Carb adjustment

[Mick Taylor]

Just saw your post after I posted mine Richard......all very interesting and informative to me thank you..

Do you think this jet has no function then despite the fact it does connect to the venturi of the carb?

Mick.

[Mick Taylor]

As a (hopefully) last word on this subject, looking at the starter valve body, it has a smooth internal surface and the valve spindle turns inside that, but although it's a smooth fit, it is by no means a perfect smooth fit, there is play, so I wonder how it retains the fuel that passes through it.

20181008_170300_resized (1280x720).jpg

There are two machined grooves that surely have some purpose.....but what.....anyone know?

Mick.

[Anthony Duffield]

Mick,

The valve spindle on both of my spare carbs are not a perfect fit, what is important are good O Rings in the outer part, I have experienced a failed O Ring resulting in excessive over fuelling such that the bike could not be used. I was able to tell which carb was at fault because the induction tube was so much colder on the faulty side.

Your thread had me thinking about the small brass jet, one of my spare carbs has the jet the other does not, the jet connects to the cold start enrichment valve, so how does the one without the jet get cold start fuel to the engine, hopefully my photo attached will help, I have attached a photo showing the hole that connects to the cold start valve, on my carb with the brass jet both the jet and hole are connected.

The cold start enrichment valve when open draws fuel from the float chamber up through the valve and out through the hole as shown in the photo.

This means that with a carb with the brass jet the engine is being fed with cold start fuel from both the jet and the hole, is it a problem, no not in my experience, both carbs as currently fitted to my Commander have a brass jet, it starts and runs OK so I will leave well alone.

Hope this helps

Tony

[Mick Taylor]

what is important are good O Rings in the outer part

As mentioned previously I have had a couple of issues with these O rings, they seem to swell, lose all their tension and no longer do the job, so this time I'm trying a generic nitrile rubber O ring that seems to be a good smooth fit and is supposedly fuel proof (resistant)....fingers crossed.

While checking the inlet housing gasket today (fine, both holes clear) I got to thinking about how I previously measured the jet height using a digital vernier gauge, I had always thought it to be OK, or as good as I could do, but a while back I bought a digital depth gauge together with a really nice articulated arm and magnetic mount and it occurred to me I could use that....and as it was all apart, no time like the present.

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Here it is, the carb is held steady in the vice and the gauge is equally rigid.....getting the zero position correct with a steel rule and an LED torch to confirm when it was exactly flush with the venturi body was probably the hardest part.....setting it to 3.2mm was a simple matter of winding it down; however 3.2mm on this gauge was not 3.2mm on the vernier....or even very close. Which one to believe?

The test was to re set the jet to zero then wind it down three and a quarter turns as per the Norton manual which came out amazingly close to the 2.79mm Norton quote at this point....but not according to the vernier gauge, so at least I feel confident this method is reasonably accurate although it does tell me that I've previously got it way out .....I think I would have been better off with a tread depth gauge ......live and learn.

Mick.

[Mick Taylor]

Oops.....forgot to say, I had been wondering the very same thing about the additional brass jet, I have yet to remove my right side carb, but if it's the same as the left there will be a tell tale underneath where the jet is pressed in....if there is one, I will probably open the outlet end to clean it, if not I'll leave well alone and continue wondering how it works with just one fitted.

Mick.

[Mick Taylor]

Update on my carb saga; I've just done twenty miles and it's a different bike ......it's lovely now, I was pretty much convinced it was fixed from the moment it started, it just sounded so different, the spitting and hesitation is all gone, once she is up to temperature the idle is a rock steady and smooth 900rpm.

I've learned a couple of things......firstly, setting the jet height using a vernier gauge just didn't work, it was way off.....(too lean) whether that's me (very likely) or the gauge is open to debate, but using the digital depth gauge seemed to get it spot on and the vernier never agreed....not even close......I also learned that the Norton workshop manual method of setting at three and a quarter turns out from flush for 2.7mm is remarkably accurate, confirmed by the depth gauge and I guess a mathematician could work out how many more turns would be required to get an equally accurate 3.2mm without the need for special tools.

The other thing I think I have learned is that the enrichment device O rings are always suspect...I'm hoping the nitrile versions I have fitted will work, fingers crossed......if only the 'choke' was on the accessible side of the carbs the job would be vastly easier.....

Mick.

[Mick Taylor]

Resurrecting an old thread, a further update on my carb saga.....I dragged the Classic out today for a run over to Rye where all the bike congregate, luckily it's always been a brilliant starter, exactly the same process as usual....but not this time; I suspected it was flooded, so I gave up before the battery did and used my 1970 CB750....which hasn't been anywhere for nigh on two years but started and ran there and back like a champ.

By the time I got home, the battery had been on the optimate for a few hours, I cleaned the plugs and she reluctantly cranked into life....so I took her out for twenty miles and she ran just fine.....except, now she has a slightly raised idle speed....approx 1250rpm which was not the case previously.

Pretty much every running problem I've had with this bike has been down to the O rings in the enrichment device; the last time I had the carbs off I replaced the sloppy Burlens items with generic Nitrile O-rings in the hope they would withstand exposure to fuel better.....so my initial suspicions are that they may have failed. I don't like repeatedly taking the carbs off, so I'm just looking for suggestions for the poor cold start and raised idle speed in case I'm missing something.

When it was put away late last year the bike was running as well as it ever has done, so it's a bit of a disappointment. I might start with a new set of plugs and try another cold start tomorrow if I get the chance.....it should start instantly as it's been recently used......if it doesn't I guess I'm looking at those O rings again.

On an entirely separate note, the fast idle from cold start has always seemed a bit cruel to me...straight up to 3,000rpm and I back it off as quickly as it will allow.....is that a normal 'choked' fast idle?

Mick.

[johnbirchjar]

I expect you will have to re-adjust the idle rod to get the choke to do its thing without loads of revs,(it took me quite a number of miles of "trial and error" before I had mine sorted)and it is a real pig of a job 'cos one has to wait for the engine to down after each adjustment,good luck ,J.B.

[Anthony Duffield]

Mick,

I do not have an air cooled classic but for what it is worth herewith my experience with my Commander.

I have only once had an issue with the cold start O Rings, it was very obvious that there was a problem, massively over rich on the left hand rotor with induction tube very cold when compared to the right hand side.

High idle speed for me has always been due to air leaks between the card(s) and the rotor housings, any leaks here will increase speed.

Regards setting the high idle via the fast idle rod, herewith the instruction from the workshop manual:

When replacing an idle rod, the effective
length and therefore setting, is extremely
important. The length of the rod assembly
must be adjusted and firmly secured by means
of the locknut provided to ensure the throttle
linkage is operated in relation to the operation
of the choke cable.
In the case of single rotor idle models, the
adjustment should be set to just initiate the
audible "click" from the left hand idle by-pass
micro-switch when the choke cable has
reached the full-oul Position.

Operation of the micro-switch as described
assumes the correct linkage gap (Section B9 -
Fig.!rG) has already been made.
\ I3
The fast idle rod adjustment on twin rotor
idling machines should be set to €nsure
maximum engine rpm does not exceed 3000
with choke full out, when starting a COLD
ENGINE.
Once correctly adjusted, there should be no
further need to alter the final setting.

Hope this helps
Tony

[Anthony Duffield]

Mick,

High idle speed for me has always been due to air leaks between the card(s) and the rotor housings, any leaks here will increase speed.

Should read "the CARBS(s) and the rotor housings"

[Mick Taylor]

Hmm...thank you all for that, as it happens I have always had a very small leak of dirty brown fluid from the left side carb/rotor housing joint which (I think) I smeared a little sealant on last time they were out....but I did notice yesterday the same thing (tiny amount) on the right side.

I truly hate taking these carbs on and off......but I wasn't aware of the fine detail concerning the microswitch and choke cable adjustment....I'll look at that too....it's a shame my hearing is rubbish; it might be working spot on and I might miss the click.....I'll get the boss to listen for it, she doesn't miss much

[Mick Taylor]

I didn't read that very well did I? ......my bike is twin rotor idle.....does that include an audible click from a micro switch?

Mick.

[Anthony Duffield]

Mick,

I do not have any experience with the air cooled classics, just the water cooled Commanders, you should try to contact to Richard Negus.

Sorry I cannot help further
Tony

[Mick Taylor]

I very much appreciate any input.....it all helps the climb up the learning curve.

Does anyone happen to know the part number for the enrichment device O rings?.....they don't seem to be shown in my parts book...nor does the enrichment device as a whole.

Or.....better still, does anyone know the dimensions of the O rings....inner and outer diameter and thickness as it may be possible to find better ones.

My current problem may well have nothing to do with this, but I feel sure those O rings have not finished with me yet, so I'd like to have a few to hand.

Mick.

[Anthony Duffield]

Mick,

I purchase spares from Burlen no one else, if the enrichment device and carb is clean and the device is lubricated with engine oil during assembly I have not found any issues in use, the only issue I have had was my fault I was not sufficiently careful when assembling the the device and nipped an O Ring.

Later today I will have a look at one of my spare carbs and will get back to you.

Tony

[Mick Taylor]

Thank you for that.......I have had problems with Burlen O rings that lost their integrity....presumably due to Ethanol in the fuel. (which is just my assumption).....in any event, they were no longer the same size they were when fitted.

In the hope of preventing that in future I only run the bike on high octane fuel now, of whatever brand, on the understanding that most of the high octane varieties do not (yet) contain ethanol, so hopefully, that might prevent future problems.

If you happen to have one that can be measured that would be great.....every conceivable size of O ring in pretty much every material available can be found online nowadays so my plan would be to buy a few in fractionally different sizes in the hope of finding that perfect fit...the ones I have fitted at present felt OK, but I would have been happier had they been just a fraction tighter in the bore.

Mick.

[Anthony Duffield]

Mick,

See attached used but good O Ring removed from the cold start enrichment device from a spare HIF4

As accurately as possible it measures 1.75mm O Ring cord, 15mm OD

[Mick Taylor]

Brilliant......thank you for that Anthony, much appreciated, from that I will see if I can find some that are a perfect snug fit, made from a material resistant to modern fuels.

This site popped up and gives a simple layman's terms guide.....it's looking like Nitrile or Viton at a glance.

https://www.martins-rubber.co.uk/blog/a ... ion-guide/


Mick.