1st Overbore & Running Lean

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Tornado

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850 MK2 running a bit rough. Just completed break-in period after first overbore (20 thou). New MK1 Amals, Wassell EI, recent new coils (Lucas), New wiring harness. Been having hard starting last few weeks where it used to be nearly always first kick. Seems to like more tickling and a cracked open throttle to fire up. Just checked timing and was over advanced, now back to about 30 BTDC. Plugs indicating weak mix...no soot visible and electrodes light grey all over.

Should I move the needles up a notch (should be on middle unless the shop that did the work moved them)? Is this something normally needed after an overbore?
 
Lift the needles and see what happens, not all carbs are the same, the middle is just a recommended and not set in stone and might have to play with jet choices as well, did you clean the new carbs out sometimes there is crap caught in the pilot jet passage even from new.
Always pay to check new carbs before fitting might have wrong jets to start off with.
 
Lift the needles and see what happens, not all carbs are the same, the middle is just a recommended and not set in stone and might have to play with jet choices as well, did you clean the new carbs out sometimes there is crap caught in the pilot jet passage even from new.
Always pay to check new carbs before fitting might have wrong jets to start off with.
Yes. My new carbs had different jets in one vs the other.
 
850 MK2 running a bit rough. Just completed break-in period after first overbore (20 thou). New MK1 Amals, Wassell EI, recent new coils (Lucas), New wiring harness. Been having hard starting last few weeks where it used to be nearly always first kick. Seems to like more tickling and a cracked open throttle to fire up. Just checked timing and was over advanced, now back to about 30 BTDC. Plugs indicating weak mix...no soot visible and electrodes light grey all over.

Should I move the needles up a notch (should be on middle unless the shop that did the work moved them)? Is this something normally needed after an overbore?
Needles have nothing to do with starting and having to crack the throttle means that something is wrong with your pilot (idle) circuit or you are flooding. I never open the throttle on any of my Amal equipped bikes when starting and none of them have chokes either. If you're over tickling thinking that's what is needed might be why you need to open the throttle. If your pilot circuit is blocked or partly blocked you can have these problems with starting.
 
Chokes are removed on my setup. I did check the carbs were config'd with correct jetting as supplied. After a few rounds of initial issues, I did get the pilot working well after pressure spraying lots of carb fluid until the pilot holes gave good sprays. That was late last season, prior to engine work. Could be a fresh blockage, will do the rituals...

But, what of the absense of soot, light grey spark electrodes? Looks as lean as I've ever seen them. Overbore not a factor?
 
Light grey is normal with modern fuel.
We don't see that tan colour anymore.
White would be worrisome.

Glen

 
I be pulling the carbs down again, even a good spray with carb cleaner can still have a blockage, I am returning my old Amal back on my Norton after 10 years running PWK carbs I pulled my Amals down and soaked in vinegar for a few days, works better than carb cleaner and when I put them back on the Norton fired up first kick then stopped, low fuel, top the tank up and it fired straight up then stopped the right header was hot but the left was only warm so pulled the carbs again and soaked in the vinegar for a day or so then use the small guitar string down the pilot jet and soaked again when I blew the pilot jet out with the air hose and had my finger over the hole on the left carb something blew out the pilot hole and hit my finger hard even after having carb cleaner spraying out of the passage.
Soaking in vinegar works a treat its a light acid and will break down old fuel crud and cleans the carbs like new without damaging the carbs, but if something is solid is stuck in the passage you need the old guitar string trick and more soaking and a good air supply to blow out any crap after.

Ashley
 
Over advanced ignition will heat up the plugs and give the impression of weakness. Open throttle required on start up can be due to over rich conditions.
Dave
 
What pilot jets do you have, they used to come with #17s which many people find too lean and therefore go to #19s.

Even in my 650 Bonnie it needed #19s..

I’d say this sound more likely to be your starting issue. But as Glen says, I’m not convinced you’re generally running ‘overly lean’ from your plug colour description.
 
Was this after sitting over the winter, or did it happen all of a sudden? I have diagnosed a bunch of bikes with carburetor varnish issues this year in my area. Fresh gas, a bottle of fuel injector cleaner, and patience seems to rectify things. Carbs don’t just suddenly go lean for no reason.
 
As mentioned, what are your pilot jets? I've found the 850's like a #19 pilot but it seems like the vendors always ship them with #17's. Unfortunately on a Commando, one of the carbs will have to come off to pull the pilot jets.
 
As mentioned, what are your pilot jets? I've found the 850's like a #19 pilot but it seems like the vendors always ship them with #17's. Unfortunately on a Commando, one of the carbs will have to come off to pull the pilot jets.
If a vendor ships a correct set in the past 2.5 years, those for 850s have had #19. Some ship generic carbs and, in theory, put in the right jets for your bike but that does not mean that you've got the Norton spray bar or needle and if the generic carb has #17 pilot jet they probably don't change them because they are quite expensive.

This is why I stock the correct set for every Commando when they are available from Amal which is spotty. Amal sells Premier sets by "PACK" number. To learn what your bike needs according to Amal, look at the last table here: https://www.gregmarsh.com/MC/Norton/CommandoID.aspx

Also, today I order the correct 750 PACK numbers but with #19 pilot jets - Amal still thinks #17 is OK for them, and they do work, but in my experience #19 work better, especially for Combats.

As Fast Eddie said even Bonnevilles want #19. Amal says #17.

It is no trouble getting the mixture right with #17, even on 850s, But, the amount of mixture is where the #19 is better. Having the right ratio of gas and air is one thing, how much of it you flow is another.
 
They are 19 pilots as supplied. Issue seems to be a week or two after getting bike back from shop doing engine work. Had a few days of fairly easy starts, they then became inconsistent and remain so. Multiple tanks of ethanol free fuel. Will post up a pic of plugs soon.
 
What pilot jets do you have, they used to come with #17s which many people find too lean and therefore go to #19s.

Even in my 650 Bonnie it needed #19s..

I’d say this sound more likely to be your starting issue. But as Glen says, I’m not convinced you’re generally running ‘overly lean’ from your plug colour description.
#19's in my stock 850 (Premiers). Excellent running. Note: My Premiers had drill swarf in them when new out of the box.
 
They are 19 pilots as supplied. Issue seems to be a week or two after getting bike back from shop doing engine work. Had a few days of fairly easy starts, they then became inconsistent and remain so. Multiple tanks of ethanol free fuel. Will post up a pic of plugs soon.
In that case it sounds like we’re back to a partial blockage of some kind.

In the absence of an ultrasonic cleaning bath, boiling your carbs in a pan with some dish washing liquid in there can have great results. I jest not.

Probably best done when there are no witnesses…
 
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They are 19 pilots as supplied. Issue seems to be a week or two after getting bike back from shop doing engine work. Had a few days of fairly easy starts, they then became inconsistent and remain so. Multiple tanks of ethanol free fuel. Will post up a pic of plugs soon.
Another thought.... Assuming the shop had the entire motorcycle at the time of rebuild, you may want to look for damaged/loose electrical connections that may have been disturbed during the work. Also check/clean the cutout switch.

And another since the break-in/run-in period... recheck tappet clearance.
 
Shop installed a new wiring harness. I'd given the kill switch contacts a little emery cloth treatment a few months back.
Once fired up and warmed up, seems to idle well and run well. So not likely an electrical fault. It came back from shop with ngk 5k Ohm plug caps and bpr8 5k Ohm plugs, cooler than the 7's I had fitted. I've swapped those to non resistor champions but made no improvement. Still on the 5k caps.
 
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