Modern Vespa

Do both senders have heat shrink covering most of the metal bits? I have a sip plug ring and it's exposed up to where the wire screws in; the TTO plug ring has heat shrink right down to the ring itself.

Got a picture of their locations?

Are they both the same brand? Just wondering if the actual thermocouple is reading differently rather than just location.

A mate did a test with two different brands of gauge under the plug and go two different readings. Can't recall what the actual numbers were, it was some time ago.

393f sounds scarily high. Wonder how accurate these sensors are? Boiling water test?

Awesome things are keeping in the happy zone.

Setup sounds super stable.

Wow, that much difference between the two - very good to know! Thanks for the scientific experiment.

And BTW, if you haven't noticed - the Orange Unicorn is in a class unto itself. It's the only one in the "70s with Sidecar" club

I saw the same thing on my Blue P. Temps were 50°C to 80°C higher with the in head sensor. Last week's 250Km didn't give me any headaches so I don't care too much for now since I'll be installing an EGT soon…

The sensors are both as sold, un-modified. Koso. Pics below. Yup - Koso makes it - and it's the one pictured. I think you're on the right track with these questions.
1. The exposed metal (aluminum) of the under plug can dissipate heat.
2. Its position (how it's clocked, is it touching the park plug at the nut) could have a significant effect. I suspect mine isn't touching anything - perhaps sitting in direct flow path getting cooled. I've had to get used to seeing those numbers. At 393°, I am apparently at least 40°+ under seizing. I can get it down into the 375-380 range with the richer rod (needle) - but it literally won't rev out on that rod. The in head temp is real - and for sure it's very different than under plug. Suspect in head is both more accurate and more consistent due to the exposure of the under plug's stem, as Ginch notes.

But in hindsight - one thing doesn't feel right.
My past experience (different cylinder) with under plug sensor would SURELY have produced 330°+ temps climbing that hill with all that weight. Something doesn't seam quite right with the under plug sensor. I'll have a good look tomorrow and perhaps repeat the test.

Before you do, put a bit of heat shrink on the stem. See if that makes a difference. But in the end those in-head temps are a bit alarming!

Do you have a picture of a plug chop from the top of the hill? If this looks good then the temperatures are fine.

What is the ignition advance at 65mph? Could be more gains to be had here.

Very interesting with the sensor differences. Is the in head sensor at the top or bottom?

Another vote for cover any exposed metal on under plug with heat shrink tubing. I did that with Koso as that part is in air stream and was being cooled on mine.

Next experiment, thread head for the smaller under plug sensor. Then you can use same sensor on both to remove any calibration errors.

Would also love to see the plug chopped at the top of the run.
(Not bc I can offer any help... just to satisfy my curiosity.)

Mornin.
Been a while since I chopped any plugs...
I'll put it on the list tho - and order a few new ones for it.

393 feels, well, explosively high, but the next richer rod (which brings down temps about 10°-15°) won't rev out.

- I've run this set up for ~ 18 months/ 3K-4K miles - two rallies, and now a summer of hill climbs. No outward signs of deterioration (yet)
- Up hill for 4+ minutes WOT with 200LBS of additional weight is a lot of resistance for one of these motors.

Tuning:
- I've been playing around with some different jetting. Poi Dog turned me on to a new set of "steeper" rods for the Smart Carb.
- Running on such fast long roads, under load, has increased my experience with the motor/carb/pipe.
- One thing that really stands out: when really truly deeply heat soaked (something that is rare riding around town in my old days), the pipe changes the tuning completely.
- Example: coming off the hill climb, pipe fully warm, scoot feels fantastic. However, idle is up 400-500rpm.
- This is probably an argument for wrapping the pipe with fiberglass - to create a more stable state - though I do love how it looks unwrapped...
- I've considered giving it more inlet timing. As previously noted - I'm just under 180° with my "L" shaped inlet. Perhaps wrapping pipe and opening the inlet a little more would allow a shift to the richer rod. Interesting question. Sensor is on the exhaust side of the head (bottom). I'm not sure I want to make it any hotter... 🙂 I suppose I could. Since we all often post temp info - and more in head temp sensors start to get used - I thought it would be worth highlighting. Think it makes sense to be more specific when describing temps. 🙂

Just don't wrap the header.

What's the science on that?

The fresh charge gets sucked out into the header and then stuffed back into the cylinder. You don't want it to pick up any more heat than it must while it's there.

On proper LC cylinders the water cooling goes completely around the header and even cools the back of the steel exhaust stub mount.

it will be the only one ever but you've earned it

If the timing is either too high or too low at the 65mph rpm, a little performance could be lost, while pointlessly increasing temperature.

Makes sense.
Thanks! . Got it. I'll have a look - haven't been paying attention to tacho- so not sure RPM.

Ginch - below are the pics.
Took cylinder vowel off so I could snap - and discovered that the under plug was not tight.

Figured this gave us an undercount on the temp so I tightened up nicely.
Re - ran the the hill test on my way to the shop, expecting 330/340 range.
Surprisingly, it simply leveled at 298, finally peaking at 300 as I topped the hill.

So my numbers are: 300 with under plug and 393 in head.

Note:Couple suggestions for wrapping the aluminum ring - which seams smart. I'm more interested in the variance than fine tuning the under plug method - but do suspect this would add some temp. I'll see if I have some tubing of size.

Dang dude - that looks Tasty!!!

Ok - one last round performed.
Double heat shrinked the sending unit for the under plug.
Ran it right up and over the nut to ensure nothing can loosen and no metal is exposed for cooling.
Had a significant effect*.
Same run - bit warmer out now - went from 300 to 333°.
Interestingly - this is exactly where I would expect my under plug to be on this type of long heat soaking WOT under load - when I am really well tuned in.

But... about that*
When I went to adjust where I positioned the under plug sensor - I found the plug wasn't tight...
Put "lack of reliable crush washer" on my list of reasons I hate the under plug unit.
No idea at what point it loosened itself - but let's assume that this mornings 300° run was compromised at least a little.
(let's also celebrate not blowing the engine up doing this test).

So the scores on the doors:
- In head = 393
- Under plug with double heat shrink protecting it = 330
- Under plug, slightly loose plug ( ) with no heat shrink = 300

** No, I will not re-test no heat shrink loose plug. Tks.

I might be tempted to do a plug chop when I remove the under-plug sender - if I can find someone local selling my plugs.
All this blasting up the hill is wearing me out.

Well. I guess it's time to throw out the under plug sensor then. I did notice that they are like a crush washer themselves, unlike the TTO which is a flat copper ring. Obviously the temps don't seem to be doing any harm (as yet)? And that run certainly sounds like the acid test.

It would be an interesting experiment to see what adding a bit more fuel under those conditions - without changing to the richer rod - would do. Does the SC have a choke, and does it remove air or add fuel? I'm actually thinking power jet that kicks in manually. I mean I'm sure you don't need it, but that certainly hasn't stopped you in the past!

It's tru - I'm not a fan - but mostly it's cause they seam to always bind and tangle when I'm taking the plug in and out frequently (during tuning rounds).

The under plug works fine - it's just 50-60 + degrees cooler. Since we talk a lot about temps, I just thought it would be interesting to see the delta on a consistent run.

Perhaps worth noting what the set up is when talking temps. Great minds…
For the ride home today I put in the richer rod. I want to see what temps I get from under plug going up the hill in the morning.

I've considered a power jet - but the richer rod actually runs great down low. Smooth through the pipe coming on, and thumpy down low at idle.

So no need per day for power jet - unless this rod is just too rich WOT.
I noted it won't rev out on this rod - but I want to go back and retest with the pipe hot.

I've also considered trying a reverse power jet: using this rod with a skim coat of epoxy on the last 1/8+ of throttle. So when I whack it open - it goes like a bat out of hell, but if I back off to 7/8 or 3/4, it fattens up a bit and cools off.

Pot Dog is playing around with a smart carb on a smallie. He has the opposite problem. Can't get enough juice WOT. he and I were discussing some innovation/ collaboration that might include a unique power jet solution.

Ordered up some new spark plugs to tot around with. Plug chop between he richer and leaner needle will be interesting.

Well the power jets are such a simple thing. I don't know anything about how to trigger them, but I think some are triggered by vacuum. And some electrically? Not so sure about the last bit.

I have seen some 2 stroke forums talking about power jets as a regular ingredient of the jetting recipe - ie the main ends up smaller than a non-power jetted carb because it has this next stage to go to.

If only someone who had a machine that could precisely turn plain brass rod into a shape that would fit into a carb would come to the rescue! They would save the day, huzzah!!

400F is often the number given as the threshold for air cooled engines, as in the temp where you pay more attention. If it goes a little above 400F going up a hill and falls off when cruising down the other side, no problem.

Most of that info seems to come from under plug sensors since they have been used for a long time with many different applications. I would bet that temps could be hotter or even cooler if measured at other points in the combustion chamber. These temps would also vary a great deal between types of vehicle. Probably more hotspots on a 2 stroke with no cooling from valves or oil circulating through them. So an underplug sensor would probably be more comparable to data from other vehicles using the same sensor type. I don't necessarily think you're running hotter than you thought.

My temps actually came down when switching from a plug to a screw in sensor, but I think I also fixed an air leak from the head in the process.

Really like the Zoolander Blue Steel look you give at the end of the vid. You've got my vote for the Coolest Scooter on Earth award.

Watching all this with great interest as usual. Hoping you and "Pot" Dog continue your smart carb rod collab.

Sidebar- I see no tortilla with that breakfast... Please know that is misdemeanor in the entire state down here. IJS.

This is true. Double-true in Austin, but only half-true in Dallas.

As to Temps, don't forget that Thermocouples are sensitive to variances from their baseline temp, typically 75F, as measured at their Cold Junction.

As the air temperature at the cold junction rises above 75, it will cause the CHT to under-read by the same amount. I was looking for the detail on it yesterday and ran into it in the Westach instructions for OopsClunkThud's temp PDF.

So if it's 100F, the CHT will read 25 degrees low.

Say what? one might think I was colaboratong with Pot Dog when I downed that burrito bowl. I've been working on it for years. 🙂

Gonna go up the hill with the richer rod today. Keep it simple…
Running the under plug sensor.
Whack of new plugs come this week - and I will plug chop just to see what's going on.

Keep in mind: this whole thing started because the commute is my norm - and its demands may eat up my motor prematurely if it's too hot on that climb everyday.

This richer rod - with slight build up on tip to lean last 1/8 throttle - might still provide best solution - tho leaner rod with power jet could also do the trick.

you could install a power jet solenoid that lets you turn it on/off at will.

That would be pretty slick…

Imagine if with a push of a button, we could all just cool our motors when under heavy duress.
CM - I'm looking at you.

But in truth - I think I can get to optimal without a lot of complexity.
The scoot runs pretty fantastically with different rods.
I'm playing with 2 main variables.
1. Rod taper: this affects how quickly the fuel curve is delivered va throttle position (making it richer quicker - but not richer overall once at full throttle)
2. Max richness at WOT. This is the difference between rod numbers

There are of course trade offs.
The E-F rods get rich quick. (!)
I have them in 27 and 28.
28 is leaner at WOT then 27.

The scoot seems to feel better through mid range.
Fuller.
Thumpier at idle.
Smoother.
But they probably use more fuel.

The EK rods are just a little leaner meaner through the middle.
Raspier.
Fuel efficient.

I hate refilling my tank more - but I like the smoothness from E-F taper.

The 27vs 28 is max fuel delivered at WOT.
I dyno'd this and got about 2 more HP out of the 28.

That was always fine.
I've ridden multiple rallies and what not.
Don't think I saw more than 360 on temp gauge. (In head = 300-310 under plug)

But my new surroundings are just so filled with wide open Cali hill climbs where 65 is the norm for extended periods. That's what started all this.
In my heart of hearts (scientifically speaking) my gut says - this is too harsh on the motor using the 28 rod WOT.

Im kinda liking the idea of basically making 7/8 throttle to 8/8 throttle a 28 rod - so when I absolutely peg it I've got full power, while settling for the cooler set up of the 27 rod at 0/8 - 7/8.

That test is coming….

As the creator or the ideal customer?

Both? Not only a member but also the president!

Not to wander too far off - but CM: a power jet on your baby would kinda be ideal.
It works through vacuum.
You adjust its amount delivered through a turn of a screw outside the carb.
You could turn the screw until it starts lowering your RPM - then come back a 1/4 turn and know you had just the right fuel delivery for 9K RPM tearing up a California road - at a rally - going of course, in the totally opposite direction from the rally group.

Elsewhere:
Today's climb: E-F 27 needle, 323° under plug.
That relates to about 373°/383° in head I suspect.
Scoot seams pretty happy

So a powerjet would let me go the wrong direction even faster. I like it!

(And it was 11K RPM's of wrong direction. Just sayin' )

Belly laughed.

I didn't think I'd imagined it. Is there a kit that has this, or something you need to make?

They are out there, used on the TZ an others. Normally gets wired into the ignition system and programed to turn off on over rev.

https://www.tz250.com/forums/showthread.php/8899-TZ125-TZ250-Carb-and-Power-Jet-solinoid

Mikuni has an add on power jet kit also.

The solenoid type are pricey, aren't they?

The Mikuni kits seem to be the most common result from a search.

Lectron, which use a similar tech to Smart Carb, utilize a power jet.
They sell a kit as well - looks a little nicer quality then the Mikuni one.

CM. 11k.
Indeed.

Thunder Products has this:
https://thunderproducts.com/product/thunder-powerjet/

The first iteration could do 13k before it grenaded. One of the more expensive seconds of my life.