Triumphrat

RICHO

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

Old Cafe Racer

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-re...ml#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.

Triton Thrasher

Drop the needle and try that for your midrange response, then try a smaller main jet. If that helps full throttle, go down one size at a time until no further improvement.

Caulky

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?

mach1970

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

Caulky

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.

jwitt

Are the chokes all the way up?

Old Cafe Racer

I do feel the OP's dilemma, after a top end rebuild a WOT plug chop isn't really an option till things loosen up a bit so where to start?
(just been through that scenario myself)
.

Mr.Pete

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.

RICHO

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.