Early Fastback main jet size qu

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macca49

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Jul 1, 2012
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Hi guys
i have a 1970 fastback with the the original early style pipes , ive also fitted a tri spark system, and it ran ok it was a dog to start but we used to get there some times ,so i bit the bullet and bought new amals [ the premium ones] and while it is a breeze to start it just is not running right i think its running too rich , the main jet size is 220 and the technical info i have got hold of states it should be a 220, 210 or 180 size main jet so which is correct? also i live in a hilly area about 500 m above sea level.
cheers
macca
 
If you run ar wide open throttle alot then main may need adjusting. Otherwise, drop the needle one notch ( raise the the clip) and see how it goes.
Check the plugs.
 
macca49 said:
Hi guys
i have a 1970 fastback with the the original early style pipes ,
cheers
macca
Click to expand...
Hi Macca49
Roy Bacon's "Norton Twin Restoration" has the 1970 setup as follows:
R930/46/L47, 30 MM bore, Mains180, slide #3, needle position #2 and .106 needle Jet
Cheers
Thomas
CNN
 
pete.v said:
If you run ar wide open throttle alot then main may need adjusting. Otherwise, drop the needle one notch ( raise the the clip) and see how it goes.
Check the plugs.
Click to expand...
ok thanks Pete ill give that a go today
CanukNortonNut said:
macca49 said:
Hi guys
i have a 1970 fastback with the the original early style pipes ,
cheers
macca
Click to expand...
Hi Macca49
Roy Bacon's "Norton Twin Restoration" has the 1970 setup as follows:
R930/46/L47, 30 MM bore, Mains180, slide #3, needle position #2 and .106 needle Jet
Cheers
Thomas
CNN
Click to expand...
hi Thomas
thanks for that info which i may well action that after trying the clip adjustment , the old carbys had a 220 jet and amals technical dept confirmed it should be a 220 so it appears that 220 is right but if roy bacon thinks it should be 180 maybe thats the way to go. :D
cheers
macca
 
Macca,
Try it with the 220's as you have them. Change the clip setting on the needle and go for a run. The needle and clip position will give the 1/4 to 3/4 throttle positions. Needle up will give richer, needle down leaner. The mains will only be of use when the needle is out of the needle jet and your main orifice is just used from 3/4 to Wide Open Throttle. Find a slight grade from which to test your WOT and do a plug chop (hit the Kill switch, declutch and coast to a stop). Have your sparkplug wrench with you and then on the side of the road examine your plugs. This will determine your mains. Again this forum has good technical links for Amals. Go there study up and test.
Cheers,
Thomas
CNN
 
Bought a new pair of 930's for my '69S. Out of the box 220's on main, N/jet 106, valve 3. Pretty much one kick fire on points. Idles great from the get. If idiled too long, might take one blip to clear. Pulls from off idle 'till my ass off the seat. Clip setting u/k, sorry.
Hope this helps

Tom
 
TJKII said:
Bought a new pair of 930's for my '69S. Out of the box 220's on main, N/jet 106, valve 3. Pretty much one kick fire on points. Idles great from the get. If idiled too long, might take one blip to clear. Pulls from off idle 'till my ass off the seat. Clip setting u/k, sorry.
Hope this helps

Tom
Click to expand...

Yes Tom
Bacons spec for a 69 is 220 but for the 70 is 180. go figure? :?:
Thomas
CNN
 
My S book says for the 930 220 main, 107 jet, but mine came with 240/107 and it seems to run fine.
 
DogT said:
My S book says for the 930 220 main, 107 jet, but mine came with 240/107 and it seems to run fine.
Click to expand...

DogT,
So you are running fine with 240/. 107 ? is that what your bike is running now? Ok…Good to know. I learn something new everyday.
And my Norton shop manual also has the needle jet for the 1970 at .107
Macca stated that he "thinks it’s running too rich". By going from a .106 to a .107 would make it richer. Yes?
With today’s fuels I think a .106 may be the better answer. Macca has to report back after his needle change experiment. But for curiosity sake I would do a plug chop test with the throttle in the 1/4 to 3/4 setting to find out what’s happening to this part of the circuit at the throttle position from the Amals.
Thanks for your input.
Cheers,
Thomas
CNN
 
Oops, 240/106 is what is in my bike. It runs fine, but I use avgas and Wassal pea shooters and also I haven't run it WOT so I'm not sure what it does up there. I just don't worry about it since I'm not going there.

I tried some Hooker glass packs long ago and it backfired with that combo, but I didn't like the Hookers anyhow and got rid of them.
 
hi guys
i wish i could report back but the weather here has been so crappy that when the sun was shining yesterday i was in a dilema do i work on the norton or tale the trumpy for a ride ? and well the trumpy won and it was a great ride that i felt i needed 8)
cheers
 
ah the needle clip on the right side is broken :shock: not sure how i did that :evil: ! it was about half along the needle when i opened it up so i better order another one !
thanks for the help
cheers
macca
 
OK all done
main jet 220
needle on 2nd clip position
she runs perfectly at all throttle settings and is idling at 1000 rpm nicely
i pulled the plugs as suggested and they look good
thanks for the help :D
Macca
 
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