Carb adjustment

[Mick Taylor]

Hi all, I took my Classic out for a few miles this afternoon and that ride convinced me I need to do something with the carbs. The bike has 5,000m from new so it has spent a lot of time standing; it was moly'd etc by Richard Negus in late 2011 and after that ran superbly, really clean and smooth. Long story short I probably did just a few hundred miles on the bike at the time and sold it to another rotary enthusiast who, as far as I'm aware never actually used it on the road although he did keep it in running order.

I bought the bike back a few months ago and it came with a new set of carb needles as the previous ones (which I fitted in 2011/12) had suffered from exposure to fuel and lack of use. The previous owner told me he had just fitted new O rings etc to the enrichment device (choke) so I didn't look at that.

I fitted the new needles using a digital vernier gauge to set the height and I'm happy they are correctly set....although I didn't compare numbers on the new needles at the time against the previous set (which I still have).

The bike is a brilliant starter, it runs a nice fast idle on choke, but is very very cold blooded, as soon as the choke is pushed in it becomes very unhappy hesitating, bogging down, huge flat spots etc etc......barely rideable at times.

This afternoon while riding back with just under 100 degrees on the gauge (it never runs hot while moving) I pulled out the choke and it picked up and took off just like it used to......it's clearly not getting sufficient fuel.....but where to start when looking at the carbs?......SUs are a bit alien to me, so any advice, where and what I might be looking for would be much appreciated.

There are fuel filters currently fitted and I will check the flow through them first.

Mick.

[johnbirchjar]

Hi Mike,sounds like you are sucking in air somewhere,
Did you disturb the carbs where they bolt onto the frame?if not,check the "O"rings anyway,just to make sure they are seated properly all round.THIS IS MOST IMPORTANT .and seeing as you have taken the carbs off anyway,just renew every "O" ring in every orifice,especially the "Enrichment" ones( which is what I finished up doing when I was experiencing the same problems with the Classic/Commander that you are having ,The fiddliest job was having to re-set the "Idle Rod" ,not knowing how,(and with no info in the "Manual")it was just trial and error,most time consuming

I assume you have the "Workshop Manual" for the IP2's(to tune & balance the carbs)I don't think one exists for our Classics,but the carbs are the same.(and just about everything else mechanical wise )Happy fetalling ,J.B.

[Mick Taylor]

Hi John, thank you for that, I think I have all the available books, but of course they don't always tell what someone on here might know from previous experience........I'm really just looking for someone who might have experienced the same thing and solved it.....I have searched but came up blank.

There may be an issue with sucking air, but the idle speed doesn't run away with itself......I will order a set of O rings any way and I think I have the remnants of a previous carb overhaul kit to use.

I'm not really suspicious of the enrichment device simply because it's the one part of the carbs that seems to be doing its job properly, it definitely works. I do recall buying some O rings for that when I last owned the bike and they were affected by fuel

I wont rush into it....(haven't got the time until next weekend now) so I'll go through the book of words and maybe someone will mention something in the meantime.....I will be careful to compare the old needles to the new replacements as they are the only changed part I know of.

Mick.

[Richard Negus]

Hi Mick,
Places to start looking:
.carb needles should be stamped 'AEF' just below the flange; SU's prototype of this was marked 'QX51', but is exactly the same needle.
.check the gasket between the carburettor and its inlet casting. Original Norton ones were symmetrical but the Burlen ones can be fitted upside down, blanking off the air passage to the vacuum chamber. That really screws up the carburation.
.dashpot oil must be straight SAE 40; SU specialists, including Burlen, say 3-in-1 light oil but that is only correct for carbs handling cold air.
.John's point about the air inlet to frame O-rings is very valid. I use high temperature RTV as well as, or sometimes instead of, those &#@&%£ rings.
.you're using C8E plugs?
.it's worth checking the strainer on the fuel tap, inside the tank. I could be almost blocked with old paint debris and fuel residue.
.with the tap off, dismantle the lever end and see if there's any gunge in the passages.
R.

[nednortonrider]

When I rebuilt my carbs on an Interpol 2 I contacted Burlem fuel the SU parts suppliers they had no knowledge of the needles stamped qx51 so sent me what they said was a perfect match . Ha Ha ,nothing like .They would only travel half way through the main jet .Refitted the old qx51's .They are working fine . Point is ,if you have had parts from Burlem check them against the originals .Apparently everything is on there computer now , before there was a chap who had all the info in his head and knew the Nortons .Now it's a case of "computer says yes/no".

[Richard Negus]

I had a few AEF's from them not so long ago so they do know about those.
Some owners of early IP2's, originally single rotor idle, may find they have an 'ADR' needle in one side. Most were converted to twin rotor idle and should have AEF needles in both sides.
R.

[Mick Taylor]

Thank you very much Richard, a few things there to look at.....in any event I will start with the fuel supply from the tap, with and without the fuel filters....I'm not sure they are needed on this bike as the inside of the tank looks as clean as a clean thing, but they will get checked.

if you have had parts from Burlem check them against the originals

Thank you for that also.....valuable information that I didn't have; I don't know where the current set of needles came from as they came with the bike, but I still have the packaging as I put the old needles in there for safe keeping......fortunately I tend not to chuck anything of this nature out, the old needles will have little or no wear on them but they did look a bit mucky.

Much appreciated..........Mick.

[Richard Negus]

but they did look a bit mucky.

A bit of fine Scotchbrite with cellulose thinners will fetch them up like new.
Usual precautions, etc..
R.

[Mick Taylor]

No time yet to tinker with the bike, but I did find the old needles, they are actually in much nicer condition than I thought and will definitely be usable; they are marked AEF. The plastic tube the replacements came in is marked NZX 4030 Needle (AEF) so I suspect they will be identical and I will be looking elsewhere......but I might change them anyway just to be sure.

Mick.

[Mick Taylor]

Had a few spare minutes to check the fuel flow today, it looks fine to me.....with or without the filter, which has been ditched for the time being.

The tap functioned well, cutting off properly when the vacuum was released.

If I was a betting man I would say that fuel tap is almost a dead ringer for the Suzuki GT750 part......which has an additional useful function in the form of a 'prime' setting......no need to spin the motor to fill empty carbs.

If I can get hold of one I will check the dimensions.

Mick.

[Richard Negus]

Mick,
Your fuel tap still has a prime function, but the lever plate (held with two screws) was replaced with a Norton one that doesn't allow prime to be used.
This was because, if left in the prime position with a hot engine, fuel evaporates from the float chambers and ends up in the engine. The float chambers are continuously topped up until the carbs enough. It was believed that the condensed fuel, which could wash oil off the end plates, led to some IP2 engine failures. Without the prime position, fuel flow is automatically cut off when the engine is stopped.
For the same reason, the manual reserve tap on the left of IP2 bikes was blanked off.
Interesting to recall that some of the early prototypes, prior to the IP2, had a solenoid-operated tap; switch the ignition on and the tap opens. I'm not sure how a reserve function operated though, unless there were two separate taps.
R.

[Mick Taylor]

Thanks Richard, that is very interesting, the only time I ever used prime on my Suzukis was when they had been standing a long time simply so I didn't have to spin the engine just to fill the float bowls.

That said, you did have to remember to always turn it back to a vacuum controlled setting or it could result in hydraulic lock....I've heard of it happening only rarely, but often enough to make me careful.......the Norton tap is working just fine, so I'll leave it well alone, but I will look at that front plate to see where it's been altered......it really does look like a Suzuki tap.

Mick.

[johnbirchjar]

I still have the original fuel tap on my Classic/Commander,and it has a "Prime" position"(which also works as a"Reserve" ) ,which again is handy should one run out of fuel on the main tank,'cos one doesn't have to remember which way to turn the tap to get to the extra fuel )
I didn't know about "Not leaving the tap on Prime,'cos the fuel continues flow" ,(Not that it affects the Commander/Classic,'cos I have done away with the "Vacuum"system , I got fed up with the p***y Ethanol rotting the rubber diafram's & "O" rings )J.B.

[Mick Taylor]

I believe the only way around the ethanol issue (at the moment) is to use the high octane unleaded fuels which form what I have read usually don't contain ethanol whereas the basic 95 will always have the ghastly crap as part of the mix.

I believe E10 is on the way for the UK, so it's going to get worse before it gets better

[Mick Taylor]

.check the gasket between the carburettor and its inlet casting. Original Norton ones were symmetrical but the Burlen ones can be fitted upside down, blanking off the air passage to the vacuum chamber. That really screws up the carburation.

Hi Richard, as suggested I've had a look at these gaskets (just the left side thus far) and I'm a bit stumped; the original gasket as you will see from the photos has a very obvious cut out around an air passage, it also has a hole for a second upper air passage; the new gaskets, of which I have several have neither of these

20181005_172513_resized (720x1280).jpg

Here is the face as found when the gasket was removed

20181005_172313_resized (720x1280).jpg

And the opposite face.

20181005_172355_resized (720x1280).jpg

I realise the flat machined face of the inlet housing leaves a void between it and the cylindrical carburettor body which is effectively an air passage, but what of the cut out on the original gasket, if I fit these as they are am I going to be in more trouble?.....confused

Mick.

PS I found the float was too low by about 2mm and the jet was at 3mm instead of 3.2mm.....I am happy I've made a better job of that this time, checked and re checked....not guilty for the float though..

[Richard Negus]

Mick,
That's the outlet gasket and casting. Look at the other end of the carb for the gasket that might be wrongly assembled..

By the way, the gasket you show should have a cut-out from the main bore to match the machining on the outlet casting. Your third photo shows that machining.
Did AN supply that new gasket or Burlen? The latter wouldn't know about the cut-out which is unique to Norton rotaries.
R.

[re5rotary]

Hi all so is the tap really a Suzuki one or something else? I would like to replace the 'cloverleaf' seal in my tap but AN only list a complete tap. regards Terry

[Mick Taylor]

I did wonder if I'd got the 'wrong end' of the stick so to speak.......and having looked at my parts book it shows a cut out in the gasket for the left side carb and comments that it's for twin rotor idle.

I'm pretty sure the gasket will have come from Norton as part of an overhaul kit, and looking at the parts on their site, they are all shown sans cut out, so I guess I will be creating the cut out in one of the gaskets I have......I have a set of hole punches, but the trick will be doing it without splitting it as it's so close to the edge.

Startright did have the correct gasket, but sadly all sold out.

I'll have a look at the INLET end once I've got this right .......interesting set up in any event with an air passage created by machining a flat to creat a gap, never seen that before...

Mick.

PS Re the fuel tap, I'll have a look to see if I have a Suzuki cloverleaf seal for comparison.....no guarantee as I got shot of most of my Suzuki parts

[Richard Negus]

Thirty years to notice there's another error in the IP2 and Classic parts list!
Fortunately, the Commander and F1 Sport lists are correct in specifying 50.0374 as the correct gasket for all SU installations. Andover don't list it as an available part, but easy enough to make from 55.0453 with either a hole punch or nail scissors.

DSC_0079.JPG

The flat on the lower side of the outlet casting, and the hole in the gasket, are to allow the idle air mixture to bypass the main bore and pass down the idle pipes to the engine.

There is/was a company in Manchester city centre who supplied Mikuni tap spares but, with so many variations of design, it was difficult to be sure of ordering the correct kit. They didn't know anything about the Norton application.
R.

[Mick Taylor]

Thank you again Richard, I shall have a crack at converting one of my gaskets today.....I think I'll leave the other side alone, but I will have a look at the correct 'Inlet' gasket as I have never been in there before.

Would the Mikuni stockists be these people? http://www.allensperformance.co.uk/ very comprehensive Mikuni parts availability.

Re the cloverleaf gasket, happily I still have a new Suzuki one in the packet...no guarantee it's correct of course, but it surely looks like a Suzuki tap.

Here it is.

20181006_080210_resized (720x1280).jpg

Part number:

20181006_080217_resized (1280x720).jpg

The diameter of the gasket is 24.3mm....that is the point at which the vernier gauge lost it's grip on it.

If it's leaking out the front of the tap from the plate it's the cloverleaf gasket, if it's dripping from the supply pipe it's the O ring attached to the diaphragm piston at the rear of the tap.

Mick.

[Mick Taylor]

Following on, I have adapted a gasket which was simple enough, however, before I put this back together I would like to be certain of something concerning the idle air mixture; I can see where it is drawn through the void created by the 'flat' in the outlet housing and thence into the idle tube, but as it goes through this void it passes over a small jet pressed into the body of the carb.

This one

20181006_142619_resized (720x1280).jpg

What exactly if anything does this jet do?....following the casting features it appears to link up with the cold start enrichment device, but if I try squirting carb cleaner or air down this jet it goes nowhere, irrespective of whether the 'choke' is on or off. Does it serve a purpose or is it blanked off?

I looked carefully at the oblong orifice in the face of the carb that seems to relate to this same jet, however that is blocked by the body of the jet and again appears to do nothing.....

20181006_142758_resized (720x1280).jpg

am I missing something here or is this jet redundant for the rotary application? I have looked online and can find no mention of it anywhere.

Mick.

[Anthony Duffield]

Mick,

I can confirm that the jet shown in your photo connects to the cold start enrichment device.

Incidentally, when I acquired my Commander the left carb did not have the jet but the right hand one did?

Tony

[Mick Taylor]

Thank you for that, I haven't removed the enrichment device, mainly because the previous owner replaced the O rings just before I bought it.....however, no amount of spraying carb cleaner (as best possible) into that jet seems to produce any flow elsewhere, it seems to be a cul de sac.

I will try removing the enrichment device to see if that makes any difference, I would like to be certain that jet and passage is clear before I put it back together.

The section on carbs in the workshop manual is pretty limited, no flow diagrams or even a proper exploded diagram to show what goes where and what it does, and these carbs are unlike anything I have tampered with before, so I'd rather ask first.

Any advice as to whether there should be an obvious flow of carb cleaner from that jet to the enrichment device would be appreciated.

Mick

[Richard Negus]

Thank you again Richard, I shall have a crack at converting one of my gaskets today.....I think I'll leave the other side alone,
despite the parts list pictures, both gaskets should have the cut-out as they both have a fuel/air flow at idling.

Would the Mikuni stockists be these people? http://www.allensperformance.co.uk/ very comprehensive Mikuni parts availability.
But only carburettors and parts, I think.
The company in Manchester is nrp-carbs.co.uk. Their kit listings are by bike model now so it will still be tricky to get the correct kit.

In discussion with another ex-Norton technician, we came to the conclusion that the brass plug/jet only blanks of a passageway, the rectangular hole being one open end of that passageway.
I've got an old carb body so I'll try to remove the plug and see where it leads.
R.

[Mick Taylor]

In discussion with another ex-Norton technician, we came to the conclusion that the brass plug/jet only blanks of a passageway, the rectangular hole being one open end of that passageway.

Hi Richard, that's interesting.......are you saying that 'jet' is placed there simply to block the passageway and does precisely nothing?

Mick.

[Richard Negus]

I recall also squirting carb cleaner up that passage and not coming to any conclusion; tomorrow will tell.

I'm not clear whether Tony Duffield's comment suggests there was a hole but no jet, or no hole at all in one of his carbs.
Nighty night!
R.

[Anthony Duffield]

Richard/Mick,

I removed the cold start enrichment device on one of my carbs and found by spraying carb cleaner that there is a passage way from the cold start enrichment device to the jet as shown in Mick's photo.

When I first acquired my Commander only the right hand carb had the brass jet, the left hand one did not have the jet at all.

I will take some photos and post here.

Tony

[Anthony Duffield]

RH carb has a brass jet the LH carb does not

[Richard Negus]

Tony,
Thanks for the photo; confirms what I suspected - the brass jet is redundant in the Norton rotary application, a left-over from the same carburettor with a throttle spindle and butterfly for car applications.

In the flat area of the carb bore, there are two holes drilled at about 45 degrees:

DSC_0080.JPG

The hole on the centreline, marked 1, connects to the brass jet, proved by a squib of carb cleaner.
The other hole,marked 2, connects to the cold start mechanism and eventually to a small brass jet inside the float chamber:

DSC_0084.JPG

The brass jet in the bore can be knocked through revealing it has a bore of just over 2 mm; not a fuel jet, perhaps it was a mixture jet.

DSC_0082.JPG

In the car application, with a butterfly in the carb body, that jet would be in the approximate position of the edge of the butterfly and might have provided mixture enrichment just as the butterfly was opened. Just a guess - any other ideas?
The drillway and jet may have been deleted as a cost-saving exersize by SU.
R.

[Mick Taylor]

RH carb has a brass jet the LH carb does not

Excuse my ignorance, but would that be anything to do with single rotor idle?

This afternoon I removed the enrichment device from the left hand carb...naturally it was stuck...but eventually let go without damaging anything. The first thing I noticed was the O ring, recently replaced by the previous owner ..... had all the tension of Norah Batty's nylons, I don't think it was doing a lot....I wasn't entirely surprised as that is exactly what happened to the new set I installed when I first owned the bike back in 2012; they don't seem to be fuel proof.

It may not notice in the photo but that is a loose O ring

20181007_164433_resized (720x1280).jpg

Having removed the 'choke' I tried spraying some more carb cleaner down the mystery jet and to my great surprise it surfaced right next to the main jet, in the photo it is the larger of the two drillings next to the main jet, the flow is good, works both ways so now I'm happy that path is clear.

20181007_164117_resized (720x1280).jpg

The second smaller drilling to the right of the main jet goes directly to the enrichment device......how it all works I don't know, but suffice to say they are not blocked so they should do whatever they are intended to do.

The floppy O rings are a bit of a problem, but I have a box of Nitrile O rings that are supposed to be fuel resistant and one of those happens to be both tight on the brass choke cylinder and tight within the carb body, aided by a smear of silicone grease.....they can't be any worse than the ones I have been using......even more fortunate, I found a pair of new paper choke gaskets and some new tab washers in my parts box so I can crack on.

The rotating brass rod which is threaded one end appears to be entirely symmetrical, it's quite a loose fit inside the outer cylinder of the 'choke' and it has a pair of machined grooves, I thought I'd have a look at the exploded diagram in the parts book, just to check I wasn't missing anything.....and can find no mention of it anywhere, so I looked on the Andover site and again, the enrichment device doesn't seem to exist...although the overhaul kit contains all the necessary parts.

Mick.