classic motorcycle forum

Motorcycle Discussions => British Bikes => Topic started by: toz on July 21, 2014, 02:18:50 PM

Title: 1972 T120 Bonneville prob.
Post by: toz on July 21, 2014, 02:18:50 PM

I'm sick of trying to find the problem here.

Bike starts and runs ok but revs don't drop immediately when changing gear, it seems to stick a bit, yet the slide is dropping fine. Oh and tick over isn't great.

Had the carb off more times than I care to mention, float is set, jets all clean, timing is ok I think.

Any ideas chaps?

Title: Re: 1972 T120 Bonneville prob.
Post by: mark2 on July 21, 2014, 03:37:07 PM

sucking air , sounds like to me

Title: Re: 1972 T120 Bonneville prob.
Post by: Revband on July 21, 2014, 06:13:25 PM

Slide/carb body worn?. Open throttle slightly and feel if the slide moves around.

Title: Re: 1972 T120 Bonneville prob.
Post by: toz on July 21, 2014, 09:34:34 PM

Thanks,......... I must say sucking air is just right I think. Cant see where other than by the slide so I must consider that to be the problem.

Cheers.

Title: Re: 1972 T120 Bonneville prob.
Post by: mark2 on July 21, 2014, 10:32:02 PM

make sure the carb flange is flat , take the rubber o ring out , and lap on a lapping plate

Title: Re: 1972 T120 Bonneville prob.
Post by: toz on July 21, 2014, 11:05:54 PM

Ok will do. ta.

Title: Re: 1972 T120 Bonneville prob.
Post by: mark2 on July 22, 2014, 07:40:20 AM

the mechanical advance/ret unit is working all good ? no sticking

Title: Re: 1972 T120 Bonneville prob.
Post by: toz on July 22, 2014, 03:34:31 PM

Took it all to bits again, made sure all surfaces were flat, made new gaskets, raised the float just a little...... checked for play in the slide and there is a little bit, hmmm,...... put it back together and she runs like a dream ;D.

I think it was air sneaking in at the carb flange or the bowl. Anyway its sorted.

Thanks.


On another note, I noticed a little oil in the timing housing, it has electronic ignition, could this cause a prob?

Title: Re: 1972 T120 Bonneville prob.
Post by: mark2 on July 27, 2014, 03:13:58 PM

I don't think so if its a bit , but the oil seal is easy to change its in the outer cover .

Title: Re: 1972 T120 Bonneville prob.
Post by: toz on July 29, 2014, 12:35:53 AM

Thanks then.