Modern Vespa

Sounds too lean. Need a much richer pilot. BGM make a 5 set from 58/160 up to 68/160 . These might be enough. Got a T5 idle jet?

Thank you Jack.
No I have no T5 idle jet.

The richer jets what I have is:
45/120
50/120
52/120

The need for such a rich idle jet may indicate for air leak or other issues with engine?

I'm not sure where your throttle is in these videos. I can't hear the lean, but that's why I'm no good at this. Hard to tell between lean and rich sputter.

I think if the throttle were held at 1/4 the scooter would continue to accelerate. Maybe that's what Jack means by too lean.

Ray8, I like your suggestion of carrying the other jet stacks in your pocket. And that they work pretty well for this level of tune. It seems that Roland and I are setting up engines for the same kind of purpose and that neither of us are aggressive riders.

Roland, hope you don't mind me commenting so much on your thread. We're both at the same point of the engine tuning path.

Any idle jets recommendations for this stacks? Yes mate I try, honestly The throttle on videos is near 1/4 and on 3rd gear I tried to hold 4k rpms as Jack said. No way! I'm really appreciate any advice and sharing of experience. And I'm grateful to you all guys who help me here!

Here is how spark plug looks with
AC 120
BE 4
128
52/120
Mix 2.5 out
Riding is not perfect have some random small jerks mostly under the 1/2 throttle.
I also tried to out mix screw 3-3.5-4-4.5-5 turns but it only seems to get worse.
But I worry more about temperature. While I cruising on 4th gear with 5-5.8k rpms it easily heat up to 125-130° C fast enough.
The problem is that I don't know what temperature range is ok or critical for my cylinder kit? I search a lot but nothing.
I remember that my friend seized his DR 177 at 160-165°(temp sensor is a ring under spark plug)

That's the new plug?

Just took out my BGM 177 touring bike with a threaded sensor to see how it would respond compared to your video. I don't have a tachometer on that bike (and taller gearing/warm day), but cruising more or less at that speed on a flat road I easily got 105C or more after a few kilometers. Yours seems to level at 100 or so(?).

At 4k suddenly open the throttle. Rich will like the sudden oxygen and take off. Lean prefers a slower throttle.

Threaded sensors don't compare in relative terms to sensors under the plug! They spike rapidly under load and level sooner.
From my run-in-parallel experiences, a threaded sensor will drop while a sensor under the plug continues to climb. At max CHT a threaded sensor read 20C higher, but they never really read in parallel.

My temps quickly got up to 155c when I first started riding with the kit, but have come down to about 130c with normal riding. A combination of improved jetting and breaking in. It seems like a tight kit compared to the Polini I had before.

I also found that my temps would get high pretty quick when staying at 1/4 throttle for extended times. During normal riding, using the main jet more, temps would stay around 260-280F.

Finally I received 55/100 and 48/100 idle jets.

Put in 55/100.

Now jetting is:
AC 120
BE 3
MJ 128
IJ 55/100
Mix 2.5 out

By my feelings it is maybe still too rich but scoot rides good.

I also like temperature. When I cruising on 75-80 km/h it holds on 100-110º C and when on 90 km/h temp is 120-130º C. And when stop on traffic light is quickly go down to 95-100º C.

Changed spark plug to 8 and here how it looking after 60-70 km.

Those are good temps. Sounds like you are close. Good work!

Temps are good but riding on 4000-4700 RPMs not so good.

Yesterday I made good 140 km(87 miles) run on countryside roads and on the highway.

As for me it seems that 55/100 idle jet is richer than needed. There is noticeable jerks and unevenly riding on the 4000-4500(maybe 4700) RPMs. After RPMs is passed 4500-4700 RPMs it have very noticeable power punch and flying really nice, smooth and massive linear accelerating.

I'm also very happy with temperature readings on the highway run.
It was road with slight ups and downs and flat also.
Outboard temp was near 25º C(77º F)

When I holds for a 15 km(9 miles) long:
- 90 kmh(55 mph) temp was 125-133º C(257-271º F)
- 96 kmh(60 mph) temp was very slow raises to 140º C(284º F) and not higher.
- 100 kmh(62 mph) temp was near 146-149º C(295-300º F) and not higher.

Max speed what I reached was 110 kmh(68 mph) but hold it only for few seconds. And it seems that it can give more but I really don't need it for now.
It is 23/68 primary with original P150X gearbox.

Also engine is noticeable quick cool down when I reduced speed or stayed on traffic lights. Maybe you can give some advice? I also have 48/100 idle jet but I remember that you said "Don't use a pilot jet any smaller than 50".
Or maybe it is possible to use 48/100 for daily commuting and change to 55/100 for really long trips?

Here is how 8 spark plug looking. Maybe a very little darker in reality.

Those are still great temps. I'm running similar jetting.

Seems to be going well. Plug is a bit dark, what number is it? Was that after riding slowly?
Which main jet number gave some WOT splutter? I think you said 130. If it was you could go to 125MJ to try to see if the splutter at 4700 clears up. Typically this is in the slide issue area. I guess you're already running a 04. If the main is too big the slide won't cope.
Pretty good overall though.

Thanks Jack. I also think about going 125MJ.
Plug is 8.
It was after mix riding. But last few kms before engine off was not very speedy, maybe 50-60 km/h.
You absolutely correct about 130MJ WOT splutter.
Now 128 is in.
Slide is 04.

If you put a B9 in there it will be pitch black.

"I'd" keep the 128 mj and try a 140 ac (5/8mm drilled filter).
That will reduce the overlap you're experiencing at 3-4 or so k.

Did you play with the mixture screw with that 55/160?
If it's a Spaco, assume it's more like a 58-or-so/160-or-so.

Cruel joke getting played on us with these stamped jet sizes

Thanks for the tip Ray! I will keep it in mind.
With 52/120 I was need to unscrew mix for 5 turns and then it was more or less ok when riding but still not ok with temperature.

I'm running a b9 plug and it's pitch black. Maybe I should try a B8? Also running the #4 slide. Would a flat slide be better?

So I put 125 mj in and ride for 220 km. It was few highway rides for 30-50 km and city riding.

The problem with jerks and unevenly working on 4000-4700 rpms is gone. Now scooter goes really nice and linear.
The temperature is bit higher than with 128 mj but nothing that scares me. Not higher than 143° C. And it was only when I try max speed. It was 114 km/h and it feels that it can do more but I really not need it.

It is 23/68 primary.
Now I'm in doubt if I really need longer primary? I saw some advices here for 23/65. For highway cruising 90-95 km/h is absolutely enough for me.

Here is how spark plug looks with
AC 120
BE 3
125
55/100
Mix 2.5 out.

Sounds like this one is done. Just over 70mph is a good result.

Is there any air filter or vortex? I can't remember. If you have a 7 plug, try that for a similar distance.

Original old Piaggio filter drilled above jets. And Polini carb box cover. I also have SIP T5 air filter but is seems absolutely useless.
I don't have 7 plug on hands. But if it really need to try - i can buy some.
8 plug on photo. But manual for cylinder says 9 plug.

Glad to hear you're making progress. I'm getting closer and will probably end up with similar jetting.

Now weather become more cold esp. in the morning. I noticed that idle become 500-700 rpm higher. So I added half turn out mix screw.

Soon I need to ride near 140 miles on highway.
Is it worth to change spark plug to 9(now 8) and main jet to 128(now 125) ?

Here is how spark plug looking after few hundreds kilometres of mixing style riding - city traffic lights ripping highway cruising.

Looking not bad. I would leave the spark plug at 8. Check to see if it would take a 128 but I expect not. Finally adjust the mixture screw when fully hot at the side of the road.
Seasonal weather out there changes temperature considerably but with the low humidity it sort of evens out. I think you'll get away with it.

Thank you Jack. BTW scoot runs really nice and smooth. I totally pleased with it and I really appreciate your help.

I done my trip and was not happy with temperature readings.

I start with
AC 120
BE 3
125
55/100
Spark plug 8

If I hold 85-90 km/h for a while temperature easy go up to 159º C(318º F) and seems that it can go even higher but I reduce speed to 75-80 km/h and temperature stay under 155º C(311º F) for long steady running.

Then I put in 128 main jet. I still can get to 159º C at 85-90 km/h but it takes noticeably more time.

Next step was 9 spark plug - same story, I can get to 159º C but it takes more time than with 128 main jet and 8 plug.

Is my temperature dangerous high? Or my worries are groundless?
I really don't know what safe temperature for my cylinder.

Is not correct. Looks more like too rich. But might not be. How is WOT feeling? Maybe some sound recording.

WOT and all others modes feeling really nice. I absolutely like how scooter runs.
125 main jet feels better than 128.

It is a problem to record engine sound now.

I forgot to mention that for long highway ride I add 2.5% oil instead of usually 2%.

I've better stay on rich side and know that temperature is safe. But WHAT temperature is safe?

But doesn't adding more oil actually lean the mix out? That's less gas in your mix than with the same amount of air coming in which leans the mix?

There isn't a number that's safe. The cylinder will go up to 500F but that's not important. The piston is the issue. Trying to guess the temperature of the crown, which is changed by many factors.
Normally with a single cylinder bike, air cooled, under 300F is fine. Under 200F is usually too rich. Typically somewhere in-between is the best performance and long service.
Rapid increase in temperature is not good even if still under 300F.

No need for extra oil. This is probably the issue.
Plug looks really black. Put in a 7 and try to get a better colour before deciding it needs a colder plug.

Just for reference, many with threaded CHT's (BGM port) are getting 160-165 max at 90kph. These are guys with egt's, afr's, pistons inspected after many km's...

Like I mentioned, you're not going to get the same readings from a tapped sensor vs under the plug or under a stud nut.
I trashed the threaded sensor on one of my bikes, and put an under-the-plug sensor there. Pretty much 40F or so less max, and much more delayed response.
Been riding with that for 8 months. The numbers just look better to see

Thanks for inputs friends!

I just remember that with DR177 and under plug sensor it shows 145°C max at long trips on 80-85 km/h.
My friend with same have the case when he got seized at 163°C.

Thats why my readings is scaring me.

But, theoretically, I can go up to maybe 170°C without problems?
More speed = more cooling? Right?

Those are exactly the temps I'm getting on the VMC 177 with screw in sensor.

Glad to hear but what exactly temps do you mean?

160-165 @ 90 kph

Great! Now I have hope)

It's actually more like 80-90kph. It seems to only get that high cruising on a flat road at low engine loads when not much throttle is needed. Seems to run cooler when there are some big hills in the mix even though engine loads are higher.

After road trip I get back to 125 main jet and 8 plug.

Here is how plug looks after near 250 km of mixed style riding:

In the shade


In the shade


On the sun(bit darker in reality)

On the sun(bit darker in reality)

Plug is defianate rich. It looks safe to reduce the main jet one more size. Do a WOT plug chop to confirm it's ok.

I have question about primary gear and any advices is highly appreciate.

Weather turns colder and colder. I'm riding only to work and back. Most of time outboard temperature is 7-10º C(42-50º F).
Here is 7 plug after near 200km of short city runs.

AC 120
BE 3
125 mj
55/100 ij
Mix 3.5 turns out

It bit darker in reality.