Sooty plugs, running rich - where do I start?

[CrispinA10]

 *conf*Thought it would be straightforward to sort out the R300 930 concentric on my RGS replica, but despite having read the Amal pdf, the Hitchcocks tuning guide and assorted Britbikes articles, I still don't really know where to begin.
I don't want to start dismantling the carb, which looks new, until I know I need to.
Basically the bike starts beautifully on new plugs, ticks over evenly and runs beautifully. But after about 20 miles on new or cleaned plugs, they gather enough soot to cause a misfire. I never go out without a spare set and a spanner.
Because I'm running in, I never exceed a third throttle - top whack has been 60mph on the flat on fourth, so I am assuming slide cutaway and main jet would have nothing to do with it. Tried lowering the throttle stop screw until engine falters and then screwing in the air jet until it runs better, but the end result so far is sooty plugs after a few miles.
I have tried using a variety of hotter plugs, but they still get sooty.
Is there a method that I've missed in the guides for working out what the problem is? If it was float level, for example, I could be confusing matters by tweaking around with the air screw.
Any suggestions gratefully received.
PS: Not that the plugs are at fault, but I've tried NGK, Bosch, Champion and have just ordered some Denso. I will at least have plenty of spare plugs once I've sorted the carb.

[Triton Thrasher]

If the carbs have done more than a few thousand miles, the needle jets are worn and require to be replaced.

Otherwise, the needles may be in the wrong notch.  The middle notch is correct on most bikes.

[CrispinA10]

Thanks for that. The carb has done less than 500 miles and appears to be new, fitted when previous owner completed rebuild, so I doubt the needle is worn. I will take it off this afternoon to check that it's on the middle notch though. A useful starting point - thanks.

[morris]

If, like yo say, it starts well then the pilot should be ok.
Have you got an air filter on? May be worth a try running without for a while to see if that improves matters.
You could also try an air slide with a bigger cutaway.

[CrispinA10]

No air filter - just a polished stack. The carb was fitted when the previous owner built the bike and I understand that it was supplied correctly set up for a 650 Road Rocket. I suppose it is possible that the slide has too small a cutaway. I have some Amal spare odds and ends because my Enfield GT Continental also runs on an R300 930, however all the slide are identical, ie marked 30. Quite an expensive investment to try a larger one, like 3.5. on the off chance, but I might end up having to do that.
Have to wait a bit now as no more time off work until Friday, when I'll get some daylight and the chance to fiddle and investigate further.
At least my new plugs will have arrived by then, so I can get out for a spin until they too soot up...

[duTch]

 I thought the normal slide is 3-1/2..?

 I had a richness problem initially, and changed to a .105 needle jet and it made a massive difference (also played with differing idle jets but back on 25)

[CrispinA10]

Right. I have some time off on in daylight on Friday, and will be pulling the carb apart and ordering new 3.5 slide (cheaper than I thought) a .105 needle jet and probably an alternative main jet, although I don't think I've run the bike at sufficient throttle for the main jet to come into play yet. Third throttle maximum for running in, I was advised.
Does anyone think it worthwhile trying one of these posho new black floats? No reason to think that float level might be wrong but if I'm starting from scratch and aiming for perfect, or at least non-plug-fouling, carburation then could be worth a pop.
Any other ideas on slide or needle jet size options before I order?
Have just received box of Denson W20ES-U 3051 plugs, but little point in bunging them in before the running rich problem is sorted.

[CrispinA10]

Not getting anywhere fast. Decided to start from scratch and ordered a new Mk 1 Amal from Draganfly, set up for a 650 A10. It finally arrived after four weeks and I was slightly irritated to find it's actually a Wassel copy of an Amal. But I don't want to wander off on that. The quality looks and feels fine. Bunged it on last weekend and fitted yet another set of properly gapped plugs. Ran really roughly, fair bit of smoke (although it hadn't run for five weeks) and the plugs were covered in soot after about two minutes. Had some time off today so raised the needle clip to top (ie lowered the needle) and screwed the air screw in as far as I dared, as suggested in tuning book to tackle rich running. Starts first kick, but still running horribly rich. Plugs sooted within a minute.
How on earth can it run that rich? Could there be another explanation for sooting? There is no air filter, just a bell mouth. Could that make it run rich?
I am running in, so only using slight throttle opening, less than a quarter twist and never over 3,000 rpm, so I don't think main jet would have any effect. I think the slide cutaway is 3.5 but I will check in case Draganfly supplied a 3.
Any ideas much appreciated.

[muskrat]

G'day Crispin.
The pilot screw (air screw) turned in is rich, out is lean. Start at 1,1/2 to 2 turns out from seated. Bell mouths would make her run leaner as well. The float height might be a bit high, fuel height should be 5mm below the bowl/body gasket face below the idle screw. I suggest getting a colour tune and setting the mixture with it.
Then we start looking at "most carb problems are electrical" .
Cheerss

[CrispinA10]

Sorry, that should have said "screw the air screw OUT as far as I dared".
But grimly fascinated and disturbed by suggestion that there might be an electrical cause behind all this. What? Joe Lucas, King of Darkness? Argghh. Is it possible that the Dick Van Dyke levels of soot might not be due to air/fuel ratios but something more sinister?
Not sure how colour tune could help. I don't have any colour, just a really thick layer of soot after a few moments running.

[morris]

Not sure how colour tune could help. I don't have any colour, just a really thick layer of soot after a few moments running.

A colortune is a glass spark plug that shows what's happening in the combustion chamber;
https://www.youtube.com/watch?v=ve_7Qby7f-E
Useful tool to tune a carb.

[chaterlea25]

Hi Crispin,
Dont believe the "W" jet size markings
There are lots of spurious jets on the market !!! the proper Amals have a partial groove machined  on the hex
Which ever carb you work with the first check is the fuel height
As the alloy head BSA has a downdraught angle this can lead to too high a fuel level at the pilot jet
If you have a spare no3 slide you can experiment by filing the intake side a little more to equal a 3.5
The "3" is the number of 1/16ths of an inch that tha slide is cut away

Johns 2 cents worth 

[metalflake11]

Not getting anywhere fast. Decided to start from scratch and ordered a new Mk 1 Amal from Draganfly, set up for a 650 A10. It finally arrived after four weeks and I was slightly irritated to find it's actually a Wassel copy of an Amal. But I don't want to wander off on that. The quality looks and feels fine. Bunged it on last weekend and fitted yet another set of properly gapped plugs. Ran really roughly, fair bit of smoke (although it hadn't run for five weeks) and the plugs were covered in soot after about two minutes. Had some time off today so raised the needle clip to top (ie lowered the needle) and screwed the air screw in as far as I dared, as suggested in tuning book to tackle rich running. Starts first kick, but still running horribly rich. Plugs sooted within a minute.
How on earth can it run that rich? Could there be another explanation for sooting? There is no air filter, just a bell mouth. Could that make it run rich

Send it back and order one off Burlem.

930 Concentric. 250 main. 106 needle. No.3 cutaway. That will run fine with a bell mouth.

Denso W20ES-U plugs.

[muskrat]

Ah, John hit the nail on the head. Concentric's are a BUGGA to set up with any sort of downdraft. Even with the adjustable stay up floats. Best I could get was 0.300" which is way below the quoted figure of 0.240".
Made a fitting to fit the drain plug and use clear hose.
Cheers
ps, the pilot screw is mainly for idle and just a tad more but it does affect the whole range, as does float/fuel height.

[metalflake11]

G'day Crispin.
The pilot screw (air screw) turned in is rich, out is lean. Start at 1,1/2 to 2 turns out from seated. Bell mouths would make her run leaner as well. The float height might be a bit high, fuel height should be 5mm below the bowl/body gasket face below the idle screw. I suggest getting a colour tune and setting the mixture with it.
Then we start looking at "most carb problems are electrical" .
Cheerss

True.

My latest carb on the bike is due to a defective H.T. lead, all the symptoms suggested fuel problems, but it wasn't.

Also after running on NGK's for donkeys years (never ran well on Champions) I suffered from 'sooty' plugs. No amount of carb adjustment would fix it, but a set of Denso plugs and the carb put back to its origional settings did!

As for setting concentrics up, the last three I've put on have needed no more than a minor tweak of the air screw to obtain perfect running throughout the range. The last one from Burlem/Amal was what they class as the standard A10 set up (see my earlier post) It started second kick after fitting.