Modern Vespa

Here's the problem: Plug chop at throttle open as far as it will go in 3rd gear leads to a very light plug. It's not white and crispy, but I wouldn't call it chocolatey brown in any sense. Sort of a gray with a hint of purple/brown (a hint).

Here's the confusing bit:
The idle doesn't race. The idle doesn't linger high when I quickly open the throttle and then let off it near as I can tell. The idle doesn't seem to hunt around at different RPMs. In fact, at idle the plug is dark and wet. It's very rich at idle.

Here are the specs:
Sea level.
Stock P200E. Stock, unmodified air filter. Running a Spaco Dellorto 24/24E carb. Jetting is: 55-160
160 / BE3 / 118

Mixture screw 2 turns out.

Here is what I have done to search for air leaks:
I have spritzed WD-40 thoroughly around the head/cylinder joint. No change in idle. There is absolutely no blowout at the cylinder head.

I have spritzed WD-40 thoroughly around the exhaust and exhaust flange joints. No change in idle.

I have spritzed WD-40 thoroughly around the cylinder/casings joint. No change in idle.

I have spritzed WD-40 around the carb box base/casings joint (it's a bit hard to get around under there, but I used the little red focus tube on the WD-40 can). No change in idle.

I have spritzed WD-40 around the carb/carb box joint. No change in idle. I have lapped the bottom of the carburettor. I tightened the carburettor down to 13 ft/lbs (per haynes and vespamaintenance).

New seals. No oil in gas.

WTF? I have no evidence of an air leak either in engine behavior (as far as I can tell) nor can I find a point where spritzing WD-40 (even in heavy amounts) affects the idle speed. Yet I don't have anywhere near a rich chocolatey brown plug even with a 118 main.

Where else can I look for an air leak?

Does it die out when you add choke after its well warmed up?

What happens when you stuff a rag in the tail pipe while it's running?

What does the plug look like after a 30 min ride around town?

Oh yes. In fact if I don't push the choke in immediately after first cold start of the day it'll splutter out. That I have not tried. I'll add that to my to do list.


After a 30 min ride around town the plug is a light tan. I've been told by EP (mechanic in Allston) that the 30-min-ride-around-town plug looks ok, although perhaps a little light.

Just giving this a bump for the fresh eyes of the new day.

Frankly, I wouldn't care because it runs well and around the city I don't think I'll seize it as it is. But I occasionally take longer trips on it and want to go on a 200 miler in about a month... that scenario seems ripe for seizure if I don't get this sorted.

Try a 120 main jet and see if your plug chop doesn't look better. Maybe you're only lean due to the main jet.

Perhaps so! It just seems sketchy with an all stock setup... why would I need a 120 when the stock is a 116? Is that normal? Is it just an unspoken thing that sometimes stock isn't right for the individual scooter?

I'm running autolube, BTW (I know premix can make a slight difference on fuel/air ratio).

An air leak will be seen on the plug for the whole range of the throttle.

I always run a colder plug as well when going distances further than around town.

How could i forget to mention my plug type! I'm running a B8ES.

So what you are getting at is that I don't have an air leak? Why would my plug chop be so lean then with a shiny new oversized 118 main?

+1

You running the stock pipe or a Sito+?

Stock.

Hmm...shouldn't need the 120 but who knows?

ive gone through this before, but in my case the carb was just really dirty. i had to buy and use the chem-dip in the paint can. submerge all the parts in the tray and let sit overnight. big difference. i used to just use the spray.

Could you tell that the carb was dirty by looking at it when rebuilding? Or did it look clean, but you decided to try the chem-dip anyway?

Good question Mathias - Mine certainly LOOKS clean and has been spritzed out with carb cleaner before.

It seems I have two chores once the weather lightens up: shove a rag over the exhaust and see what happens, and drench the carb in gumout.

i was running lean and did all the above but it did not clean out the carb. so i sprayed it but still the same. so a buddy of mine here in town let me try his dip can. worked like a charm.

Ok, update: In answer to a question above, covering the exhaust snuffs the engine.
Just as a reminder, all stock except I'm running a 118 main instead of a 116 (so I should have a rich plug chop I would think). But I'm getting a lean plug chop. I lapped the base of the carb and retightened to 13lbs.

I discovered that although WD-40 does not affect idle RPMs, I can affect them with starter fluid. If I spritz around the base of the carb, I can bog and even kill the engine.

HOWEVER - I am not sure this means I have an air leak there for two reasons:
1) fumes build up like a mofo when I spritz, and I have observed that if I spritz it into the air intake of the carb or even just in the air above the carb I can kill the engine as well. So, it seems possible to me that I'm not really getting starter fluid into the engine VIA the base of the carb, but that the fumes are simply building up around where the carb is drawing air and are snuffing it out.
2) the engine needs oxygen to burn - so (correct me if I'm wrong here, this is my own logic) I think if I had an air leak (too much oxygen) then adding starter fluid should do what starter fluid is meant to do, and BURNNN. However, if I have a correct amount of oxygen to burn the gasoline running through the engine (so no air leak) then starter fluid in the air intake would deprive the engine of oxygen to burn with and snuff the engine. It took me a bit to come to this idea, but it seems in line with the fact that simply spritzing starter fluid over the carb will kill it... not make it run even faster.

I recorded this phenomenon so you guys can be the judge - is this behavior an air leak or is it a not-leaking engine being snuffed?

Someone asked about my "around the town" plug color. I mentioned before that it isn't bad. I've attached a crappy picture to show you. Looks good to me!

Keep in mind, this ISN'T my WOT in third plug chop - the WOT plug chop is quite a bit lighter, and that is where I am concerned. I'm pretty sure I'll never seize in "around town" riding based on this plug color here. It's the 55-60mph for prolonged period riding I'm worried about based on my plug chop.

Oh, FYI I totally blasted the jets with carb cleaner and put a thick dose in the tank - I'm not sure my jets are clogged leading to a lean condition at WOT. Maybe a full chem dip is needed like Jamesjohn suggests, but it's worth noting the carb is only a few years old.

Bump - I know it's not the most exciting topic, especially since it is generally running well, but if anyone who has done this before could help I'd really appreciate it! The local vintage crew is really tied up right now so I'm mostly on my own.

dip it. 24 hours and then blow it out with a compressor. 8)

That's what she said!

I'm running a118 main with a sito and a B7 plug. But I will add my two cents here and add I think its just a matter of up jetting by one. its not going to make that big of diff. to your all around ride but it will give you piece of mind.

Also Starter fluid is Strong shite it would definitely stuff out your bike being that close to the carb.

Edit 118 oopsy