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[Brazilla]

Bike is 350 pre uc iron barrel with standard mikcarb.
Been running great up until today when on a longish ride I noticed the engine seemingly missing a beat slowing and then speeding back up when above approx 1/3rd throttle. This seemed to most frequently happen in second and third gear. Made it home by being pretty gentle on the throttle. As I rode I tried to take note of the conditions under which it happened but it did seem a bit random.

My initial thought was water in the fuel, I don't think this is likely though due to the problem seemingly being linked to throttle position, also it carried on for about twelve miles.
I also wondered about it being clutch related as it feels like it needs adjusting and the back wheel turns slowly when the bike is in neutral and I start it on the stand.
Another thought was dirty carb or air filter?


Any thoughts of what to investigate first based on symptoms, the bike is due some attention as I've just taken it past 2000 miles

[Norm]

The list of causes and fixes can be endless I'm afraid, plug,coil,coil lead, condensor,points, ignition switch to 50 carby options, they will all be along shortly

[mauri]

the wheel turning slowly in neutral is normal.



water in the fuel bowl or a clogged stationary jet is maybe the cause of the missing beat.

also take a look at the manifold rubber so see if everything is still tight

a spark plug on its way out can also do this.



and many other possibilities,you can already have a look at the above.



are you running the standard filter and exhaust?

[Brazilla]

Yes, all standard!

[jaffa90]

I`m with mauri on this one, stationary jet / pilot jet getting blocked. Have you a in-line fuel filter fitted inbetween the tap and carb?

[Alan R]

Tank cap air vent ??

[Alan R]

Maybe a long shot but can you borrow a carb from a running bike ??..ie test by substitution..

[mauri]

with standard exhaust and filter, that’s one cause solved.



find a container that fits under the carburetor and undo the drain plug, so you can inspect what comes out of the float bowl.

with the plug stil removed, put the container back and open the fuel tap.

with petrol cap in place, fuel should start running immediately and continuously.

when screwing the plug back it just need to be tight, no need to pull to hard.

if this i all ok, you should have a look at the pilot jet.



you where not falling on reserve neither?

[Scalyback]

Alan R, if we could take the carb from a running bike, (without it stopping) then I am not worthy.

[Brazilla]

Removed and cleaned carb and now seems to be running fine. Thanks for all the input chaps, guess it was a bit of muck somewhere!