Modern Vespa

Been buggering with this for awhile now.
I've cleaned and rebuilt everything involving the oil pump and lapped the carb box bottom.
Still leaking.

I've used permatex gasket maker, hondabond and lord knows what else to try and seal the gasket to no avail.

Anyone have any ideas on how to get this to stop? Maybe more sealant? This is driving me batty.

Is the hole next to the drive gear blocked? Should be fully open.

Had a little oil in it, stuck a toothpick in there and it slid down easily though.

Isn't there an o ring underneath the brass insert/bushing?

Just spit-balling here...
Some oil pump motors came with a 3-4mm fiberglass/plastic spacer sandwiched between the airbox and motor. Legend has it that it was to alleviate vapor-lock from heat of the motor causing the carb to boil over. I believe it was a US model thing, due to emissions and leaner jetting leading to hotter running engines. Most, if not all of those were binned, tossed, chucked, etc.

I included a picture (red-circle) that possibly shows evidence marks of the top of the pump drive possibly rubbing, and keeping the airbox from sitting all the way flush with the engine at that area?

Possible things you can try:
1) run two or three airbox gaskets to have the airbox stand higher and a see if the leak persists.
2) locate one of those fiberglass spacers and run it to see if the leak persists.

Again, I am just throwing ideas out there... not sure if it will work, but something relatively easy to try.

That's a good idea. I also have a question about that bushing that locates the carb box to the pump drive. How far should that protrude from the bottom of the carb box? Mine doesn't extend very far. Wondering if that might also be an issue. Although it leaked prior to me rebuilding the oil pump completely and lapping the bottom of the box where I had to remove that bushing and reinstall it, not sure if I may have pushed it back in too deep.

Have you changed carb recently?

It really looks like the leak is around that oil hole.
It was mentioned to try more gaskets. I would give this a try.

Funny (not really), I'm dealing with this same exact problem atm on my P2 engine. I noticed the casing was oily under the carb, and despite degreasing the surfaces in anticipation of opening the engine, they became oily again despite the pump being disconnected from the oil tank. Turns out the remaining oil in the system kept leaking from that same spot.

If both surfaces are straight and the thick green Piaggio paper seal covers the whole sealing area, it shouldn't leak. I suspected the bathtub wasn't straight: it's easy to file metal off while lathing the tub if the sandpaper you're using isn't stuck to the lathe (a plate of marble in my case). Even when wet, the sandpaper can lift if you're not paying attention, and wear the aluminum at the edge as it's pushing the sandpaper back down, creating a slight bevel.

I don't know if it's been successful yet, but I wiped some wd40 on the block side of the mating surfaces, degreased the bathtub side, applied some JB Weld around the hole, and torqued it down (without the paper gasket of course) so the JB Weld would fill the void left by any mismatching between the surfaces. The wd40 serves to keep the JB Weld from sticking to the wrong surface obviously. Hoping it'll fix the issue...

I haven't. I did buy a non auto lube carb and carb box just trying this again since not mixing oil is friggin convenient!

Gonna try this today or tomorrow if I have time. Will report back.
Any idea about that protruding bushing and how far it's supposed to sit proud of the carb box?

Seems fine as it is. It is only used to center the pump around the cog, and if it had been too far out, it would have slid back in place when you pressed down the carb box (or as I referred to it earlier, the bathtub).

Do you see any oil leakage on the inside of the carb box? I had an oil leak from the pump cover not being tight enough. You may have already checked. It's hard to get a leak free seal on the carb box. I always get some down the back of the engine no matter what I do.

.... or simply not being straight. Happened to me lately with a brand new NOS box with autolube. It leaked straight away despite being tight. I checked if the surface was straight by sliding the cover over sandpaper and a plate of marble, and only 3 points around the screw holes turned out shiny.


The cover had been cast but not machined. So I kept on working the cover on the improvised lathe, and once the whole surface was shiny (hence the gaps worn down), it stopped leaking.

Nope, surprisingly dry in the box. And I could live with a little, the problem is it's a lot and seeps into my brake drum causing heinous squeaking and no brakes at all. So not safe to say the least, especially on a bike that does well over 70mph.

I did this with my carb box too. Sandpaper industrial glued to a mirror. Got it all shiny so I know that's at least flat.

Gotchya, I asked because recently I was working on a Rally 200 and the autolube kept leaking. Turned out the carb was not autolube and was therefore blocking the oil passage at the the very end. Pressure would build up and the leak would form.

Yikes, you're talking large volumes apparently. Mine just keeps the area under the carb box shiny.

Alright got it all put back together. Gonna let her sit till tomorrow before I give her the old college try.

Double gaskets, permatex aviation gasket maker on both sides to both gaskets and the bottom of the carb box. Regular old grease under the carb itself. Which had been fine before so fingers crossed that's kosher still.

Did find I cross threaded the fuel banjo bolt. So luckily I have that spare carb and just swapped the float bowl cover and the float needle into the current carb. New carb had a black tipped float needle, so I swapped over the viton tipped one.

Fingers crossed.

Yeah, with the small holes and the narrow canal needed clear to allow the oil to run through, I avoid liquid sealant on those surfaces. The sealant moves to the "free" spaces when it gets squished between the torqued down box and the casing, and those are spaces you don't want to see plugged.

Not a good idea as the gaskets will compress under the fasteners and warp the carb base. Milled mating surfaces should only use the thinnest of gaskets.

+1

Welp, tried the 2 gasket idea. Worse than one gasket.

Seems like the check ball isn't stopping the flow of oil. I reassembled everything and let it sit for a few days. Went to go check and there was a bunch of oil under the bike. Flows down the engine case and drips off the low point.

Going to double check the bushing/spring/check ball set up tomorrow. Engine wasn't run yet the oil is flowing through the carb. Had oil in the back by the mix screw. Flowing out from the oil hose under the carb. If the spring bushing ball set up is installed correctly when I check tomorrow I'm giving up on the auto lube.

I have the plug from scooter center. I have a non injected carb and air box. What else do I gotta remove? The cog behind the clutch? Or can I leave that in?

Sorry to hear it was worse.

I thought the check ball was to prevent reverse flow...?

The pump itself seals the oil from flowing when it isn't turning. It has some seriously tight tolerances on the silver shaft that is attached to the gear going into the pump body. There are also 2 o-rings on the pump body that goes into the carb box that need to seal well so oil does not flow by gravity. Are those o-rings still good? I would check those also.

Hope you get this sorted. Auto-lube makes life so much easier when on the road a lot.

Yes I replaced the o rings when I rebuilt the pump thinking that could be the problem.

I also wish I could get it sorted cause it is so much easier to just fill up with gas and go.

It's not just the ease of use: it's the possibility to get the right amount of oil in each rev range, instead of whatever ratio you mix in the gas all the time.

Something to think about…the 2005 US market PX150 mixer box didn't come with a check ball or spring. I dunno about the rest of the PXs in the world though.

just sayin.

I know there are different versions of the pump. The one on my P200 only uses one o-ring on the pump shaft. And is prone to leaking. As it's not much, I'm leaving it, as it otherwise works. 2 different engines built decades apart with many attempts with designer sealants to stop leaks from the carb/carbox. My solution has been to wipe down the engine every so often. If it wasn't expected to leak, Vespa would never have gone through the expense of adding a fuel tap.

I've given up. It's not just a drip or two a day. Leaves a puddle.

Put the oil plug in, new 24.24 carb, carb box and waiting on the air box lid to arrive today.

Do I need to remove the cog behind the clutch or can that be left in there?

you can leave the cog and use it as your spacer, my p200 ran that way.

Thanks. I'm kosher now then as the lid arrived right after I hit send.

Gonna let the loctite on the plug cure over the weekend and try again to ride on Monday with this one.

Just to cover all my bases,

Is there a change in jetting going from auto to premix?
May be an obviously dumb question but I'd rather ask and have it come back no then seize on the road!

Not that i've found.

Very little, like +2 or so #'s on the MJ.
Premix increases viscosity through the jets.

Whodatschrome said... Not necessarily wanting to be a contrarian here, but my 2005 US market PX150 did. However, that didn't seem to prevent oil from constantly seeping from somewhere in the general area despite all efforts to prevent it.

Difference in jetting is that premix ALWAYS has a main jet that is one size larger.

All 2005 px150 oil injection models had the ball, spring, plastic retainer (in that order), but during cleaning and blasting with air those small pieces get shot across the shop and people don't realize they were even there. Just as I've seen missing needle jets on lx150 Keihin carbs; people need to turn down the compressed air and turn up their attention to detail.