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750cc Commando 72 idle

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Hi Fellow Owners,

After nearly 20 years working and riding Norton's [Single Cylinder SV. ONC & OHV]. i have finally brought a 72 Commando [750]. I picked it up last night. It started first kick and sounded great, the only problem is i cannot get it to idle. Before I start the usually investigation, is their something i should look at first??. 

Thanks in advance for any help!

Kind Regards

Steve

 

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Steven

Would you provide a bit of background, e.g. has the bike been in regular use?  Has anything been changed recently?  Running points or electronic ignition? What plugs are fitted? Does the bike have fresh fuel? What make of carbs are fitted?

Do you have a workshop manual and riders handbook?

I'm sure folks will chime in with a bit more info to work with.

Cheers, Andy (72 Roadster)

In reply to by andrew_heathwood

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Hi Andy,

The bike was rebuilt a coup of years ago, all the parts came from Andover Norton. The bike has electronic ignition, i put fresh fuel in it today. It has twin Amal carbs. I have not had a chance to check the plugs.  I started it up and it sounded great and a quick ride the bike is really running well!. I read on a forum that sometimes leaving the commando to idle restricts the flow of oil to the camshaft?. Any help would be great.

Cheers Steve

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Steve:

When you say that you cannot get the bike to idle what exactly do you mean?

1. it will not idle at all???

2. It will idle but too fast???

3. Is the bike fitted with the stock (original) air cleaner?

4. When the throttle twist-grip is wound off, is there a minuscule amount of slack in the cables at both the carb tops?

5. Are the idle jets screwed out the same on both sides?

6. Are the slide needle clips in the same groove on both sides? 

Since the bike is new to you we have to presume that you have not dismantled the carbs. Is that correct?

Have you asked the previous owner about the situation?  He might have some insight into the situation.

Let us know.........

Mike

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The idle circuit on Concentric carbs is easily blocked. Particularly with modern fuel. Take the mixture adjusting screws out and squirt carb cleaner in. Let it soak a bit and give it a good blow through, ideally with an airline. If you feel the urge to poke something through the jet, the hole in the jet is 16 thou I think. Sometime the crap is behind the jet though which is impossible to get to unless the carbs are the newer Premier type where they put a blanking screw opposite the mixture screw.

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The smaller the jet size the more likely carb cleaner on its own will not work as the flow is just too little, so use the 16 thou drill also called a #78 drill.

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My experience is that 0.016" drills can help a bit (so a useful addition to a touring toolkit), but when I had pilot jet problems the ultimate cure was a visit to the ultrasound bath (at I Cleenz Machineez (https://www.icmhome.org.uk) in Penge, if South London is within your range).

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A big thank you to you all for your help. I took the mixture screws out and used carb spray, then i kicked the bike over and re-set the idle to around 1000rpm.  I check the balance on each carb tomorrow night and take the bike out for a test run.

Thanks again all great club, if every you are in the Scottish Borders tea is always on the go.

Cheers

Steve

 

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