Amal needles and poor running (2014)

At very low throttle openings, there are usually other jets which take over. - The slide cutaway has an effect, and I think you will find the air jet and pilot jet as well. I never bother with any of that because I use methanol and can afford to be fairly crude. I set the idle, then concentrate on the needle and needle jet which are critical, the motor always spins up cleanly however that doesn't mean that it is jetted at the optimum. On a road bike you probably use those very low throttle openings quite a lot in traffic.

OK, I took it out for a run yesterday and got quite confused again. The changes I've made since last time are:

New needles ( 2A1)
new needle jets ( 106)

RH carb has the choke blanked off ( both the choke jet and the air supply to it) to see if it's the choke leaking.

As I pulled out of my drive it was hard tokeep it running, popping and banging, spluttering. Once I got into the traffic it was better but still not great. 30 MPH is a struggle and it seemed to work better with a bit of throttle. We got to the open road and it went better at anything between 1/4 and 1/2 throttle.
I gave it a few full throttle blasts and it won't accelerate on full throttle. It just goes flat not accelerating and not dying.


So I stopped ( on a steep hill to aid starting) and the plugs were black, but the popping and banging felt lean, so I put in a set of richer throttle slides ( 3.5 instead of the 4s that came out).

Then it ran miles better right down low. I could happily ride at 25mph in top gear and it would pick up much more cleanly. So I gave it another run for a few miles ( having cleaned the plugs) and looked at th eplugs.... they looked leaner. A touch of brown on the electrode tips , but still black everywhere else.

Obviously I'm confused here. It felt lean ( in places) but had black plugs and when I enriched it, the plugs went lighter!!!

I'm begining to think I should be looking at the ignition.... on that score the Tri Spark looks good, but here's a question: If an ignition has idle stabilisation, how do you set th eidle mixture? The traditional method is to adjust th escrew and notice how the revs go up or down, but if it's electonically stabilised, how can you tell if you're improving the mixure?

pommie john said:

I gave it a few full throttle blasts and it won't accelerate on full throttle. It just goes flat not accelerating and not dying.

So I stopped ( on a steep hill to aid starting) and the plugs were black, but the popping and banging felt lean, so I put in a set of richer throttle slides ( 3.5 instead of the 4s that came out).

Then it ran miles better right down low. I could happily ride at 25mph in top gear and it would pick up much more cleanly. So I gave it another run for a few miles ( having cleaned the plugs) and looked at th eplugs.... they looked leaner. A touch of brown on the electrode tips , but still black everywhere else.

Click to expand...

Through the many references to plug color throughout this thread, has anyone noted what heat range the plugs are? I tried to jet a '78 Yamaha XS650 (I know, I know...) based on plug color. Once I increased the mains far enough to go from bleach white to brown, the bike was so rich, it would lope and refuse to accelerate under full-throttle runs. The stock plug turned out to be much hotter than you'd think proper, possibly to avoid fouling.
1978 was a transitional year of sorts for that bike; emissions and all. Once I had it jetted for best power/cleanest transitions, the plug heat range was dropped until the color was right. A little backwards, sure, but it worked. 'Funny thing; the plugs I ended up with were the same heat range as for the earlier, pre-emission models!

I ramble on about this based on what appears to be contrary results you've recently noted. Do you have access to an EGA meter? It might be be very enlightening! You may find that you're trying to jet to a plug heat range that is no longer right for your current state of tune.
Nathan

Nater_Potater said:

I ramble on about this based on what appears to be contrary results you've recently noted. Do you have access to an EGA meter? It might be be very enlightening! You may find that you're trying to jet to a plug heat range that is no longer right for your current state of tune.
Nathan

Click to expand...

I've gone from B8ES to BP7ES to see what happened... not much. I have an EGA on my other race bike. I guess I'll be welding a boss onto the Norton's exhaust to swap it over

I suggest you should fit the recommended heat range plugs and ignition timing prescribed for the standard commando and tune to them. If you lower both needles one notch, the bike should miss and become difficult to ride at mid-throttle openings, if you had them set correctly before lowering them. I normally use #3 slides, and the idle screws are usually enough to get the low end correct without playing with pilot jets. When you are reading the plugs, if you have heat range ignition timing and mixture correct there should be a 2mm black bank on the porcelain, right down inside the plug where the porcelain meets the metal. If the plugs are sooty right up to the electrode and on the metal, you have something drastically wrong and flooding is probably happening. I usually only use plug readings for setting the main jets, On a race bike you usually don't stay at max revs with full throttle for very long. The critical thing to get right is the needle jet size and the needle taper and height of the shoulder. That affects from 1/4 to 3/4 throttle - if your midrange is crappy, you know straight away you are too lean, if acceleration is sluggish - too rich.
Make sure your tank breather is clear, if the carbs are starving then refilling you won't know where you are. Treat your bike like your dog - you are the boss of it, don't cop any shit.

acotrel said:

I suggest you should fit the recommended heat range plugs and ignition timing prescribed for the standard commando and tune to them.

Click to expand...

Problem is it's not a standard Commando . It has 10.5 compression, PW3 Cam 36mm Amals etc etc. The standard plug is BP7ES and I was using a B8ES on the track. I've gone back to a BP7ES because it's not being used hard on the road and I wondered if the plugs were not getting up to temperature.

Anyway , I have a plan for the future: Take off the closed end caps from the supertrapp exhaust and see if that's what was restricting the top end. I have a pair of 105 needle jets to try to lean up the mid range.

I'll take it from there.

I might take the O2 sensor off my BMW and put it on the Norton just to make sure where we are.

Having pee'd about for a week to get a Triumph 650 running well, this is my two pence worth.
I THOUGHT the mixture was to lean, which caused a splutter on opening up.....so i raised the needle...no differance.
So i machined some off the slide base..approx 1mm [to richen up the lower-mid range] ...no improvement!
so i fitted electronic boyer system , this improved the 1000 rpm range...the mag was weak at lower rev's...but the bike still spluttered at mid range.
Getting fed up by now!
It dawned on me that cutting down the slide had lowered the needle hight, so i raised the needle in an attempt to put things right?
This action made thing's no better!

So i filed some off the cut away on the slides [yes i am in a world where no standard is applied!] i road the bike up the road and it splutted again.
I lifted the needle and it went better!
I picked the needle up to the highest point and ..BLOODY HELL it went like a rocked, clean smooth power all the way up the range !

I was just lucky to get the Slide cut away/ needle position in the correct balance.
The tuning of amals is not as straight forward as we think, the correct air/fuel mix at all rev's it no that simple.. .and sometimes [with luck] some old git with files and lathes can get it right...factory settings are a good start...after all someone spent lots of time on testing...but when those factory settings fail to work..and they do..its then time to get Nutty!

After market Meggers can throw stock setting out of the window, do something extream with settings .frigging about with little adjustments are not enough :!:

john robert bould said:

..... do something extream with settings .frigging about with little adjustments are not enough :!:

Click to expand...

Yeah, I think maybe you're right. The question is what should I do. Maybe I will move the needle to the richest setting and then try the leanest setting. I have been thinking about going to a dyno. It's often the simplest way. You can cover so many settings in such a short time without risking your licence.

It you carn't get the exhausts to black smoke and the motor to run cool by lifting the needle then you donot have a carb range, meaning a swap to differant carb parts,
My basic [Phil Erving] tuning for speed start is the slide cutaway, this in conjunction with the needle is the KEY start . you can have a rich slide 2-3 and a weak needle,
This can be oposite weak slide and rich needle...or both weak, or rich!
The slide cut away is critical , early Manx had 1/2 slides...eg 2, 2,1/2, 3, .
Many years ago i made up some new slides for a BSA B26 trials bike, the rider wanted just a bit more "lower snap" i filed a very small amount off the cut away...and this this knackered the job! Just shows how sensitive that cut away is! filed some off the base and restored the snap..Remember you can only remove so much of the base [which lowers the slide [NOT THE CUT AWAY] as the slide will drop below the choke bore and a gap at the top appears.
Small cutaways , cause high vacuum which drags in more fuel from the needle jet at small opening, but as soon as the slide lifts the vacuum suddenly drops and the engine demands needle/jet extra to make up the differance..but then the revs increase causing more vacuum... the mixture "runs" between rich, lean,rich..untill the slide as dissappeared and the main jet comes in,
CARBS are a compremise as long as the mixture [air/fueal ratio] is near the 14.7 the engine is happy .
Imagin riding down the flat road at a 1/4 throttle at 2000 RPM....you hit a sleep hill to maintain the 2000 rpm you now have 1/2 throttle , the cutaway is almost redundant..but the needle is now adding more .. time for tea . Good luck PS COLOUR TUNE? for starters

I run the dirt bike floats (much bigger)they seem to keep this richness down low at bay with the 2A1's Kenny Dreer had set mine up on another bike and than gave up glad he did bikes been very good for many years. Also if you are not using a rubber band to dampen the rubber spigots do nothing.

See the alum. square stock just above the inlet? That is for a shoulder screw that when tugged on by a rubber belt counter wts. the carbs body. HTH

I suggest that if bigger floats cure richness you probably have a frothing problem. The carb mount might be too rigid or the head steady might be loose and your balance factor might be causing too much vibration..

Could someone explain what these deep floats do? Does the fuel level stay the same or do they lower the level and cure richness like that?

I was told most of the problems were at over run and idle a smaller lake keeps the ripples down. I know it works and I had to go back to the standard 25 idle jet from a 20 to get back easy starting. For me this all got worked out 12 years ago so it is all well proved and known around these parts. I can't see the problem Make the lake smaller it's to big and dampen the whole carb your fixed when in dought replace the NJ they can go very quickley and mess it all up. Back about 1998 I was visting the pits at Mid -Ohio all Nortons with mark twos had tons of rubberbands from the carbs to the frame.....

Cool. Another thing to try.

Thanks

I can't remember exactly how to set the float level on Amals however usually the level is set by measuring from the gasket to the lever arm. The size of the float should not change the fuel level unless the float is deeper, tends to float higher and keeps the float needle seated when it should open. There must be instructions on the web on how to set the float level, it is important to get it right before you start changing jets.

htown16 said:

On a Mark II the mixture screws meter air just like on a Mark I concentric. I have a set on my Triumph and it seems to like to run best with them at about two turns out. The Triumph shop manual calls for them to be set at 2 1/2 turns out on bikes with the Mark II's. One major difference on Mark II's is they have an enricher circuit instead of a tickler. It consists of a plunger with a rubber cap. When the plunger is up a passage is open allowing the more gas to flow to help starting and warm up. When down it seals the passage. First make sure the lever and linkage is working correctly and when in running mode the lever is up holding the plungers down. The plunger rubber also deteriorates over time and starts to leak.
This can lead to an over rich condition as the carb is essentially flooding the engine all the time. You can supposedly test for this by holding the plunger down with your finger while the bike is running and see if rpm picks up. However, if the plungers haven't been replaced in a long time it might be a good idea to just get some new ones.

Click to expand...

If you need to use more than 2 turns out you need a bigger pilot jet, the 1 1/2 turns out is only a guide-it’s not written in stone.
I always set my pilot adjusting screws at night (preferably a dark night) with a warm engine with a Colortune kit, it becomes much clearer.
They are a motorist boon :!: If you are sharp, you can detect a low speed misfire using these.
You need to first get both the throttle slides set to be open at the same using a a welding rod, and no matter which type of throttle adjuster you have got, get them to open exactly the same at the time.
The slow running malarkey could be the result of other factors, I once had a cam in my 750 made by a well-known Norton engine tuner, only one lobe was accurate, the other three were out, meaning 75% inaccurate camshaft, I binned it and fitted the original Norton cam, which only had one lobe inaccurate when fully open by 5 degrees- (25% inaccurate) the engine went much better.
I would also use a degree disc with a strobe to check the ignition timing, both cylinders must be identical.

Re; “I've recently converted my race bike to be my road bike, and I'm having a couple of hassles getting it to run well low down. It has a pair of 36mm Mk2 Amals ( big I know ) and when I open it up it goes really well, but stuck in traffic it's terrible.”

The size of the carb is into full racing territory, in this case, normally an engine tuner would fit a pair of Amal GPs-these do not come with slow running pilot jets.
It is possible that the 36mm size is far too big to enable the pilot/air jet to work, there simply is not enough vacuum in the engine at slow 1,000rpm speeds to enable the engine to suck up the petrol from the pilot system. It could be made even worse with the throttle slides not having a sufficient tight clearance on the carb body, ( if they rattle like cans in a dustbin, well…..) or a small air leak anywhere else.

Bernhard said:

Re; “I've recently converted my race bike to be my road bike, and I'm having a couple of hassles getting it to run well low down. It has a pair of 36mm Mk2 Amals ( big I know ) and when I open it up it goes really well, but stuck in traffic it's terrible.”

The size of the carb is into full racing territory, in this case, normally an engine tuner would fit a pair of Amal GPs-these do not come with slow running pilot jets.
It is possible that the 36mm size is far too big to enable the pilot/air jet to work, there simply is not enough vacuum in the engine at slow 1,000rpm speeds to enable the engine to suck up the petrol from the pilot system. It could be made even worse with the throttle slides not having a sufficient tight clearance on the carb body, ( if they rattle like cans in a dustbin, well…..) or a small air leak anywhere else.

Click to expand...

As far as the need to detune goes, I would think carbs will get you most of the way home. Better look to a couple 32mm's or look into my big TM40-6 situation. For a stock bike it seems to be a little too much but for a modified bike, as yours, it might just be the ticket.

I am not one to recommend this unless there is a special situation like yours.

I think you need to keep the compression to satisfy the cam so it's between the carbs and the exhaust opening were you will find your balance for street usage.
As if I actually knew what I was talking about......

The clue is in the question and the answer I have given – I am of course only referring to lower rev range, tick over section of the engine/carb performance, I simply cannot deal with someone who appears to think you can fit the biggest bore carb (36mm in this case!) that they can get away with and expect to get uninterrupted power throughout the whole of the engine rev range. It never works.
With these big carbs you are simply going to get a whole lot of sputtering in the lower rev range, try sucking some tap water using a small bore plastic pipe- this should be easy, now try doing it with a 1inch bore pipe and tell me you don’t notice the difference. That is exactly the same conditions you are trying to run your engine.
This engine clearly is a, or close to, a stage 3 tuned engine, with an aim to get the maximum amount of power, regardless of anything else, it can only be made to work cleanly on the upper stages of the engine revs,- some people want to have their cake and eat it.

Perhaps you should buy a cheap Colortune on flea bay warm the engine up on a dark night and fit the Colortune to see exactly what the mixture is doing up to about 3,000 revs.

The situation is made worse if you keep going on fitting different type needles e.t.c. expecting to find the answer where no one has boldly gone before.

Duh guess why some 'too big' carbs came fitted with accelerator pumps and GM's QuadraJet 4 bls were such a treat before EFI. If I was put in charge of Norton carbs I'd have a big signal carb with straight shot into head with a tiny carb sticking off to the side as no need for efficient flow path while just tootling about in traffic or parking lots or off road creeping. Just give er a blip to get tire burn out w/o any brake drag needed. My P!! dragster had dual Amal 30 mm carbs, first tickle starts, 600 rpm idle I could snap throttle and run through 4 gears up over the ton and not move a bike length on street tire smoke. I was never ever thoughtless on throttle use after it pulled vertical steep down hill wheelie on first timid test ride naked in go to class clothes. If ya have educated throttle hand most over sized carbs work fine down low tootling about but do have to build some rpm before WOT snap don't bog.