Modern Vespa

My US 2005 PX150 has been running great since I got the jetting dialed in. However, yesterday when I tried to start it, it ran rather poorly. It would not idle, it would bog off of throttle, and I had considerable four stroking while cruising at around 35 mph. It was difficult to keep it idling at a stop. So I removed the float bowl cover assembly to check out the needle, etc. Below is a photo of what I found in the upper chamber of the float bowl assembly. There was a considerable amount of sandy-like crud in that chamber. Some of it also passed the little filter and got into the float bowl. I will replace this assembly shortly. The fuel I use is a 93 octane 10% ethanol gasoline. I did add the Star Tron additive at each fill up.The bike sat for 15 years with 368 miles on it before I got it. I have put 4000 miles on it before I checked the float bowl assembly.

I would like to know what caused this crud and where it came from. Was it the long storage, the ethanol fuel, the additive I used, or perhaps the lining in the fuel tank? If anyone has a good explanation, I would appreciate hearing from you.

This happened to mine 20 years ago, when I was living in New Mexico. That crud looks just like sand; the scooter started to run intermittently and very badly shortly after filling the tank.
I called the gas station where I filled up to make a complaint; the manager offered to have the scooter worked on at their expense at a motorcycle shop.

I did not trust any of the local Japanese or Harley shops to work on it, so I fixed it myself. I drained and cleaned the tank, replaced the fuel tap and cleaned and rebuilt the carb. I filtered the drained gasoline through a fine cloth and it sure looked like sand from the desert, but used it later in the lawn mower without further issues.

I decided to pull the tank and check out the fuel and oil lines. The US 2005 PX150 is 14 years old with only 4000 miles on it. What I found was a terrible fuel line with a large crack in it. The line was somewhat pliable but really in bad shape. Even the spring clamp at the tap had slide down the fuel line. I will replace this fuel line with a new OEM fuel line from Piaggio. The oil line seemed okay but will be replaced as well.

Looking into the fuel tank, I can see some sediment. There appears to be no rust. Perhaps this sediment is the source of the crud I found in the float bowl assembly. Just how to proceed in cleaning the tank I am not sure. If someone has a good method, I would like to hear it.

The bottom line is the fuel system in a 14 year old PX150 with just 4000 miles is a mess from the fuel tank to the carburetor. Did age or the ethanol fuel cause these problems? I do not know.

http://www.scootermercato.com/Scooter-Parts/Fuel-Taps-and-Parts/FUELLINE

Thank you for your input Tierney. I have one of those fuel lines from Scootermercato but plan to install the Piaggio OEM fuel and oil lines instead. The Piaggio fuel line is 27 inches long making it easier to install. It also has very thick walls and will not collapse when bent. The Piaggio oil line also has very thick walls. In addition, I can use the spring clamps on both of these lines. I got these parts at Scooterwest. They are more costly but I feel overall, they are the better lines. Only time will tell but if they go another 14 years, I will be pleased.

looks like Tygon fuel hose, top of the line stuff.

I installed a new fuel and oil line on my US 2005 PX150. The fuel line I used was a Helix racing line that has no plastisizers and will not harden with time. I also cleaned the float bowl assembly. Then I made a main jet stack with the following: 106/BE5/150 and slow idle jet of 45/140. I chose the BE5/150 combo since I want a richer mid range and the BE5 mixer is what SIP recommends when using a 150 air. I also trimmed back the slow idle jet from a 55/160 to a slightly lesser 45/140. I was getting some four stroking riding around 35 mph and felt the 55/160 was a bit too rich for my riding style.

The test ride was amazing. There was no four stroking at any cruising speed. The bike took off and was very strong up through the gears. I got up to 56 mph and it just hummed along with no problems. A photo of the plug with just 20 miles is attached. It was certainly richer than the previous tests using the 102 main. It was a little wet and may be on the rich side. But the way the bike performed, I can live with that.

So it appears to me that I have been under jetted in the main jet with a SIP Road 2 muffler and drilled air filter, the usual 102 must be increased. I am at 106, which is 8% above the stock jet, and it runs great. (SIP recommends using a jet between 5 and 10% over the stock jet for a Road 2 muffler.) I have a 104 jet coming and will try it as well. But for now, the 106 is working great.

That's great way to keep at it!

I felt the 106 main jet was a little too rich for the 2005 PX150 with SIP Road 2 muffler and drilled air filter. Therefore, I tried a 103 and 104 main with the BE5/150 combo and 45/140slow idle jet. The bike ran well with both, however, the 103 seem to have a better overall response. The 103 is also within the SIP recommended range (5 to 10%) for installing the Road 2 muffler. With the 103, it was 5% over the stock 98 jet. The spark plugs for both the 103 and 104 main jets are shown and are very similar. They both look good.

I still want to try the 103-104/BE3/160 stacks with the 45/140 slow idle jet. Weather permitting, I should get that done this week.

I was able to test the 104/BE3/160 stack today. Overall, the bike performed superbly well and there was no four stroking while cruising at 35 mph on a level road. It responded quickly to the throttle and there was no bogging or "fuel starvation" issues at 55 mph. Overall, this seems to be the best combo so far. The 104 main jet is about 6% larger than the stock 98 main. The slow idle jet was the 45/140 which is slightly leaner than the usual 55/160. This jet was chosen to minimize the four stroking in the low throttle range. Going from a BE5 to a BE3 also help lean out the low to mid range. The low to mid range is, however, still richer than what I had at the time of the soft seize. Increasing the main jet to 104 and using the BE3 and 45/140 seemed to reduce the lean condition that lead to the soft seize.

The plug is shown below and is starting to get the brownish tan color on the electrode. It does not appear to be too rich nor too lean. It looks quite good.

To summarize:

US 2005 PX150
SIP Road 2 Muffler
Drilled air filter
Main jet stack: 104/BE3/160
Slow idle jet: 45/140
Plug: NGK BR7HS
Fuel: 90 octane ethanol-free gasoline
Oil: Motul 710 in auto lub system

Why are you using a resistor-type plug? Unless, it is called for in the owner's manual to have R type plugs, the plug cap should be a 5K Ohm type, which means that, by coupling it to R type plugs you have 2 resistors in series in the ignition lead, which could possibly generate a weaker spark.
On my 1985 PX it calls for a standard plug, either NGK B6ES or B7 ES, and the cap is a 5 K ohm type.

The owners manual for the US 2005 PX150 recommends the use of a resistor spark plug. The spark plug wire goes directly to the spark plug and there are no plug caps used.

My latest jet combo seems to be working the best so far. It turns out I am nearly back to where I was when I started. The current jetting is as follows:

Main stack: 102/BE3/160
Slow idle jet: 50/160

I was simply running too rich with the previous jet settings. The sputter and four-stroking while cruising around 35 mph were bad. Above 40 mph they all performed very well. I reduced the the main jet to 102 and the slow idle jet to a leaner 50/160 and that fixed the problem. This 50/160 slow idle jet is nearly identical to the 40/130 stock jet in the 2005 Stella in regard to the fuel/air ratios (3.20 vs 3.25). I also replaced the drilled air filter with the stock non-drilled air filter. I could not tell any difference in performance between the two. The non-drilled air filter will richen up the jets a little.

The US 2005 PX150 with SIP Road 2 muffler is running great for now. I will leave it as is and perhaps do some final tweaking next spring. A photo of the spark plug is shown below and with this current setup, it looks very good.

My slow running jet is 48/160, almost the same as yours, and my air filter is drilled. You don't mention it in most of this thread, but how many turns out is your mixture screw? have you made adjustments as you have experimented with your slow running jet sizes, or has it been always in the same position?

Your 48/160 slow idle jet is leaner than the 50/160 and with the drilled air filter it would be even leaner. But if it is working and you do not get sputter and four-stroking in the low to middle range, then you are probably okay. I got the soft seize with the 50/160 while riding around 35 to 40 mph. There are other factors at work here as well including the makeup of your main stack. So check your plug after you have some miles on the bike in your riding range. If it is lean, then I would suggest you make some adjustments to enrich it. It took me a lot of testing to get that brownish tan plug.

As for the idle mixture screw, the stock US 2005 PX150 comes with the screw 1 3/4 turns out. I have turned my idle mixture screw an additional 1/2 turn CCW from stock and have not messed with it since. Turing it out 1/2 turns from stock did eliminate an off idle bog I had. Getting to that idle mixture screw can be challenging with the electric starter in the way. I used a pair of 11 inch pliers with the tips bent 45 degrees. You can get these at Home Depot or Amazon.

I have the stock muffler, as well as the stock 100/BE5/150.
The motor runs, idles, and accelerates vey well, with no four stroking, bogging, or hesitation. And the plug color is light brown, very similar to your plug.
When I replaced the old, warped carburetor, I had to change the slow running jet from the stock 42/140 to 48/160 . Both have the same 3.33 air/fuel ratio, but with the 42/140, no matter how many turns out of the mixture screw, it was hard to start and it was bogging down when opening the throttle, whether the motor was hot or cold. With the 48/160 and the standard 1 and 1/2 turns out, no problems at all. The only things that have changed with my set up is the fuel consumption: around 70 mpg now vs. 85-90 with the 42/140. And the engine cools down very quickly; it wants the choke after 45 minutes of no running. With the old carb, up to 2 hours, no choke was needed. Very puzzling, I'd say.

It looks like you have your jetting dialed in correctly. As for the 48/160 slow idle jet, this jet, while having the same fuel/air ratio, will have more overlap with the main than your stock 42/140. So while the 48/160 and 42/140 are identical on paper with the fuel/air mixture, there are other factors, like the main jet stack, drilled air filter, etc., that change the dynamics. Since your plug is good and your bike is performing very well and you are pleased, I would leave it alone.

With the issue of the engine cooling down quicker with the 48/160, it may be the engine is running cooler than with the stock slow idle jet. Perhaps the engine was running lean with the stock 42/140 and thus running hotter. The higher fuel mileage you noticed would also point to the leaner condition. That could explain the differences in the rate of cooling.