Modern Vespa

So it turns out all of my jetting woes from the last 4 years come from a case airleak at the top of the reed block area... The case gasket was cut too short and I did not use any sealant so air was sucking in after the reeds. Somehow I never had any erratic idle or any symptoms other than my temps marching up when cruising at 50+mph.

I re-sealed the case with Hondabond and it held 5.0psi for ~8 minutes without the gauge needle moving a fraction. Thought everything was good so I took it to this year's Snakes rally in Nashville and it rode great. However, on the way home one day I decided to try a top speed run; I held it WOT in 4th for about 30 seconds and my CHT jumped from ~300F to 365F before I let off and pulled the choke to cool everything down. When I listened back on my helmet cam I could hear it pinging as well.

Here is my setup for anyone unfamiliar:
LML case, no porting
57mm Mazzu economy rotary valve crank
BGM 177 kit at ~0.88mm squish, no head spacer with thicker base for raised port timings, no extra porting
MRP 30mm intake + SIP DSRC28 (PHBH clone)
SIP Performance 1.0 expansion chamber (stamped JL)
23/64 primary with short 4th
SIP fast flow tap
Stock LML ignition, 18deg BTDC at ~4000rpm+ as per the BGM spec sheet

55 pilot
AV264 atomizer
X2 needle on 2nd clip from top
138 main
5.2mm 350 float needle seat with hexagonal float needle

I am going to try a 145 main next, and if it still fuel starves I am going to set up a fuel pump. Narrowed down my picks to either a Dellorto vacuum pump with the internal bypass regulator (part #D11023), or a Facet Posi-flow 12v 1.5-4psi electric pump, although I am leaning towards the vacuum one. My plan is to tap into the intake manifold elbow for vacuum, between the carb and reed block.

I have heard that I may need to select a different float needle seat size for use with a fuel pump, but that may be more relevant for non-regulated pumps.

Thoughts? Feel free to pick apart any aspect of my thought process as I am still learning!

Fuel starvation with a non modified 177 kit seems weird.
I would check the gas flow from the tap, making sure it is ok, check that the fuel hose has the right length and is not kinked. The vent into the gas cap is free ?

My fuel line is the metal coiled type from scootermercato, it is slightly below 2 feet long as they should be. My fuel flow into a bottle with the cap on is excellent, about 1L per minute. But sidedraft carbs sit higher than SI carbs and the fuel "pressure" is lower as a result.

I put a 142 main in, will test tomorrow to see if it is really fuel starvation or my setup just having an abnormally high fuel demand.

If you remove the main jet and it all becomes more obvious where the fuel issues are.
A 142 main jet is not big for this. Its not even near the 30mm carb's limit!

How full was the gas tank when this happened? The scoot sounded good in Nashville, but as you know, the side draft carbs sit higher than SI's, which means you lose head pressure. I have to run a pump on my GL because the gas won't flow into the carb at much less than 1/2 tank.

Try reproducing with a full tank of gas and see if the problem is any better. If so, you need a pump.

And while .88mm is technically within the spec for the BGM177, a .25mm head spacer will help reduce your temps and detonation.

I'm also in the process of setting up a PHBH and also wondered about fuel starvation.

Doing a road test without the main jet is a great idea. It can be ridden pretty normally without a main jet up to 1/2-3/4 throttle….then it totally bogs like an off switch was suddenly flipped. The pilot and the needle are responsible for a lot more of the throttle range than on an Si carb.

I know it is nowhere near the carb's limit, but a 142-145 main seems large for my basic setup pushing "only" 17-19whp. My cylinder is still plug and play, no case porting and I left the gates in on the cylinder ports. Following Scooter Factory's PHBH setup videos on youtube, he listed off a bunch of setups they tuned and all but the most racey tunes were using ~125-138 mains. Whether that's worth anything, I'm not sure. I will try with no main jet tomorrow. I had just filled up and the tank was about 80% full on that run. I did a test today with a 145 main and the same symptoms occurred.

I only have the 0.5mm head spacer included in the kit; and I ran that with the thinnest included base gasket and was stuck with a ~1.15mm squish. I later learned that the head spacer is only intended for a 60mm crank to get the port timings back down, and that on a 57mm setup you should use no head spacer to get their advertised port timings. I didn't know this originally and was a little disappointed at the performance of this kit vs my old Super G; little did I know

Anyway, I may throw a thicker base gasket in to get the squish closer to ~1.0-1.1 just to keep things a little milder.

With gravity feed, air trapped in the fuel line is very bad. With the phbh the curve in the line can be an issue. Every time you refit the carb, do it with the fuel on and hold it low first to let the air out.

With a stock bgm, 130 MJ is probably plenty. You're right to be suspicious.

I would go as high on the base as gives 0.8mm squish. This is in the bgm spec as far as I know. Exhaust port is on the low side on these, so port timing of less concern.

I suffered for years with seizes, pinking, fuel starvation etc with a PHBH28 & it appeared to come down to low fuel levels in the float bowl, mainly due to the carb (bowl & needle/seat) being higher than original SI carb.

In the end I had a vacuum pump fitted & fuel problems went away.
This week i rode at WOT for a few hours, with the MAX temp being 265f & TOP temp over about 6-7000km in past year or so has been 305f.

Re JETTING: well, i used to use a 132-145 pre-pump & i had been using a hand drilled jet, so, no idea what size it is.
Recently, I tried a 125 & decided it was a bit rich, so went 122, then (as I had left some of my jets behind) I threw in a 115... it went well & no heat issues... so I left it in... now I've thrashed Speedy for about 2000km in the past week & haven't got over 301f, with most runs around the 260f mark.... now in going to give a 112 a crack!

Any ethanol in that fuel? Little bit of a coincidence.

And yes, you can drop the float needle size to 150 or so.

Yes, E0 is very expensive around me and I ride often enough for ethanol related fuel system issues to not creep in. I use 93 octane E10.

I have settled on this Dellorto vacuum pump with an internal bypass circuit: https://www.accelerationkarting.com/product/dellorto-fuel-pump/

What is the thought process behind lowering my float needle size? Especially with a pump like this designed to not overpower the needle?

I think that with a smaller float needle fitted and the same floats, there is less likeliehood of the pump overcoming the needle. Pretty sure chandlerman fitted one of these "self-regulating" pumps, but I'm not sure how that turned out for him. Really you need absolutely minimal pressure increase so as not to interfere with your jetting.
Of course it costs you nothing to try your existing float needle. If it's being overcome, in my experience you will notice it first by flooding after coming to a stop following a fast run.

That's the exact pump I've run for years to overcome fuel supply issues on my PWK. The self-regulation works great. Other than the hose barbs being nylon instead of metal, making them relatively fragile over time, there's nothing else I'd recommend.

Thanks for all the help and input! I ended up purchasing a Facet Posi-Flo 12v 1-2psi pump (7gal/h max, 4gal/h @ 0.75psi average) since I always plan to have a charging system and got a little scared by some of the threads here going over return lines, adding flow restrictors to change the pressure etc. Just looked complicated for me, and even though the Dellorto pump does not need any of that, I like the idea of an inline plug-and-play solution that doesn't involve tapping a vacuum port. It also wont need manual priming if I run things dry.

Going to try it with the 350 float needle first but I am prepared to get a 200 from casalambretta if needed. Fingers crossed!

How are you setting that up? Are you fitting it in line to the carb, and are you going to be running it all the time?

I was planning on cutting halfway down my 24in fuel line, and either wiring it to ignition power or putting a switch on my oil sightglass port plug. Should be fine to run it all the time, right?

Maybe? Haven't tried that pump previously, hopefully it's the type that automatically turns off when the float is closed. If not you can always add a bypass loop.

From the product's descriptions it seems like it turns off based on backpressure, but should automatically turn back on when needed? If I make a bypass loop will I be tuning its restriction with inserts and all that?

EDIT: I misremembered, it claims to have a "built-in pressure relief, to prevent flooding after shutting down a hot engine". But one of the reviews states they used it on a garden tractor and claims it works great but floods while idling, implying that it is overcoming the float needle, so it might not have an auto shutoff? If I have flooding issues I will just downsize my float needle though.

I guess you'll find out soon enough, idling is the danger area. In the meantime here is the "complicated" setup you were worried about. You can put this into the line if the pump causes flooding.

The bypass line allows excess pressure and flow back into the section of hose before the pump, if the needle and seat are closed.
The large restrictor (top from a spark plug) limits pressure build up because it allows most of the flow... if you used a main jet (as used to be recommended) then the small restriction would limit flow more and raise the pressure seen at the needle and seat.

I'll just mention again that the dellorto pump really does self-regulate.

I have taken one apart and it does have a simple (spring-loaded ball bearing) regulator.

I've tried the dellorto pump with a by-pass line, with and without a restrictor and had varied results, none perfect. Maybe others have faired better.

I am running the same pump now on one of my current engines, with a vacuum line tapped into the reed block below the petals and a fuel return line to the top of a long range tank instead of a by-pass line. Also have reduced the float jet to 1.7mm (PHBH28). This has now been tested over a few thousand miles and works great. Very happy with it and now have a 120 mile tank range on a PX with a happily fuelled 35hp motor.

Sounds great!

Trying to work out how your system operates... Where does the pump sit in relation to the carb, does it tee into the carb on it's way back to the tank? And when the tank is low (below carb), does the pump create pressure or just rely on the head of pressure in the fuel line going back up into the tank?

What kit are you running on that? Is the tank one of David Hampson's?

Trying to work out how your system operates...

Where does the pump sit in relation to the carb, - its on top of the motor. Just above the height of the carb top. You can see it in the images.

Does it tee into the carb on it's way back to the tank? - yes. Well its a 'Y' connector but much same thing.

And when the tank is low (below carb), does the pump create pressure or just rely on the head of pressure in the fuel line going back up into the tank? - not sure exactly what you mean here. The pump creates enough pressure to pull the fuel from the bottom of the tank up to the pump and beyond. There is no lack of pressure ever, even when the tank is low the return line gushes into the tank like a custom little waterfall.

What kit are you running on that? - Quattrini 244.

Is the tank one of David Hampson's? - the tank is one of Dave's yes. The pump and bracket I sourced separately.

Cheers Dunf. That makes sense. Interesting to see alternative arrangements.

Did you dent your frame to allow the carb to sit more upright? I have mine installed at a slight angle with no frame dent.

Well its not quite a 'dent' lol. It was cut out and a reverse insert welded in place! But you're entirely correct - it was done to allow the carb extra clearance under suspension travel without having to compromise the angle. I carry a lot of rally luggage and spares. However it wasn't done specifically for this engine. Its a 1999 PX200 i've owned since new and its now on its 4th engine incarnation. The frame indent was cut and welded right at the start of that journey - 26 years ago.

Got everything hooked up and went for my first test ride today.
55 pilot 1 turn out, AV264 + X2 needle on 1.5 clip, 135 main, 350 float seat

At idle it is flooding the bowl so I definitely need to either reduce the float size or do a bypass line. Gonna try a 200 first.

The float needle is spring loaded, should I look for a solid one?

Once I fitted the pump , I had issues with bowl overflowing.
Return line fixed that & it was amazing to see just how much excess fuel there was

I ended up ordering a 150 float seat with the 4.5mm solid float needle. For PHBHs there are 150-225 float seats for the 4.5mm solid needle, and 200-400 seats for the 5.2mm spring loaded one. I ordered it from SIP through Scootermercato, but they have not charged me for the order yet so I expect it will be a couple of weeks before I see it.

I want to see if I can fix the flooding in the way that Dellorto intended; by using the smaller float needles + seats to restrict flow. My pump maxes out at 2.0PSI so I think this would work.

If it comes down to it, I can run a return line (but I would need to use 5/16" line unless someone makes a 5/16" to 5/16" and 1/4" T fitting) if I wanted to use the threaded spark plug nut as an inline restrictor. That being said, I have a huge collection of PHBH main jets including 155+ so I might be able to fit one of those in. I also have <70 size mains that I could drill out since I don't expect to ever need them otherwise.

150 float fixed the flooding but when I stop at a light sometimes the idle stays low for about 20 seconds before raising back to normal. The throttle response is still snappy right off idle though; so maybe the bowl is just overfilling slightly during decel? But other than that I don't think I need to run the return line for now. Definitely going to pick up a spring loaded needle though.

I have encountered another issue though; the pump seems to be drawing too much current for the charging system to keep up. While riding even at 55-60mph for extended periods the battery seems to drop about 1v every 45 minutes. I noticed when after a longer test ride my turn signals were malfunctioning, so I pulled back home and read 8.4v at the battery!

Multimeter shows that the pump draw fluctuates between 1.7A-2A; roughly 21-24w. To offset this I replaced my tail and brake light bulbs with LEDs but the charging system still can't keep up. Worst case scenario is idling at a light with my brake on + turn signals, so I can switch to LED turn signals to help there but the pump will always be drawing about 24w.

I have been eyeing a VAPE ignition but I am a little disappointed that my hand might be forced to it. Are there any other ways I can maximize the 95w the LML stator is purported to output, as per the service manual?

You could try checking the flow without the pump turned on, if it keeps flowing then you have the option to only run it when the tank is low. Or find a timer circuit that can cycle it on and off to (hopefully) halve the consumption. Not much of a fix tbh.

This pump is made in NZ and the company told me it consumes 0.8 - 1 amps, so half of what you use now.
https://fuelflow2020.nz/?page_id=163

Vacuum is still an option and cheaper than a Vape.

After some research last night I'm going to see if i can convert to a full sine wave rectifier without doing a full DC conversion just yet. My Stella has the blue/black wire stator. Either going to use a generic China scoot full sine rectifier alongside the stock AC regulator or splurge on the Trailtech one or a Shindengen r/r, unless there are other options I should know about.

When I get a VAPE ignition I'll get a DC variable timing one and do a full DC conversion then.

DC won't help with the pump though?

Going from the stock half wave rectifier to a full wave one will double the charging output which should be plenty to sustain the pump.

I still don't understand why you didn't just install the self-regulating dellorto impulse pump and be done.

Interesting! So are you saying they have a 95 watt stator but the regulator only puts out 45-50?

Sunk (time) cost fallacy I guess. That and I don't want to tap my case or intake for a vacuum port for some reason, just a weird hangup my neurodivergent brain has decided to develop. I only have the 12v pump right now too, so I would have to buy the Dellorto pump separately if I wanted to go that route. If my current plan works out, itll cost $10-15 for a r/r and materials+tools I already have.

And i am using this as an excuse to learn electrical systems and get some soldering experience that I've been meaning to teach myself for years now. I kind of enjoy the problem solving process that bike modding gives me because it forces me to learn and expand my repertoire. Until now I've had a kindergartener's level of electrical knowledge, and just from this last week I've learned a lot of the basic concepts, and how to use multimeters for stuff outside of measuring battery voltage.

I can respect that. I've certainly done my share of roundabout problem solving because I wanted to learn something.

Yes. Stops at 45w pretty much exactly according to my friend who did a current draw test on his last night, using variable load generators. Half wave rectification basically just chops the bottom half of the AC voltage waveform, while full wave flips the bottom half.

So is this just for any DC output? Is the stator actually capable of putting out 95 watts in total - AC and DC together?