brand new AMAL 376

[berger]

advice please before it gets the hammer---- eh big jim I have just fitted the brand new amal and she is choking up with the air screw nearly dropping out. this carb has all the proper shooting star spec jets and was sold stating it was for a shooter. it is a 376/1inch with jets 270 main  106 needle- needle position 3   slide 3/1/2 and pilot jet 30 which is correct according to the bible, my experience has always been air screw about 1/1/2 to 3 turns out. now the question is do I drop the pilot jet to a 25 or 20  or is there also some hidden magic that the main jet also effects the pilot and tick over? apart from this super sooty rich tick over she picks up ok on the throttle

[BigJim]

Keep the hammer to hand Berger it's the ultimate cure! Mine runs rich at idle after a bit of novice tuning, I went for the concentric option so my pilot size is not negotiable. I must admit i prefer rich to lean and i still getting over 50 to the gallon so it unlikely to be washing out the bores. If the thing starts and runs well enough, doesn't soot up too much to restart then i'd call that a goer. Mind, i am a bad person, with so many other things to worry about. So no help from me, only support that you can sort it, and hope that the teeth/gums are on the mend.
 

[Black Sheep]

Back to basic tuning. Book specs are these days only a guide. Drop the pilot jet down a size and try again.

[RDfella]

Unlike other carbs that drive us both insane, the Amal does at least operate normally – ie tickover is the domain of the pilot jet and screw. Sounds like you need a smaller pilot jet. And whilst you’re at it, is 106 standard for your motor? I know some bikes use that size, but thought the standard was 105 - but I could be wrong. At least Amals are straightforward to tune!

[berger]

RD fella 106 needle is correct, and all other jets are by 3 different authors and parts books, I will try my 20 pilot jet but just can't get my head round why it is so choked up with the 30 that this bike should have in the carb so tomorrow it is having the 20 , time will tell.

[Swarfcut]

Bergs. They used to say the final quality check was the Customer. Maybe just quick check that there are no extras included...... the odd moulding flash, the odd missing spacers/ gaskets etc. For the money you expect it to at least run without being on the extreme edge of sanity.

 Swarfy.

[RDfella]

Just another thought - a carb may be assembled with the correct jets, but are they right for today's fuel? And secondly, is the fuel height correct, or did the assembler presume it would be?

[berger]

one thing I haven't taken into account but just remembered. I opened up the inlet tracks on this head 40 years ago. would the bigger tunnels be sucking more petrol from the carb , or am I talking s**t again?

[ellis]

More poo berger 

ELLIS

[Swarfcut]

Bergs. Even the most basic  carb is designed to provide a consistent mixture strength (stochiometric ratio) over all throttle settings. They all do this with varying degrees of success, now outperformed in these environmentally and strange times by modern fuel injection precise metering systems. Fixed jet carbs do it some of the time, constant vacuum do it most of the time.  AMALs are a variation of the constant vacuum type, being a manually controlled throttle (rather than a vacuum controlled)  valve linked directly to a tapered needle/needle jet metering system.

 Size of the inlet tract should have no effect on the mixture, but the resultant higher speed of gas flow and consequent mixture volume down the hole  enables a higher rate of  combustion and more points on your licence.

 Signing in to the Forum today involved an agreement that all advice offered is done so with the best intent, and that no liability is accepted or expressed as to the suitability of the advice in the event that something bad happens as a result.

 So, to recap, in my opinion you can rest easy, the problem is the carb.

 Swarfy.

[berger]

cheers Ellis, I had an inkling on it. now confirmed swarfy thanks for that, so tomorrow when I fit the 20 pilot jet I hope to get a result of some sort. I just don't understand why it is way to rich when set up to the book. anyone else had a shooter that has run super rich with the 30 pilot jet?  RD fella just read your bit, I will check fuel height when changing the jet cheers.

[chaterlea25]

Hi Berger,

Float height is the first thing to check even on a new carb !!!!
A piece of suitable plastic tube shoved onto the pilot jet of a mono and line up with the pip on the chamber cover
make sure there are no metal particles inside the carb passages that might stop the pilot jet seating ???

I have to disagree with Swarfie about the pilot system statement, My 2 cents worth is that the pilot system continues to contribute to the mixture at more open throttle positions on Amals and other motorcycle carbs

John

[Swarfcut]

CJ    No conflict here, your assertion is correct. I never mentioned the pilot circuit, and my post was a brief overview of the basic workings and differences of two approaches to maintaining a workable mixture strength. Both methods (fixed and variable jet ) have their place in automotive history, being a basic trade off between performance and economy.

 Although the instrument is brand new, as you rightly note a basic check of what is inside and correct assembly looks a first step.

 Fingers crossed for good news tomorrow. Simple float height adjustment maybe?

 Swarfy.

 

[berger]

ooohh baby chips& gravy , checked float height and it was about 2mm below pip. put 20 pilot jet in gave her tickle fired up first kick. got her warm and set up air screw for a nice tick over and she responded to the first bit of throttle without 8 stroking. air screw is turned out more than normal, I stopped her and she fired up perfectly so while I am excited we are going for a run with 4 more spark plugs and screwdriver to see what happens. 

[mikeb]

late to the party here bergs, but to note on my super rocket the new 389 from burlen was super rich at idle and lean at the top.
i've ended up with a 20 pilot (was 25) and a 440 main WITH a filter (spec is 420 with no filter).
maybe they are drilling the holes with metric drills these days???