Jet sizes for 750

Classic Norton Commando Motorcycles.

Jet sizes for 750

Postby Stillreel » Mon Jul 08, 2013 7:50 am

The previous owner has installed 210 jets in my Amal carbs. The needle is at the top ring (lowest level in the jet if I'm correct) and the floats are operating properly. The mixture screw is a full 2 turns out on both sides and yet its still burning far too rich and fouling the plugs after 50 miles.

I've read:

fouling-spark-plugs-t16797.html and followed but wondering if the 210s are too big. Other possible solutions??

Thanks

BC
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Re: Jet sizes for 750

Postby Torontonian » Mon Jul 08, 2013 8:04 am

The manual lists 210 for modified megaphone mufflers ,107 needle jet middle needle position and throttle valve 3. Maybe you need the viton tip type float needles. Also the needles and needle jets must be replaced as a set ,they wear out eventually from all the brutal vibrations.
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Re: Jet sizes for 750

Postby pete.v » Mon Jul 08, 2013 8:07 am

Remember, mains are for WOT. You could literally take them out and ride around with little to no affect, so I do not think this is your problem.

However, needles and needle jets wear out. My first incination relating to your state would be to replace these items. Secondly, look to see what cut out slides you have and lean it up by change the slides. You may have a 2.5 and need a 3.0. Or may have a 3.0 and need a 3.5. But do the needles and needle jets first.
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Re: Jet sizes for 750

Postby Stillreel » Mon Jul 08, 2013 8:19 am

I'm also considering replacing the Amals entirely. What's the popular choice there?
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Re: Jet sizes for 750

Postby Stillreel » Mon Jul 08, 2013 9:36 am

Also: does ayone know the proper jet sizes for the peashooters?

To add further grief, the gear box is now acting up too. Turns very stiffly in 4th and 2nd is hard to find after a long run. Looks like the Norton is out of service for a bit. Disappointed. :(
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Re: Jet sizes for 750

Postby MikeG » Mon Jul 08, 2013 10:16 am

As pointed out above, the mains have very little effect till you get past 3/4 throttle or so. I have 106 needle jets and 220 mains. 3 1/2 slides(? not too sure on the slides :oops: ) needles in the middle notch. Spend the $40.00 bucks and replace needles and needle jets and check float levels, it made WORLD of difference in my 71.
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Re: Jet sizes for 750

Postby Torontonian » Mon Jul 08, 2013 7:24 pm

Indeed ,size 106 seems even better. Your slides could be toast too, reach in and grab one with 2 fingers and if it's at all sloppy then the carbs are shot . Many choices for new one$.
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Re: Jet sizes for 750

Postby Stillreel » Tue Jul 09, 2013 4:00 am

Yes, the slides do seem loose, and the jets don't have the 45 degree cutaway that appears to be specific to Norton. The slides are 3.5 already so as much as I'd like to keep it as close to stock as possible, I think I'm going to have to replace the carbs for practical purposes. Hopefully Walridge can come up with something. Is the single carb conversion a good option? I run that on the Triumph TR6 and have never had fouling issues.

Thanks
BC
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Re: Jet sizes for 750

Postby DogT » Tue Jul 09, 2013 7:12 am

The Premere Amals seem to have gotten good reviews here. I got mine working better by just replacing the jets, floats and anodized slide. They still could work a bit better. I should have had them sleeved or bought the Premeres. I'm not one to replace the carbs with something different although lots of people do.

In the technical section on this forum, is a list of jets and slides for the carbs as from the factory for various years. That should be a good place to start.

Good luck with the trans.
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Re: Jet sizes for 750

Postby pete.v » Tue Jul 09, 2013 7:20 am

Stillreel wrote:Yes, the slides do seem loose, and the jets don't have the 45 degree cutaway that appears to be specific to Norton.
Thanks
BC

What are you talking about? What 45 degree cutaway? Are the 32's? What are the numbers on the side of the carbs?
If you are talking about the spray tubes and a 3.5 slides, then you may have 850 carbs.

Something is not right here and you need to offer more details on exactly what you have.
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Re: Jet sizes for 750

Postby Stillreel » Tue Jul 09, 2013 8:29 am

After reading:
http://amalcarb.co.uk/rebuilding-mark-1 ... arburetter

I take another look tonight but think I have the following:
Twin 930 carbs with 210 main jets, 928/063 needles, unknown needle jet, a non-cut off spray tube, 3.5 slides, no pilot jet (bushing instead).

I'll do some more research.

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Re: Jet sizes for 750

Postby X-file » Tue Jul 09, 2013 9:09 am

Stillreel wrote:The mixture screw is a full 2 turns out on both sides and yet its still burning far too rich and fouling the plugs after 50 miles.

Is that giving you the fastest idle with a hot engine at 2 turns,or are you deliberately leaning the idle to counteract richness at higher throttle openings?If that gives the fastest idle,the pilot jets are slightly too big.That might not really cause a problem,but you can fit screw-in pilot jets if it does.

Plug fouling is usually caused by worn needle jets,and it only takes about 0.0005" wear.That will mainly affect the mixture between 1/8 throttle and 3/8 throttle,where the straight part of the needle is still in the needle jet (which is what you mostly use).The needles don't wear much,but the needle jets are lucky to last 10,000 miles.

You can always adjust the idle mixture to get that right,but as soon as you open the throttle it starts going rich.

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Re: Jet sizes for 750

Postby Stillreel » Tue Jul 09, 2013 10:16 am

When leaning out the mixture initially, I was have trouble as there was no perceptible change in idle speed even when 2 full turns out. I turned counter clockwise (out) until it ran rough then back in 1/4 turn. (then 1/8 turn). Still, very sooty plugs after 20 minute 50-60mph drives. Perhaps it is the needles; .0005" wear would not be visible to the eye.
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Re: Jet sizes for 750

Postby CanukNortonNut » Tue Jul 09, 2013 2:59 pm

pete.v wrote:Remember, mains are for WOT. You could literally take them out and ride around with little to no affect, so I do not think this is your problem.

However, needles and needle jets wear out. My first incination relating to your state would be to replace these items. Secondly, look to see what cut out slides you have and lean it up by change the slides. You may have a 2.5 and need a 3.0. Or may have a 3.0 and need a 3.5. But do the needles and needle jets first.



+1
Change the needle jets and needle as a set. Somewhere it is mentioned that it should be done every 5000 miles.
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Re: Jet sizes for 750

Postby Stillreel » Wed Jul 10, 2013 3:39 am

Thanks all. New needles and jets from Walridge. Mike concurs. Last question: is the special tool (jet key) really necessary or will a careful used wrench work?

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