my bro got a Vespa ET-4 a little while back. he attempted to break it in responsibly but he did use full throttle a lot and went past 60 mph a couple times (73 mph top speed).
650 miles later he had the initial tune-up and check-up. i am not sure what all they did.
at about 700 miles, the bike started bogging down at COMPLETELY random times. this happened a lot. we would just put it on the stand and rev it with no load and it would correct the problem some of the time. but these bogs are complete nonresponsiveness. full throttle will occasionally correct it.
why is this happening?
couple other possibly important things: the bike has been rained on a couple times. the bike starts right up after these exposures and shows no immediate sign of damage. (it’s supposed to be waterproof). also my bro turns the key off while riding about 15 mph, without hitting the kill switch on almost every use, and EVERY time the bike backfires once a second or two after engine stops. (he parks the bike in a special place where you must be quiet and unseen… the backfire doesn’t help, but the light is too bright) (don’t ask!)
Could be any of a large number of things. I’m not familiar with the ET250 (that’s the 4-stroke Vespa isn’t it?) but there are a couple of things you should check:
If the “bogging down” is completely random then it’s possible that you’ve got some crap in your fuel that’s run down into the carbie/s (I don’t know how many carbies an ET250 has). Turn off the fuel tap and drain the float bowls on the carbie/s and that may fix it. If it has a lot of crap already in the carbie you may have to get them blown out. Either way I’d suggest putting some aftermarket fuel filters on the fuel lines leading into the carbies- actually, fuel filters are a good idea in general and I always put them on any bike I have.
Rain shouldn’t affect the bike but it’s always good to park it under cover. However, you might have some water in the fuel. Water won’t dissolve in the petrol and can cause the sort of problems you describe. Put some fuel cleaner in or a bit of methylated spirits.
Undo the spark plugs and have a look at the electrodes: Are they black and oily looking? Alternatively are they white and scorched or blistered? Either way you need some tuning done.
Is the “bogging down” at a particular area of the rev range, especially just off idle? If so you’ve developed a bit of a flat spot that will require some tuning.
The bogging down and the backfiring (was the bike backfiring before the service?) suggest that it isn’t tuned properly. I assume that it’s still under warranty so I’d be taking it back and getting it fixed.
Hope this helps. I’m sure others will be along with further suggestions.
It sounds to me like the spark plug is fouling; running the scooter on the stand cleans it off. I’d replace the plug with one that I’m sure is the correct one for the bike–the mechanic may have used too cold of plug for the tuneup.
the bike just about had a bog-free day for many miles! btw, it’s a four-stroke 150cc. very nice little bike.
the bogs happen at any RPM except the very high end.
it has never backfired (or “pop”) unless we do the little turn key off at 15 mph and coast to stop, without hitting kill switch. it does it on cue, every time. weird?
by the way, what is the difference between hitting the kill switch or turning the key off?
There’s no real difference, both simply kill the circuit as far as I’m aware.
From what you’re saying it does sound like a tuning, fuel or spark plug problem (though I’m not really sure about the backfiring). Go through the things I suggested above or, as cornflake suggested make sure that you’ve got the right sparkplug in there - you’re owners manual should tell you what is the correct plug to use.
Wouldn’t the backfiring be caused by the engine continuing to turn over with the spark off, causing unburnt fuel to go through the cylinders unburnt, then exploding when it hits the hot exhaust? It sounds to me like the problem is caused by turning off the key while still moving, not by using the key as opposed to the kill switch.
Can I just clarify that the unburnt fuel referred to in the first sentence of my last post is unburnt fuel that is not burnt fuel that emerges unburnt, through not being burnt? Just in case anyone had any doubts.
for those who care, the bike ran fine for a couple days, then abruptly wouldn’t start. if there was any doubt that pure randomness exists, there isn’t anymore. totally random times the bike would not start.
my bro took the bike to shop… dirt in the carb. no idea how that got in there. go figure.
Good to see I can still diagnose bike problems by remote…
Crap in the carbs usually gets in there from crappy fuel (though sometimes it falls in when you’re filling up the fuel tank). Do you usually get your petrol from the same place? If so, you might want to consider going somewhere else.
Regardless, I’d still put on some fuel filters -see my first point in my first post above.