Sv low on power

[True Blue]

I have an SV here and it seems to me to be low on power. I struggle to get it over 80 mph (on my private road ) It ticks over and runs fine, but I seem to be getting a lot of back pressure if I unscrew the oil filler cap off. Any ideas why I would be getting so much pressure from it and would this cause the bike to be down on power?

Cheers

Ritchie
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[loply]

Too much oil?

This might cause the crank the be completely submerged, which saps a fair bit of power. No idea if it would sap enough to reduce top speed that much though.
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[True Blue]

Oil is right on the max level, but I shouldn't think it was too much. I'll try and take a wee video to show how much pressure I'm getting out of it.
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[instigator]

Most likely don't know whats going wrong with it Ritchie but as a question that might aid otehrs:

How much has it been used since October? And when did it develop the problem? I.e. How many miles have you done since?

I can't say I had a power problem when I had it. And it's not done THAT many miles has it?

[True Blue]

[instigator]

Undone it just there.

A little bit of back pressure, perhaps more than I'm used to but nothing to suggest there is anything wrong.

EDIT : Just watched avi...hmm, I didn't know you were supposed to run the engine with the oil filler cap off. I'll try tomorrow though and let you know. It's too late just now, bikes too noisy.

[colin1]

[sickpup]

Very few people seem to understand an engine is basically a high powered pump. When the pistons rise in the cylinders it causes negative crankcase pressure, when they descend they create positive crankcase pressure.

When the pistons/piston rings are on there way out you end up with even higher crankcase pressures as the rapidly expanding combustion gases are passing the rings.

The only way to diagnose this without stripping the engine is to do a leak down test. Basically you pressurise the combustion chamber with air and open the oil filler hole to see if you hear air escaping past the rings.

As to whether your bike is down on power, when was it last fully serviced by someone who knew what they were doing? is it restricted? What modifications have you done?

[instigator]

[True Blue]

[sickpup]

To whether you have blown a head gasket, why do you think you have and whats a piston seal?

Try getting it serviced by someone who has a gas analyser and knows how to use it.

Did ayone adjust the fueling for the can? Is the air filter clean? are the brakes dragging? are you getting full throttle tube movement?

Throw me a bone here. You've told me nothing yet expect a diagnosis.

Hold on just reread all the posts. Has it not been serviced since last october?

[True Blue]

[G]

Haven't watched vid (at work), but... Sure it's firing on both cylinders?

I went for a practice session with a rather lazy SV at lydden - as my veypor was working but dash tacho wasn't it was fairly obvious it was only running on one cylinder, as they are connected to different coils.

[sickpup]

So service it changing plugs and checking the valve clearances and see how it runs.

We need a baseline to work from.

[True Blue]

I'm fairly sure it's running on both cylinders. They sparkplugs are new. Haven't checked the valve clearances yet, Looks like an arse of a job, especially if I have to adjust them.
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[G]

Mine was just one of the wires going to one of the coils had slipped off; definitely worth a check, I would have thought.

[Kickstart]

Hi

The SV is a V twin, and on one of these the crankcase volume varies far more than on an inline 4 (that I presume you are used to). On a 4 the crankcase volume is pretty constant (2 pistons going up at the same time, 2 going down). With a proper V twin both pistons are at TDC only 90 degrees apart (and the same for btc), so crankcases volume will vary by probably 1000cc on an SV with one turn of the crank. Worth checking the crankcase breather hose is clear.

All the best

Keith
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[True Blue]

[instigator]

How many miles has it done ritchie? I can't seem to remember. Think I got it at 7800 and I done what 4000 so the valve clearances wouldn't need done for anotehr couple of thousand by the Suzuki service manual, would they not?

[the grim reaper]

I'd also check the crankcase breather hose, make sure it's not kinked or trapped on it's way to the airbox. Also check the airbox in case, as I've seen before, a friendly mechanic has left a rag in there

If that is clear then the back pressure could be normal and you're probably looking at a fuelling or electrical problem.

Cheers

Grim
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[True Blue]

I think it's done about 12000 miles. Greg checked his and reckoned that amount of back pressure is normal.

[the grim reaper]

Depends what you mean by 'a bit of oil' in the airbox. If a bike has been ragged with a fairly full sump then you will get a bit of oil in the airbox as the excess oil mist uses this as a route to escape. As long as there's not loads of oil in the airbox (i.e swilling around in the bottom) it should be OK, sounds like you've overfilled the oil slightly.

As far as the lack of power goes, I'd do a spark plug check after a ride, see if one or other of the pistons is running rich or lean. If both are fine, then you're getting the right fuel/air mix to the pistons and it's burning OK. In which case I statr to run out of ideas. Does the bike stutter at all or does it pull cleanly to 80 and then just run out of steam? Do the revs continue to rise but the bike get no faster? Some more details would help.

Cheers

Grim
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Adverts don't always work: Remember that advert, where the army are running across the desert and they have a wounded man on a stretcher. They get to a ravine, the bridge is down and a caption pops up that says, 'What are you thinking?'. I don't know about you but I was thinking, 'Christ, I'm glad I'm not in the f***ing army'.

[True Blue]

Yeah, not too much oil, just a smearing really. The bike seema to be running ok other than the lack of power. It almost feels as if it's restricted.
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[the grim reaper]

OK, is that a general lack of power or a sudden tailing off at 80mph? If I was you, I;d go and get a dyno run done, that'll tell you fuelling and horsepower, so you'll get an idea of why the bike is doing what it's doing. £35 quid for a pretty good indicator of how healthy the bike is, good deal if you ask me.

Cheers

Grim
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Adverts don't always work: Remember that advert, where the army are running across the desert and they have a wounded man on a stretcher. They get to a ravine, the bridge is down and a caption pops up that says, 'What are you thinking?'. I don't know about you but I was thinking, 'Christ, I'm glad I'm not in the f***ing army'.

[True Blue]

Just a general lack of power really, I was thinking of a dyno run actually. Greg, where was it you got your bike dynoed before?
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