Modern Vespa

After a few years of finally getting the set-up of the BGM 177 Im really pleased with it, but as with most of us I would like to move forward with the next level of tune.

Current Set-Up
BGM 177 -- cases matched to cylinder base, otherwise plug & play
Mazucelli 57 sport crank
Polini box
BGM Fast Flow
23/68 Clutch
Standard 125 gearbox
Pinasco VRX 24 carb
Drilled standard air filter
Jetting:120mj AC120 BE3 52/140-idle Jet

It runs nice now and revs out well.
However I feel like it could pull more on the top end in 4th.
I was thinking of splitting the cases this winter and fitting a 60 BGM crank.
If I split the cases it would also be a possibility to change the gearing and fit a
Mallossi 24-63 primary drive.

By doing this would I see a big improvement in touring performace?
I can currently make 115 -120 KMH or 70-75mph.

Would removing the gate on the ports of the BGM make much of a difference to performance?

Appreciate any thoughts

Cheers

Ha, chasing the dragon. Power corrupts and Vespa power corrupts absolutely!

Sounds like you're on the right track. Can't speak to removing the gates in the BGM, but I have yet to experience any real downside to a longstroke + upgear. Both significantly improved the overall riding experience on my scoots. Don't know if you'll achieve a higher top speed - or necessarily want to, 75mph is pretty damn fast - but the engine won't work as hard and will generally perform better.

If more top end is what you're after you'll probably need to start looking at expansion pipes and a bigger carb.

I got quite a few grey hairs from my adventure of hitting 74.

Truer words were never written. All good advice here.

Having done this a few times...

First off, your gearing is probably in a pretty good place with the 23/64. I wouldn't mess with that.

60mm crank is going to be almost mandatory to go from here because you're going to need to start working on hitting specific port timings. Probably something like 125TD/175ED to be making good power at 8K RPM's. The BGM, in my experience, is hard to keep in power past about 8,500 RPM's--it's a touring cylinder, after all, but 8K should give you 80 MPH with your gearbox.

probably a 2mm base spacer and 1mm head spacer will get you in the ballpark. Squish should be down in the 1.0-1.2mm range unless you can't keep it cool.

Personally, I'd rather shorten 4th and then still have good acceleration at high speeds, but whatever you want to do is fine.

Next...remind me...are you on rotary or or reed intake? If you're on SI reed (i.e. an LML motor), you'll need to get a proper reed block and side draft carb. If you're on rotary, then you're going to need a cut crank and still want to extend the intakes on the cases, too.

As to cutting the gates in the BGM, if you're going to also port the cases, then it has to help. I'd suggest getting some Pinasco 177 spacers and use that as your porting template. They match the BGM after you cut the gates perfectly.

If you're going to be touring, you might want to have a look at your crank's balance factor. I've only done that a couple times, but I do believe it makes a difference in how smooth the motor feels, especially at higher RPM's.

You can still get away with a box on a build like this, but it'll want to be something like a SIP RoadXL or a Malossi Box (though I know not everyone is a fan). The Malossi keeps power a little higher than the RoadXL, but I wouldn't complain about either one of them.

Let us know what you decide. It's a good project and you can run a motor like that for a lot of miles if you build it well.

Yes chasing the dragons....
Yes lowering the revs, is exactly what Im after.
Im in Switzerland where the rules on mods are extremely strict unless you like taking risks and have a big wallet ...LoL. So I need to stick with something unnoticed like my Polini box...

Thanks SoCal..

My gearing is 23/68 at the moment... i was thinking about going to the Malossi 200 primary.

I have a rotary intake.

Im a tuning virgin, so excuse my basic questions
So basically fitting the 60 mm crankshaft I would need to fit a 2mm base & 1mm base gasket and check the squish? No other maching or dremel work would be nescessary?

23/64 straight cut will work. 60mm rotary crank. Dremel out the inlet, wider and longer. Open the cylinder base and match. Raise exhaust port slightly. Base packer around 1.0/1.5mm should get the transfers to about what CM said. SI24 will just about manage. And keep autolube. Polini pipe might struggle with the higher rpm but worth a try.

Would expect high 70s mph. 80 maybe downhill. And able to roll on all the way in 4th gear. If it all goes well.

Thanks Jack
Autolube I removed long ago...unfortunately.

still time to put it back.

I went from SI to PHBH carb on my BGM 187 and the difference was noticeable. However my SI tuning was probably not all it could be.

Thanks Ginch...
When I first moved to Switzerland in the late 90s I was riding around on my PX200 with a beautiful JL exhaust.
I had no idea the trouble I would have gotten into if I was ever stopped by the Police. I would have been in deep, deep trouble.
So anything noticeble is definately a no-go here.
Everything has to look original, even when its not.

I miss the JL Pipe, but here, A PHBH carb would be playing Russian Roulette

Thanks for the feedback though

My rule is any tuning needs to be internal and something that cant be seen.

Right! SI it is then!

Opening the gates on my BGM and case matching the VMC did so close to nothing I'd say nothing vs bolt-on.
Maybe with a long stroke crank it'll be different, idk.

Stock inlet duration is a restriction. There's a BGM template you could use to open it up if you don't want to measure yourself.
Speaking of cranks, the SIP Performance crank is awesome.

Interesting jetting. I've never seen that jetting on a 177. To me it looks like a restriction.

https://www.scooter-center.com/en/milling-template-intake-rotary-valve-bgm-pro-vespa-channel-engines-from-tdc-tdc-vespa-px125-px150-lml-sprint-veloce/p-47527.html

I got the P200 version for my Rally. This version has a different intake geometry vs stock but there are two versions.

https://www.sip-scootershop.com/en/product/long-stroke-crankshaft-sip-performance-for-vespa-125-gtr-2-ts-2-150-sprint-v-2-super-2-p125-150x-px125-150-e-lusso-my-cosa_45216200

Thanks Ray..
Not sure I understand your comment about my jetting being restrictive?

It runs beautifully..

One of the big Lambretta tuners built a moderately tuned motor and did no porting at all, dyno'ed it, then did all the porting work he would normally do and re-dyno'ed it, and the difference was within the margin of error for the dyno.

If it runs beautifully ignore that comment!

On my 177's and 210, a bigger AC and correspondingly bigger MJ (more or less 1:3) always results in more power in 4th. Total guess is more emulsion flow at a given negative pressure in the bore.
At some point, depending on filter/no filter/venturi, 160/150/145 for now, it doesn't seem to affect it as much.

Kevin aka Savage Scooter takes a BGM 187 already with a venturi/big air box from a 130MJ (way too small) to a 177
Huge AC as well.
Confusing.

Good luck on your Winter project!

&t=1260s

Hi Ray.....
I have never heard of a 177 main jet or 190 AC used.
Seems extreme?

All I know is my BGM runs the best its ever run.
Runs cooler at WOT.
Its more enjoyable to ride and I now have no fear of running it hard on trips.
Generally more responsive and a beautiful plug colour also.

Cheers...

Running lean AC jetting gives better Dyno numbers, which is also better for track racing.

I don't know what size AC he put in, but if it was huge then it would be leaner, right? Then he'd need a really big MJ to counter the big AC. Think that's how it would work.

Yes it seems from the video he used a huge rich MJ with a lean high numbered AC.
Or in my case with Jacks kind advice, a lower numbered MJ with a lower numbered AC (rich)...

Often the lean AC is 185 or 190. These are not necessarily going to immediately seize up an engine but even when set up well, because of their lean nature, increase cylinder wear.

There are a few stolen screenshots on the GSF of his "secret recipes."
160-170mj/185 AC. Vesptec venturi and airbox cover.
And sorry, 177 was a typo. 170, from 165 (lean) on the 1st try.

Yeah that's super extreme

You and I are lucky and unlucky.
Lucky, in that the BGM is pretty damn bulletproof. One of the engineers rode 10k km with a 118/BE3/160 before it was released, just to see.

It's relatively rare to see an "I seized my BGM" post.
And in every post I've seen something else in addition to lean jetting contributed to it, like fuel flow restriction, air leak, un-drilled float bowl passage, incorrect ignition advance.

Unlucky, in that this CHT port gives #'s unlike what others with under the plug sensors consider "safe." This sensor's readings are VERY different.
Highly suspect we're dumbing down these kits too much.

What's your max CHT now?
I'm at 325F. The Lemarxon X234 atomizer dropped it 40F with no other changes.

*Don't widen the inlet. Too risky.

Thanks Ray
"Whats your max temp?" Is very difficult to answer 😂

When Im crusing at 60 on a rural country road it will show around 300 Fahrenheit. 350 when im pushing it.
I set the rev counter to turn an led red light when it reaches 350.
But unti I seize it I cant judge the max temp...🤣

You're not alone with this problem.

@ Jack...
Whats your experience & theory on Temps...
In your experience how do you judge when things are getting to hot 🔥

300F is operating temperature with this sensor, maybe 220F(?) under the plug.
Rode for a bit with both just to see. Really frustrating experience.
The readings are not parallel between the two, and under-plug CHT comparisons should be disregarded.

I rode quite a while stuck on the hwy with a head leak at 420+ a few years ago.
Pulled the cylinder, nothing. There are a few similar experience posts on the GSF.

Pre-2021 pistons are different vs the newer version.
They piston slap up until 300F or so.

CHT - when do you get nervous? (Post 2755624)

All depends what it is. If you stop at a light after a fast run and can smell the engine, see smoke coming not from where it should and hear the cylinder fins clicking; this is definitely too hot.