Modern Vespa

Here is a pic of the sip speedo instructions. I have the koso RPM signal reader adapter #KOBA0400 plugged into my speedo box. So i'm assuming
that with my DC system i need to have it at setting "1"?

Mine works fine. I have kept the original Ducati regulator, brown is connected to regulated 12V AC… Seems like it…

Ah so you ended up using the old regulator with the vape and binned the vape regulator?

Yeah that makes more sense.

I couldn't get a proper reading with the vape regulator…

Actually, why isn't everyone doing that?? Save adding the koso sensor and drawing more DC power.

I used a third tachometer today for testing my RPM. I had all three tachs hooked up at the same time. Each of them were within a couple hundred RPM of each other. I'm still reading about 10.4k as a max. I then swapped out my 135 main jet for a 140. It still reved to over 10k (indicated) rpm.


So still don't see 10k as being possible or accurate on this cylinder. Maybe it isn't even possible to have a tach that's compatible with the SIP digital speedo on a DC system? My idle rpm seems accurate though. It reads around 1800 rpm (FYI the idle is currently set kinda high).

I see a couple solutions-
-swap out the JL right exhaust for a standard issue box exhaust (such as a Sito+).

-swap out 24/24G carb for a 24/24E.

-possibly even removing the SIP zero squish head for a stock head.

-swap out the 60mm crank for a 57mm.

-swap back to a static vape CDI.

By doing all of that i'd be 100% confident i would have the timing and jetting dialed in just a few minutes.

Not a lot of online numbers to reference to with a unique sensor!

If your experience is like mine, they can get 100F apart under load
Went backwards at stops.

Btw shame you didn't try the static cdi, at least to compare performance before/after switching it out.
With a threaded cht sensor you can see the cruising temp-creep much faster.
Also see it drop faster at higher rpm.

It'll be fine. Timing is already close to good. Jetting is not quite enough, that's all. Change the AC to 100. I'm guessing after that, you'll need a bigger pilot jet too.
When jetted over rich it won't rev, then adjusting begins.

Not to add to the workload, but do you have a video of it hitting the 10400rpm?

Should be able to tell the difference between 7000rpm and 10000rpm by ear.

I can believe you'd get 10,400 RPM's out of a motor. My BGM's do 10,500-11k and the Smallie just waves at 10k on the way past (doesn't count, I know, but still wanted to mention it)

You can also validate pretty easily with gearing charts and GPS speed. Probably not something you want to try in 4th gear, though

Unfortunately I'm not able to post up videos

I can believe an engine will do +10000rpm, just not a Si carb powered rotary valve engine.

You don't see many hit 8.5k

Is your BGM a rotary engine? You'll have to post a revving video of that!

One of 'em (the one that's in the VBB) is. Extended intake timings make the magic happen.

Mine does 14k

How???

On a rotary valve?? And 95km/h?

JK. Wrong setup on first start with the VAPE…

This is the most I did in the summer…

Scared me man!

The last photo makes me happy.

I can't even imagine. I think the fastest speed I've hit is 57 mph on the Stella. It has a lot more to go, but starts to feel sketchy. Not sure if it's my own fear or the bike itself.

It's not really doing 10,400 rpm. It's just revving on the stand with lean jetting. Because the jetting is lean, riding it WOT in 3rd it will be lucky to make 8000 rpm, then seize up, probably. Lean jetting is always loads of revs and no power. Could just have a massive air leak but I doubt it. Get the jetting nearer and all this gets more as expected.

Yeah I can't see it doing 10,400rpm on the centre stand…

No si carb setup I've seen will do those numbers. Even with reeds, it'll have to be some special setup.

I'm pretty sure my T5 hits 10k. Tacho goes to 99 and then blinks...

Video proof, or it didn't happen… lol

My rotary valve O tuned 200 revs to 9k in gear. And that is jetted in correctly. Don't diss the valve.

A little bit of an update. I removed the JL right pipe and installed a Sito+ that i found on my shelf. I didn't even know i had it. And since i installed the sito i decided to reinstall the Vape static CDI as well. I also found a 24/24E carb (and air filter) on my shelf as well. I took a stab in the dark on what jets to use...

-undrilled 24/24 injected carb
-AC160/BE1/130 MJ
-idle jet 52/140
-Sito+
-Vape static timing. I'm thinking set it @ 22 degrees @ 4k rpm?
-BR8ES plug
-1.6mm cylinder head squish
-60mm crank
-transfers 170/127 degrees


I might even have some time tomorrow to do a test ride?

Don't believe you. Lol

I'm currently trying to jet the carb rich enough so that the engine doesn't rev so high. I swapped some jets around today and installed AC120/BE4/128MJ,
idle 52/140 into the 24/24E carb. The engine will still easily rev above 10k while on the stand. I went for a short ride and the engine pulled pretty hard though the whole rev range.

Perhaps i have a huge air leak? When the scooter is on the stand the engine will rev up to 10k right quick at about 1/2 throttle. Is there a richer set of jets that i should be using?

I installed the koso under the plug temp sensor this afternoon. Perhaps it's because i changed my jetting around, but previous my "threaded in the head" sensor read 410F. The under the plug sensor now reads 270F. I'll definitely have to experiment a lot more with both sensors.

And this is why i have really bright headlights and spot lights on everything i own. I did a short test ride late afternoon and saw a herd of deer about a mile down the hill (from where i live). It's common to see deer during all times of the day or night. It's sketchy as all get out. The one fun thing to do is chase them with the scooter down the county road. Lots of the time they're too dumb to jump off the road, so i'll just chase them for a few hundred meters.

That seems like a huge difference between probes. Don't know if you've tried this but you could test both probes in a little pan with oil over a heat source with a thermometer in it. Candy or instant read thermometer. We all know oil past 245 gets smoky but grape seed oil can get hotter. At least you'll know if both probs read the same on your speedo and it's not a placement issue on the head. Hold up! Forgot to add, if the probes don't read on your speedo run a jumper wire from the probe back to engine ground. All the probes at my work are the grounding type so no jumper needed, I just plop the ends in the oil. Hope this helps. It would be cool to double check the speedo against a known source anyway. Don't know how good the Koso probes are accuracy wise.

[quote="whodatschrome"]
I swapped some jets around today and installed AC120/BE4/128MJ,
...
Perhaps i have a huge air leak?

Who dat - based on my experience - there has to be one of two things going on.
1. You don't have a large enough hole in the float bowl to allow the main jet to be doing its job. The hole is serving as the restriction. I would think you gotta be 2.3mm. Note - more than one person has thought it's drilled out - only to find that there was a void they drilled into - but dint go all the way through. Simple test: take the main stack out, put a drill bit in the float bowl, and make sure you can look down the stack hole and see the drill bit head.
2. Air leak. There was a time when checking air tightness on motors was an option - but I think the community has come to understand - its pass fail. It's either tight enough to be utilized as a blimp - or it leaks down.

In my view - its focused on one of these - confirm them and you are in the clear.

I haven't drill the float bowl out in this particular carb (i did drill out the hole in the 24/24G carb that i was installed on the previous test). Even though it's a 208cc setup, it's not like that it's a performance build (at least i'm not after a performance build). Just a longer stroke crank and a tighter squish. No additional porting has been done to the piston on cylinder.

I will admit that i haven't ever done an air leak test on any of my engine builds...but air leaks after a fresh rebuild hasn't ever been a problem in the past for me. Not saying that i'm flawless though. Looks like i need to gather up whatever materials it takes to build a leak detector tester.

Keep the air leak tester simple.
Million ways to do it.
Some combo of cheapest CVS blood pressure cuff, a rubber stopper from Home Depot for the exhaust, and a part from the old leak down tester you have in your tool kit somewhere on one of those shelves...

I would expect your stack (with a 120 AC) to want to be around a 120-123 MJ max - as long as the carb is drilled - and unwilling to fully rev out with anything 128 or larger.

Since drilling the carb only takes a few minutes - you might start by drilling it out with a 2.2 ish MM bit, and see if that makes you suddenly fat with no other changes. If not - leak tester is probably worth cobbling together.

How about 140/BE3/big mj?
Just to see what it does. 120/BE4 is the T5 combination.
Plus 6-7 mj per plus 20 ac, so 135 "should" be close.

And speaking of deer, doesn't "a deer caught in the headlights" mean they freeze in place?

140 should be the right AC for this build with a mid-120s main.

Float passage might need to be drilled, but not necessarily unless it's stumbling at WOT.

Yes, AC120/BE4 is T5 jetting. So how is the AC140/BE3 different?

One is like a forehead thermometer, and Whodat's is more like the type generally used for infants.
They only time they'll line up is when the engine is cold, or when they cross paths at a stop.

Used to have that happen from time to time at my old place. Not with deer, with kangaroos. Never hit one (so far) but been hit by one!

We have a growing deer population here. Somebody brought them into the country for sport in the 1800's when previously there weren't any, now (surprise) they're becoming a problem.

I'm looking at the blood pressure testers on both scamazon and fleabay. I was kinda hoping to find the version that has the rubber bulb incorperated onto the pressure gauge, but seems like all of those are four times the price as the once that have two air lines that lead to the cuff.

I suppose bulb attached or separate will get it done.
🙂

Regarding jetting, I wouldn't worry about your AC at this point.
Changing to a 140 is only going to worsen the carb restrictive issue.

The critical thing right now is to drill the carb.
Lemme clarify why: (strictly my own experience)

The carbs came from the factory frequently with Maine jets smaller than 100, perhaps up to a 110 or 115.
The passageways in the carbs are not suited to jets in the 140s.

In my experience, those passageways are arguably, not suitable for anything over about 123.

In an undrilled carb, you will get no difference in richness of fuel mixture using aa 130 or a 150. In fact you could put in a 160 an it would not make it any richer.

The carb channels are limiting you.

By drilling, the carb, and getting rid of it as the restriction, it's going to shift your jetting back down.

The smaller AC has a similar effect.
So a 120 AC, will take your main jet down, perhaps 6 to 10 points.

I don't know why you would want to run a 140 main jet in an SI carburetor. Is be concerned anbout other channels, that potentially could be creating restrictions, that you risk having an effect from.

My rule of thumb, is is that if I have to go above 125 with my main jet, I need to go down on my AC size.

Get this and this:
https://www.amazon.com/gp/product/B000RWB03W/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B08SC447W6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

I have a spare blanking plate that goes in the airbox if you want to try it.
IIRC a 1 1/2" bilge plug should fit the exhaust stub.

Thank you for those scamazon links and thank you for the offer, but i had already made a blanking plate this morning out of 1/4" aluminum.

That is certainly a quality plate.
It's gonna need some rubber of course…
I've had some luck just pinching some thin rubber between the carb box and motor.
It's definitely not as elegant.
Also doesn't test for carb box leak - so urs is better.