At wit's end! Jetting Norton Tech Digest 850

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The mikuni is a whole different ball game
Has the mikuni just been fitted?
What's the history?
 
Curt13 said:
Power Arc
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A funny ignition system that some can live and rave about with but most can't and dump it for something simpler. Setting the timing correctly is a real issue as the multiple sparks mean it can't be strobed.
 
If you find no solution via ignition and carb settings, it's time to pull the timing cover and check that the valve timing is correct. Mine was off one tooth by the previous owner and pulled to about 3k then nothing.
 
Do you get any hint of fuel overflow and what do the plugs look like at 1800rpm?
Kill it when its bogging out and look at the plugs. sooty, dry, I assume they are going to look black.
Toughest part about this is going to be sorting out if this is the carb or a sparking issue.

Easiest thing at this point is to make sure there are no air leaks at carb to manifold flange to engine but more importantly
double check your float height, VM34 is 22-24mm from the RIB to the top of the arm, set it at 23mm.
Needle e-clip on number 2 or 3, usually on middle groove No. 3.
The lower the clip is on the main jet needle, the richer the setting.
It raises the needle off the seat allowing more fuel through. Leaner 2 – 4 richer.
Air screw: 1-1/2 to 1-3/4 turns out.
I would change the needle jet to a 159 O-6 and the idle jet to a 35.
At wit's end! Jetting Norton Tech Digest 850


At wit's end! Jetting Norton Tech Digest 850


At wit's end! Jetting Norton Tech Digest 850
 
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Update: I've checked every thing that has been suggested with the exception of what I previously posted. I did change the idle jet to a 35. I don't have a 159 06. After all the rechecking and jet change it wouldn't even pop. Checked spark again and it was intermittent and week. Time to spend a bit more cash! I don't mind that as much as I do waiting for parts.
 
Curt13 said:
Update: I've checked every thing that has been suggested with the exception of what I previously posted. I did change the idle jet to a 35. I don't have a 159 06. After all the rechecking and jet change it wouldn't even pop. Checked spark again and it was intermittent and week. Time to spend a bit more cash! I don't mind that as much as I do waiting for parts.
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TEST, don't guess. Good luck!
 
Curt13 said:
At wit's end! Jetting Norton Tech Digest 850 spec, I followed the spec for 850 commando at sea level. Idle is perfect. From around 17-1800 it cuts out badly with any needle setting. Everything is set properly, Cleaned and rebuilt ,tappets, plug gap, fresh fuel, no air leaks. I had changed the jets that previous owner had installed and it had ran the same way. I had bought it this past winter and couldn't ride it due to ice snow. I put a lot of work into it including a sump breather I have spent many hours and shipping time for parts. Any suggestions would be appreciated. Who knows someone may save my sanity.
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Buy a AEM or MTX-L wideband air fuel ratio gauge,weld a 18x1.5 bung in somewhere before muffler , the aem is very fast reacting and has i think 4 easy modes . cheers Vaughn
 
I am willing to suspect the Power Arc. Do you have a spare Boyer around? My biggest headache with the PA was kick starting. Perhaps buy a Pazon or Boyer plus a pair of 6V coils and sideline the PA. Is the rubber adaptor carb - to - manifold new?
 
seattle##gs said:
I am willing to suspect the Power Arc. Do you have a spare Boyer around? My biggest headache with the PA was kick starting. Perhaps buy a Pazon or Boyer plus a pair of 6V coils and sideline the PA. Is the rubber adaptor carb - to - manifold new?
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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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Curt13 said:
Every thing is new. needle true double checked for tightness. 1/8 to 1/4 no go past that. Not just a stumble. It has no restriction of fuel flow to carb either.
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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.
 
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.
Click to expand...
Your local motor mechanic usually has an oscilloscope which can monitor the sparks department when the motor is running. With ignition systems, you need certainty - sometimes you need to buy that.
 
I have a Power Arc E/I with a single Mikuni both work well. Check your manifold for leaks, make sure all four cap screws are tight. Clean the carb again just for kicks. Setting the timing on a Power Arc is fast and simple. No need to strobe. Find TDC on either cylinder and turn the Power Arc until the LED comes on and then tighten it up. Done. Good luck.
 
Curt13 said:
At wit's end! Jetting Norton Tech Digest 850 spec, I followed the spec for 850 commando at sea level. Idle is perfect. From around 17-1800 it cuts out badly with any needle setting. Everything is set properly, Cleaned and rebuilt ,tappets, plug gap, fresh fuel, no air leaks. I had changed the jets that previous owner had installed and it had ran the same way. I had bought it this past winter and couldn't ride it due to ice snow. I put a lot of work into it including a sump breather I have spent many hours and shipping time for parts. Any suggestions would be appreciated. Who knows someone may save my sanity.
Click to expand...
Yer not running a stoopid kill switch I hope ?
 
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