Modern Vespa

Hi folks. Was wondering if any of you have ever experienced this. I've now noticed this a few times on my bike (180ss, with p200 tank). The bike would run okay most of the time, at times feeling a little lethargic. The other week, i knew the tank was a little low, maybe 1/3 of a tank of gas left. I started the bike and switched the lever to Reserve. Right away i noticed the vespa was running quite well, more "lively ". Is this normal? What could be causing this?
Thanks
Fab

Lazy float syndrome.

Also your fuel pressure is already quite low with the bottom of the tank just a little above your carb. Most ppl who have thirsty modified motors do things like drilling out float bowl passage, using a 'fast flow' fuel tap and keeping their tank more often topped up so they don't have this common problem. Some who have bigger side draft carbs which usually sit higher than the stock down draft SIs have added a fuel pump to make sure carb gets all the gas it wants.

Your SS180 would benefit from a stock SS180 tank with more capacity so you could go longer between top ups. Meanwhile just switch to reserve when it wants to slow down and head for a gas station.

Now... how about a few pics of this fussy SS?

Spot on explanation!

Gravel....what is lazy float syndrome??

V oodoo...i changed out my seat and tank for a p200 tank and seat, which is way more comfortable than the 180 seat. The carb itself is all stock, with original float and needle inside.
You got me thinking now...are the 180 tanks different (besides fuel capacity) then a p200? Does it "sit" lower in the frame a p200 tank? 🤔.
I'm just wondering if maybe something got damaged (internally) in the fuel tap?
Btw...when i switched it over to reserve and noticed the performance, the fuel level was above the screen filter part of fuel tap.
Thanks

I think both tanks sit about the same depth? And you could see if a Rally200 seat is comfy for you, it shares the taller tank too.

You might wanna check out your tap for any clogging on the normal 'run' position. You can compare fuel flow between run and reserve position with maybe a half tank of gas. Just time how long it takes to fill a 1 liter bottle in both positions.

If your float has a small leak and is half full of gas, you may have a lazy float and could be your main problem.

Voodoo explained lazy float syndrome perfectly 👌

Other possible causes are the potential blockage as noted.

Or your float needle isn't sealing quite as well as it could. There are a few posts on here detailing how to Polish the needle seat, also a good idea to swap the needle as well when you do this for a new one.

Thanks guys, will be looking into these things. Thanks 😊

Update...
So i did some testing, i filled up a 1L container with gas (with the p200 gas tank). With the tap opened to normal flow, it took about 2 minutes and 20 seconds to fill. With the tap flipped to Reserve, it took about 2 minutes and 10 seconds.
Are these times normal?
I also took measurements (heights) of the p200 tank and the 180ss tank and they are both the same height (from bottom of tank to the top-lip...not including fuel tap in the equation ).
Thanks
Fab

No that's not normal.
You should get at least 500ccm a minute

Change the tap
Fast flow would be ideal
No longer than 24" of fuel pipe

Gravelrash... sorry i'm a bit confused. 1L should take how long to fill up?

500 CCM =.5 L , so 2 minutes for 1 L. No?

Yes...
So
500ml @ 1min 10seconds
And In my case it was double that:
1L @ 2min 20seconds

Is this still too long?
Thanks
Fab

Doubling it doesn't change the rate. That would be 4L in 9min 20 sec. Or , roughly, 1 gallon in 10 minutes. I can't see any way you could use fuel that fast at any speed.

Okay. So is the rate that i got:
1L@ 2min 20 seconds

Is this too slow, in general?
Or is it okay?
Crazy idea...if there might be a blockage somewhere in the fuel tap line...if i drain out the fuel from the tank, remove fuel line at the carb inlet, use an air compressor. If i open the fuel tap and blow in air (going into the tank)...could this help to clean out the lines?
There isn't much gas left in the tank anyway...
Thanks
Fab

I think you are all correct in your observations but tbe flow rate is the measure of whether there is any kind of restriction

The additional weight of fuel when using the reserve, verus the main shows a restriction in the main flow. The reserve has a greater weight of fuel to push the fuel through. Both should have the same flow rate.

I hope I'm making sense here.

You could try the airline to blow it through and it may do the trick. If it were me, I would dissemble the tap first if you are reluctant to replace.

Gravelrash...yes I understand what you are saying. I will see if maybe blowing air into the line might help.
Normally, is it just debris that ends up blocking the line? I did change out the actual fuel line i think, last year. I put the 5/16 fuel line (closest to 8mm).

I'm late to the party, but I gotta jump in here...this is flat-out wrong.

Head height is the difference (in height) between the level of fuel in the tank and the float needle. Whether or not it flows through the standard or reserve intake has nothing to do with it.

See https://en.wikipedia.org/wiki/Pressure_head for more than you probably actually want to know.

Other than that, the discussion has been generally on-point thus far: OP was not seeing expected fuel flow rates, which indicates some sort of blockage in the fuel system. Now it's time to track it down.

I'd start with the fuel tap for a couple reasons. First, it's really easy for crud to build up in the tap. Second, it's the only portion of the fuel system that you can vary (on vs. reserve), which is also how the issue manifests.

My guess is that the "on" side of the tap is partially blocked, because it's the one you mostly use. To fix it, you need to open up the tap, clean out the crud, and ideally replace the rubber gasket at the same time.

This ^^^^

Buy/borrow the wrench. Rebuild the tap. Problem (likely) solved?

https://www.scootermercato.com/Scooter-Parts/Factory-Tools/T-32973
https://www.scootermercato.com/Scooter-Parts/Fuel-Taps-and-Parts/139933
https://www.scootermercato.com/Scooter-Parts/Fuel-Taps-and-Parts/13836

Thanks for the correction Chandlerman. When I'm wrong I'm usually so wide or the mark it's laughable

It's all good.

Head Height (which I really should call Pressure Head, but never do) is a little bit counter-intuitive, since it would seem reasonable that the height of the intake would matter, rather than of the surface.

Regardless, the answer is going to lie within the tap. It also occurs to me that there could also be flashing in either the tap itself or on the gasket which is partially blocking the "on" side and producing the difference. This wouldn't be the first time we've seen that around here, especially on an EBay re-pop part.

Thanks for the info, Chandleman.
I didn't think about fuel level when i did the exercises yesterday. I took a look today and saw that the fuel rests just above the filter screen housing. Could this level affect the results?
In terms of fixing the tap, is it really difficult?
Question...if the fuel tap did NOT have the Reserve option (so just open/close), would that cause less issues in terms of blockage?
Thanks
Fab
Here is a pic of the fuel level i had.

It's should be pretty straightforward, but you MUST have the correct wrench for the job - see the first link that garncarz posted. Once you have the tap out, the problem should be quite apparent.

I did this on my P200E, but the filter screen was so rotten I just replaced the whole tap assembly.

Metadaddy..
If i need to open up the fuel tap (part where the lever attaches to), do i really need to take the fuel tap off the tank? Can i work on the tank with it on?
Thanks fab

Yes you can do some investigation and repair work with the tap in place.

There are usually 2 machine screws that hold the tap assembly together. It's much better to remove the tap though, that way you can remove the filter to see what lurks underneath it

You can do it with the tap on the tank. You're going to remove the two little tiny screws which hold the tap connector on. That will, in turn, cause the whole thing to come apart.

It's not hard to do, but it's easy to get the reassembly wrong. I'd strongly suggest marking and photographing everything so you can tell alignment of all the bits.

And when you put it back together, how tight you make the screws can be a fine balance between "too tight to turn" and "so loose it leaks," so be sure to put some fuel back in the tank and test that before you reinstall it into the cavity.

But…….if the tank side of the tap is the problem (clogged with rust, filter issues, etc.) you aren't going to solve the problem.

Hi gang. Thanks for all your help. I can sense that whatever i decided to do, concerning the tap, i will most likely have to change it out. Even if I decide to work on it, with the tap in place, if i screw up the order of things, I'll probably have to change the tap... arggg...

That is pretty much the long and the short of it

It's really not an onerous task to change the fuel tap. The tap and tool are all reasonably priced items and well worth the effort of changing

FWIW.... I just set up a small tank and ran gas through the needle seat in an SI bowl cap and got 500ML in 2 minutes ten seconds. One liter /four minutes 20 seconds. Through this restriction, that is about half as fast (twice as slow) as your stated rates. I don't see the tap as your problem. Blow some air back through it in the tank if you like.

I could see a situation where the level in the tank is just about at the top of the "run" tube as in your picture and maybe intermittently supplying fuel and how turning it to reserve would take care of that. But just riding around and making the motor run livelier by switching to reserve makes no sense to me. "R" for "Race"?

One thing that bugged me when I did my SS is that the bottom of the tank is just about level with the fuel banjo on the carb. Checked with a laser. The SS/Rally tank is taller but not any deeper.

Moto64.

I might try blowing air back into the tank to see if it dislodges anything?
It seems like you stated, the bottom of the ss tank sits around the bango, isn't that where it should be?
I didn't measure with a laser (I eyeballed with a measuring tape) the height of the p200 tank and it's about the same as the ss tank. Like you said, the ss tank is a little taller on the top side, but same at the bottom. I'm debating weather to try out the ss tank to see if it flows better...

Doesn't the P tank have the oil tank tube through it? Other than that I believe they are the same. Gas flows best downhill but I have never run it low enough on reserve to see. The tanks is only supplying fuel to the tap. Changing tanks won't make any difference.Other than the SS one having more capacity from the oil tube. I guess.

Moto...
No my p200 tank doesn't have the long oil tube, it's just a regular tank, and as you mentioned, same size as the ss tank.

I wouldn't.
Whatever you dislodge won't escape the filter.

Nothing wrong with just riding at reserve

In the off-season install the SIP faster flow.
Not a lot of $ and much better.

You are right about The crud in the filter.

Update...
I proceeded to blow some air up the gas line while switching the lever from off to reserve and back. There were air bubbles coming up from the screen filter (note, the gas level was still the same as before). It seemed that there were more bubbles coming up when it was in Reserve position.
I then added about 4L of fuel to the tank and proceeded to retest the flow. This time it seemed better:
.5L @ 35 seconds flat
Also, when i opened the valve, i could rear some "gargling" sound from inside the tank.
Does this seem better?
Fab

It's better yes

BUT

Whatever you blew out as a blockage will be sat behind the filter and would eventually work it's way back to cause a blockage all over again.

You appear to have proved the blockage was evident in that area at least

I would think the crud would settle on the bottom and clog the reserve port.

Hi guys. Well it's a start. Could it be that whatever was there (if there was), could have been dislodged, broken down, and maybe pass out of the fuel line( if it's now small particles)?
The other thing is maybe the tank had gotten low and didn't have enough force to pass the fuel?