CB500 sluggish

[adam277]

Hello there. I should preface by saying I'm not mechanically minded.

Recently got a cheap £1000 CB500 97 plate.
Bike is great but it feels very under-powered.

Its hard to describe but I'll try its like 1st and 2nd are pretty much useless I'll probably get 20mph out of 1st before having to change up and 30 mph out of 2nd before changing up.
Anything over 5000rpm feels pretty bad so I assume the power band is like 3-5k.

This is quite hard to articulate when you don't have a fucking idea what you're on about....

Basically I suspect it is restricted but I can't really check until next week. So based on the little information I have gave does it sound restricted? I think I've had 80mph out of it before I bottled it so if anyone knows the top speed of a restricted cb500 that would be a great way to check .


Also I'm thinking of changing the sprockets as they look quite old and are quite cheap to change along with a chain also I suspect they might also be a potential culprit. I was thinking going with JT 15/42 sprockets as they are cheap on eBay. Unless anyone can suggest an alternative.

I would ask a friend this crap but no one I know has ever owned one.
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Bikes: Previous Bikes: Piaggio x8 125: 2012/2013, YBR 125: 2013/2013 BMW R1150GS 2013/2017, Honda CBR600RR 2017/2017, Honda CB500 2018/2018, Suzuiki Address 110cc 2019/2020, BMW R1200GS 2021-2023
Current Bike: Honda CBF 125: current

[jaffa90]

Google, CB500 97 restrictors

[Courier265]

new plugs, fresh fuel, I suggest Esso and some redex.... (halfords sell it) run it on a dual carriageway for a good few miles.

[adam277]

[Courier265]

[stephen_o]

Those figures are consistent with when my GPZ500 was running at half power.
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current scoot 2009 Yamaha YBR250 + Current Pootle 2013 Nissan Leaf

[stevo as b4]

A full service and check of chain, sprockets and tyres including pressures, followed by a £30 dyno run will tell you all you want to know.

A decent standard CB500 will spit out 50ish bhp at the wheel and that comes at an engine speed of about 9800rpm. Yours does sound nothing like this, and if your description is accurate then it's either been restricted or there's something wrong.

You need to check everything first to make sure it's not a fault like for example a broken carb diaphragm etc. But the most likely scenario given that CB's are a common restricted A2 bike is that there is a form of restrictor fitted to the carbs or inlet tracts.

[stephen_o]

i should add that my old GPZ500 would rev briefly to the red line but in terms of use it would not run at more than 5k for more than a minute before starting to missfire and on stopping (breaking down) there would always be a loud whistle from the tank so I guessed I had a breather problem but in 4 years of having the bike running, checking and clearing tank breathers, changing the petrol tank cap and having it in for servicing several times the culprit was never discovered.

Running at below 5k was sufficient in 6th for 80mph.
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current scoot 2009 Yamaha YBR250 + Current Pootle 2013 Nissan Leaf

[Rogerborg]

[Teflon-Mike]

There's many ways a bike could be restricted to meet eithe the old 33bhp limit or newer 45bhp one. Carb washers are one way; throttle stops another; or it could just be knackered!

It should run to the red-line on the center stand though; and it aught pull to the line in 1st and second; any restrictor wont limit the revs it can pull, hence the speed in the lower gears, just the amoiunt of air the engine is sucking, hence the power its making at any revs, hence how fast it will acelerate to them revs.

Power shouldn't effect speed until the thing is topped out in a tall gear, and it is the amount of power the engine that can make that's stopping it going faster.

OTMH, the unrestricted CB500, has a quoted top speed of about 120mph; A 33bhp restricted version, 'should' be able to just about nudge a genuine 100mph; what the speedo may say though is any-one's guess! But, you need to max it out; if it betters 110, its likely not restricted, if it struggles to better 90 it probably is... but watch for speed traps whilst trying! Or take it to a Dyno.

We are talking an old commuter twin though; so whether it is or has been restricted or not; odds is that the thing is far from sparkling service wise; and its a 'cheap' commuter bike, odds is that its been starved of vecent servicing for a large part of its life, and suffered an inordinate number of bodges.... and that is as likely as any proprietry means of restriction to licence limits.

Whether restricted or not, getting your hands on the Haynes manual, and doing ALL the basic service procedures in the book, from changing the oil to checking the tappet clearances; replacing spark-plugs renewing chain and sprockets, changing fork oil, and greasing the swing-arm, ~IS likely a very worth while bit of attension, and likely to 'find' any PO bodges or mods like a power-restrictor along the way... as well as base line the thing for any further diagnostics.

Without that 'super-service', and especially here on a web-forum, we are peeing in the dark, guessing what 'might' be up with it... if anything....

So... Go get your mitts dirty! Report back after if its still in doubt.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[adam277]

Got it in for a service next saturday so should hold out to then.
Basically full service with valve clearances/carb balance etc. but gonna get some fancy pancy sprockets and chains. If anyone can recommend if should look into getting any cb500 specific things done that would be great.

Anyway.
Thought I'd check the air filter and its black so that probably doesn't help. So I suspect the spark plugs will be the same.

FYI checking the air filter was a big of a job for me, bolts for the engine crash bars were practicalitly seized on and you have to take them off to get access to the air filter... that has taken over an hour to get off and thats letting it sit in wd40 overnight. Still haven't got it back on yet as one of the bolts need replacing so gonna pop over to halfords/B&Q and pick up a fresh one.

That's put me off checking the spark plugs because you have to take the tank off and I can't be dealing with anymore seized bolts/rounded heads today.


Edit:
That is a good idea about the dyno.. I'm tempted to give that a try before servicing it just to see what its currently doing
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Bikes: Previous Bikes: Piaggio x8 125: 2012/2013, YBR 125: 2013/2013 BMW R1150GS 2013/2017, Honda CBR600RR 2017/2017, Honda CB500 2018/2018, Suzuiki Address 110cc 2019/2020, BMW R1200GS 2021-2023
Current Bike: Honda CBF 125: current

[Teflon-Mike]

Engine bars? That hints at school use.
Seized bolts, though dont!
School bikes generally get pretty well serviced and bolts undone and re-done a lot, hindering seizing; mechanics doing stuff often on bikes like that also tend to be coppa-slip freaks, cos they know they are the one likely to have to suffer a stubborn nut next time round!

But either way... fact you have encountered stub born screws... more reason to get out there, with a pot of coppa-slip, and DIY, of only taking off the tank and bash-guards etc and refitting....

Its a PITA but its cheap and pretty easy.... leaving it to a paid mechanic is easy-er.... until you come to pay them.... and what would you rather be paying for? 2hours faffing with a feeler gauge or dial gauge or vacuum gauges you don't have in your tool-kit let alone savvy to use them properly, or 2h wrestling with a rusty nut?
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[adam277]

https://imgur.com/a/RkLgFlP



So its not restricted.
Well unless its a 47bhp restriction but I don't think it is.
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Bikes: Previous Bikes: Piaggio x8 125: 2012/2013, YBR 125: 2013/2013 BMW R1150GS 2013/2017, Honda CBR600RR 2017/2017, Honda CB500 2018/2018, Suzuiki Address 110cc 2019/2020, BMW R1200GS 2021-2023
Current Bike: Honda CBF 125: current

[temeluchus]

[Rogerborg]

[stevo as b4]

Shows a nice curve on the dyno run, but your still 5-6bhp down at peak to a very good std bike IMO. Now would be the time to give it a major service and check all possible issues or reasons as to why it's not running as well particularly lower down as it should. I think after a change of filters and all fluids, and a valve clearances check, I'd be having the carbs off for a good nose around at everything. A compression check would be an easy thing to do while your fettling.

If the bike is a good example cosmetically I would stand the cost of the mechanical work, as I think it's worth it to get a CB500 working perfectly.

[adam277]

[Pete.]

Before dropping a load of cash on it get someone so ride it because it sounds like the clutch is slipping. Your dyno chart says the bike is making almost standard power but is 25% down on torque. It it's the clutch that's slipping that will show up much more on the road because you're trying to accelerate a quarter of a ton of bike plus rider not just a small steel dyno drum.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[stephen_o]

That's a good call imo. I Have had cars with slipping clutches but not motorbikes but my yam book says that using the wrong oil can cause clutch trouble.
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current scoot 2009 Yamaha YBR250 + Current Pootle 2013 Nissan Leaf

[adam277]

I've delt with a slipping clutch before so I don't think it's that.

Think I'm just gonna wait til the weekend and go from there.
Noticed a marked improvement with some redex in the tank seems to be running better the more I drive it.
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Bikes: Previous Bikes: Piaggio x8 125: 2012/2013, YBR 125: 2013/2013 BMW R1150GS 2013/2017, Honda CBR600RR 2017/2017, Honda CB500 2018/2018, Suzuiki Address 110cc 2019/2020, BMW R1200GS 2021-2023
Current Bike: Honda CBF 125: current