Buddy 50cc loss of power

[etiol8]

I've had my buddy for just about a year now (bought it second hand so impossible to know how it was used/maintained, but only about 1000 miles on it), which I use for in-town commuting. About 4000 miles total on it now. It's awesome, had been running great, though always seemed to under-perform a bit.

Last week I basically experienced about a 30%+ loss in power overnight, really seems to struggle both accelerating and on the top end. It really only gets up to about 27-28mph (buddy mph), and is sluggish off the start.

Has no issues starting up cold, sounds normal, just seems to have lost all its oomph. Battery tests fine. Replaced the spark plug and didn't see a change.

Any ideas? Carb issue? Don't see how that would happen all of a sudden though.

[TVB]

The only thing I can think of* that would explain this happening so suddenly is a tank of bad gas.

*not really an expert, so that's not saying much

[Robbie]

Either a carbon plugged exaust port or muffler but due to the low mileage that is debateable.
However, a very dirty air filter can do this, especially if it gets damp....the damp dirt closes the air filter cells.

I'd be looking at the filter.

Rob

[etiol8]

Thanks for the responses, I've been working on the scoot off and on over the last week and here is where I'm at right now.

-Bad gas is definitely not out of the question, especially as they may be switching over to winter gas around this time of year out here. I emptied out was in there and filled up a new tank, which may have helped a little but it might have been placebo.

-Air filter looks fine but Robbie you were dead on with the carbon plugged exhaust port. I took the exhaust off, which itself looked okay, but discovered some pretty large chunks of carbon on the engine side of the port. I did my best to clean it out but without taking the whole thing apart I couldn't get it really spic and span. Here's a picture of what it looks like now (along with evidence of the toll a Boston winter takes on an exposed engine in terms of rust):



-Took apart the carb, which looks very clean. No fouling of jets/ports.

-I pulled out the sparkplug (which is basically brand new, from last week) and noticed a significant amount of carbon (oil?) fouling on the edges:



I'm aware that carbon fouling is sort of a fact of life with a 2-stroke engine, but this seems more significant than usual. So-

Am I running too rich? I've got a stock 75 size main jet, and air flow doesn't seem to be an issue. I don't have a smaller jet on hand but I could get one and see if it makes a difference.

Could it be an oil issue? I'm using a royal purple 2-stroke synthetic.

Cleaning out the exhaust port got it almost all the way back up to normal in terms of performance, but I don't want this to turn into a long term problem.

Thanks in advance for any advice-

[PeteH]

I'm by no means an expert on the 2-stroke Buddy 50 motor, but in the manual for my Vespa P200E, it calls for 'de-coking' of the engine (the aforementioned carbon cleanout from the cylinder head and exhaust system) every 4000km or so. I don't recall hearing about a similar maintenance item for the Buddy, so it _may_ be a case of '80s vs. 'modern' engine technology, oil properties, etc. I only point it out because at least some two-strokes suffered (by nature) from carbon buildup and needed attention. Perhaps the prior owner fed it a diet of bad oil, causing a buildup? Standard motor oils aren't designed to be burned and exhausted like two-stroke-specific oil.

[etiol8]

Yeah, it doesn't seem too uncommon I guess, and fuel quality has probably decreased even if the engines have improved slightly. The gunk on the new spark plug may be just due to the fact that the combustion chamber is so gunky already. I'm going to try a decarbonizing spray like ValveTect and see if that makes any difference.