Is my k3 engine out of tune?
 

When I first got the bike 2 years ago mpg was around 55 mpg and engine ran smoothly. It's now does about 40 mpg, it backfires on deceleration and occasionally gives a 'cough' and conks out when slowing right down or stopping.

I first thought the drop in mpg and engine misbehaving went hand-in-hand with the engine being out of tune but I'm not sure so I have some questions for our experienced members:

1) What's the most likely cause for the above misbehaviour?

2) Is the drop in mpg likely to have another cause like brake drag, bearings? Neither of these are obvious but the rear pads have always 'rested' on the disc causing very slight drag (ie: the wheel's not totally free to rotate if you pop it off the ground).


3) Best course of action?




Bike specs are: SV650S K3; 30K on clock; Fuel exhaust; Pipercross air filter (cleaned 3K miles ago); due for 15K service; idle speed 1300rpm (warm engine).

Re: Is my k3 engine out of tune?
 

If you have a dragging brake, that won't help.
Tyre pressures OK?
Chain and sprockets OK?

SO many little things will affect mpg.............how much did you weigh 2 years ago compared to now etc etc. :-)

BUT. If you have a running issue, that's going to be the most likely cause.

Are the throttles sync'd? Are the plugs OK? Do you have an H/T lead breaking down?

Have you noticed a drop off in power? If you have, you will be opening the throttle more to compensate for the lack of oomph, therefore using more fuel, allbeit, that extra fuel might not be getting burnt properly.

Re: Is my k3 engine out of tune?
 

Thanks for replying Speedy.

Tyres pressures checked regularly and are OK.
Chain and sprockets are good (about 3000 miles old).
I'm the same weight and so's my helmet :-)
The plugs are those that came with the bike (and should be replaced in the 15K service).

If there's a power drop it's slight. As for throttles being in sync, I have no idea. Are there any tell-tale signs I can watch for? Are they easy to check and balance?

Re: Is my k3 engine out of tune?
 

That brake drag sounds like a likely culprit/something that needs attention anyway


Think a symptom of unbalanced throttle bodies is rough tick over

Re: Is my k3 engine out of tune?
 

"Due for 15000k service"
Your symptoms are those of a bike due for a service.The 15000k one is a big service with everything done.That should show up any issues.

Re: Is my k3 engine out of tune?
 

Wet front spark plug?

Re: Is my k3 engine out of tune?
 

Problem turns out to be a disconnected map sensor vacuum hose. Apparently these occasionally blow off at high revs.

I also found out it's normal for the rear pads to be just touching the rear disc.

Thanks for your help guys.

Re: Is my k3 engine out of tune?
 

Consider changing the oem hose clip to a band type clip. Most of the clips round that area are rubbish and a blow off tells me the tensions gone in it.