Modern Vespa

Damn, wrote long post and it disappeared while doing attachments.

This one will be short. Did a quick dirty test, here are some numbers....

Average Difference from Under the plug to the Under the Stud #1
9.61 deg F
Average Difference from Under the plug to the Under the Stud #2
12.58 deg F
Average Difference from Under the Stud #1 to the Under the Stud #2
2.97 deg F

Max Difference from Under the plug to the Under the Stud #1
15.52 deg F
Max Difference from Under the plug to the Under the Stud #2
17.61 deg F
Max Difference from Under the Stud #1 to the Under the Stud #2
6.23 deg F

Short on time these days, anyone wanna take this hardware and log some real data? I'll mail ya the HW and the TrailTechs, just mail back when done. Also allows ya to control timing (retard only), has 3 Trail Tech inputs and 1 K-type thermocouple input. I log using my little Asus Eee through USB.

Plots of data and OpenOffice SS attached. Data labeled IAT and TPS are the under the stud TTs. The CHT is for the under the plug TT. The EGT is for the K type, in the exhaust. The TT are in F and the EGT in C.

I did this in a hurry. Tell me if I messed something up.

I give up on adding the attachments. PM me if you want the spreadsheet or wanna get the stuff to log your own data.

great info, what two studs were used?

Yeah!!! Fantastic.. thanks brother!

same question which studs!

Cheers man! err guy!

I had to leave on travel unexpectedly, hence the rush job. I don't recall which 2 studs. Will take pic when I get home sunday or monday. I'm in spotty wifi hell. Will do better info uploads when I get back too.

I just go under the plug. Good enough for me.

Location of studs and their corresponding labels used in plot and data.

Offer still stands, anyone wanna borrow hardware and do some logging on their engine? I'm not gonna get to this again for a while. Would be nice to see some RPM/CHTs/EGT plots.

Hell, image got rotated after I uploaded to MV. Hmmm, well, you can probably sort it out based on plug position.

Excellent info, thanks for that!

So you're saying that the stud furthest from the plug gave a reading that was closest in temperature to the plug?

Also, I don't know if that's where you always place the plug sensor, but I found if you turn it around so that the sensor lead is at the bottom (in your picture), then when you put the plug in and do it up, the ends of the fins either side hold it from turning. That position doesn't block the airflow as much either.

I'll try that, its always seems like a pain to hold the CHT and seat the plug.

Yes, the stud further from the plug did track a bit closer to the plug CHT, but that stud is closer to the exhaust side.

and furthest from the fresh cooling air. That's the stud I tend to use.

What's the X axis on those graphs? Elapsed time in seconds?

Its crank syncronous. So the x axis is just the sample number. The time varies with rpm. The cht values are sampled many times between revs, but the last sample before cdi trigger is what's logged.

i just got a new cht, for one my old sensor got bent a bit attempting to seat the plug - as it was used on both my lambretta and my vespa, and for the other because some runt stole my digital gauge. i'm drilling holes and bolting this new one down.

perfect timing, perhaps ill seat the old sensor under a nut and not have to run the new wire through the frame.

Just found this again in a FB group and thought it could be useful. This was written by a friend of mine.