Help please, n00b in distress

ambro25

Just a quick cry for help, as my 125cc twist & go is ill, far from any bike shops (in Knocklyon) and I just don't know what to do with the thing
It's a Benelli, 2003, and about 9000 kms on it. Overdue a service (booked a while back with "Mr Benelli" off North Circular, waiting to hear from him when he gets parts), although it's never given any hassle and it's not drinking oil or coolant or anything. The power plant is a Yamaha 125, same as on Majestys.

Symptoms: starts and idles fine, revs fine when on its stand, but as soon as it's off the stand and some throttle applied (so, some 'weight' (e.g. me) on it), engine goes in start-stops & backfires (a bit like carbs icing up in v.cold weather).

I'm really not mechanically-minded enough to start doing anything myself, nor have any time available at the moment to sort it out - but it needs to be sorted out very soon.

(I may have to sell it due to emigrating soon, and it's been brilliant so far, so I'd rather sell it in good nick rather than a spares/repair lot)

Anyone know someone or a backstreet garage in the area? Or, if anything at all, at least give me a clue as to what problem could be?

CrazyRabbit

Hey Ambro, didn't know you were a biker.

I had a similar, but not identical issue about 2 years ago. Whenever I took the bike off the stand, the engine would sputter and cut out. Turned out to be a damaged cable that lead to the spark plug. Taking it on/off the stand bent the cable slighty and over time it damaged the copper wiring in it, causing the spark plug to loose it's electrical supply when bent in a certain way.

Now, I know this was caused due to the poor design in my bike. The spark plug cable was stretched horizontally across the central engine mount joint thus causing a bending action everytime I hit a bump or put the bike on it's stand. Might be completely unrelated to your issue, but it's worth checking.

Leave the bike on it's stand, idle the engine. Then start moving the spark plug cable around with your hand (if possible) and see what happens.

Best of luck.

ambro25

Hi CR,

Well, I'll not insult The Great Bearded Ones (:D) around these parts by calling myself "a biker", but yeah I've been a 2-wheel convert awhile

The problem isn't when I take it off the stand (I may have explained poorly): it doesn't matter if it's on the stand or not. Since it's a "twist and go", you can only rev it so much before it clutches in and the back wheel is driven, so I leave it on the stand when I rev. It also revs fine when it's off the stand.

It's only when I'm on it and I feed enough revs to pull away that the problem starts: when the clutch kicks in and the back wheel starts to be driven, the engine then begins to fire erratically and backfires every now and then. This manifests itself as the bike pulling away then 'poof'-nothing, then keep pulling away, then again 'poof'-nothing (irregularly, on and on).

I compared the problem to icing carbs in cold weather earlier, could also be like sh*t petrol (although it's always been fed at Texaco Rathfarnham and never been an issue ).

CrazyRabbit

Check there are no holes/cuts in the Carb manifold. It could be sucking in air, which would cause the symtoms you describe.