Exhaust pressure differs.

Well I think that I have finally got my Amals set up nicely, albeit a bit lean at medium to high revs, not an issue at this stage.
I'm pretty happy with everything related except that there is definately less air pressure comeing out of the right hand exh pipe.
First thoughts were towards unballanced carbs, so I did idle that side up a bit but it only unballanced the idle.
I did recheck the slides for even movement, and they are good. Air mixture is good.
I guess my next stop will be valve adjustment as they haven't been redone since the 500 mile checkup.
The valve clearances were done (on new motor inc Cam) at.... Just after initial start up, then at 100 miles, then at 500 miles.
Motor done 1,000 miles now.
Any thoughts.
What is the general opinion on valve clearance, with warm cam (4s)
We set them at .016 " previously, as recommended by Les Emery for performance.
Is this overkill.?
AC.

Aussie , sounds like unbalanced carbs. Back off both idle adjustment screws. Get 2 thin long nails or old carb needles and insert them under the slides at the engine side of things,not the cutaway gap side. They should stick out of the carb mouths evenly and by gently twisting your throttle observe which needle decides to move a little bit first. That slide adjuster at top of carb needs to be dropped down a little. The goal is for both observation indicator needles to match movements on ultra slow throttle twist. Pull out the needles then start the motor and play with the 2 carb idle screws. Mine had your symptoms before I did this. Peter.

I assume you are not feeling the exhaust pulses while rolling so only concerns idle which I get evenly puffing pressure balls by adjusting the lesser side carb slide stop up till matches the other then from that matched state I diddle em both back to desired/needed road going idle 900-1000. Glad ya reminded me to check 700 mile old Trixie this week, might go to Texas on her 9-ish hours away.

It is likely to be very difficult to accurately sync carbs by feeling the exhaust pulses of an engine. You can roughly set the slides up using twist drills of the same size, but the only really accurate method is some form of vacuum gauge. Some info here regards BMW twins, but pretty much all of it also applicable to Norton: http://bmwmotorcycletech.info/synchcarbs.htm

Main difficulty if you are trying to sync Amal carbs though, is problems with wear, and clearances even on new carbs differing so much, that it might be difficult to get proper sync under any circumstances. Best method to use in this case is a to remove air cleaner, and listen to intake suction on each carb through a length of plastic tube, and then adjust till each side sounds pretty much the same.

Ran .016 on a 2S in mine . Quite gear , you could hear them flinging the valves open @ a 500 rpm idle .

I always use Just Firm on the inlets and Just free on the Ex , in regard to the feeler guages .
If youre holding the throttle on the stop for any length of time , the valves grow with the temperature,
so I dont like to see the exhausts tight , to avoid not only burning , but pitting the seats.
They want to shut decisively .The inlets run cooler and arnt pronee to burning . :lol:

Setting to tight , if youre stuck in traffic , temp control can go awol . so overtights a no - no .

3S is .016 too , which is what I degreed the cam to , about .

P.S. , if the exhaust pressure differs , side to side , Take the mufflers off , to see if theyre the culprit . :wink:

Carbs, cam timing and lash...Of course a norton twin is 2 one cylinder engines siamesed together. Therefore ANYTHING different/nonsymetrical will make it sound off beat. As Matt suggested the mufflers?
I notice you have not mentioned ignition timing accuracy Right vs Left or what kind of ignition...could make a big difference...Whats the full story. :mrgreen:

Setting to tight , if youre stuck in traffic , temp control can go awol . so overtights a no - no .

Click to expand...

Dare ya to keep the same temperature mis-formation judgment after you put 3 temp probes on your C'do to find sitting still in still air idling on hottest full sun summer day as that condition will be the coolest state of running your C'do will reach. Soon as you give it slightest bit of gas to move the slightest bit under its own power all the temps will rise towards normal hwy speeds temps. Still good advice on the lash gap setting of course just expect more loose noise when at coldest idle temps.

Could set by ear like many do their Chevy V8's at good temp by a hose or rod or just listen by ear. Its oil splatter messy of course.

16 thou? As opposed to 6 and 8 thou for stock cams?!?!

Hey Ausseroony , how many miles on those Amals ? Are you going to wait for the over 10,000 mark and then we can help you with the slide fracturing and going through the combustion chamber thing. Loads of fun ,then you can experience some real huffin' n' puffin' unevenly carbeuration balancing n' headscratchin'. Strange rattle in the muffler to explore. Lose the airfilter, reach in, grab the slides and wiggle to see how much you really need new carbs. Lean is good though on these oldies. Normally they go rich from all the vibration.

LIke Torontonian says if one carb is more worn that the other it'd be hard to get the same sound and puff balls out each side. I put grease on my worn slides to verify that was Trixie's failure to return to idle and told me what to spend on again or give up getting it better. A very rather large number of items on Commando we don't usually think of as consumables like tires, actually are too.

Oh yeah here's review on degree-ing a cam and determining which ya got and its gross condition.
http://www.cranecams.com/uploads/instructions/803.pdf

BrianK said:

16 thou? As opposed to 6 and 8 thou for stock cams?!?!

Click to expand...

indeed , long story . Got the cam , stamped along the curve ' S S ' was told it was ' 3 S ' .
which , as the stamping wasnt entirely clear due to the curve , it appeared to be . When I
later put a stock C'do cam in , the detective qualities discerned the top leg of the 3 was
curved .assumeing a > type top leg of the 3 Not round as typed , it wasnt 3 but SS .
The middle top third being invisible along it :shock: . SO ,
at the time , assumeing it was as Id been told , at great length we found the 3S timing specs,
which are someting like .270 lift on the inlet follower at TDC ( DONT quote this, 'SOMERTNING like )
which was eventually got by moving it a chain tooth and a gear or two fwd & back , SO was 5 deg. ' Early ' .

Worked out quite well . slight stutter @ 3250 rpm , but usualy ' took off ' @ 3000 , if playing with the throttle
style rideing . If cruisin at low rpm in suberbia (23T G'box sprocket) , after 3500 the ' Fuse was Lit ' .

Ran W & S valve spring set , shimmed .and 36 deg. BSA Adv for points and 32 Mk 2 Amals .
A ' Dunstall Commando ' rider had taken it for a strop once . He Eventually came back . :lol:
Thought it was quicker than any of the eleven Commandos He'd ridden . :| :!: Head was to Mk 3 specs .
Had had a ported Combat head Id never fitted . Was expecting ' a improvement ' with the big clean straight through ports .)

But thats a longer story . summed up by ' ALLWAYS see the timings CORRECT , and ALLWAYS lead with the REAR brake
on Gravle roads . as the contact breaker unit is quite VULERABLE out there .

WHEN I say ' ' Just Tight ' and ' Just Loose ' on the feeler guage , theres MAYBE a Quater thou total Diff.Firm & Free Slideing
Takeing the time to get the adjustments spot on beats watching television of other excuses for being in a rush .
If you put aside twice as long as you need and take a break after completeing Ea Step , you can be suficently fastidious .

Therell be the ' Aircraft Standards ' lecture if youre not Carefull .
" IF YOU WANT IT TO FLY , WORK TO AIRCRAFT STANDARDS "

Now , if your going for ' a quite cruise ' ( fast enough to leave the noise behind ) and come into heavy traffic , and dont
use it as mobile chicanes . the suddenly reduced cooling can lead to heat soak . As in when pulling in at night where the Exhausts glow dull red , on Triump Twins anyway . .

Discerning rich snots with Ferraris and Aston Martins , Reall ones from back pre 75 , not the robotisied exciteable rich snot ones . would , After start up and idle ( 14.000 rpm for a minute to circulate full oil twice ( or TWO minutes )
would stay below 1/2 throttle untill the Oil Temperature was ' NORMAL , therfore Pressure Normal , before using the
' fully Open ' position . 8)
also for the last 10 minutes + of the trip , gradually ease off throttle setting , so as to maintain cooling flow whilst lessening heat generatted so as not to pretzle the engine at rest .
Much as in the manner of a Turbo Diesel cool down . Shut off hot the coke the oil & block the oilways in the turbo .

So as our machines wernt made by a 20.000.000 dollar computor , we should pay as much care and attention as
the blokes who made it , hopefully , did . :| :mrgreen: Er wot day was it made . . . :lol:

Hey guys,
Sorry if I did not explain the situation properly.
New motor, old boyer, sleeved carbies.
The bike is running very well, just a bit finicky at idle, when out riding.
Starts easily, idles at 600/700 after 30 seconds, (without air slides), then creeps up to a solid
1200 as he warms up.
Revs and performs very well on the road, but will not return to idle, (stops sometimes) unless idled up to 1200 +
I thought the problem was worn slides, got that fixed, and the bike is much better.
However I am starting to think that there may be a weak coil, or that the old Boyer is
dying.
I set the carbs up the same way I've done any bike for many years, and that is the... slides right up method.
I always double check them with a mirror placed behind them so as to see the slides move in sync, and I like to listen-in
with a piece of garden hose.
I am sure the carbs are set evenly, but will try the two pin method.
Thanks for the imput, the bike is very rideable, just concerned about the low exh pressure on one side.
This weekend will see a compression test and valve adjustment, and hopefully a swap over of the coils.
AC.

Mate, when you got those carbies sleeved did you reattach them to the manifolds too tightly ? Those carb to manifold bolts are a really low footpoundage,too tight and you risk warping your newly sleeved thinner bodied carbys . It's too late after that. Boyers and coils either live or die. Pull your ground to frame and clean it up too.Peter.

Hey pete, I don't think I've done them up too tight, mainly because the carbs have been so easy to get along with since the
sleeveing. I am very wary of the prospect of permanenet damage.
I do have another set of Carbs that I had sleeved at the same time, If things don't progress after looking into
the valve clearance etc, I'll try the other set.
Who knows it might be as simple as two slightly different exhaust pipes.
AC.

Substitution with a known good second part is the best way to troubletrace a perplexing headscratcher situation. One substitution at a time ,then test. Many owners do not have the luxury of this as it requires plenty of good spares. I once had a parts dealer say to me "You need spares for your spares." Sounded good.

Hi
just wondering if you managed to find a soloution as mine is doing the exact same thing!

Hey Mattt,
Yes, well pretty well anyway.
I resynched them again and again, and they weren't too bad.
Tried the other pair that I had and they were much the same, took a bit of fiddling but ended up
as good as Amals get, I think.
Used them for a while (1,000 miles) with no problems, started to get paranoid as soon as something seemed different,
took them off and put them away for "the future" and fitted a pair of PWKs.
Tuning problems and consistant Idle problems over.
I did have a problem on one Amal with a slide that got tight all of a sudden, don't really know why that happened as I
hadn't touched them, but I loosened the mounting bolts (as Peter, Torontonian had suggested ) and luckily all was good.
BTW, when that slide was tight, (warped body) the screws on top of the Carb also became tight.
I did post a thread about... Rubber carbies ? Because I couldn't understand how they just, seemingly, bounced
back into shape. They ended up not much more than finger tight.
I notice even with the new carbs that the left side sounds a bit fluffy at Idle, as it has ever since I rebuilt the motor, (not sure about before as I only
had it a few weeks before it blew)
Not concerned anymore, it Idles great, anywhere, anytime, is crisp off of idle and right through the rev range,
so at this stage I will put it down to the 4s Cam being a bit lumpy along with the modified lifters.
Might be the Boyer, but I don't want to know. G/box and swinging arm rebiuld coming up for Winter.
AC.