Sooty plugs

[Daddy Dom]

Hi All,
long-time reader/first-time poster, so be gentle! I have a 1982 triple-disc Sport (in red ... no, really) that was recently serviced and is running great. I know almost nothing about engines but I know a cool bike when I see one, so I find myself in need of your collective brainpower.

My plugs are pretty black, so ...
Dork question 1: do I need to tweak my mixture screws?
2: which is the mixture screw on a VHBZ25HS?
3: does it go in or out to weaken?

By the way, is anyone on the forum running any esoteric plugs like NGK iridiums?
Thanks in advance,
Dom

[hendre]

Dom,

First a question: do you run you bike hard or just around town for fun? And second: have the atomizers and needles been changed/renewed at some point?

The tiny screw on which you do not see a spring is the idle air screw, the larger one close by you do see a spring on is the idle slide screw. Carb adjustment usually begins with turning the idle air screw in completly and turning it out 1 1/2 turns. After that liscen carfully if the slides drop to the stops simultaniously when turning the gashandle back, if needed adjust the nipples on top of the carb's to reduce/increase cable play so the do drop on the same moment. Then start up the bike and let it warm a bit, it should idle around 1100/1200 rpm. then adjust the air idle screw a bit untill the bike runs most smoothly/fastest on both sides and then screw out the slide screws so the engine idles at 1100 again. Keep repeating untill turning the air screw does not result in higher revs. Then check the dropping slides again and adjust nipples. This should set up your carburation 95% accurate without any fancy tools.

André

[EVguru]

My plugs are pretty black, so ...
Dork question 1: do I need to tweak my mixture screws?

Shiny black or sooty black?

Modern fuels don't necessarily give the classic biscuit brown colour even if the mixture is correct. In addition our Morinis tend to run rich at idle on modern fuel. Does the bike have a hesitation/stumble pulling away if you've been idling for a while? I'm down to 43 idle jets from the original 50 as per NLM's recommendation and that usually solves the problem

2: which is the mixture screw on a VHBZ25HS?

Exploded diagram here; http://www.dellorto.co.uk/editor/upload ... HBdiag.pdf

3: does it go in or out to weaken?

Since it controls the fuel rather than the the air, it goes in to weaken.

By the way, is anyone on the forum running any esoteric plugs like NGK iridiums?

Some probably. I stick to the nice cheap NGK BP7ES available anywhere plugs. I've probably not even looked at them for three years. The bike starts easily and pulls cleanly way past the indicated redline (flat out in 4th gear along the main straight at Cadwell).

[Daddy Dom]

Thanks for your replies Gents, I am unable to do anything about it for a few days yet but will report back. From memory, the plugs are sooty black, and our fuel in NZ is reputedly of 3rd-world quality, so I'm not sure how "modern" we are talking, Paul ...
I ride a mixture of in town (mainly) and weekend runs but haven't noted any hesitation in pulling away but will try all these ideas.
Cheers,
DD