Plug chops and colour - happy ending

[Stevepshipley]

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

[Rich Oswald]

Yep defo very lean Steve. First thing i'd do is take out the half clip and put it on 2nd position. Are you using at least a 300 float valve or is it still on the 200 that it comes with?

Rich'

[Stevepshipley]

Still on the 200...

[Rich Oswald]

Still on the 200...

Then all I can say is change it Steve, Corrado (Just Lambretta) does them,

Your settings look in the ballpark to me so eliminate everything.

Rich'

[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

[coaster]

I'd agree with the above re the fuel valve size although that shouldn't be a problem at half throttle tbh. There does seem to be some 'particles' around the plug which I think might indicate pre-ignition? what have you got it timed at? Do you know what compression ratio and squish you have?

[Nelly]

I would also say the plug is not sealed properly looking at the sealing ring, causing an air leak. I had this problem and a leakdown test found it straight away. I used some Loctite 55 pipe sealing string around the base of the plug to seal the leak.
http://www.gasproducts.co.uk/acatalog/L ... wgod7wMBWQ

[Stevepshipley]

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.

Thanks

[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.

[Stevepshipley]

Thanks Adam, I'll check tomorrow
Cheers
Steve

The kit is about 7 years old

[Stevepshipley]

Moved the needle to 3rd clip, wouldn't run on 3 1/2 or 4. Also replaced float valve with 300.

1/4 throttle


1/2 throttle


3/4


Full


I think it's better but still too lean for comfort, I don't have any more spares at home. I still need to check timing as Adam suggests, but what's your thoughts please.

[Adam_Winstone]

Reset timing to 17.

What grade of plug are you running?

[Stevepshipley]

Ok will do,

It's a ngk 8

And thank you

[Stevepshipley]

Timing was at 19, re-checked TDC and set timing to 17.
Waiting for a X13 needle to see if that makes a difference. Worrying about air leak now, I'll see how I get on with a richer needle.

[Raveydavey]

The needle isn't doing much at full throttle, the main needs to go up a couple. That will help at 3/4 too. That's after changing the timing of course

[Stevepshipley]

Right ive learned some lessons today......
Finally managed to get it safe enough to take to scooterotica. What a top bloke Dan is.
I was sold a carb with a 40 slide but never checked this. BIG learn for me, Dan spotted it was a 60!! No wonder i was struggling to get close. Anyway Dan's sorted it. 35 slide 52 pilot 122 main 266 with x7 on 3rd clip. Removed air filter.
Results below, its lovely to ride im well pleased.

So thanks for your advice, if it hadn't been problematic i would not have addressed the potential issue with the timing.
Great help as always on the forum.

[Adam_Winstone]

Well done you... and well done Dan.

60 slide OK, that'll go a long way to explaining things. I've run a 45 with a filtered carb and even played with a 50 but I can't imagine how weak/restrictive a 60 is!

I'm really happy that you've got this resolved.

Adam

[Stevepshipley]

Thanks to you guys for your help too, ive probably managed to salvage a disaster by resetting timing to 17 degrees.
Thanks Adam, wise counsel confirmed by Dan. I'm passing this advice onto other guys in my club.

Great help, great forum

PS - 69.2 mph down the bypass on GPS today, before i bottled it and backed off. Reckon i could have got 70

But more importantly its a joy to ride

[Adam_Winstone]

Cool