To Lambda or not to Lambda, that is the question.

[OneFootInTheGravy]

This is probably one for Data as it's a Vespa related question, but my mechanical knowledge is very limited so please feel free to chip in with any thoughts or anecdotes.

I have just ordered a new Scorpion exhaust for my 2008 GTS 300 (which I believe is a euro 3 engine right?). The question is whether I need to also get the Molassi Lambda Emulator to stop the bike from running too lean? Google is giving me mixed results and the actual emulator isn't the easy to find (for a reasonable price) for the older engines.

[Data]

Hi OneFoot, interesting question!

I fitted a Scorpion to a 2010 GTS300ie a few years back and it didn't need an emulator. Like your 250 it was a euro 3 engine. But I did dyno the bike (I had the equipment in those days) just to check out the fuelling. Apart from a very mild case of being very slightly lean at 3000rpm for a few hundred revs (it was only very slight from memory and made no difference to engine running), everything was ok. Since 2500-3000 rpm (the weak fuelling area) isn't a working area for these motors it was safe to leave well alone. It manifested as a slight fluffiness on the throttle during hovering in those rpm areas. Can't say if it will be the same for your 250. My advice would be to get the exhaust, fit it and take it for a run. You can take some plug readings to see how the motor is running after you've been out on it, but check the plug reading before you swap exhausts first so you have a comparison. Ideally I always like to dyno a bike to check the fuelling if it's running a non standard exhaust just to be sure everything is ok. Don't want to burn valves or guides or damage the motor over time by running a weak mixture.

This is probably not much help but you could fit the exhaust and take it to get it dynoed before splashing out on an emulator if you don't want to mess about.

[OneFootInTheGravy]

That all sounds like good advice (as always).

The exhaust arrived today so I'm planning on fitting it this weekend. I'll let you know how I get on. It's the full system but looks fairly straightforward.

When you say 'take some plug readings' I'm guessing I'd need a specialist bit of kit to do that?

There is a bike dyno not far from me in Burton-on-Trent , any idea what I should expect to pay for this? I've never used one before.

Also, it is the 300 model (278cc) so the same engine as the 2010 you had. I think officially the 300 wasn't released until 2009 but there were 600 odd of them registered in the back end of 08 https://www.howmanyleft.co.uk/vehicle/p ... _300_super

[Data]

By 'plug readings' I am just referring to spark plug colour readings. These give a good indication as to how well the engine is burning it's fuel air mixture. If it's a bit weak the spark plug will look a more white colour than brown. There are online charts showing differing colours for the spark plug readings. If you are not sure it's best to get some advice or just use the dyno. Cost for the dyno can vary vastly. About £60 for a small bike on an inertia dyno is not too far from the ball park figure but some charge much more. Interesting about the 300's coming in during 2008. Just a tip...before undoing the manifold nuts soak them in a penetrating oil several times. The studs going into the cylinder heads tend to corrode quite a bit. One or two of my friends have had problems with the manifold studs breaking off. They are not very substantial but should be ok if you go carefully.

[OneFootInTheGravy]

Thanks. Yeah, I googled 'vespa plug reading' and discovered the rabbit hole on this! lol That will be some good bedtime reading. I'll probably take some photos of the plug to use as a comparison. I have a new plug that i never fitted with the last service, as the old one looked fine. Should I just swap to the new one while I'm at it? And yes, I'll take my time with it, it's always my biggest fear that I'll shear/x-tread something. The day after I got the bike I sheared the wing-mirror trying to adjust it and had to have it drilled out

[OneFootInTheGravy]

Well this is no fun. I got the first nut off the fine, but the 2nd is a pig to get to because of the lambda sensor, and it will only come down the thread about 10 turn before it jams up and won't budge. I might have to take to my local garage to do. I'm too scared of shearing it

[Data]

Yeah, they do tend to shear off in situations like that. The other thing that causes them to shear off is over tightening the silencer to downpipe clamp. It's only meant to be done up to 13nm but many folks (including technicians who don't know Vespas) wrench them up to nearer 30nm. This stops the graphite gasket from sliding & moving with the engine vibration during normal riding. The net result is extra strain on the front down pipe manifold studs leading to cylinder head exhaust stud shearing. Make sure you tell the techs at your local garage this news!!

[OneFootInTheGravy]

I managed to work it off in the end. Lots of penetrating oil and a few swear words was all it took. However, the O2 sensor is another issue all together. That badger is rusted tight to the header pipe. I'll keep soaking it in WD40 but I have ordered a new one just in case.

[Data]

Well done! To get the lambda out you can use some heat. That's what we often did in the workshop. But NOT a flame. A flame can damage the insulator on the lambda. Use a heat gun around the pipe but not on the lambda itself. Maximum heat for a brief period (so as not to heat soak the lambda as well). This will expand the metal around the lambda & it will come out intact. Regarding using WD40; although it helps it's not actually a penetrating oil so won't work on items like this. You need a dedicated professional pen oil. Even diesel fuel works better than WD. It creeps everywhere. Good luck!

[OneFootInTheGravy]

Thanks. I don't have any diesel but I found an old bottle of ACF 50 lurking at the back of my tools. I've been liberally applying that, and even with the heat gun I can't get the thing to budge. I think I'll have to wait for the new sensor to arrive in a couple of days.