Modern Vespa

I've searched the forums and haven't found anything quite as specific as my issue, so figured I'd post to get input.

Recently got my first Vespa ('84 PX200e). Has run really well during my learning curve in flat parking lots and during MST Course. Starts easy and plenty of power. When I started commuting to work in my hilly neighborhood, I noticed that on uphill climbs, the power sort of dips and surges, almost as if I'm pumping the brakes. When it's happened, the scoot never stalls, and after I pull over, it seems to return to normal pretty quickly to get me going again. At first, I thought I shifted into 4th too early, but the next day, I stayed in 3rd and it happened again.

After looking at the forums and talking to a mechanic friend of mine, I think my strategy will be to replace the plug then clean and service the carb (new float/needle/gaskets, clean jets). It seems that perhaps the fuel is getting inconsistent on an angle? My mechanic friend thinks that the throttle being open more on these climbs might be flooding the engine.

There is a small drip of fuel when the petcock is open, but stops when closed, so I'm not sure if that factors in or not. I usually cut the fuel and let the scoot run until it stalls to reduce the spills and gas smell in my garage.

Any ideas that I may have missed? No mods on the engine from what previous owner told me, or that I can observe.

Appreciate any info to be shared!

By small drip of fuel, where is it coming from? Also, try taking the fuel line off the carb and opening the petcock into a gas can to see if it flows at an acceptable rate.

Sounds like a potential fueling issue.

Check tank venting.
Verify strong flow from the petcock.
Remove and clean the carb. Particularly the float bowl, float needle, main jet and passages.
Verify the carburetor's float/needle operation.
Verify the main jet and carburetor settings.
Is the exhaust plugged?

@gummy879: Drip seems to be coming from the banjo, as the packing and gaskets didn't look too great when I examined the carb. Drip is landing just under the carb in front of the axle, so makes sense.

garncarz, definitely my plan as soon as the parts get in. I cleaned all the vent holes pretty good the other day, and this morning seemed to ride better, but I plan on giving the carb a good cleaning, replacing the float and needle for sure.

Thanks for the input!

Lots and lots of tiny passages in these carburetors. Blow everything out with compressed air. A small ultrasonic cleaner is your friend too.

Ok, I got a new BR6ES plug, and when I pulled the original plug, it was a BR7ES, tip was ashy and white, lean mixture. After reading a few old threads, it seems that the general consensus is to stick with the 7 or even go to an 8.

I may try the BR6ES for a ride and see what the plug looks like, but I'm hoping that after I clean the carb this weekend that the mixture might balance out. I primarily ride around town, shorter trips, so from what I've read, the 6 should be ok, but open to more experienced suggestions.

I took your advice and ordered an ultrasonic cleaner to help get things sorted out. Thanks!

Here's a pic of the current plug

Holy cow that's lean. Is that bits of aluminum on the top of the ceramic?

What jets are in there currently?

Best I can tell with my old eyes is 118

Old plug gap was only .03 as well; not sure if this makes much a difference. I've gapped the new plug to .06

That's what it looks like to me! Super lean! Time for an air leak test! If a borescope is available, remove the spark plug and see what the top of the piston looks like.


Hec

All the jets. What are all of them currently?

Ah... only one I pulled last night was the main jet. I'll pull the rest tonight and see.

Previous owner gave me a random bag of bits and parts; had what looked like a set of old idle and main jet, and as much as I tried, could not read any numbers on them.

FWIW:

I got a closer look last night when the fuel was turned on and found that the gas was coming out of the hole in the back of the airbox where you adjust fuel mixture. Somehow pooling there and dripping out. Ugh..
I'm cleaning and rebuilding everything this weekend, so hopefully new gaskets, float and needle will help with that.

Leaking from the float bowl cover or banjo/hose connection.
Take the cover off and open the fuel lever before removing the carb to see.

Needle leak will go into the engine.

Do you know its history, like when it was last rebuilt?

I pulled, cleaned and rebuilt the carburetor tonight, new gaskets, air box seal, etc. and found that the banjo was definitely the culprit, and I found what looked like a lump of cotton or paper towel at the entrance to float bowl. (See pics). I think I found my fuel starvation issue…

All I need to do now is readjust the idle screw and pilot mix screw, then test ride tomorrow

Hopefully final update:
Cleaned and rebuilt carb working great, power dip and fuel leak issues gone. She's riding great!

Hi Ray

I read your reply with interest.

I am currently running a stella/vmc177 with a 24G carb while I rebuild my PX200 engine.

It has always leaked out the back of the airbox and made a mess on the back of the engine.

I always attributed this to a leaking needle valve but after reading your post it would seem my assumption was incorrect and I should be looking at banjo/Carb top hat.

Can you help clarify my thinking/process.

Cheers

Grimmripper

No real history. Previous owner said it was running great, and was maintained by Mossimo's Vespa Shop. He had some service records, but it was mostly cable lube, bearing replacement, and some new tires.

Was definitely leaking from the banjo, as the gaskets had deteriorated and flaked off, which led to clogging the banjo inlet.

It's simple to check.
Excessive blowback (or riding without a filter) will also do what you describe.

This is rotary, but I imagine tired reeds would do the same.
Also simple to check:

Massimo is very well known around here!

Sounds like front end work.
Engine bearing replacement would be a full rebuild. A damaged banjo seal would for sure have been replaced.

The saga continues... ugh...

Last weekend, after rebuilding the carb and installing new plug, scooter ran great. Took her on two longer rides (roughly 10-13 miles total) at varying speeds up to 50mph and it felt very strong, idle was steady, etc.

Two days ago, I had some time off work and decided to go for another ride, same route, speeds and conditions. About 20min into ride, I started feeling weird pulses in the power, then throttle seemed to get strange and scooter started to stall out, power loss. I backed off the throttle and it acted like it was coming back, but as soon as throttle started to open again, same power loss and stalling.

I was able to pull over and took a look at carb, no drips or leaks evident. Had plenty of gas in the tank. I leaned out the mixture a tiny bit, as when I pulled the plug, it looked a darker brown/black than after the last rides where I had a nice milk chocolate color. I started it back up and it ran normal for about 30 seconds. Throttle just seemed to be stalling the engine somehow, and I could maintain super slow speed if I stayed in 2nd with minimal throttle, but couldn't get enough power to climb an incline. If I was I was stopped with clutch in, idle seemed ok. It was very odd, so I ended up calling a tow truck to be safe.

I've found a local mechanic that was recommended by a local, but I'd love to hear ideas here as well. Hoping it's something I can do on my own!

Now I'm perplexed... and hoping I don't have a blown engine or something terrible. I'm planning on replacing the fuel tap and fuel line, checking oil pump for function, but I'm open to ideas of what to check next.

Change all filters with original ones.

Whenever it's weird, it's likely to be a crankshaft oil seal leak. Sudden loss of power is common. They come and go until they are gone.

Clean out your carb? Could have something in a channel or a jet.

I'd check that before splitting the cases to change a seal anyways. Easy enough to do to make sure also. Then that's at least ruled out if there's no change.

Decided to pull the head and just inspect piston head and top of cylinder. See pics, but didn't seem odd to my limited knowledge. Cylinder wall was smooth, no evidence of vertical scoring, coated in thin film of oil.

Spark plug is darker brown and wet looking.

Also discovered that the air tube from frame to carb was disconnected at frame side, just sorta sitting there, so fixed that

Looks like 'Oil Sucker' issue. How's the gearbox oil??

I changed it the day I got it. Anything specific I should be looking for?

Nevermind.. looked up the oil sucker issue. Seems to be what I'm dealing with for sure. I have an appointment with Massimo's Vespa Shop next weekend as this issue may be beyond my current skill and shop ability. Appreciate the info!

I guarantee it's not beyond your current skills. I'm an idiot can do it! But really it all just seems harder or more daunting that it actually is. Just grab a torque wrench and you'll be fine.

My 79 P150X is doing the same thing. Losing power up a hill. It seems like it's not getting enough fuel since this also happens during high speed WOT situations. This scooter sat for 10+ yrs and I'm still getting it sorted out. I'm thinking of cleaning out the tank, new fuel lines (easy job?) petcock rebuild and clean the carb. If that doesn't work I'll take it to Slabtown motors in Portland and do a 177 kit, new carb and exhaust.

It doesn't leak while running. It leaks down the back of motor out the back of the airbox if I forget to close the fuel tap overnight.

Got it.
Take off the airbox cover, turn on the fuel lever, and take a look.
Small leak between those I mentioned above.

Needle leak will flood the bike and not start without a lot of work.