Amal Concentric Mk2 R2934/3

[DewCatTea-Bob]

" Extract from Norton site re Mk2 concentrics,,, "

____ Thanks further-much for the follow-up info on the Mk2-carb's common flooding-issue, as I believe that's more likely what Dave probably has to deal with.
However before Dave jumps-forward with THAT probable-possibility, I hope he will first try lowering his throttle needle-valve back-down all the way, and lean-out his low-speed idle/pilot-jet circuit, (to find-out if doing that may then make his Duke run well enough).
Also, I've now seen that lower float-settings (than just "2mm") can be achieved, so if the two adjustments I've suggested don't achieve the desired leaned-out results, then next Dave should try lowering the float-level down to as much as about 6mm.
__ And then if Dave STILL has rich-running issues, he can THEN expect that HIS-own Mk2-carb is also suffering from the common flooding-issue that others have been dealing with.

Take a look at the float valve seat and compare it to a MK1. What you'll see is that the the MK2 has a bigger valve area than the Mk1. The problem is that as standard they use the same float. The result is that when you bounce the Mk2 around, and Commando's do a lot more shaking than most bikes, there's a much greater tendency for the Mk2 float valve to unseat and flood the carb.

____ Okay, what seems to be claimed here is that the (original/small-sized) float doesn't have enough lifting-pressure to keep the flow-valve's needle-tip properly seated against the Amal-Mk2's larger surface-area/opening in it's valve-seat, (which is supposed to control fuel-flow into the float-bowl/fuel-chamber, despite the increased pressure exerted by the fuel [due to the larger valve-seat area] ), WHENever the engine shakes the carb.
__ So if indeed that's the actual case, then (besides the suggested updated float), clamping-down the inlet-end of the carb.body should cut-down on it's being shook (to a lesser degree, at least) by engine-vibration, and thus-then help alleviate the flooding-issue.


Enlightened-Cheers,
-Bob

[lloydy1]

" No I can't use the cold start, she will not fire at all, "

____ So I gather that that means that even when the engine is stone-cold, activation of the starter-circuit then enriches the mixture to such a great degree that the engine won't even report-back with any clue at all that it may fire-up ?

Hi Bob, that's correct.

____ Wow! _ Then there's certainly something wrong that's causing there to be way too much fuel available (even with the starter-circuit kept shut-off) !


" The full break down of the carb is; Needle jet 106, main jet 260, needle 2A1and throttle cutaway 3.5. plug black and wet. "

____ Okay, you've checked-out (most of) the installed jetting and found:
main jet 260;
Needle jet 106;
needle 2A1;
throttle cutaway 3.5
all of which should have your carb's jetting in the ball-park (of that which would be optimum for your 350), and likely not too overly rich (for the metering-circuits which those particular carb-parts are expected to control).
__ However, you haven't included the jetting-sizes of the lowest-throttle metering-circuits, (which can also have an effect on rich running below half-throttle),, but chances are that they have also been set within a similar standard-range, and-so may not be the cause of your rich-running issue either.



" Just checking the float hight and the float is dead level with the float bowel. the carb is possible flooding. "

____ With the fuel-level set so high (and with your carb's intake-tract mounted at the [slightly] steep angle it's at), then not only is it possible that your set fuel-level is possibly actually even higher than the bottom of the venturi-port, (thus allowing fuel to freely flow [without flowing-air to pull it up & out] ),, but there's then a probable chance that (whenever the petcocks are opened) fuel is also constantly flowing down-through the intake-port and not only flooding the cylinder but also flowing-past the piston-rings & into the crankcase.
So since there seems to be a fair chance that your float-level has been previously set so high as to not be able to properly curtail fuel-flow through the bowl & into the venturi-port, there's thus-then good reason to suspect that the oil in the crankcase-sump has become contaminated & diluted with fuel. _ So you should check into that possibility, and if your oil-level is too high & smells of fuel, then you should dump & refresh the sump-oil.
Let us know how that checks-out.

Hi Bob, I dropped the oil today and there is no sign of fuel contamination. I have dropped the needle to the lowest setting, but haven't had chance to test her on the road as yet. I have the in-laws coming for dinner, so will have to report hopefully tomorrow. I was going to order up the same spec jets etc as the aermacchi you posted Bob, what do you think?

[DewCatTea-Bob]

" I dropped the oil today and there is no sign of fuel contamination. "

____ Are you REALLY sure ? _ You could make-sure by dipping a damp towel into it and then see if it easily* lights-off with the flame of a match-head.
(* Cuz if it's JUST motor-oil, it won't quickly catch-flame before the 'match-head' burns-out.)



" I have dropped the needle to the lowest setting, "

____ That should help, but, whenever the throttle needle-valve has to be set at one of it's extreme-positions, that's then a possible indicator that it's mated needle-jet might need to be replaced with the next-size.
__ Don't forget to also lean-out the idle/pilot-jet circuit.
You'll know when you've adjusted it's screw too-far lean-wise, as it will then cause exhaust-popping whenever the throttle is shut-down from higher revs.
So if you note any such popping after leaning-out that low-speed/mix adjustment, then turn the screw back 1/4th-turn (at a time, until the popping stops).


" I was going to order up the same spec jets etc as the aermacchi you posted Bob, what do you think? "

____ Since you already have the #106 needle-jet & #2A1 needle-valve, it sure wouldn't hurt for you to also have on-hand the #105 needle-jet & #2C3 needle-valve, for later possible needs, but, you may as well hold-off ordering until after you learn what other Mk2-parts you may possibly need. ...
__ Have you read-through all the other recent posts (posted here in this thread) since your last/previous-post ?
Cuz it's since been looking more likely that 'jetting' is probably not exactly the main-cause of your rich-running issue.
After you've tried-out your Duke with the needle-valve lowered all the way, (and with the screw-adjustment leaned-out),, then next, try further lowering of your float-level. - (Cuz you may then not have to order any other parts.)


Hopeful-Cheers,
-Bob

[lloydy1]

" I dropped the oil today and there is no sign of fuel contamination. "

____ Are you REALLY sure ? _ You could make-sure by dipping a damp towel into it and then see if it easily* lights-off with the flame of a match-head.

Hi Bob, I have had ago at burning some oil out and it didn't combust that easy, so just to make sure I did the same test on some oil that has not been in the little Duke and I have to say that it burnt the same, so I am fairly sure that I am safe concerning the fuel contamination.

__ Have you read-through all the other recent posts (posted here in this thread) since your last/previous-post ?
Cuz it's since been looking more likely that 'jetting' is probably not exactly the main-cause of your rich-running issue.
After you've tried-out your Duke with the needle-valve lowered all the way, (and with the screw-adjustment leaned-out),, then next, try further lowering of your float-level.

I will give this a go as the next step, but I will do 1mm increments up to the 6mm and see what effect it has if any.

Thanks for all the guidance, I must say thanks to everyone for their contribution on the subject. Cheers, Dave

[LaceyDucati]

Hi Dave,
I have been away this week and just got back and noticed this thread, I have a lot of experience of these carbs and there are a number of reasons why it could be running rich, I am back in the workshop tomorrow, give me a call and I should be able to point you in the right direction. (I did post a long reply here but as usual it probably timed out on me as it disappeared after I pressed submit! grrr.) Best Wishes Nigel

[DewCatTea-Bob]

" (I did post a long reply here but as usual it probably timed out on me as it disappeared after I pressed submit! grrr.) "

____ I used to have much "grrr" also, (due to the 1-hour time-limit*), back before I developed the habit of just posting that which I've typed-down thus-far, well before the limit gets a chance to foul-up my completed-work.
(* Even if ya have logged-in, ya automatically get logged-out if ya don't change/turn any w.site-pages here for over an hour.)
Still however, the hour-limit has many times since gone-by before I realized that an hour had past, and I'm then forced to log-in/sign-in AGAIN,, and it's at THAT point when I've always had to worry that what-all I've thus-far written may have become completely lost, (which many times in the past, had turned-out to indeed be the actual case ! - 'GRRR!'). _ And back-THEN, I recall that either web-browser -(Internet Explorer & Firefox) that I used, could possibly suffer from that inconvenient-process (of having to RE-login) and possible resulting page-loss.
However in more recent times, I've found that in the event of such page-loss, Firefox had become improved to the point that ya could easily find the lost-page (complete with all missing typed-wording), by exploring Firefox's 'History' button (which would drop-down a list of all pages recently viewed, [including the lost-page along-with all typed-wording !] ).
So that CONVENIENT-option can help keep ya sane (and also possibly save your PC from a fast/hard trip to the floor).
__ HOWEVER, those people who are always trying to update software, always seem to go one step backwards whenever they've gone two steps forward, and-so that nice option has come & gone a couple times (depending on update-version), so therefore it may be possible that YOUR loaded version of Firefox may not include that useful (full-blown) option,, however I think that all the most recent updated-versions have kept that convenient option available.
So therefore, if you were (luckily) using Firefox, then there's a good chance that your lost-page of printed/typed-wording could still be recovered fully in-tact, (at least if you haven't yet since shut-down your PC).
__ I hope you can now recover all that which you had written, as it would no-doubt be good-reading !


Wishful-Cheers,
-Bob

[DewCatTea-Bob]

By: lloydy1...
" I have had ago at burning some oil out and it didn't combust that easy, so just to make sure I did the same test on some oil that has not been in the little Duke and I have to say that it burnt the same, so I am fairly sure that I am safe concerning the fuel contamination. "

____ Alright, good then ! _ That then indicates that your float-level really had been set right-at the top-edge of the float-bowl (and not possibly past/above it).

try further lowering of your float-level. -

I will give this a go as the next step, but I will do 1mm increments up to the 6mm and see what effect it has if any.

____ If 'float-level' has indeed been a main-factor contributing to your rich-running issue, than further lowering of the level will have a positive-going effect towards it.
__ You didn't yet confirm whether lowering-down the level "2mm" had then provided any notable positive effect or not... So did it ?


Hopeful-Cheers,
-Bob

[lloydy1]

try further lowering of your float-level.

I will give this a go as the next step, but I will do 1mm increments up to the 6mm and see what effect it has if any.

____ If 'float-level' has indeed been a main-factor contributing to your rich-running issue, than further lowering of the level will have a positive-going effect towards it.
__ You didn't yet confirm whether lowering-down the level "2mm" had then provided any notable positive effect or not... So did it ?

I didn't want to take the chance of running her until I had checked the oil, I have dropped the needle back to the lowest setting, so I will be giving her a run later and report back of any effects. Cheers, Dave

[DewCatTea-Bob]

__ You didn't yet confirm whether lowering-down the level "2mm" had then provided any notable positive effect or not... So did it ?

I didn't want to take the chance of running her until I had checked the oil, I have dropped the needle back to the lowest setting, so I will be giving her a run later and report back of any effects. Cheers, Dave

____ Okay but, you had stated before that you had lowered the float-level "2mm" from the top of the bowl (where the level was first found to be at), and that a test-ride after that change revealed that your Duke STILL ran poorly (as if still too rich), but you have never yet really confirmed whether or not the change resulted with any good/notable improvement.
So, do you think there's been any positive change, (as a result of your having lowered the float-level), or are you not too sure about it ?


Duke-Cheers,
-Bob

[lloydy1]

__ You didn't yet confirm whether lowering-down the level "2mm" had then provided any notable positive effect or not... So did it ?

I didn't want to take the chance of running her until I had checked the oil, I have dropped the needle back to the lowest setting, so I will be giving her a run later and report back of any effects. Cheers, Dave

____ Okay but, you had stated before that you had lowered the float-level "2mm" from the top of the bowl (where the level was first found to be at), and that a test-ride after that change revealed that your Duke STILL ran poorly (as if still too rich), but you have never yet really confirmed whether or not the change resulted with any good/notable improvement.
So, do you think there's been any positive change, (as a result of your having lowered the float-level), or are you not too sure about it ?

Hi Bob, not a vast improvment no. 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 hope to get the jets in a day or two, so fingers crossed I will be reporting positive news.

Cheers, Dave