Magneto timing

Hi guys. I'm still trying to get my Atlas on the road. I finally got the K2FC magneto on the bike last weekend and my friend helped me time it. We set it to 32 degrees full advanced BTDC and it started up on the very first kick. I was very excited.

It runs like shit though. Idles nicely. but when giving it a bit of throttle, it pops and seems all over the place.

So question is, was 32 degrees BTDC full advanced the best way to set the timing? Thanks!

32 deg is what Norton books say, but that was written when 100+ octane could be found at any pump. Also, the factory Atlas's had a paltry 7.5 CR. I recently timed my Atlas to 30, to allow for the present day fuel, and a higher CR. That said, 30 or 32 degrees, or even 28 is irrelevant to your description of how it runs.

How was it running on the old Maggie? Did you not simply replace the original with your NOS K2FC? This sounds to be more of a carb problem .... any changes to the carbs while you were swapping mags?

Slick

texasSlick said:

32 deg is what Norton books say, but that was written when 100+ octane could be found at any pump. Also, the factory Atlas's had a paltry 7.5 CR. I recently timed my Atlas to 30, to allow for the present day fuel, and a higher CR. That said, 30 or 32 degrees, or even 28 is irrelevant to your description of how it runs.

How was it running on the old Maggie? Did you not simply replace the original with your NOS K2FC? This sounds to be more of a carb problem .... any changes to the carbs while you were swapping mags?

Slick

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Well I never ran the bike ever when it had the old magneto... I only started it a couple times. I never did replace or pay any attention to the plugs but It does appear to have Champion N5C plugs in it and I think that is not hot enough. I'm going to get the recommended Champion N6Y or NGK BP8ES before I really do anything else with the timing.

I did overhaul the carbs though... The throttle bodies were so warped that the slides could barely move... That could be an issue.

did you leave the choke on? idling fine but popping and spitting under throttle could be lack of spark or lack of air.

I'm sure you've heard the line that 90% of carb problems are electrical and visa versa.

Johnnymac said:

Well I never ran the bike ever when it had the old magneto... I only started it a couple times. I never did replace or pay any attention to the plugs but It does appear to have Champion N5C plugs in it and I think that is not hot enough. I'm going to get the recommended Champion N6Y or NGK BP8ES before I really do anything else with the timing.

I did overhaul the carbs though... The throttle bodies were so warped that the slides could barely move... That could be an issue.

Click to expand...

I would look to the carbs first before fettling with the timing. At worst, 32 deg will ping a bit unless you use an octane boost or have access to 100 LL. I would / do run the N6Y plugs, but the crappy running you describe cannot be attributed to a slightly colder plug, unless one or both plugs are bad aside from the heat range.

Keep us informed .... good luck

Slick

When I had mine timed to around 32* it ran like crap, cough/studder and spitting at take off throttle opening (~1/8 - 1/4 opening), worse at highway speed (~1/4 - 1/2 opening), and popping with throttle blips in neutral. It started like a champ, even when I was just pushing through finding a good compression stroke to kick the bike over on it wanted to light at times. Part of my problem was the main jet was way too small and I had a fuel starvation condition. Going larger helped a lot but my plugs were showing it was still too hot with a BP7ES. In addition, the plug strap heat mark was way too low showing the timing was too advanced. At ~28* it ran really well with the heat mark at the apex of the plug strap. Using Commando pistons which are rated at a higher compression with a lower timing made me lean towards Commando specs for set up versus the Atlas book specs. +1 on the comment by Slick about octane rating.

Scott

Changing multiple significant aspects of an engine (carbs, ignition) then attempting to figure out the best way forward can be frustrating.

Having never ridden it before making any changes doesn't help either; you need a baseline.

Before resorting to jetting, I'd try first adjusting the needle height after a quick plug chop at whatever speed you can coax out of it.

Well I had a clogged pilot jet. So that wasn't helping. I also out better plugs on it and it's running much better but still sluggish at idle to 1/4 throttle. I pulled the plugs and one is getting fouled.

Both needles are all the way up on both carbs. I'm thinking I need to lower the needle on the carb that's shooting up the plug?

If both carbs are jetted identically, and both cylinders have equally good compression, and the float heights are both good,
you'll probably find that one cylinder is burning oil to do that.

Light fluffy carbon is a bit of oil, wet and dripping is a lot of oil.
See any trace of blue smoke coming out of one pipe ?
Especially in a light at night, when it becomes really visible.

It might settle down with a few road miles, or it may need looking at.
You'd also want to thoroughly check that carb first too, obviously.

Could also, just possibly, be a weak spark on one side to do that.
Only way to test for that is to retime the maggie so the cylinders swap sides.
If the sooty plug swaps sides, its ignition. (Unlikely though ?).

Rohan said:

If both carbs are jetted identically, and both cylinders have equally good compression, and the float heights are both good,
you'll probably find that one cylinder is burning oil to do that.

Light fluffy carbon is a bit of oil, wet and dripping is a lot of oil.
See any trace of blue smoke coming out of one pipe ?
Especially in a light at night, when it becomes really visible.

It might settle down with a few road miles, or it may need looking at.
You'd also want to thoroughly check that carb first too, obviously.

Could also, just possibly, be a weak spark on one side to do that.
Only way to test for that is to retime the maggie so the cylinders swap sides.
If the sooty plug swaps sides, its ignition. (Unlikely though ?).

Click to expand...

Thanks Rohan,

It does appear that there are two different slides in there. One is a 3 cut out and the other (with the soot) has a 3.5. I know that can affect it, but I wouldn't think it would be that dramatic?

I would definitely change something to test out if the slides are responsible.
Either both the same as the clean running side.
Or just swap the slides side to side, and see if the soot changes side.

It doesn't take much to make things different.
And any difference could make the difference (you get the drift, even if the words keep repeating).

3.5 should make it leaner, so being sooty is about the opposite of what you would expect.
It could still be oil burning. I've seen that in too many worn engines to ignore,
and new engines are not immune either, due to a variety of causes.

Rohan said:

I would definitely change something to test out if the slides are responsible.
Either both the same as the clean running side.
Or just swap the slides side to side, and see if the soot changes side.

It doesn't take much to make things different.
And any difference could make the difference (you get the drift, even if the words keep repeating).

Click to expand...

Good idea Rohan! I will give it a go.

For you guys with Monoblocs on your Atlases, what size cut out do you have?

Also, on the pilot air screw... which way is richer/leaner? Thanks guys.

Roy Bacons Norton resto book says all monoblocs on Altas had 3 slide (useful book).
Winding the idle screw out gives it more air, so it runs leaner.
Or should.
If the pilot air/fuel passages are blocked, it will try to run on the needle jet, and that can give woolly running and sooty plug(s).

If you switcheroo the slides over, make sure they have free travel in their new homes over all the throttle range.
Having a stuck throttle takes all the fun out of it...

Johnnymac said:

For you guys with Monoblocs on your Atlases, what size cut out do you have?

Also, on the pilot air screw... which way is richer/leaner? Thanks guys.

Click to expand...

My Norton Owners Manual Publication P106/P lists for the 750 Atlas and Scrambler the following data: (No publication date is listed)

Twin carbs:
Monobloc type 389/88 RH
389/87 LH

Main Jet 350
Needle Jet 106
Pilot jet 20
Throttle valve 3

Needle taper D
Needle position 3

Single carb:

Monobloc type 376/294

The remaining data is 400, 106, 20, 3 1/2, C, and 4 respectively.

You cannot expect smooth engine operation unless both carbs have identical set-up.

I hope this helps.

Slick

Thanks guys!

Why does it have mismatched slides? Perhaps a previous owner was trying to solve exactly the same problem you have now. In which case the problem may be more serious than ignition or timing, although you should obviously try both of these relatively easy things first.

I would start with both carbs set to the same specs, try retarding the timing a couple of degrees and see where you are with it.

You may have more than one issue so the best thing is to work step by step through it.

Firstly based on bitter experience I strongly recommend you check the ignition timing on BOTH cylinders. Old K2F mags are notorious for having different advance each side due to out of alinement of the mag rotor to the body or worn cam rings. Up to 3 degrees you can split the difference between cylinders. More than that you will have to fix it. I have seen more than 12 degrees difference. One way to tell is if you have more points gap on one lobe of the cam than the other. There is an excellent thread on the Britbike forum whcih covers this type of mag. I will post a link to it soon. If the timing is out you are wasting your time trying anything else until it is fixed.

http://www.britbike.com/forums/ubbthrea ... Post446733

So far as actual timing advance the other guys have it right. Somewhere between 28 and 31 degrees based on CR and fuel type. I use the Gordon Jennings advice to determine my ignition timing. Another link

http://www.strappe.com/plugs.html

I agree with Rohan. That looks like oil. Which cylinder? If it the right hand side it could be a leak on the drain down hole from the head. They can be difficult.

Next the carbs. Certainly it doesnt make sense that the sooty plug has the 3.5 slide. Thats the opposite to what you would expect. I would clean them perfectly using an ultrasonic bath if you can find one and check that everything is identical before trying to tune anything

good luck

I have the timing on my Atlas (w/Commando pistons) set to 28°
It spit-back like crazy when it was initially set to 32°

johnm said:

You may have more than one issue so the best thing is to work step by step through it.

Firstly based on bitter experience I strongly recommend you check the ignition timing on BOTH cylinders. Old K2F mags are notorious for having different advance each side due to out of alinement of the mag rotor to the body or worn cam rings. Up to 3 degrees you can split the difference between cylinders. More than that you will have to fix it. I have seen more than 12 degrees difference. One way to tell is if you have more points gap on one lobe of the cam than the other. There is an excellent thread on the Britbike forum whcih covers this type of mag. I will post a link to it soon. If the timing is out you are wasting your time trying anything else until it is fixed.

http://www.britbike.com/forums/ubbthrea ... Post446733

So far as actual timing advance the other guys have it right. Somewhere between 28 and 31 degrees based on CR and fuel type. I use the Gordon Jennings advice to determine my ignition timing. Another link

http://www.strappe.com/plugs.html

Click to expand...

Good advice by johnm. I know your K2FC is NOS and should not have mis-match between cylinders, but it would be a good idea to check the point gap on each ramp. I have measured 2 degrees of timing mis-match for each 0.001 inch difference in point gap. If you do have point gap mis-match, let us know.

That said, I still think your problems are in the carbs.

Slick