Weird RPM issue after service - Video embedded

satanicguardian

satanicguardian

satanicguardian

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Solihull
Hi guys,

Odd issue with my bike after service (no chinese bike jokes please! It's just hit 15000km and was fine before the service haha!)

I know the video is a bit wobbly (my cam is mounted on my bag strap temporarily) and it is a bit dark, but watch the rev counter bottom left, riding along in 4th gear about 50mph and for no reason the rev counter will fly up to 13000rpm and the bike will start spluttering (as if I'm riding with the choke full open and fuel mix is far too rich) and I won't be able to accelerate at all until I either change up or release the throttle. This happens in all gears and is inconsistent, sometimes it won't happen and sometimes it will!

I'm taking it back in to the garage tomorrow, I spoke with them after I got home and noticed the issue - they reckon it's cause I'm using different ratio sprockets to the ones I had before (but came as a kit for this bike specifically).

To me it feels like it's more like the rev limiter or something weird going on with the carbs!

Anyone got any ideas? Thanks!

 
What jobs did they do on the service?

It's usually fueling,running rich or sucking in air ect if the revs rise for no reason like that, or maybe sticking carb float/needle
 
Are the revs actually going up to the limiter and bouncing off it? Doesn't sound like it is from the video - which means electrical issues. And if there's electrical problems on your dash there could also be the same issue affecting the spark getting to the cylinder(s).

Have you checked the earth cable on the battery, could be something as simple as that - otherwise electrical problems aren't easy to diagnose, especially if they're intermittent.
 
It was a full service (oil, jets, new chain and sprockets, all filters etc).

I haven't actually checked anything myself yet as it's going back in tomorrow morning.

The actual revs don't rise at all, they are maxing at 13k rpm but they are actually about 5-6k rpm from what I recognise as normal!
 
Could be sprockets then if they are different size,could be fuelling/jets aswell if they have messed with those
 
Are they larger size rear? Not sure without googling as I've never messed altering sprocket sizes,but a larger rear would cause the engine to rev higher to compensate(I think)

Just take it back and ask them to check it over
 
if the rev counter is showing as redline when it's actually doing 5k rpm, then unless it's a cable driven speedo/rev guage it's electrical. Which would point to an electrical issue.
 
Erm I think the front one was different, can't remember if it was more or less teeth, they said I should get slightly less acceleration but a bit more top end, it seems I have neither and a misbehaving bike haha!
 
TallPaul_S said:
if the rev counter is showing as redline when it's actually doing 5k rpm, then unless it's a cable driven speedo/rev guage it's electrical. Which would point to an electrical issue.
Click to expand...

Hmm, it could be cable driven, it's fairly cheap bike remember - I've never taken the speedo apart on it (yet!)

If I'm anything like the way I am with technology it's bound to get taken apart haha
 
If its spluttering like u say,and feels like the chokes on then get em to check the carbs again

If they have swapped the front sprocket for a larger one then that should give you slightly lower revs for the same speed

It shouldn't splutter at all
 
I don't think it's going to be the sprockets, if it was mechanical like that the fault would be consistent surely? Makes me think it's the carbs or something

Tallpaul, it's definitely carbs, none of that fancy fuel injection stuff on my chinese bike haha
 
No I'd say carbs

If they have opened it up to change the jets then chances are,carbs can be funny when you disturb them
 
"4th gear about 50mph and for no reason the rev counter will fly up to 13000rpm"
that sounds like clutch slip. the stuttering will more than likely the rev limiter
in the service you say jets, why did they need changing
 
ShakenNstirred said:
"4th gear about 50mph and for no reason the rev counter will fly up to 13000rpm"
that sounds like clutch slip.
Click to expand...

It's a symptom of the clutch slipping, except the OP has said that the actual engine RPM remains the same.

If this is the case then the stuttering is probably a misfire, and combined with the random tacho reading it points to an electrical problem, nothing to do with the carb or the sprockets. Unfortunately it's impossible the hear what's happing in the video.
 
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