Amal Concentric Mk2 R2934/3

[DewCatTea-Bob]

" not a vast improvment no. "

____ Then lowering the float-level even lower may make no further/worthwhile improvement either.
__ But have you gotten your idle/pilot-circuit properly adjusted yet ? _ As it too could be adding to your overall rich-running (if not properly adjusted).


" I have order a 105 needle jet and varing main jets from Amal 220,230 and a 240. I have spoken to Nigel (Lacey Ducati) and folowing the conversation we had it would seem that these two jets are likely to be my offending parts. "

____ I have no doubt that Nigel has superior knowledge on your carb but, I'm fairly surprised that (at this point) your main-jet's particular size is at all considered to be in any contention concerning your stated/particular richness-issue, since you had indicated that you haven't yet been able to run up-near full-throttle (which is the main-jet's domain),, and besides that, even a #360 main-jet would not be able to cause any interference-effect with the normal-operation of the starter-jet circuit, (as those two separate fuel-circuits can't possibly combine-together during starting-throttle),, and-also, I believe your #260 main-jet certainly is-not out-of-the-ballpark -(as would have to be the case in order to cause EXCESSIVE over-richness [or excessive-leanness] ), and really may-not be too rich considering the fairly-large size of your 34mm-carb.
I will however (more easily) accept that your 106 needle-jet may be overly rich.
__ I'm still much suspecting that your Mk2-carb may be suffering from the (so claimed) common-problems concerning fuel-flooding due to the (smaller-sized) float's inability to easily keep the fuel-chamber's (enlarged) inlet-valve fully under control. _ And-so you may yet end-up also ordering the updated/larger-float as well as an updated/superior-replacement float-valve needle-peg, (as has been claimed to now exist for solving the overflowing float-level issue [that's said to exist] ).


" I hope to get the jets in a day or two, so fingers crossed I will be reporting positive news. "

____ Well don't make too many changes all at once (between test-trials), or then we won't clearly learn what the main-cause of your rich-running may have actually been due to.
__ Even though I still trust whatever Nigel claims, I have fair doubts that changing your jets (to those you've ordered) will make any night-vs-day difference concerning your (out of the ball-park)- excessively-rich running-issue. _ So I wouldn't expect such a small-incremental jetting-change to accomplish much more than merely-just help diminish the effect of whatever's the actual cause of your main-issue.
However if your (previously-intended)- next test-run indicates that a quite notable improvement resulted from you having lowered your needle-valve back-down all the way, THEN I'd expect that the #105 needle-jet will next-then solve any remaining richness (within your 1/2-throttle range).
But if not, then you'll next have to fully investigate the flooding-issue that's said to be a common-issue with the Amal-Mk2 carb-model, (as I much more suspect [rather than jetting], in this particular case of yours).
__ In any case, be sure to continue including your (previously established) test of blipping-open the throttle, to see if that puffed-cloud of black-smoke you've been getting, continues-on being expelled-out (from the exhaust) or not,, as I still more suspect excessive fuel-supply (over any small jetting differences), as the main-cause of your overly-rich carb.issue.


Hopeful-Cheers,
DCT-Bob

[lloydy1]

Hi, Update on the Amal Carb.

I have installed the 105 needle jet and I left the needle on the top groove, I also left the 260 main jet in place at this time to see how she ran, wasn't picking up very well, so back to the garage remove carb and lifted the needle two notches. She started a lot better, so helmet on and off again for a spin . picked up lovely, got to some open road to see how she would run in top. started to 8 stroke at about 3/4 throttle, although a lot better than before! get home still have a sooty plug so I have swapped the main jet for a 240. started lovely, although I wont know if the 240 main jet will perform at this point, so I will have to continue with how she runs on the open road tomorrow as I am running her with out lights and it was a bit late to have a further run. brake down on the make up so far;
105 needle jet
needle 2A1 on middle notch
240 main jet
pilot 25
slide 3.5
And hair lose through some frustration! To be continued. Cheers, Dave

[themoudie]

Any further updates to this thread on Amal MKII Concentric settings?

Thank you, Bill

[Jacks the Lad]

I have been following this thread with some interest as my recently acquired scrambler is running a little on the "rich" side, the plug is coming out quite black.However mine is fitted with am Amal MkI, not a carburetor I am a fan of. As it is main jet 220, cutaway 3, needle jet 106, pilot who knows, the MkI just has a hole drilled in the casting. I am tempted to just side-step the whole thing and fit a JRC carburetor instead.

[Jordan]

How old is your Amal Concentric MkI ? They really were made to wear out pretty quickly. I'm told you can get chrome plated slides now.
I had a 1969 250 Mark3 non-desmo that I tried different carburettors on. The MkI 30mm gave the best running - "perfect".
A Dell'Orto VHB29 was also good.

The Concentric's settings were:
Model R930/300, no air filter, short horn instead.
Main jet: 250
Neelde jet: 106
Pilot jet: 40
Slide cutaway: 3
Jet needle: 2 ring
JN clip position: centre

The pilot jet (this carb had one screwed in place) seems a large number. It was what was in it, and as it performed well I left it.

[blethermaskite]

Same as Jordan, I am more than happy with mk1 Amal concentric, I have been running my 74 350 mk3 on a 32mm mk1 for over 40 years and it runs perfectly on it, however as mentioned they do wear out quite quickly, I seem to have solved the problem by using the now available hard anodised alloy replacement slide in a new std mk1 body. I am running the same set up (30mm) on my 250 desmo and again getting perfect running,the only point I would make is you really need to fit a proper Amal velocity stack air trumpet to get the best possible performance on these carbs.
Over the years I have tried nearly every carb on the market on Ducati singles .........top two?......best best... Gardner flat slide racing carb on a 250 desmo, bike went like stink on it but it was far too much trouble a road bike, 2nd best... SSi Delorto on a 350 widecase, bike went beautifully on it but it cost me a fortune to buy and another small fortune for all the bits to get it tuned correctly.
So now I just stick with the good old mk1 Amal.....cheap to buy, cheap spares, and easy to tune,
Cheers,
George

[Jacks the Lad]

Jordan, The carburetor was fitted new around 400 miles ago by the previous owner who just fitted it as it was. The pilot jet is just a hole drilled in the casting which means it can't be changed or even cleaned properly. It was originally fitted with a Spanish Amal which was by all accounts totally worn out.

[themoudie]

Aye John,

Amal MKI carbs do wear, but I have found that the chromed brass slide replacement is a very good move, along with the ethanol kit and a 'Stay-up' float kit. All direct from Amal and their catalogue is a must.

Amal link: Amal_carb_site

Running a MKI Amal 32mm, 3.5 cutaway on the slide, 220 main jet, 106 needle jet and the needle 2A1, on the middle slot of the 5 slots, with a short bell mouth. All this fitted onto a two part alloy inlet extension with a MKII rubber inlet to join the two alloy flanges. The unadjustable pilot jet drilling in the MKI has a flow rate of 20cc per min and a pilot jet of 25 is advised for my 450, but I have had no troubles with the 20 drilling until I increased the slide cutaway size. The MKI 2-stroke carbs are fitted with the replaceable pilot jet, whereas the MKI 4-stroke carbs only use a single drilling.

Rebuilt my MKI this time with a 4.0 cutaway in the slide and this has proved incorrect. Minimal revs are now 1,500rpm , with the pilot screw only 0.5 of a turn out from seated and this is due to the increase in size of the cutaway increasing the airflow over the zero to quarter throttle drillings in front of the slide.

I have since spoken with an experienced Ducati single race machine builder and he has advised that the MKII is a better carburettor than the MKI. I have a spare one in stock and to use the same size settings as in my original MKI in it as the starting point; but, with a 3.5 cutaway slide. So, after cleaning; a 220 main jet, 106 needle jet, standard needle on the middle notch, 25 pilot jet and a 3.5 cutaway slide have been fitted into the MKII body. I have yet to fit the MKII to the 450 and will post an update ASAP.

Regards, Bill

[Jacks the Lad]

Thanks for all the advice, always useful. Decided to give the JRC carburetor a try, the UK importer is a member of my local M/C and he has let me have one to see how I get on.

The thing about JRC carbs. is that they are designed to run on modern fuel as it is now, and not as was 40+ years ago.
Will report back as to how I get on.

[themoudie]

Aye John, look forward to an update. Thank you.

My regards, Bill