the carb and found that sitting around with old fuel had gummed up the carb. Now it doesn't run rich but it's misfiring on the left cylinder and curiously when the ignition is advanced the left cuts out totally.

As both my Triumph vertical twin knowledge of 50 odd years ago and my Imperial tool kit are now rather diminished, are there any recommendations for a Napier/Hastings mechanic/tuner with Triumph pre-unit engine experience? All the settings need to be checked and 'fettled' so that it can be ridden with some confidence. Just a couple of days ago I pushed it exactly 3 miles back home. Yes, 3 bloody miles, not kilometers!

[Voltaire]

Old magnetos are know to play up.
You might want to check out the local VCC motorcycle section or go up to the Classics Club by the prison on a Saturday arvo, whenever I have been there lots of Brit bikes.
Cool Club.

[Banditbandit]

are there any recommendations for a Napier/Hastings mechanic/tuner with Triumph pre-unit engine experience?

Get hold of the local classic club - Gary Baines would be a good person to talk to, but there will be others in the club who will know. The Hawke's Bay Classic Motorcycle Club is pretty good. (Yeah - as Volatire says - they get together at the clubrooms by the prison. )

Timmo's Motorcycles in Onekawa may be your best bet (If he's still around) or maybe try Barry's in Karamu Road, Hastings.

[Motu]

When you unscrew the pilot jet cap, sometimes the jet comes out with it...looks normal if you've never seen one before, but the jet needs to be removed and screwed into the body and seated.

Looks like you have a BTH magneto, much better than the Lucas, but harder to get parts for these days I'd say. Pickups are at the front, pull them out and have a look - sticky brushes, damaged or crumbling body. Put your finger in the hole, needs to be a small finger so a neighbours kid will do - sometimes the bakelite wears away leaving the brass contact sitting proud, this will play hell with the brushes.

[denill]

Thanks all. Will let you know the outcome - as it's all good knowledge if/when someone else has a similar experience.

[denill]

Who are the best guys in NZ for pre-unit Triumph bits?