Carb adjustment

Mick Taylor
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Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Re: Carb adjustment

Post by Mick Taylor » Sun Oct 07, 2018 5:55 pm

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
moderator
Posts: 168
Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Re: Carb adjustment

Post by Mick Taylor » Mon Oct 08, 2018 6:04 pm

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.
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Anthony Duffield
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Re: Carb adjustment

Post by Anthony Duffield » Tue Oct 09, 2018 3:13 pm

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
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Mick Taylor
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Posts: 168
Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Re: Carb adjustment

Post by Mick Taylor » Tue Oct 09, 2018 5:54 pm

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.
20181009_122715_resized (720x1280).jpg
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 red face .....I think I would have been better off with a tread depth gauge cry ......live and learn.

Mick.
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Mick Taylor
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Posts: 168
Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Re: Carb adjustment

Post by Mick Taylor » Tue Oct 09, 2018 6:00 pm

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
moderator
Posts: 168
Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Re: Carb adjustment

Post by Mick Taylor » Sat Oct 13, 2018 6:09 pm

Update on my carb saga; I've just done twenty miles and it's a different bike Very Happy ......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.

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