Plug chop and plug colour help please - happy ending

[Shipleystevep]

Can you help interpret these plug colours please.
Running a 186 mugello and just fitted MB bgm clubman and 30 mm Dellorto with remote filter.
Jetting etc is as supplied/recommended 120 main 55 pilot AV 266 slide 40 needle X7 set at 1 1/2 clip.

Did these plug chop today

1/4 throttle



Half throttle


3/4 throttle


I didn't do fu throttle because I was worried these are far to lean and also I chose a crap road and traffic was starting to interfere.
What do you think?
Thanks Steve

[holty]

hi, i would say that your running very weak, either jetting is too small, or an air leak, or fuel starvation caused by fuel tap, what does it ride like, do the revs take ages to die down when you close the throttle ?
holty

[Shipleystevep]

Thanks,
It rides well (too well?) revs shut down immediately with the throttle. New fuel tap which I checked and is good.

[Adam_Winstone]

Very weak or very hot!

The jetting doesn't look too far out so I'd immediately be looking to retard the timing and ensuring that there are no restrictions to a decent fast fuel supply.

Too many miles with a plug looking like that and you're going to have problems!

Adam

[Daggs]

1/4 throttle .......... eeek!
1/2 throttle ...........eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeek!
3/4 throttle........... Firk me nooooooooooooooooooooooooooooooo!




You're running dangerously lean. Supplied/recommended jetting is a starting point, nothing more. Every scooter is different (ish)

[Shipleystevep]

The top end did have a 42af clubman and 26mm dellorto and ran well but rich ( which I was comfortable with)

I don't know the squish or compression ratio but I think the timing was at 19 degrees. As it ran ok before, do you think I should retard the timing and if so to what?

I stupidly left the 300 needle valve on the bench so I'll change that and drop the needle half a clip as suggested. I'll check the plug again before I tinker with anything else. Do you think the 200 valve is starving it of fuel ?

[Adam_Winstone]

Who said 19 ? !

"A general rule of thumb is static systems this should run at around 15 degrees before top-dead centre (BTDC)"

http://www.lambretta.co.uk/downloads/cy ... tting.html

... that might explain it. You want to be no more than 17 static, with it going towards 15 if you fit an expansion.

Adam

NB: These instructions are for the current Mugello kits, previous versions may be a little (little) more forgiving.

[Shipleystevep]

Thanks Adam, I'll check tomorrow and report.
( the kit is about 7 years old)

Cheers steve

[Daggs]

If the timing is causing that degree of lean running, I'll eat your expansion chamber. That plug is displaying lean mixture.

[Chris in Margate]

I strongly disagree. 15 degrees BTDC is far too far retarded and I don't know who bandied that figure around. There is no evidence to suggest that 15 is better than 19; no evidence whatsoever.
19 degrees is fine, might dtop to 18, trust me; that's 4 degrees retarded from where we used to be with Innocenti recommendations when the fuel was purer.
You don't have a timing issue. You have a burn issue with either dangerously weak mixture and/or an air leak somewhere. Check exhaust nuts.