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First time Norton Owner; need some tuning help #784017 09/12/19 2:54 am
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Andrew Dunham Offline OP
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Hi everyone,

First time Norton owner here. Was able to pick up a very nice (looking) 73' MKI 850 about a month ago.

[Linked Image from i.imgur.com]

Stock air box, stock filter, stock exhaust. Boyer EI with NGK BP7ES plugs installed.

Upon initial inspection after getting it home, it became apparent the carbs needed replaced rather than cleaned. Easy; the new AMAL's seem to work well and I've used them 3-4 times previously. Ordered a couple and popped them on (after figuring out the Commando rite of passage with removal/installation of the carbs.) They came with 260 mains, 3.5 slides, and 19 pilot jets. I figured it was a good place to start as I had seen those specs elsewhere online.

Fast forward to the first start. Bike starts easily and idles (not great, though) so I figure the mixture screws are wrong. I had them at the recommended settings of 1.5 turns out, but the bike seemed to run most efficiently around 2.5-3 turns out. Anyway, the bike would hardly rev at all. I pulled the plugs and they were VERY sooty and black. Not wet, just black and sooty. Figuring it was a horribly rich mixture, I dropped the needle down to the top position. This helped quite a bit, and allowed the bike to be ridden but it would cut out round 4,000 RPM.

Fast forward to today and I've just installed size 17 pilot jets and 3.0 slides per a few recommendations. The bike is running significantly better and now will rev to 5000 - 5500 before just cutting out and returning to idle. Like it will not rev past 5000 or so. Just will not.

Any ideas? I am trying to approach this methodically, but feel as if I could spin out of control quickly here. I am currently thinking the advance is screwy or something. I have yet to check the timing. Hopefully in the next couple of days.

Thanks!

Last edited by Andrew Dunham; 09/12/19 3:02 am.

1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
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Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784027 09/12/19 6:25 am
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kommando Online Content
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Set the fuel level in the float chambers first, assuming these are premier's you have the adjustable stay up floats.

Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784033 09/12/19 8:23 am
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Rohan Offline
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Its always worth pointing a strobe light at the timing and verifying that it is somewhere in the ballpark,
or you could be chasing your tail for some time....

With sooty plugs like that it might be helpful to have a new pair ready to try when you know everything is set correctly too.

Nice looking sparkly FireFlake Blue cycle there.

Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784091 09/12/19 9:49 pm
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Andrew Dunham Offline OP
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Thanks, guys. I appreciate it.

Kommando, any idea what the float height should be? I checked the fuel level according to AMAL specs and it was very close. I've ordered a new air filter, so having the carbs off to check the float level and change that will be a good time.


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784109 09/13/19 1:44 am
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Andrew Dunham Offline OP
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Interestingly enough, I stumbled across this thread... where C.B.S was having a very similar issue. Even more strangely, I chimed in with the same issue on a BSA!

I'm going to take a good look at the air as well.


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784302 09/15/19 12:07 am
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Andrew Dunham Offline OP
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UPDATE!

Bike is running decently now, but still not quite right. The plugs are still sooty around the end of the threads and top of the ground electrode. The center electrode and bottom of the ground electrode are nearing a nice tan, but still dark.

I lowered the float height to .080" below the surface. They were almost level with the surface when I started. A new air filter and 240 mains replaced the 260's that were in it.

It still cuts out and bogs down around 5,000 RPM but pulls nicely up to that. It is rideable if ridden conservatively, but if I get on it a bit, it breaks up. So I took a look at the timing and here are the results:

At idle, we were seeing 18 degrees BTDC on the RIGHT edge of the boss that the mark sits on. NOT on the mark.
2,500 RPM = 23-23 degrees BTDC
3,500 RPM = 26-27 BTDC
5,000 RPM = Bouncing between 28 and 32, so probably 30-31.

My Dad thought he saw some exhaust gases coming out of the head when it was first started today, so new exhaust seals will be on the way. Hopefully that will solve the backfiring it is doing.

Any other thoughts are welcome!


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784388 09/15/19 10:08 pm
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Rohan Offline
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As we see in chatchat elsewhere, are you measuring the float height or fuel height ?

A #3 slide is enrichening it, the opposite of what is needed, once you get the fuel height ?

Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784411 Yesterday at 12:08 AM
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Hi Rohan,

I had done both, actually. But I think perhaps incorrectly. Initially I had hooked up a hose to the bowl drain, held it up beside the carb and measured the fuel level in relation to the top of the bowl surface joint. This fell between the .17 - .24" spec that I found from AMAL.

The bike was still running rich, so I thought I would lower the float some. It was previously (at the .17-.24 spec) approximately flush with the top of the bowl. I dropped the TOP of the plastic float so it was .080" below the top of the bowl mating surface. So presumably the actual fuel level dropped fairly significantly when I did that.

At least changing the slide is an easy job... so that makes sense. The cutaway is LESS, allowing less air in... duh!


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784417 Yesterday at 12:48 AM
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So how is it going now ?
You'd expect that premiers would come in the box fairly well dialled in by now, they've supplied enough. ?

I remember fitting a new pair of Concentrics to an 850 back in the 70s, and they were just wonderful out of the box,
gave it that like-new running. (not that I bought it new).

btw, you have played with the carb syncronization ?
If both slides are not lifting perfectly equal, it may not give its best.
Which is quite an understatement...

Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784425 Yesterday at 01:51 AM
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Andrew Dunham Offline OP
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I didn't get a chance to play with it today, but it starts easily, idles well, both carbs respond to idle and mixture adjustments easily. The mixture is 1.5 turns out to achieve best idle conditions. It is only during riding that the bike will cut out or bog down around 5,000 RPM.

We checked the advance and it appears to be hitting full advance (31 degrees) at 5,000, so I'm fairly confident that is OK.

The next thought is a potential air leak at the exhaust in the head. My Dad thought he saw some exhaust leaking there, so I've ordered new gaskets and will fit them in about 10 days when I return home from a work trip.

That's the interesting thing; I think they probably were fine as is. I have fitted several other Premieres and haven't had to adjust them


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784485 Yesterday at 04:59 PM
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when I got my 74 it ran great but had this intermittent miss between 3500-4000 rpm, tried everything, it had a Pazon EI,,replaced it with a new Boyer and all is good..maybe ur Boyer is going bad, not sure how to test..

Re: First time Norton Owner; need some tuning help [Re: Andrew Dunham] #784514 Yesterday at 08:40 PM
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