Quick question regarding A/F screws

Forum rules
Please can you post items for sale or wanted in the correct For Sale section. Items / bikes for sale here will be removed without warning. Reasons for this are in the FAQ. Thanks
Post Reply
Vincent
Settled in member
Posts: 66
Joined: Sun Jul 06, 2014 12:49 am
Bike owned: '89 NC30 T1, '92 NC30 T8
Location: New Zealand

Quick question regarding A/F screws

Post by Vincent » Thu Aug 21, 2014 8:40 am

I removed my factory exhaust system today and put in a cut system with a 'Zorst' muffler on it. While everything was off I also put in the 90+ shock with remote res. Seems to turn in a little better now, and doesn't run wide on corner exit as badly.

The new pipe sounds great, didn't realise how much of a difference it'd make from stock.
Went for a run with it jetted 118/115 and didn't have any issues. I'm still running the stock headers, so perhaps I don't need to go up to 120/118?

Anyway I just have a query concerning the A/F screw position:
My A/F screws are currently set to 1 & 6/8 turns out. At 2 turns out I was getting a rich idle when it was hot. I tested with the new exhaust and the idle was steady and didn't hang when returning to idle after revved, which indicates that it's not lean. This is a bit odd, because 2 turns out is for factory setup, so running leaner should not work well with an open exhaust, but it seems to be pretty good :?

So I had a bit of a think about it, and I think maybe I am not seating them fully when adjusting them:
When you guys are setting your A/F screws, how far are you supposed to screw them in? My old 1200 Bandit was running Mikuni carbs, and if you screwed them in far at all you'd fuck the passageways that the tip of the screw goes into, so you just had to lightly seat them.
Is it the same deal with the Keihins on the NC30? Or should I be bottoming them out as much as I can. I have been stopping when I feel too much resistance, which means that they could be screwed out further than I think they are when I set them.

User avatar
vfrman
Senior Member
Posts: 1390
Joined: Sat Apr 05, 2008 7:54 pm
Bike owned: NC30, 1098s
Location: Layton, Utah, USA

Re: Quick question regarding A/F screws

Post by vfrman » Thu Aug 21, 2014 2:28 pm

Nope. You did it right. Lightly seat them.

richyrd5
Regular Member
Posts: 743
Joined: Fri Feb 21, 2014 1:31 pm

Re: Quick question regarding A/F screws

Post by richyrd5 » Thu Aug 21, 2014 5:48 pm

Same for every carb ive worked on! Lightly seat em.

Vincent
Settled in member
Posts: 66
Joined: Sun Jul 06, 2014 12:49 am
Bike owned: '89 NC30 T1, '92 NC30 T8
Location: New Zealand

Re: Quick question regarding A/F screws

Post by Vincent » Fri Aug 22, 2014 11:07 pm

Great, thanks guys. I'll continue troubleshooting to figure out what's going on.

Vincent
Settled in member
Posts: 66
Joined: Sun Jul 06, 2014 12:49 am
Bike owned: '89 NC30 T1, '92 NC30 T8
Location: New Zealand

Re: Quick question regarding A/F screws

Post by Vincent » Tue Aug 26, 2014 6:49 am

So they're still at 1 and 3/4 turns out, this is fine at 80 degrees and under, but when I get up around 90 the idle lowers and gets a little bit lumpy.

This is indicative of a rich idle right? (idle drops and becomes a little erratic when hotter but is fine when colder). So it seems as though I need to turn them in (leaner) a little more.

I'm just a bit worried that I am deviating so much from the factory recommended setting for the screws. Has anyone else had to run them this lean?

Neosophist
Moderators
Moderators
Posts: 8172
Joined: Fri Jul 04, 2008 1:01 pm
Bike owned: CBR954

Re: Quick question regarding A/F screws

Post by Neosophist » Tue Aug 26, 2014 12:22 pm

Vincent wrote:So they're still at 1 and 3/4 turns out, this is fine at 80 degrees and under, but when I get up around 90 the idle lowers and gets a little bit lumpy.

This is indicative of a rich idle right? (idle drops and becomes a little erratic when hotter but is fine when colder). So it seems as though I need to turn them in (leaner) a little more.

I'm just a bit worried that I am deviating so much from the factory recommended setting for the screws. Has anyone else had to run them this lean?
No something is wrong unless your like super high up.

Valve clearances and carb rubbers ok?

float heights ok?
xivlia wrote:i dont go fast on this bike so really do not need a rear brake.. /
vic-vtrvfr wrote:Ask xivlia for help, he's tackled just about every problem u could think of...

Vincent
Settled in member
Posts: 66
Joined: Sun Jul 06, 2014 12:49 am
Bike owned: '89 NC30 T1, '92 NC30 T8
Location: New Zealand

Re: Quick question regarding A/F screws

Post by Vincent » Tue Aug 26, 2014 12:32 pm

It's fine everywhere except idle and just off idle, and the issues there only occur when it's hot (85 - 90 celcius).

It's not really a huge issue, and the bike is perfectly rideable.
It's a classic rich idle condition, and I have been incrementally leaning out (screwing in) the A/F screws to remedy it, when seems to work. The problem is that they are currently at only 1 and 3/4 turns out, and it's still slightly rich (was much worse at 2 turns out).
This is with an open end can on it as well. Everyone else seems to be fine running 2 and 1/4 turns out with an open can, and 2 turns out for standard.

2 turns out is way too rich for my bike, and I'd like to know why in case there's a serious underlying issues that needs to be dealt with.

Clearances were done very recently.
Floats done recently as well.
Carbs have been disassembled and passages blown out with compressed air, jets soaked in solvent and blown out as well.

richyrd5
Regular Member
Posts: 743
Joined: Fri Feb 21, 2014 1:31 pm

Re: Quick question regarding A/F screws

Post by richyrd5 » Tue Aug 26, 2014 12:42 pm

Whats the air filter like?? They can look new but can be past it! Check that.

Vincent
Settled in member
Posts: 66
Joined: Sun Jul 06, 2014 12:49 am
Bike owned: '89 NC30 T1, '92 NC30 T8
Location: New Zealand

Re: Quick question regarding A/F screws

Post by Vincent » Wed Aug 27, 2014 8:10 am

Air filter looks ok, and the bike runs mint everywhere except idle and just off idle so I don't think that's the issue. I'll check it anyway by removing it when the bikes is idling.

Post Reply