Modern Vespa

Hey guys, I have a few questions about a high performance GTS300ie that I built a little while ago.

I run a Vespa Shop down in South Africa, and decided the best advert for people to see what we do, is to build an all out, wild GTS.

I have since built probably my most expensive personal project, (apart from the two BFA's which are for a different discussion) and its just never pulled like it should. Now, I should add, we are no strangers to building fast GTS's, and have built several bikes that reach well over 160kph.

This one though, ever since the build began, just hasnt gone together nicely.

Its sporting a mix of parts I believe should work well, including the Polini power explosion 300 cylinder kit, a Malossi V4 head, a BGM Variator kit, a BGM torque driver rear pulley, a Polini adjustable clutch and bell, and a free flowing S/S exhaust (have tried several different pipes at this stage, all of them feel the same) and a forcemaster 2.

New parts on the engine include a new Stator, new injector, new polini airfilter with famous airbox mod, new lambda sensor, new cooling system incl pump, new oil pump, new timing chain, new piaggio camshaft, new rockers and shafts, and the usual hardware stuff.

In my experience, this bike should be an absolute monster. However, anything over 80kph, and the rpm slowly decreases and it feels like its just tightening up more and more.

Could this be cam timing? Is there a chance I was supplied the wrong Camshaft? Im fairly certain it was a 300 cam when it went in but i cant be certain. Could the new stator be supplying the incorrect ignition timing? The PADS system tells me the timing is correct according to what its aiming for but could a faulty stator be indexing this timing figure incorrectly? It certainly feels like the timing is wrong.

Im at a point where I dont know where else to look so Im hoping someone here has dealt with a similar issue and sorted it out.

Completely forgot to post up a Pic last night when I made the post! Apologies to the Photo God's

You need to put a tach on there to see what the RPMs are?

It sounds as if the variator is shifting gears too soon. Did BGM variator come with 13.5g weights? I would say they are a bit heavy.

You've done my famous airbox mod and it still doesn't perform? Never heard of such a thing!

Love the colour scheme.

No idea about your problem.

PS are you testing on a dyno or on the road/track?

Personally, I wouldn't trust BGM parts for something as important as the CVT. Polini or Malossi, they have R&D centers and they're doing this for decades…

Hey Waspmike,

I do have a SIP speedo on, according to the tach, it runs right up to 6900rpm until about 60kph, then it steadily decreases in RPM. By 120kph its dropped down to about 6100RPM and it just gets worse and worse. after extended time at WOT it the splutters a few times, and that's when I'm tapping off. It feels a hell of a lot like one of my 2 strokes tightening up and siezing.

This is why I'm suspecting ignition timing, as it feels like its running way too hot in the expansion chamber, perhaps too much squish? Comp ratio was approx 11.5:1 which should be fine, ran this combo of head and cylinder previously and it ran really well.

SaFIS, I had a 9 roller Polini on previously, but in my experience these BGM CVT's are a perfect balance between performance and a decent service interval. Imagine a CVT between the Polini 9 roller, and the Polini 6 roller EVO with the GT200 belt, that's what BGM have managed here. This CVT from BGM normally turns any bike into a monster but even it did not make much of a difference here, it just feels like no power is being made. I am pretty happy to almost rule the drivetrain out.

SteelBytes, I am testing on closed road conditions, dont have access to a dyno locally that is set up to deal with a CVTbike of this weight.

Thanks everyone for your continued input, hoping to figure this out

First question to ask in troubleshooting = What has changed.

That's exactly what I can't figure out. The only thing I can think of is that it's a component that was already built into the bike. I bought it as a non runner, so don't know how it ran before hand..

So up to about 60kph all seems normal, although I would expect RPM to be more like 7500, but then when you further accelerate the speed does go up but the RPM's go down.
Is that a correct understanding?

Just an idea. As an approach what you could do is to make a split up between the changes you made to the engine and to the vario.

Leave the engine as it is now but change the vario back to the original off factory one.
See what the scooter then does.
If the engine runs nicely probably the engine is OK and the problem is in the changes you made to the vario. If not the problem is in the engine.

maybe OEM GTS300 cam shaft differences?

^^^ do this

Just an idea. As an approach what you could do is to make a split up between the changes you made to the engine and to the vario.

Leave the engine as it is now but change the vario back to the original off factory one.
See what the scooter then does.
If the engine runs nicely probably the engine is OK and the problem is in the changes you made to the vario. If not the problem is in the engine.
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Yeah you got it. Speed does go up, but it seems strained. Rpm definitely does decrease to more the bike requires torque.

I have tried a stock CVT, and as said earlier a 9 roller Polini cvt too. The performance oriented CVT's definitely help and are better than the stock setup. I am pretty sure the problem is with a different component, but I have had the engine open 3 times now and cant seem to see anything wrong. Cam timing is spot on, and everything appears good according to the Pads system when I plug in the diagnostics.

Gonna check out the cam differences link you sent, perhaps it will tell me something. At this point I dont know what else to do

What did it do with the stock CVT? Did the engine then did proper revving, or was there also that drop in rpm at higher speeds? In the graph below (that I picked from Malossi) the black line is the stock CVT on a 300. The rpm should stabilize at around 7000 from 60 up to 100kph and then increase to 8500 to meet the top speed.
[img][/img]

It did exactly the same thing with all 3 different CVTs which is what made me realise its not drivetrain. Its as though once the cvt starts making the gearing longer the motor just isnt making any power to pull it. Under the 60km/h mark I suspect the gearing is so short that it manages to pull it just fine, but once it starts gearing up the torque requirement is too large for what the motor is making.

This is why I am approaching the Hive-Mind to see if anyone else who builds custom GTS motors has had a similar problem with incompatible parts

-Have you recalibrated the throttle position sensor for the Force master.
-Is the "high" potentiometer cranked up to max (+20%)

EDIT: According to my info when going from 278 to 295cc you need 7% more fuel. Then when going from 2v to 4v you need another 12%. A total of 19.6% more fuel than a 275 2v enguine.

On my Honda I found the top end suffered if the mixture was too rich.

So if you are already wound up to +20% reduce it a bit and go for another ride. Rinse and repeat.

Once you find the sweet spot increase it a gnat's cock.

Did you ever get your ForceMaster to work?

Does the Polini piston provide sufficient clearance for the larger Malossi valves?

No. I found it easy to muck up the performance with it, but couldn't get any seat-of-pants performance improvement. Guess one needs a dyno to set it up properly.

BGM is like Naraku, Pordoi, S23, Prima and all the other "performance" brands that have popped up since Parts Sellers discovered Alibaba, and realized that with the right box and paint, they could mark up their own line of "racing" parts to people who don't race or know much about tuning scooters. It's usually stock or slightly reworked stock components, poorly copied aftermarket parts, or even stock spec aftermarket components painted red and put in a really nice box. Basically a $6 Variator in a box that likely cost more than what's in it.

It sounds like your cam timing might be off by a tooth, or the motor is getting too much air. Sometimes you can be off a tooth if you time it to the advance mark and not the actual cam timing mark. And too much air can cause it to bog at high rpms. You are right in your assessment that the bike should be a beast.
The Forcemaster is surprisingly easy to install and verify that it's working. Have you tried different preloaded maps?

Scooter Centre predates Alibaba.

Hey Waspmike

Yeah, been all over the show with all the settings on the Forcemaster, and still no avail. it sort of runs best without it plugged in which confuses the issue further, which is why I was wondering about ignition timing? As far as I understand, the Forcemaster alters the ignition timing with all three maps, which is what lead me down that road.


Lars, The v4 does fit snugly, but clears. I have run a motor previously with this combo and it was wildly fast and easy to tune

MotoVista,

Is there any chance you can supply a pic with what you mean by the cam timing mark and not the advance mark? I've done the cam timing 3x now, so I'm Pretty certain its not wrong, but were there differing cam pulleys? Obviously I keep timing it to the pulleys 4v marks, but it just hit me that perhaps it has the wrong pulley in it? Are there identifying marks to show the difference between say a 250ie pulley and a 300ie pulley?

Hey Guys,

I just thought of something that may be trivial, but I remember in the engine build, my waterpump/stator cover was damaged and I threw an HPE one on, everything just bolted across and I blanked off the dipstick hole. Is there any evidence to suggest the ignition point is in a different place on these covers?

Could I have retarded my timing this way?!

Man I gonna be bleak if that's the problem 😂

From the manual.... Just a cheap timing light for a car would suffice.