Modern Vespa

I'm still in the break-in miles, and I get concerned about every down hill section of road. Do you guys normally shift to N and idle down long hills, or stay in gear and try to pulse the throttle occasionally, or what? I imagine that I can feel it leaning out every time I'm coasting in gear with no throttle.

I.go.down the gears and occasionally pull the clutch and blip the throttle

Don't coast down hill with throttle closed. No fuel equals no lube(unless you have oil injection).

I agree with scootermarc69.

Sometimes, when I feel the revs are very high and I don't want to close throttle but need to reduce speed, I tend to stay half throttle and brake a bit, just enough so revs don't go even higher.

Chop down a gear & nail it!

Anecdotal experience -- not advice:

Been playing with my CHT, located at the top of the bowl (on the BGM 177) and super responsive. Temperature drops when gear-braking downhill. Been rolling 1/4-1/2 a mile in 3rd, no throttle. Idle circuit feeding the engine (premix).

On the cast iron Malossi temps dropped while downhill braking as well.

Uphill temps spike quickly! There also seems to be a spike at the end of an uphill run when letting off the throttle. Been pulling the clutch and feeding it at that point. Temp drops in seconds.

Interesting, that information is very useful- thanks for sharing!

Yes, Useful info Ray..
Which temp guage are you using with the BGM?

Cheers Robbie

I don't think that would be the case because the fuel even at idle is already pre-mixed with 2t oil and in the case of oil injection is also mixed. It should be no difference as if you were leaving your scooter run at idle, I just don't see any concerns.

Personally I never had any problems going downhill but I would say this, putting it in neutral is a bad idea because if for some reason it catches a low gear you are in trouble.

The thing is if you close the throttle when running in very high revs downhill, engine will still be in high revs for some (too much?) time, so gas and oil injected in the cylinder wont't be enough to lubricate and cool down everything (because of the high revs).

Just my 2 cents...

That's the scenario that makes me nervous; top gear at, say, 50mph, coasting down a long hill with little or no throttle input. Most of the roads around me are 45 or 55 MPH, made the break in period tough. I've gone through two tanks now, so I'm sure the rings have done all the seating they are going to do at this point. Enjoying this discussion.

This one:

https://www.biketeile-service.de/en/rollerscooterparts/electric/instruments/temperaturesensorkoso0250cm10xp125adapterwhiteconnector20440.html

BTW the BGM 177 is really growing on me. Not sure how to describe it other than it feels really ballsy in its power band with the Polini.

Ray, I think Robbie was referring the gauge, not the sensor ?

depends on the speed you need/can go.

at slower speeds I just shift to a higher gear and then partial throttle is no issue.

at high speed I keep it WOT on the down hill and sit up to give more drag, roll off now and then, pull in the clutch and blip the throttle now and then.

Gear braking yesterday with the BGM (3500 rpms):

100 meters down steep hill. 6-8 degree drop at top of bowl sensor.
Idle circuit (both jet and screw) on rich side.

Uphill 25 degrees +

Again, not a recommendation. I glaze brake pads (even when pulsing) more than I'd like to continue doing.

brakes are cheaper than cylinders and transmissions.

I already had a Trail Tech monitor on the shelf. Got another extension cable (the cable that comes with it is too short to reach the headset) and changed the Koso sensor's connector to fit the Trail Tech. Works fine.

Still waiting to see if Gascooter's Runleader holds up. Much cheaper, back lit, with a tach monitor. For now I have a $20 tach taped to the floor.

https://www.amazon.com/dp/B092CDSQ33/ref=sspa_dk_detail_1?psc=1&pd_rd_i=B092CDSQ33&pd_rd_w=0VGhn&pf_rd_p=57cbdc41-b731-4e3d-aca7-49078b13a07b&pd_rd_wg=T8r5v&pf_rd_r=21DNN2W1PMCWCY3889PR&pd_rd_r=dbc94d9a-e99f-40fa-bdf8-4191f4c225fb&s=automotive&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFITUMwUEJFT01ZOUsmZW5jcnlwdGVkSWQ9QTAzOTczMzhYVDUyQU9NM0tMSDYmZW5jcnlwdGVkQWRJZD1BMDQwMTM4NTFTOE9TTFRIUjRSWUMmd2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWMmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

True.
But I'm passive braking, in that I'm not slamming into a lower gear to avoid normal braking. Basically coasting downhill in gear and seeing the CHT drop.

what's the result if you just pull in the clutch and coast down using brakes? or have you not done that test yet?

I have!
CHT drops less than half as much vs in gear.

Some notes:
This is CHT, not necessarily translating piston temperature(?).

Aluminum cylinder.
Vs cast iron, aluminum dissipates heat (and I'm assuming reacts to the 3x spinning flywheel) 10x+ faster.

interesting!

good to know...

So far so good. I've got that unit on two scoots. But if I was mounting another one, I'd:

Cut off both connectors and feed the wire from the unit, through the space below the column lock,
Then solder and heat shrink it to the sensor & RPM wires and pull both through the tunnel and out the air duct.

That connector is flaky, and is at the bottom of the tunnel, and hard to reach. This would eliminate any glitchy issues with the unit.

BTW, Runleader did send me another unit because of the crazy glitchyness I ran into, because of the connector. I figure if it's soldered, that would be one less thing to be concerned with.

We'll see after the main riding season is over (september timeframe).

Sensor under PLUG will drop quickly (20f) with a few squirts of fuel, BUT sensor under HEADBOLT will only slowly drop (up to 10min) & you can watch it rise back up soon after ! It really needs time & fuel to cool the cylinder /barrel.

on my smallframe the sensor under stud changes very quickly. pulling a long uphill at that spot between 3rd and 4th bogging a bit in 4th will see the CHT climb and the EGT below the limit, downshift to 3rd and the CHT will drop in less than 1min and the EGT will jump up.

I find the CHT lowers fastest at high RPM, low load, and fuel. the crest of a hill is the most dangerous as the load and heat is still there an my instinct is to roll off thinking "I made it", but it's best to accelerate over the crest and into high gear before starting to roll off or blip the throttle at all.

For guys using under bolt or plug CHT, put heat shrink around area where sensor tip is inserted in ring. That way sensor isn't being cooled by air movement over sensor.

What temps do you see on your smallie, with sensor under bolt? I have mine under the top left bolt, and am just getting the motor broken in with a polini 130 iron barrel; so I'm curious for comparisons sake

Good tip!! I have my wire sheathed from the sensor to the connector. sam principle

Some notes...

Tried throttling over the crest in a higher gear. Saw no improvement in CHT drop vs a blip at the crest and coasting in gear thereafter. I don't have an EGT sensor.

Using Motul 710 oil in premix.

Idle speed set at 1150(maybe higher than most?) to avoid dangerous once a month stalls in city traffic.

The engine is for sure getting enough fuel without throttle. More vacuum at higher revs, along with the faster spinning flywheel.

Shutting down the engine just past the crest: Takes two minutes for CHT to drop vs 30 seconds downhill in gear no throttle.

I'm within a known CHT safe zone. Cylinder clean and compression solid. Done this ride maybe 30x.

The hottest spot in an air cooled cylinder is where this CHT bolts into, at the top of the bowl (not a spark plug sensor), maybe 40% higher than where the rings meet the cylinder.

Just some offhand notes/speculation -- not advice!
Corrections welcome.

I see what you mean about the connector. Tried forcing the retaining clip to connect as hard as I could, even with pliers -- no way. Trimmed the male side sheathing back with a utility knife about 1/8" and it clicks!

Temped the Runleader to run in parallel with a 10mm Koso insert at the top of the bowl. Temperature reading differences are nuts! Runleader takes a minute vs seconds. Bolt-in sensor drops, while the spark plug sensor rises.

Eventually they come to a kind of agreement. I'll follow up after more miles.

*Runleader is reading the same as the Trailtech did, on known rides.

Bought a Runleader, and just sitting at my desk the temp display seems unreasonably slow.