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New AMAL setup question

7K views 18 replies 8 participants last post by  Old Cafe Racer 
#1 ·
Hello folks,

I have fitted my new AMAL 930's to my t140v 1977 after a top end rebuild, so still running in.

Timing is fixed (thanks to all for the help).

So, back to the Amals. They are brand new, with a main jet 200, needle 106 on the middle clip and pilot bush valve 3. According to the manual, the standard main jet should be smaller at 190.

Here's how she runs.

Start and idle - fine.
1/8 speed, slowtake off - fine
18 - 1/4 speed, hesitate, then slow acceleration
1/4 - 1/2, lumpy and horrible - like its on running on one cylinder
1/2 to full, will not rev to full, lumpy and horrible - like its on running on one cylinder.

Everything gets worse as she warms up/gets hot.

Plugs are sooty.

Will dropping the size of the main jet to 190 or 180 make that much of a difference?

Any other things I should try?

Cheers,

Richo:confused:
 
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#2 ·
Oz ulp makes them run rich, I went down a jet size on my needle jets to 105's on the Daytona to get things crisp

This from my recent build thread:http://www.triumphrat.net/members-r...d-cafe-racers-new-cafe-racer.html#post2170145

Getting the jetting right with ulp... who else has had the privilege of setting up a pair of non standard carbies with the bloody stuff ?

After the second build I removed the 626 Amals (a mismatched pair) and fitted a brand new set of 900 series 28mm Wassels.
These came setup std with 180 mains, 3 slides, 106 needle jets and needles in the top groove., ran like crap, made black porridge on the piston tops and felt like the cylinders were full of slow burning wool.
I tried different main jets and every needle clip combination to no avail.
2 weeks later and I'm now finally cooking hard brown/grey/black carbon on the piston crowns and can run flat out for an hour in 100 degree temperatures with no issues on BP Ultimate 98 ron unleaded.
I gave up trying to get intelligent plug reads with ulp and started reading direct from the piston crowns with a cheap usb plug in boroscope.
What did I end up with?
Well a phone call to Preston at British Bike Spares in Brisbane to ask did they in fact stock 105 needle jets revealed a well known Norton Commando tuner in Cairns now routinely fits 105 needle jets to all the bikes that came with 106's so he had a good supply of them in stock so that was my first clue.

Further digging told me that BP Ultimate and Shell Vortex, the locally available high octane (98 ron) fuels here will both cause rich running right through the range on carburetter engines due their increased density over the old leaded and lead replacement fuels. (I found details of that on the BP and Shell websites)

Enlarged hi-res photos of the spark plugs also showed slight traces of alloy balls on the insulators caused by detonation, so I knocked the timing back to 37 degrees which completely cured that one.

I ended up with #3 slides, 105 needle jets, needles in the middle position, a 170 jet main on the right cylinder and a 160 main jet on the left cylinder.
Don't ask me why it needs different main jet sizes... I don't know.
Since the initial startup this has been the case with this engine, the valves all seal perfectly, the compressions are dead even, the tappets are set identical the timing is the same on both cylinders with the TriSpark ignition.. So, it is what it is although a half jet size smaller on the right cylinder would make it almost perfect.

Your definitely running rich, but do double check the float levels before making any adjustments or other changes.
 
#4 ·
You need to lean out the mixture.
As the plugs get sooted-up it will run crap.
If its very rich at tick-over, its already too late.
Clean the plugs.
Do one thing at a time.
Clear the piot jets, 0.016" guitar string. (file the end to remove burrs)
Set the mixture screws to 1 1/2 turns out to start with.
Check the float levels .080" below the cusp, by pressing on the tang lightly].
MY spares book calls for mainjet 210 for T140V
Does it smoke?
Try a higher octane fuel.
How`s your battery voltage?
Have you strobed the timing?

 
#5 ·
First off, assuming everything else is correct (valve lash, timing, compression, etc...) you can only tune carbs one way. You must start with the main jet. When you get that right you move to the needle, and then finally to the pilot. If you try to do them out of order or more than one change at a time, you will chase your tail forever. Definitely sounds like the main is to big, but you have to do a plug chop at WOT to find out for sure with fresh plugs. Dial in the main jet and then move on the next jet.

Rob
 
#6 ·
Sorry Rob, not according to Amal. (and my experiences).
It`s possible that the main jet is too small.
By the time the engine is warm enough to do a plug chop,
if the low-rev (starting) circuit is very rich,
the plugs will already be fouled with soot, AND the motor will be electrically misfunctioning.
But, given the state of modern fuel, do take note of what Old Cafe Racer says below.

 
#9 ·
The main jet size won't have any effect below 3/4 throttle.
Make sure the choke slides are pulled fully up by the choke cable,or just remove the choke slides and plug the hole in the carb top.If you plug the hole,make sure whatever you plug it with can't come loose and damage the engine.

If it 8-strokes at full throttle with 200 mains,try 180.2 sizes less than the smallest jet that causes 8-stroking is usually about right;it's a lot easier and quicker than trying to read plugs.
 
#10 ·
Ok lads, progress so far. Totally disassembled my carbs, checked the main jet was cleared, removed the chokes and choke cables (do we really need a choke in Australia's climate?) checked the float levels, reassembled the carbs with the clip at the top ring and needles dropped as low as possible.

Checked and reset valve clearance front and back - inlet was tight, possibly incorrectly set by me to the ex setting?

Changed the fuel to BP 98 (had Shell 98 - now a no-no, apparently).

Tuned the carbs for tick over and 1/8th throttle - is now approx 2 and 1/4 turns - not as rich as it was. Seems to idle quite happily now.

Inserted new, hotter plugs NKG B6ES - went for a short run and she revved and pulled as hard as I was prepared to go considering I'm running her in.

Running rich appears to be my perpetual issue, so if this hasn't worked, it's the 180 mains and back to a middle clip on the needle?

I don't want to introduce too many variables into the equation or I'll get lost chasing my tail.

Overall, feeling less frustrated.
 
#11 ·
It's probably still too rich on the needle.Needle clip position has an effect from about 3/8 throttle to 3/4 throttle.
It might pay to check the size of the needle jets to make sure they are actually 0.106",regardless of what's stamped on them.A number 36 drill measures 0.1065" at the flutes and a little under 0.106" at the shank.Measure the #36 drill and see if it fits in the jet.The flutes should not pass through the jet.

If they are truly 0.106",then try 105 needle jets.Needle jet size has a big effect below 3/8 throttle.
 
#12 · (Edited)
Whoops...

Hi Mr Pete, I forgot probably the most important point!

I'm running straight pipes with a small internal baffle - see drag pipes in link to photo.

If I read Caulky's post with the paper, it suggests I should fit a leaner cutaway slide - a 4?

What do you think?

Richo

 
#13 ·
Didn`t realise your bike is non-standard.
Velocity stacks make the whole fuel system leaner.
Main jets need to be larger.
I`d suggest that the poor running in your first post is due to lack of fuel. [as the throttle is opened].
If you can get the slow-running correct, then you can play wth the other jettings.
Do a plug chop soon.
There is a risk of holed pistons.
Then if its running reasonably, run it in.
Then re-tune.
I was going to ask if your pipes are blue :rolleyes:
Strobe the timing, may need retarding a bit.
 
#14 ·
Sorry, have changed stacks for pancakes while getting through this. The stacks in the picture have custom foam and alloy filters inserted, so not true velocity stacks.

It did feel in the beginning like it was fuel deprived, but the change in filters and needle drop seems to have improved. I'll do a plug chop next week weather permitting. The timing is a degree or two retarded. Under the wrapping, my pipes are indeed blueish. What are you looking for in my blue pipes? : eyes rolled:
 
#15 · (Edited)
Everything changes with a restrictive exhaust system.A muffler that doesn't have much volume is either too restrictive or excessively loud.I prefer my mufflers to have about 2 litres volume or more.

I think you should go over to "britbike.com",and look in "British motorcycles in General".You will find "Tuning your AMAL".

Generally it goes like this:
*An open pipe (no muffler) will require a smaller main jet (one size),and a bigger slide cutaway.That's compared to you normal factory-fitted muffler and standard jetting.

*I've found that a very restrictive muffler can require a smaller main jet.


You need to play this by ear.It only takes a few seconds at full throttle to know if a main jet is too big.You can do that even on a newly re-built engine.If it 8-strokes,the jet is too big and you should go down 2 sizes and try again.When the engine is more run-in,at least 50 or 100 miles to seat the rings,try it at 5500+ rpm.8-stroking will be more noticable at higher rpm.
Reading plugs is mostly BS,although a handful of people on this earth can do it.I don't count myself as one of those people,but I still get good results.If you want to know more,Google-search "Gordon Jennings spark plug".Most people can tell if a plug shows rich running,at the throttle opening they mostly use (usually about 1/4 throttle).

Leave the ignition timing as it is,for now.I'm usually happy with about 35 degrees.Your pipes will run a little hotter (they look good blue),but chances are you'll make more power at full throttle.

It looks like you will need smaller needle-jets (105).I know AMAL say to check the main jet size first,but there is a test you can do before that:
*Leave the main jets out,completely remove them.
*Set the needle to its leanest position.
*The engine should at least run to 1/2 throttle without 8-stroking,if the needle jet is not too big.If it doesn't 8-stroke before 3/4 throtle,the needle-jet is too small.
 
#18 ·
Thanks Mr. Pete!

So, I fitted 105 needle jets and 3.5 slides and retuned idle by setting the revs at around 1500rpm and adjusting the air screws in turn from almost stalling to lumpy and going half way in-between. As it turns out, it ended up being exactly 1.5 turns out plus one poofteenth.

I then readjusted revs to idle at 800 rpm, cleaned the soot off the relatively new plugs, and went for a quick ride around the river in Hawthorn/Richmond.

Bugger me if it didn't pull sensationally throughout the whole rev range - no popping, no hesitation, no flat spots, no eight-stroking - nothing but unending pulling power! (as much as I dare, considering I'm on hour two after a full rebuild!)

Got back home after 6 or 7 kms, pulled the plugs and they were a healthy looking poop-brown.

I am now an advocate for persisting in getting the tuning right, but credit this forum and people like you with your knowledge and preparation to share it.

Many thanks,

Richo

:D
 
#16 ·
I know if doesnt really fit your bike but mine really never ran great until I put some decent mufflers on it. I had a pancake filter and shorty pipes at first. Im sure you can tune it since many people run your setup.

Also, if your valve settings tightened up you may want to retorque your head and then reset your valves. My head torque and valve settings took 3 iterations for them to settle in and stay put.
 
#19 ·
So to go back to the first answer to you post, it looks like my take on the 105 needle jets is spot on.
Oz ulp makes old carby engines run rich all through the range and a smaller needle jet is the go.
I just went through this whole exercise myself so it all sounded very familiar.

.
 
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