running rough at low revs

[j77drs]

hi im new on here,

riding this morning and the bike started runnign rough at low revs ( lumpy ) in the higer revs it seems to clear

the bike has plenty of fuel

this has never happened before and i have owned the bike for 4 years

any ideas ??

[Cammo]

Welcome!

Jeez mate where to start?! These symptoms could be caused by quite a few things.

Given that these bikes have electrical system weaknesses, firstly do some basic electrical checks. The voltage at the battery should be 13.5-14.2v (or thereabouts) at idle and mid revs, check it with a simple multimeter.

It could also be a carb related problem: Pilot jets might be blocked (likely), needles might be cactus (unlikely) or the pilot screws might need adjusting (unlikely if the symptoms have appeared suddenly).

It could also be a fuel delivery issue, the fuel tap vacuum hose (comes off the right rear cylinder inlet under the carbs) might be perished or faulty.


It could also be a heap of other things, but by the process of elimination it shouldn't be too difficult to find.

[j77drs]

what is strange is that it just happened during a journey,

rectifier could be a problem couldnt it but surley this would effect the whole rev range as the battery is draining quickly

[Cammo]

what is strange is that it just happened during a journey,

Yeah, that's why I think it could be a blocked carb pilot jet issue.

rectifier could be a problem couldnt it but surley this would effect the whole rev range as the battery is draining quickly

I agree, but there's often no logic when it comes to electrical problems and nc's!


Things wear on these bikes due to age, it could be something as remote as a leaking carb diaphram. Unfortunately you won't know until you inspect all possible causes.

[j77drs]

just taken the bike home and it seems that anything below 5000 rpm is a problem, the bike is just hesitant and struggles, anything above this its fine

any ideas ?

[CMSMJ1]

do you ride with lights on? try them off... could be a weak battery not being charged a lower revs...

[j77drs]

i do ride with light on but turned them off when i got home and it made no difference,

could this be the retifier ?

the battery is only 1 year old

[CMSMJ1]

I would do some basic checks to eliminate the problems before you get stranded!

check the battery DC V when the bike is off. then check it when you fire it up and also at 5000 revs. Should go from anywhere above 12.7V to 14.5V

This would show the bike is charging.

Reason I think that is when my generator was on the way out I could get to and from work OK but only with lights off and whenever I got lower revs the bike relaly wanted to die as the partial charge from the dying genny was too low..

Saying that, it could well be a bit of smeg in the carbs that needs a clean out.

[j77drs]

i have also noticed that the longer the journey goes on the worse the problem gets, again only under 5000 revs, could this be the rectifier getting hot ??

[CMSMJ1]

rectifiers get hot - it is what they do.

You need to check the charging system and see if it is working. Very easy. Get a multimeter, set it to DC V and see what the battery reading is when the bike is at 5000revs.

Let us know what the answer is and we'll help you from there...

It will be fixable, no worries