Coughing cruiser

[kevie]

My XV750 Vtwin has been totally rebuilt about 16000km ago, When I pull out to pass or get the bike up to around 5000 RPM (100km/h is around 4000rpm) it starts to cough and splutter and cut out, backing off the throttle just fractionally settles it down again...... the carbs were serviced at time of rebuild.
It has vaccum fuel taps and I have replaced the workings in them, replaced the plugs and leads (the leads were munted) and this helped alleviate the problem a wee bit.

Im unsure if the problem is fuel or electrical related .... wondered if its the coils failing under load.

Anyone had similar and what was the solution?

Thinking I need to find a good local service centre and get the bike retuned up maybe.

[What?]

Floats set a tad too low?? (so it is running out of gas under load).
Have you tried by-passing the vacuum tap to see if that makes a difference?

[Shadows]

I have had something similar happen with another bike and found that it was leaning out under load due to a leaky airbox cover letting too much air into the mix.

If it happened to me again I would check that my air filter assembly was still done up tight and wasn't letting air bypass the filter anywhere, and that the pipes providing air from behind the filter to the carburettors were still connected properly at each end, and that they were not split.

But you've probably already checked that.

[F5 Dave]

Could be several things, does it rear up in lower gears? Up hills more? Points more to coils.

If only in higher gears would tend to be fuel. Would take carbs apart & clean fully. But my pick is carb diaphrams are perished.

[kevie]

thanks guys, yeh my thoughts were possibly the vaccume for the taps, coils, or lean mix... will experement with them 3.

I overhauled the vaccume tap units and didnt make a difference so could be hoses I guess. (Yamaha dont supply the full overhaul kit for these but Manawatu Motorcycles had an aftermarket kit)
Carbs were cleaned, checked and adjusted when motor was rebuilt about 16000 km ago, but then maybe a tuneup will fix the problem.

Coils look to be still the origionals, quite a while back I did have a plug lead problem causing problems under load but new leads seemed to fix it, one lead at the coil end was all burned.... hhhhmmmmmm I thought it was improper fitted leads but maybe it is a coil failing under load ....... guess I will be whipping them out and having them tested.

[kevie]

Update on the problem LOL sheesh

I originally thought it was plugs ... so bought new ones, still same problem so guessed its not plugs......
then decided to be game and strip the carbs, they were cloged up in the inlet filters so cleaned them out and still the same problem...... so decided to give up and put the bike into Turnbulls workshop in Palmy.

AND wheeeeeeee the problem was >>>>>>>>>>>>>>>>>>>>>>>>>>>>>> wait for it >>>>>>>>>>>>>>>>>>> a faulty sparkplug hahhahahahahaha and they were new ones too, turned out the old plug was playing up and one of the new ones was shorting within the plug and same result.
They checked the electrics, (found a battery terminal loose) and tuned the bike and reset the carbs and now the bike going like a charm (better than when it was rebuilt) and $192 well spent

Thanks to the team at Turnbulls in Palmerston North.

(Just need time to ride her now LOL)

[Macktheknife]

Glad ot hear it is sorted mate, well done.