Amal Concentric Mk2 R2934/3

[lloydy1]

Hi Bob,
I will get the carb stripped down tomorrow and post the full break down of the jets etc.
Cheers, Dave

____ I've now spent some time looking-over & comparing the lists of jetting-sizes I posted and also that of which you've given so-far,
and it seems that your carb shouldn't be jetted too far off, already just as it is.
So I'm wondering if you might've been running your Duke with the carb left in it's starting-mode (with the starter-jet remaining in it's functioning-state) ?

No I can't use the cold start, she will not fire at all, I get that bogged down sound when I kick her over and when she is ticking over and I give her a blip on the throttle I get some black smoke

If you're sure that that's not the case, then at what throttle-settings do you think your carb's jetting is running richest at, (near full-throttle running, or, at lower normal crusing-speed settings) ?

At normal crusing speed as I have not had her on song yet.

____ Also, I've been meaning to ask,, has your cyl.head's intake-port been ported-out at all, (so as to better match the size of your carb's 34mm bore-size) ?

I sent the head to Nigel Lacey for some work new valve etc and it has been ported with a megacycles cam fitted by the previous user. Cheers, Dave.

[DewCatTea-Bob]

" 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 ?


" when she is ticking over and I give her a blip on the throttle I get some black smoke "

____ That indicates jetting that's WAY TOO rich,, and considering the jetting you've mentioned (thus far), I have doubts that your jetting is the actual-cause of such richness.
__ Rather, I'm now suspecting that either your carb's float is not functioning properly (for any of various reasons), or it's needle-valve & seat is leaking,, or-else the float-level is set too high.


" At normal crusing speed as I have not had her on song yet. "

____ Then your main-jet has not gotten a chance to come into play, and thus it's not likely having anything at all to do with your rich-running issue.
So if the level of the fuel in the float-chamber is not the cause (as I suspect), then it must be that your lower-throttle running circuits are TOO rich, and need to have their jetting reduced to (much) smaller sizes, (which I'm now thinking is not going to be a likely requirement).


Hopeful-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.

" when she is ticking over and I give her a blip on the throttle I get some black smoke "

____ That indicates jetting that's WAY TOO rich,, and considering the jetting you've mentioned (thus far), I have doubts that your jetting is the actual-cause of such richness.
__ Rather, I'm now suspecting that either your carb's float is not functioning properly (for any of various reasons), or it's needle-valve & seat is leaking,, or-else the float-level is set too high.


" At normal crusing speed as I have not had her on song yet. "

____ Then your main-jet has not gotten a chance to come into play, and thus it's not likely having anything at all to do with your rich-running issue.
So if the level of the fuel in the float-chamber is not the cause (as I suspect), then it must be that your lower-throttle running circuits are TOO rich, and need to have their jetting reduced to (much) smaller sizes, (which I'm now thinking is not going to be a likely requirement).

I have just come back from a quick spin and the report is; She would not pick up clean juddering on acceleration. The full break down of the carb is; Needle jet 106, main jet 260, needle 2A1and throttle cutaway 3.5. plug black and wet. I will check the float level now. Cheers, Dave.

[lloydy1]

Just checking the float hight and the float is dead level with the float bowel. Reading Bushman's carb tuning secrets it tells you the the float should be 2mm below edge of float bowel, so I suspect you are right Bob the carb is possible flooding. I will tap the brass bush out the 2mm and see how she runs.

Cheers, Dave.

[DewCatTea-Bob]

" 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.


Hopeful-Cheers,
-Bob

[lloydy1]

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) !


" 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),

Do you think I should look at making or try to get hold of a straighter manifold to square the carb up. I have set the float up at the correct level now and I reset the needle back to the centre grove as I did have it on the top grove, I went out on another test ride and she is still juddering at half throttle not clean at all.

then not only is it possible that your set fuel-level is actually higher than the bottom of the venturi-port, (thus allowing fuel to freely flow without flowing-air),, but there's then a probable chance that (whenever the petcocks are opened), fuel is 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 into the bowl & into the venturi-port, there's 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 it & refresh the sump-oil.

Hi Bob, I will check the oil tomorrow.

Cheers,Dave

[DewCatTea-Bob]

" Do you think I should look at making or try to get hold of a straighter manifold to square the carb up. "

____ Not really but, it wouldn't hurt to,, cuz then you'd possibly have a chance to see whenever fuel is leaking past & out, (cuz if it's port-tract is leveled, then leaking-fuel would flow-out from BOTH of it's port-opening/ends).


" I have set the float up at the correct level now and I reset the needle back to the centre grove as I did have it on the top grove, I went out on another test ride and she is still juddering at half throttle not clean at all. "

____ But there was some improvement (since lowering the float-level), right ?
__ Note that the listing of the "racing" 350-Sprint with 34mm-Amal, indicates that with a '2A1' needle-valve, it should be set at the top (leanest) notch, (thus lowering-down the needle further into the needle-jet).
So it seems you should've left your needle-valve set where you had set it to.
__ Also, it could be that you have yet to adjust the pilot-jet's circuit, as it can affect rich-running up-to near 1/2-throttle.
(Although your 3.5 throttle-slide ought to be keeping you lean enough around there.)
If these two adjustments don't clear-out the rich-running well enough, then I suggest rechecking that you indeed have the float-level set as you had intended,, and if it's still right-on, then try lowering it another .5 to 1mm lower-yet.


" I will check the oil tomorrow. "

____ Be sure to report-back about that first, if you intend to replace the oil.


Hopeful-Cheers,
-Bob

[graeme]

The Commando fellows talk about "stay up" floats and different needle and seats to stop flooding.
Perhaps there is something there worth investigating?

[DewCatTea-Bob]

The Commando fellows talk about "stay up" floats and different needle and seats to stop flooding.
Perhaps there is something there worth investigating?

____ If they're in reference to the Amal Mark-II carb.model, then that's potentially pretty-important & very-useful information in this case ! _ As then it's fairly probable that Dave has been dealing with such common-troubles.
__ In any case, it's quite-good to have such member-contributions added to this w.site-forum, and helps much to make this w.site more useful to all of us !
So thanks-much for caring to bother with trying to help-out (even if the offered-info turns-out to not be directly helpful) !


Duker-Cheers,
-Bob

[graeme]

Extract from Norton site re Mk2 concentrics,,,

I've spent a lot of time playing with MK2's and am just about sorted with them after a very long time.

A couple of pearls of wisdom-

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. Answer is to fit the larger floats 622/196.

The next one is slides. There are 3 types - plain aluminium, ptfe/anodised aluminium and chrome plated brass. Both aluminium types are no good in my experience. The fit of them is poor and doesn't give an adequate shut off of the air path in the fully closed position which means the pilot jet doesn't control well as its swamped by the influence of the slide.
Fit the chrome brass type 2928/170.

I know from personal experience that without both the above you can spend a lot of fruitless hours trying to dial in Mk2's

I don't know if you can search the site without being a member so here is link to just 1 discussion re the Mk2 concentrics.
Maybe it can be of assistance?????

http://www.accessnorton.com/post69446.html?hilit=Amal Mk2 concentric#p69446

I'm a member (as I own a Commando) but I didn't muck around with Amals, just fitted a new Mikuni as it's a touring bike not a sport bike.

Dave your bike looks excellent and should go as good as it looks.

graeme