Bike hesitant / bogging down 4-6k.

[Bill_on_a_bike]

Last few rides I've been on I've noticed the power delivery just has not been smooth in lower gears. Giving it half a fist full in 1st or second the bike accelerates, then feels exactly like you've momentarily taken your hand off the throttle, then carries on again. At motorway speeds she's completely normal, pulls like a train in top etc.

Bike is a 2004 SV650, fuel injected otherwise I'd already have stripped the carbs. I'm out of my depth with fuel injection. I've seen some reports of a fuel pump pressure regulator not being super reliable on these bikes? I guess it doesn't pump enough fuel to meet demand for a moment?

What's the best way to investigate these things? I can't simulate the stutter when she's standing still.

All help very much appreciated.

[Tango]

I assume the bike is all serviced?........has it got standard exhaust and air filter.......Some non - standard exhausts and air filters can create a mid range flat spot........

[Bill_on_a_bike]

Air filter was changed about 3 months ago, for a completely generic standard one (and replaced what looked like a standard one). Exhaust can is after market, remus (came with the bike) but I didn't used to have this problem.

Oil and filter changed at the same time, not likely to be relevant. I didn't change the spark plugs........would they do this if they were on the way out?

Didn't get a lot of history with the bike so I don't know how old they are.

[Stu]

whats the mileage?

[Bill_on_a_bike]

Just ticked over 31k.

*braces for bad news*

[Stu]

scrap it......

only kidding

I would change the plugs at that mileage especially seen as though you dont know when they where changed

nothing else stands out to when it started?

you may also want to take a look at electrical connections as the vibrations at those revs could be affecting a bad connection and making it show up

double check your filter to make sure it is seated right

[Bill_on_a_bike]

The other thing, which actually now you mention it probably started at the same time is that when she starts she auto-high idles for maybe 20 seconds then drops back down to ~1500rpm. A few weeks back when she dropped down again she idled erratically then died and wouldn't re-start. After i recharged the battery she did the same thing, so I let her sit for a minute then tried again, only this time I kept the revs high a smidge longer with the throttle, 10 second more tops, and then she behaved compeltely as normal. She's done this once or twice since. I put this down to it having got a bit colder (a few weeks ago it was actually cold at 7am).

[Stu]

probably totally unrelated to be honest

[al_stu]

Could be a dodgy fi? Does the engine sound ok when you hit the flat spot, not like it has dropped a cylinder?

[Mr Fro]

How healthy is your battery?

[Bill_on_a_bike]

Battery seems to hold charge fine, starts strong.

It just feels like you've backed off the throttle, no big mechanical crash bang wollop, just dropd off power momentarily.

[Fozzie]

Mine developed a vibration and a cough like this, and it turned out the valve clearances were way out.

Seemed to be as the FI adjusted the fuelling through the rev range it caused a hesitance/cough and it carried on fine. It was beautifully smooth after I sorted it.

Start easy, change plugs and check the coils. When they start to go they sometimes cause a hiccough around parts of the rev range.

[Matt Strange]

Has this model year of SV got either an intake or an atmospheric pressure sensor? (or both) It's one of the few things I can think of that will definitely affect injector pulse/fueling.

For starters, make sure the vacuum hose and wiring is OK if it has. I don't think it's a TPS issue as you should be able to replicate a problem at idle as well as when under load.