Modern Vespa

I tried a 140 main jet. Eventually it cleans up at full throttle but otherwise, it's drowning. Please tell me I don't need to go bigger…A video probably explains it better. I tried it in 2nd, then 3rd.

What speed are you getting at WOT in 2nd?
This has the VMC177 on it right? Seems a lot slower than mine, which I assume means you're wildly rich. I'm no expert though. I'm over 40mph in 2nd WOT. On the same setup but a 24.24 carb

I'm hoping it was crazy rich as I was trying to make it splutter at WOT. 2nd gear speeds were similar when I had leaner jetting.

If you or anyone else is not sure what "too rich" sounds or feels like, try running without any main jet. That's it.

Orwell - to SoCal's point, my suspicion is - even if you removed your main jet (assuming it would start) - it would still pretty much clear out at higher revs.

Why?
Well - good find with the semi drilled hole.
It's possible that your 2.3mm is simply not going to give you enough to make that motor sputter.

In other words - its' still your carb that is limiting your WOT flow - rather than your MJ.
At least - that's my suspicion.

Personally - I would go to a 2.5 drill next - rather than trying to go bigger than a 140 jet to hit splutter.
Perhaps run the experiment with no main - and let's see what happens.

Jack/others - any reason for him not to have a 2.5mm hole rather than 2.3mm based on his results so far?

Definitely bring a gps along as a cross-check. Your 187 on 22-68 gearing should be flirting with 45 mph if it's revving all the way out in 2d.

I haven't checked lately, but 2nd is easily in that range and revs out to 9k. I will gps check next time.

CM: I can't find the thread at the moment, but Jack mentioned something about drilling a hole larger than 2.x mm would ruin the carb, so it's something I wanted to double check before making it any larger.

I switched from a BE4 to a BE3 with a 138 main and it spluttered like mad in 2nd and 3rd too…Maybe that's cheating, but splutter it did.

Not cheating at all.
Your video showed you spluttering at the low RPM's.
The change of atomizer has shifted you to where you need to be.

To me - it's more an interesting comment on how much your main can in fact influence your lower RPM - as well as how the atomizer can influence where that fuel is available within your RPM range.

With your splutter found - you can start walking your way down on main...

Can drill as big as you like. However, it only needs to be bigger than 2.0mm. there is usually enough metal to go 2.5mm but if not the carb is junk.

Take the main jet off the stack and ride. This is a fine idea. Could have a float or tank issue. Got to get the flood at wot. If this gets flood, something else is needed.

Or just finger tighten it.

Had an interesting I'm Getting Old event, riding off from my garage downhill with no main jet
It actually rode on flat streets in "I'm going to minimize the walk of shame" mode
Learned a lot from that mistake.

I will try running the stack without the main jet and check the usual things that limit fuel flow.

But I think I'm there now though with finding the too rich jet and can start working down.

I did this exact thing a year or two ago. I was working on multiple things and didn't tighten do the main jet stack. It was spluttering when I got to about 3/4 throttle, and after about a mile 1/3 throttle.

I pulled over and found my bone headed maneuver

Soon after rebuilding my VW bus engine, I adjusted the valves. A few miles down the road, I was surrounded by choking clouds of oil smoke. Then the oil pressure warning light went on. It's the Game Over light. I pulled into a parking lot and there was a puddle of oil under the engine. In a panic, I thought I had blown out an oil gallery plug.

When the smoke cleared, I found that I had pinched the wire for the oil pressure sensor between the valve cover and the cylinder head. It caused enough of a leak to make a mess and grounded out the oil sensor, turning on the idiot light. I have done many bone headed things over the years.

There is an FMP video where he deliberately runs an overly large main and a too lean idle jet. It 4 strokes like mad throughout the throttle range but the revs take forever to come back down at idle. Just shows how the different circuits interact and how it's easy to come to the wrong conclusions.

So far, the best combo has been: AC 120, be3, 125, 52/140.

The 52/140 spluttered somewhat, but pulled nicely. The 50/120 spluttered more, but still pulled great at low revs. I don't think I will go any lower than a 52/140. I don't mind a little splutter at 1/8 throttle as long as it pulls hard.

I will walk down the main until it revs out. It will be different now with the hole drilled out. Thinking I will end up at 125-ish.

Last question: Looking for fuel line that is locally available. The types sold for Vespa shrink like crazy. My fuel line is cobbled together because it shrank which might be adding to the problem. I don't see why normal fuel line can't be used if it's run carefully. I also thought of using metal line with rubber sections where it connects to the tank and carb.

I tried the green fuel line which was garbage and 2 toyox branded wire reinforced line that shrunk 2" in 6 months. Switched to Bridgestone rubber ones and have had zero issues since. No shrinking. I cut mine to 25" to give me 24" between the ends of the banjo's once installed (each banjo is 1/2" long). I have an extra if you'd like it? I got it at AutoZone, they sell them by the foot.

You can (or could, once upon a time) buy that Bridgestone fuel line by the roll on Amazon, too. I bought a 25' roll for like $12 or something crazy like that and it lasted me years.

I have been using the Toyo fuel line for the past couple years and it seems like it's been working well for me. Maybe I just have low standards for my fuel line.

Thanks. I think 5/16th fuel line should work ok.

I tried a 135 main jet which revved out cleanly and went from a 50/120 idle jet to a 52/140. Short ride before it started pouring. I'm a bit surprised that the revved out cleanly, but it did. It splutters at about 1/8 throttle, revs clean as I'm opening the throttle splutters a bit more than clean from about half throttle on.

I feel like it's not that far off.

It did stall out as I started cruising up a hill in third. That's still a mystery. I need to pull the fuel tank anyway to check a 2t leak and get rid of some old wiring so I will change the fuel line and check fuel flow.

Not sure if I should go leaner in the idle jet.

I think you should change out the fuel line - the sleeve is going to slow the fuel delivery.

I worked on a scooter that had a filter, and while the filter was clear, the barbs restricted flow, and I'm thinking that stint you've got in your fuel line is causing flow restriction

Ya know, it shouldn't, but I think it very well might…even if by making the line slightly too long. It was a temporary fix and it's served it's purpose. It might even change the jetting somewhat. It doesn't take much to mess up fuel flow.

Tried to go for a ride last night and took forever to get it to start…flooding. Finally got it started and it idled nicely for awhile, then quit and would not start. Flooded. I quit too, as I was close to kicking the bike onto its side and setting it on fire.

I'm thinking maybe a sticky float/needle valve. It would also explain cutting out while riding, either flooding or starving depending on how it sticks.

There is also electrical…you know the old saying…My LED headlight stopped working, so I threw a halogen bulb back in. It sucks the life out of the battery, so wondering if this is pulling juice from the CDI. I know it runs off a different coil, but it's just a thought.

Jets. I feel like the 135 is way rich even though it passes the WOT splutter test. Guess I really can't judge until I get the fuel delivery sorted out.

Could be a float/needle issue. Could also just be a fouled plug. Swap in a fresh plug and see if that fixes it.

I just dealt with a float needle issue. Paper towel in the carb mouth was soaked by dripping and when I ran it with the air box cover off, it was spitting back like crazy off idle to 1/4 throttle .

Yeah… little puddle on the floor. Fuel on the top of the carb lid.

So long as you don't have the SIP float bowl cover, it's an easy fix. Everyone has the needle and it's about five minutes to swap it..

If you *do* have the SIP float bowl cover, it's just as easy, but only SIP stock the 5.2mm 4x4 needle you'll need to fix it.

Thanks. I came across that info somewhere. It's a new carb, so I am thinking maybe some swarf from drilling the float bowl, even though I blew it out thoroughly with compressed air. I had it running well yesterday.

It's pouring buckets out all weekend. Good time to sort out the tank and fuel system.

Crap weather continues here, so a good time to pull stuff apart to sort out some lingering issues and questions.

Good to get the housekeeping done. Fuel flow should be measured at carb height. At kickstart level it is always better.
Red float needles are preferred.
Hopefully this helps with the jetting.

Have close look at float needle.
Sometimes hard to see the wear- but given some flooding issues - it's suspect in my view.

Looks like it has some compression set to me.

And FMP's tests shown that all that "fast flow" bowl covers with bigger needles is absolutely not needed

Huh….Brand new carb too. Well how 'bout that?

This one falls under the category of: it hadn't had a weird flooding, I wouldn't think twice about it.

Of course, it could be that some swarf got stuck in there… Or it could be that this thing sat on the shelf for a long time upside down? Hard to know. But for six dollars worth of replacement parts, I would be tempted to replace.

Oh, I agree with you. I have spares on hand.

Yeah, I swapped a stock for bowl cover onto the carb and pulled wheelies to the store and back no problem.

So a stock bowl cover would fit? It's a 26/26 carb but other than that, I don't think it's a fast flow super duper anything. I got bowl covers with new floats and needles in them. One I ran for about half a minute.

I think so. I've never run a 26/26, but I pulled one off a 20/20 and it went on the 24/24 perfectly.

Just an FYI, the float top from a 20/20 fits fine on a 26/26. The one I put on has a new needle and float.

Kind of a long detour, but replaced the sight glass and no more leaks. I ended up doing a lot of wiring repairs. Found a number of them that were breaking near the terminals.

One thing I never quite understood was the whole "floating the ground" thing for converting everything to DC. I think the idea is that the ground wire on the stator, battery and regulator all tie in with the common ground…which is a soldered snarl of black wires deep within the tunnel. I extended the ground wire from the front of the bike into the tail light and connected all the grounds there. Will see if things go better.

Hoping to get it all back together soon so I can get back to jetting. Thinking it was getting pretty close.

Do you have a link to this?

Before I switched to the (drilled) BGM faster-flow/Cosa needle I would lean under sustained load when the tank was close to reserve, but only then.

The fuel line in the well is balanced with the fuel line in the bowl. Lean the bike to the left while running (lowering the fuel line in the carb) and see what happens.

Thank you!

That's a stock Cosa cover assembly vs a so-called fast-flow.
The main restriction is the vertical bore to the needle seat.

Like I said, the stock Spaco only seemed to be an issue at very low fuel levels in the tank (at this level of tune, anyway).
But side by side, the flow rate difference between them is a lot.