Modern Vespa

So this morning I had a couple issues.

It took three attempts to get it to start this morning, and then it would idle really rough and die. I finally got it idling smoothly, and headed to work.

While waiting at a stop light about half-way to work I noticed the CEL had come back.

My guess is that it has something to do with the 96% humidity, and the lower fuel level in the tank. I meant to top it off over the weekend, but it was raining and didn't want to ride in the rain just to get gas.

I put just under 120 miles on it last week, and this morning the Low Fuel light came on, and if I remember correctly, this means that I have about a gallon left in the tank. This makes sense based on the fuel efficiency I was getting when I was last riding in (~58mpg). I'll be sure to get gas on the way home tonight.

I would suggest refilling the tank with nice clean fuel and keeping the Seafoam out of it entirely. That stuff is a 1940's era petroleum concoction. It isn't gasoline, and it doesn't make gasoline better, or the fuel companies would have added it themselves long ago.

Keeping it out may not help this problem but it might, and keeping it out rules out one factor which could explain your symptoms.

It isn't directly comparable, but my 150cc carbed Leader engine runs demonstrably between terribly and not-at-all with Seafoam in the fuel. It does nothing, good or bad, with my many other small engines so I've expunged it from my garage.

Yeah, I wasn't planning on adding any Seafoam to the tank at the next fill up, just straight Top Tier Premium.

No need to go above 91 ((R+M)/2) - that's the equivalent of the specified 95 RON.

The CEL was on yesterday afternoon when I left work.

After I filled the tank, it was off. I'm not going to worry about it.

---------------------------- Where I get gas, my options are 87, 89, or 93 (or diesel or E15). By Top Tier gas I mean that I'm using higher quality fuel, not whatever is in the pumps at El Ron's Tortas Y Fuel.

i dealt with a similar issue with my subaru...car consumes oil...was throwing cat code...swapped out the upstream o2 sensor which got rid of the code for a while...came back and swapped out the downstream o2 sensor which didn't help...swapped out the cat which got rid of the code for about a year till the cat clogged up again...started running a bottle of cat cleaner in my fuel pretty often...by this point i was consuming oil at about 600mi/qt...engine was toast

i run seafoam in all my small engines except my chainsaw where i run non-ethanol trufuel...but put the seafoam right in the fuel cans...weed wacker, lawn mower, riding mower, backpack blower, small blower, scooter...don't usually need to tear apart my equipment very often to clean carbs which is nice

91 (US) provided noticeably less zip and 10% drop in mpg than 93 in my BV350.

Higher octane doesn't give that much more power - it's just harder to ignite. I suspect a belief that higher numbers mean 'better' is at work here...

That said, if the 93 is ethanol free, then you'll gain about 3% better mpg over E10.

I always use whatever the manual says to use in whatever vehicle I own.

We used to have a 2001 VW New Beetle with the 1.8T engine. It required Premium (at least 91 octane), but would run on regular. We always used Premium in it, except for one tank during a road trip when the only gas station in the area only had regular available. Our fuel economy dropped dramatically, and returned once we filled up with Premium. I did the math on it (I understand that one tank isn't going to give me good data). If the fuel economy stayed low on regular vs premium, it was actually cheaper for us to use premium.

My truck also has a turbo (2022 Hyundai Santa Cruz with 2.5T). But the manual recommends regular (87 octane ((R+M)/2)), and explicity states to not use E85. I know that using premium in it is a waste of money, and any performance gains are purely psychological. Which is kinda funny, because its trim level is SEL Premium.

I see your point.

The CEL came back on Friday morning, when I was at 90 miles on the tank.

Everything worked normally during my commutes on Friday and Monday.

This morning it was off.

The only difference between today and previous days is that it is raining.

The current conditions are raining, 61° F/16° C, and 86% humidity.

I'll be getting gas tonight on the way home.

Mpg went from 64 to 58 when changing to 91 octane (US), for two tankfuls, and I'm sure there was noticeable loss of power (not just my perception).

Maybe what you say is true in theory, but I'll stick w 93 octane.

Be curious if others have compared 91 vs 93, and what differences they experienced.