Modern Vespa

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Drip Tray Victories

PX200 PROBLEM - FLAT SPOT - HELP !!!!!!! (Post 938890)

Let me start by nót doubting the experience of those whom cured a flat spot/hesitation by fitting a lacking one on their scoot.

Imo it was designed as a cover of the access to the cabling. Call it a hatch.
The way it is shaped it is though tony keep an occasional drop from the cables. The slightest bit more will run off when negotiating hills.
Same goes for crap coming in with the intake air.

The air flow from above is totally chaotic, turbulent and the chamber in the frame is like a still air box and particle trap with sóme centrifugal effect aiding gravity.
Any oily residue on the tray will ´trap´ some crap. If missing the residue will be at the bottom and particles will add to the grim there.

A missing lid will enlarge the volume of the air chamber. Since the air tumbling in is chaotic, more volume will most likely only have some stabilising effect on the pressure and as there is no moving air mass column as though the bellows.

Some perspective:
The opening surface of the 24/24 op my P200E is 450 mm2.
The opening surface of the entry hole at the top of its frame is 1350 mm2.
This is the ´bottle neck´ and three times as large as the carb opening.
The entry of the VMC venturi is 1800 mm2, ergo four times the carb.

I can not see it having any issue with intake air flow before the air filter housing.

Perfect Brown was mentioned.
I can't for the life of me, think that a compressor "ergo engine" sucking air at that velocity, any variable of cavitation in passive areas of the bike would make any difference. Thankfully scoots handles are held on with clamps and not nuts. Sarcastically yours,
VV

Phaeton has some good thoughts (brief flooding) in that second thread link at the top, enjoying the reading btw

The tray could be acting as a choke so to speak, in the greater sense.

Can't read second thread since the OP dismisses posts off hand, even though altruistic mechanics spend long hours helping perfect strangers who literally never thank them when solutions are found, making the maxim nobody wants free advice. The first thread is golden, will report back in a few.

Ok then, if I can finish this paragraph before someone chimes in no one will know how many times I edited this darling.
One of these days, in summary the mixture screw is variable for a reason. Be careful of jets, some wizards open them up a bit, instead of ordering a new one, when you could buy original spec jets. Now I don't even want to know what is available after reading that NGK recall and 23 other manufacturers lawsuit junk.
Suffice to say, it seems bees are in on the conspiracy too.

Yes the mixture screw Not done with that one I am afraid Just about sure it causes the pick up hesitation on mine.

I was already unhappy ordering various jet sets ( ) from BGM stead of Dell´Orto.
Did buy Dell´Orto for emulsion and idle as that were only a few.

My wyld imagination laughs thinking of the bitter feuds among neighbors on one side the street who buys a new Vespa every year to support the town factory , and the traditional one who says keeping it in good shape for years is a better way to support the town. Nice dream btw

coincidally I find there is an absolute contrast ánd parallel between NSM and the Nimbus(Touring)Club.
Both are populated by users of vintage bikes.
The NSM excels in practical refurbishing, incorporating modern performance parts.
In the Nimbus world the bikes must be more original than when they left the factory.
Despite this they are amazingly alike and differing from the modern side of this forum.
Both worlds ríde the things to beyond the limits of what realistically can be expected.
Both worlds crammed with wonderfully interesting tales by the owners of the rides.

I'm lost, does the tray/hatch make a difference or not?

I snapped one trying to make it fit so I've never ridden with it.

Scootering magazine did an article on the tray a few years ago. From what I remember they found that the tray really did help with the flat spot. I vaguely remember they had Dyno results backing that up.

I had a very good friend who was a member of the Centaurs in Trieste Italy, in the 30's, Bruno Brunello
When I met him he retired from United, he had an old French bicycle with a little engine. All rod controls, no cables. He wanted so dearly for me to get it running for him, but was afraid he'd hurt himself on it!

would be the end all if that an be turned up and explained no?!
Back issues are available as well.

I for one would be most thankful if you could trace it. I cannot stand open ends like this. I want to UNDERSTÁND

That brings back memories of the trips (from The Netherlands) to the Madonnina dei Centauri de Alessandria.
Went there several times late seventies when it was a (relatively) low key event.
Same thing the early spring ride event from Bormio up the Stelvio. Just opened so no caravans, no cyclists and wáy before the latter was ruined by TopGear fame so no boyracers either.

Both events disappeared soon after. The ´pellegrinaggio´ to the Madonnina has been revived, the Bormio event has not because of TopGear.

There is a certain amount of positive pressure at speed through the tunnel from the opening behind the horncast. The tray would block that.

The small frame has no hole under the seat and, consequently, no tray..

Without changing gears, the flat spot most reasonably would be a lack of compression, it doesn't take a lot power to move the bike and rider down the road, but it takes reserve power to have a zippy-smooth ride. That being said, the lack of a fuel pump, you're bound by compression and gravity.
But this is more indicative of basic diagnostic rules. Motor manuals used to have diagnostic flow charts within, a smart mind would learn from such. If one had never seen one, they can't be blamed.
And adjusting and tuning are so much more difficult in said state.
Anyway
I've got as many stories as Bruno did, some equally as harrowing as his. He would confess to me that he painted a car with a brush and can of paint. While seeing my show work being done and raved about and I think he was more amazed that I didn't judge anyone in their humble place. Just don't insult me unless you want the gates of hell opened.
As I lie in bed with full moon light through my window, knowing you are on the other side of the world having lunch,
Finally, I absolutely have to ask, is that you perched on the scooter sitting so pretty?

Nevvah evvah having looked that well at a small frame you have me confused.
Do those not have the air intake under the seat or not have the cable access opening under the tank?

Edit: that was easily checked by looking at photos So; answered and thanks for the learning experience.

Pointing to the nose opening you make a very valid point as yes there will be a higher pressure at that opening.
It totally varies with the speed (v squared actually) so it would explain it occur at either high or low speed, not equally at all speeds.

Also air does not transfer pressure that well and less still when turbulent. Next the opening in front is very much more reduced than the size of the tray and space under it. Still, it is most definitely a variable.

I thought of it as possibly causing the minute´surge´ when backing slightly off WOT at high revs in 4th and not 3rd but I never paid attention to any drip tray being present or not when I put the tank back in, so it may or may not be be there.
If my son were here I´d ask him to have a look with his bore scope through the top entry so I´d knów. He´ll be back in a month.

Carburettors are nigh magical things working mostly ´automatically´ with air speed variations acting on the venturi where the fuel is added. It also highlights how potentially sensitive its workings are.
Any variables in air pressure will have an effect on it. The (in)famous drilling (or not) of the heart shape in the air filter is an example.
One prime sin in carb tuning is creating differences in more than one variable. Being impatient by nature I am wittingly and unwittingly prone to that

Ahhhhh flow charts @VeloceVulture ...
As you saw in the Andalucia thread, I dug out some old books on two strokes / tuning and they are a common feature in those.

None of my Vespas still had the tray.

If you're getting a surge vs a bog rolling off 4th you're rich there.
The ram air effect riding at speed or into a headwind without the tray introduces a lean, especially with the P series.

Tape over the grille on the horncast. If you feel no difference I'd say the tray is there.

I've read somewhere that the tray gives a stable airspace for the air intake and also that the plastic mesh filter in the under hole seat on the Stella can be restrictive. Both my scooters have them. It sounds reasonable.

Thanks for the feed back,
Good one; taping off.

As to the (very slight) surge, I went MJ one smaller.

While I totally agree that the frontal intake ads an air flow/pressure variable, if it would be the reason for the tray then Piaggio had a simpler solution no?!

https://www.sip-scootershop.com/es/product/frontal-sip-219564-180215-para-vespa-pk50-125-s-ss-automatica_90075000?usrc=cascade

Even though I thínk I have the jetting of my P sorted will still do the tape-off experiment just because curiosity.
Before modding, improving jetting, fitting a different box / filter box, it had neither hesitation nor WOT roll off surge. It simply worked as a standard P200E does. Not leaving well enough alone led to the rest and subsequently my curiosity about the drip tray enigma.

By now I have no doubt that the drip tray was designed as just and only that BUT that absence adds a variable in the carburation at higher speeds.

Still curious about the magazine test article.

I'm sure there is a calculator online that tells you how many CFM that engine consumes negating any ram air

CFM does my head in I am afraid but can in SI do that simple math by head.

Even if assuming 100% efficiency and calculating with 200 cc, at 6k rpm we are talking about 20 litre per second.

For ease of calculation make it 80% for a 125 and it is 10 l/sec.

The weight of air being a bit over 1 kg = 1.000 gr per 1.000 litres.

Ergo 10 gr per second.

Hoping muy head did that correctly.

All resting is to calculate the frontal air pressure at 25 m/s on 10 cm2 (opening minus horn):



and yes the pressure does make for a difference at the nose opening but it is imo negligeable.

I do fantasize little tendrils of air flowing through the holes down inside the frame swirling any debris, or stray vapors along like a mother hen and her chicks following. When they approach that massive vacuum force it terrifies them, thankfully most times there an air filter to prevent them from being crushed and obliterated by the internals of that pump.