Valve clearances and mpg.

[Raf]

Just out of interest, how much does keeping you're valve clearances in check effect mpg?

I bought a 99 Sprint st recently which gets around 32 mpg around town. Its not great and from what i have heard they are supposed to be pretty efficient even for a litre bike, but 32 seems a little low.

It has a new air filter and plugs as well as the latest map. I have yet to sync the carbs which is the next thing on the list. But since i purchased the bike with no service history i have no idea when the valves were last done. She starts on the button and seems to run perfectly so im doubting that the valves are too far out.

On the motorway she does about 38-40 keeping under 90mph which still seems a little low, i have heard they can be good for upto 55. Maybe its just my heavy throttle hand?

Could the exhaust valves being to tight cause it to dump unburnt fuel before complete combustion?
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CBR1100xx - BMW K1100 - BMW K100 - Triumph Sprint ST 955i - Suzuki GSX-R 600 - Suzuki DR 350 - Yamaha XV 750 - Honda CBR 600 FM - Yamaha XT 600 - Yamaha Rs 200 - Honda NSR 125

[Frost]

Valves can effect timing and compression which effects power, so you'd be using more throttle to get the same amount of power therefore using more fuel. I think that unless it's a real problem it's not likely to be a noticeable effect. Carb sync, and mixture settings are far more likely to be playing a bit part.

[MaybeGuy]

what about the K&N filter, the aftermarket exhaust and richer map you're using?

I think the stock claimed MPG is constant revs at constant motorway speeds.
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Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!!
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith

[Raf]

Thanks, as i thought. If the valves were out i would have noticed hard starting and some loss of power?

Its difficult to tell if the TB's are off as its not a carbed bike, as with previous bikes i would notice rough idling and stuttering at the lower rev range. As its my first injected bike im unsure weather these bikes as well as having an automatic choke have some sort of automatic idle which would mask a rough idle linking to out of sync TB's.
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CBR1100xx - BMW K1100 - BMW K100 - Triumph Sprint ST 955i - Suzuki GSX-R 600 - Suzuki DR 350 - Yamaha XV 750 - Honda CBR 600 FM - Yamaha XT 600 - Yamaha Rs 200 - Honda NSR 125

[Raf]

[0l0dom0l0]

Might be worth checking the valves if you aren't sure when they were last done.

If the bike is running well I wouldn't start messing about with maps tbh. Possible its running a bit rich hence the poor economy figures.

Check the valves and also balance the injector bodies and see if its any better!
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CBT Passed: 30/08/2009, Theory Passed: 31/08/2010, Mod 1 Passed: 6/9/2010, Mod 2 Passed: 13/09/2010. Restriction ended 13/09/2012.

Bikes: 2007 Derbi GPR 50, 1998 Yamaha Fazer 600 (written off), 2002 Yamaha Fazer 600, 1994 CBR 600F, 2003 Triumph Daytona 600, Kawasaki ZX6R J1.....Current: 2006 Yamaha FZ6, 1998 Suzuki TL1000R and a Honda VFR 400 NC30.

[Frost]

A rich running bike is a thirsty but otherwise happy bike. The throttle response will be smooth power delivery. It might foul up plugs now and then.

[Teflon-Mike]

[Raf]

Single figures do you say? I don't feel so bad now..
Ill check and/or sync the TB's at least tomorrow as it should not take too long, and at least il know if there off straight away.
I've decided to have a "taking it easy" week, i will be trying my hardest to banish my throttle happy right hand and go for a more progressive approach. I will let her run dry and fill her back up and see if i get a significant change in mpg. God help me if the sun comes back though. Im not sure i will be able to help myself.
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CBR1100xx - BMW K1100 - BMW K100 - Triumph Sprint ST 955i - Suzuki GSX-R 600 - Suzuki DR 350 - Yamaha XV 750 - Honda CBR 600 FM - Yamaha XT 600 - Yamaha Rs 200 - Honda NSR 125

[serlant]

Still going on? It aint that bad raf get facking used to it!
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04 CBR1000RR, 1995 Husqvarna TE410, 1998 VTR1000(Sold), 1990 XJ600(sold), 1996 KH125(dead and sold)