At wit's end! Jetting Norton Tech Digest 850

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Curt13 said:
I bought the bike in February. Previous owner said it had a Boyer installed. While I was cleaning up the wiring I saw the podtronics but no control box for the Boyer. I went WTF! Opened up the points cover and found the PA. It currently has a dual lead 12V. Yes I replaced the adapter. The old one was toast. As far as kick starting , I believe that maybe the case here. I've read some (a lot of them) negative posts on the PM. It seems to be the herpes of electronic ignitions.
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What kind of 12v dual coil is it?
I'm thinking if the ride previously had an analog boyer on it, it may have a dyna 5ohm dual coil with non-resistor plug wires and/or plugs that may not be compatible with a PArc.
I know little about PArc systems but a quick online peek indicates they must use resistor wires and plugs and they seem to indicate a proprietary coil for them.
If your ride has a proper dual coil on it, maybe all your issue is not using resistor wires and plugs?
However, if the PArc is the whole kit that Old Britts used to offer it would have come with everything correct for it.
https://www.nwno.org/resources/OldBrittsWebsite/51_150101.html
https://www.powerarc.com/pdf/British CD2LM.pdf
 
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Normally an ignition system is a critical part and cannot be made out of bits, if it is to be reliable. You have two choices - if you can identify the black box - contact the supplier and find out what is needed - or better buy a complete set-up which is fit-for purpose. You might avoid tearing your hair out over nothing.
 
Chuck_Wagon said:
What kind of 12v dual coil is it?
I'm thinking if the ride previously had an analog boyer on it, it may have a dyna 5ohm dual coil with non-resistor plug wires and/or plugs that may not be compatible with a PArc.
I know little about PArc systems but a quick online peek indicates they must use resistor wires and plugs and they seem to indicate a proprietary coil for them.
If your ride has a proper dual coil on it, maybe all your issue is not using resistor wires and plugs?
However, if the PArc is the whole kit that Old Britts used to offer it would have come with everything correct for it.
https://www.nwno.org/resources/OldBrittsWebsite/51_150101.html
https://www.powerarc.com/pdf/British CD2LM.pdf
Click to expand...
Coil, plugs, wires resister core
 
acotrel said:
Normally an ignition system is a critical part and cannot be made out of bits, if it is to be reliable. You have two choices - if you can identify the black box - contact the supplier and find out what is needed - or better buy a complete set-up which is fit-for purpose. You might avoid tearing your hair out over nothing.
Click to expand...
The components for the ignition are correct. Previous owner told me that it had a Boyer installed, it didn't and doesn't have any Boyer parts on it.
acotrel said:
Is your tank breather free from obstruction ? You might be creating a vacuum in the fuel tank. When you check fuel flow you do not usually let the fuel flow for very long. It can look as though you have adequate flow, but the vacuum builds up as you ride the bike. Also many electrical issues can look like a fuel problem. From what you have said, it does not sound as though the problem is due to lean jetting. The usual mistake with jetting is - too rich - which just makes the motor a bit slower or can foul a spark plug. With lean jetting you usually get a cough from the motor as you ride the bike. But with starvation due to a tank vacuum,, the motor can give up until it gets fuel again.
Put the clips in the bottom notches of the needles and see if the motor runs when the throttle is opened past a 1/4. If you cannot adjust the problem out, you probably have the vacuum. The tank breather on some bikes is in the tank cap, and there is a washer which can move and close it. But the other thing is, if it is a vacuum problem, it usually takes time with the motor running for it to happen.
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That was checked also.
 
I been down the road with different carb set ups but have now gone back the twin Amal's the Norton ran so well with them even with my hot motor, they are so simple to set up and with the right jets they are so good, tickle, kick and fire up first kick every time when set right, been just over 10 years now running other carbs and more problems than what its been worth even when they been set up for my motor, just replace the jets and needle every so many years is all that is needed, well in my case anyway.

Ashley
 
One Thing , in RETROSPECT - Both Fuel Taps ON , if your trying jetting it .

Also Id do a few gallons flow test . Stoopid Pinhole in the cap might not
equate to a ' racing tank breather ' set up .

& if a fingertip on the carb ' buzzes ' , theres a problem ! Fuel Aeration .
 
There are three things which are in balance - comp. ratio, sparks and jetting. There is an optimum.
 
See not all carb problems are the problems, carbs and electrics can have similar faults to each other in running wise, have been down the coil road thinking its carbs and the other way around, vibrations are a big cause of a lot of faults no matter how smooth the bike is to ride, they still shake, rattle and roll and good you found the problem.

Ashley
 
SteveA said:
Do not trust whoever made this chart!

There is no 'idle air jet' on the Mikuni.....there is an 'air jet'.....it does not affect idle.....and the 2.0 size is incorrect.....for pretty much any 4 stroke.

Around 1.0 is a better choice!
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Didn't want to hijack this thread but now that the loop is closed I wouldn't mind finding out a bit more about SteveA's comment regarding air jet size. I've been running a 2.0 on my single Mik 750 for years with no issues that I was aware of. From what I can see most everyone else does as well as that's what they came with and that's what the tuning guides generally seem to recommend. Wondering if anyone else has swapped out their 2.0 and where the difference would show up on carb operation.
 
zotz said:
Didn't want to hijack this thread but now that the loop is closed I wouldn't mind finding out a bit more about SteveA's comment regarding air jet size. I've been running a 2.0 on my single Mik 750 for years with no issues that I was aware of. From what I can see most everyone else does as well as that's what they came with and that's what the tuning guides generally seem to recommend. Wondering if anyone else has swapped out their 2.0 and where the difference would show up on carb operation.
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It shows up as high rpm lean out! It will show up after revs climb above 6000 after you go to WOT. However, if you check threads by Fullauto he talks about the time and effort he put into getting the air jet right on his road bike to deliver smooth acceleration and good fuel economy, he also mentions his conversations with Jim Comstock that helped him to get the best set up.

The problem was most noticeable to me in top gear at WOT and over 6500rpm on a motor that runs over 7500, a top end misfire halfway down a straight.

The Victory Manual for Mikuni VMs is clear about it, and gives initial recommendations for Nortons of sizes between 0.7 and 1.1 covering differing choke sizes and capacities. My own bike seems to run best with a 1.0 on twin 34mms and 0.7 on twin 36mms. Main jet sizes 195 to 210.

People, including suppliers of 'ready jetted' carbs, ignore it because either they themselves are ignorant of what the air jet does, or they assume that most owners will not really be that demanding on high rpms for extended periods. The cynic in me says that it is one less jet for them to change, but honestly I favour ignorance!!

The issue can be masked by fitting an overlarge main jet. The main jet is functional at above 3/4 throttle, the air jet is most functional above 3/4 throttle, the effect varies with engine rpm. So, if you get the air jet right the benefit for a road bike should be that you can reduce main jet size which in turn should improve fuel economy.

This may also explain why you have not noticed any issues. I would suggest that with a single Mikuni on a road Norton, you aren't the kind of guy that runs over 3/4 throttle at 6 to 7000rpm for significant periods of time.
 
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SteveA said:
This may also explain why you have not noticed any issues. I would suggest that with a single Mikuni on a road Norton, you aren't the kind of guy that runs over 3/4 throttle at 6 to 7000rpm for significant periods of time.
Click to expand...
Absolutely right. That's why I never noticed it. Thanks very much for the expanded explanation.
 
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