Yamaha RS100 poor performance.

[VultureZ1300]

Hi I have a problem with my sons little Yamaha RS100, There's no power what's so ever,I've checked everything I can think of,points are spot on,plug colour is spot on,starts and run perfectly.
The bikes only done 8000 miles from new,air filter replaced last week.
Will struggle to pull 40mph but should reach 60 mph+.
I changed the crankshaft seals thinking the old ones had gone hard but no change.
Any ideas before I sell it and buy something else for him to ride.
Cheers. Mark

[doggone]

Could the exhaust be restricting it?
There used to be all kinds of tricks like putting petrol in and lighting it
As you say it should be easily able to keep up with most main road traffic.

[A100man]

Bad fuel, and/or carb needs cleaning (blocked jets ), Binding brake(s) ?

JS

[bypass2]

Clutch or clutch cabble needs adjusting or clutch plates wearing out. Any air leaks around the air filter box or the intake boot split

[andys675]

compression test? may need a new set of rings
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Some people feel the rain, others just get wet.

[VultureZ1300]

Ok,Brakes are not binding,clutch is not slipping,petrol is fresh this week,baffles removed and checked makes no difference wether they are in or out performance wise.
Done compression test 120 psi.
Going to pull head and barrel to check for wear,although unlikely after just 8000 miles.
Cheers. Mark

[N cee thirty]

has it only just started doing it or has it always done this?
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[VultureZ1300]

Hi. Only had the bike a few months and hardly rode it during the winter and now it's warming up he's started to use it.
Mark

[doggone]

You can't really be sure of the mileage I guess.
It must have some age to it?

[N cee thirty]

clean the carb and make sure the jetting is what it should be, i had a bike that came with main jet sizes 20 sizes too big and it was indeed 20mph off where it should be.
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[VultureZ1300]

Quick update: head and barrel off,no wear so a quick hone and back together,exhaust now full of caustic soda.
Because spark plug colour is spot on assumed carb is ok but will check and clean tomorrow.

[Moxey]

I'd highly recommend decoking the exhaust, had very similar symptoms with my RXS after a period of inactivity, wouldn't see 40 and could barely pull up hill to the point where I had to one day walk it up a few whilst feathering the clutch. Symptoms were as yours with perfect plug colour and air filter (even new battery).

Shove a potato (serious and don't call me Shirley) or something up one end to block it then pour caustic soda down the pipe (high grade stuff might be able to get from a pharmacists but you'll have to give an explanation so they don't think you brewing home explosives).

Leave it for a few hours then unplug and drain recommend you wear gloves it can sting if you get any on you, only saying in case you didn't know though it looks like you probably have an idea.

Other bodger method that I can't recommend really is to put a blowtorch to the exhaust pipe, get it glowing and give a few taps with a hammer to loosen the carbon.
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Current: 02 FZS 1000 & 91 Royal Enfield Bullet 350 Some Bike Pics...
'I was too busy paying attention to pay attention'

[27cows]

Definitely ignition related. Possibly ignition coil/HT lead or cap damage. Points and 2T motors were never a good combination - points may seem fine but double check that area. Also worth checking the output of everything related to the spark with a multimeter.

Though making sure the tank cap vent isn't obstructed is also a good idea...
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The RXS100: vehicle of choice for Chuck Norris

[bladerunner]

120 psi says top end was indeed in good nick.....if laid up for winter possibly best to strip the carb of all brass jets and emulsion tube and give them all a good clean to remove any gunk/varnish that unleaded fuel is so good at leaving! Also check the fuel tap filter bowl for any debris but this usually shows as bike runs fine for a while then loses power rather than what you've described.....does the ht lead generate enough to span a 10mm spark... If so ht lead and coil are sound.
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[russeleoin]

I had a very similar problem with my YB100. The problem turned out to be the float was worn and this resulted in over fueling as the fuel was not being shut off when the bowl was full. I had a thread on here, but it was a few years ago. Took me bloody ages to get it sorted. Good luck.
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I love classic merc's but bikes take up less space.
Current ride is a Yamaha YB 100 and I love it! Oooow and now a running GPZ400R!
Next stop, Direct Access hopefully by the end of summer.

[VultureZ1300]

Ok,decoked exhaust,cleaned and set carb according to manual,checked points and ignition system all ok,big healthy blue spark at plug.
Still starts and run perfect but still no power,won't pull more 40 with me on it. Also checked the chain and sprockets all as it left the factory.
Problem is I am used to a kawasaki Z1300 and a Triumph cafe racer with a tuned engine so have no idea what a rs100 should feel like but i am sure it should do a bit more than 40 on the flat.

[doggone]

I had one about 1984, it was quite lively really and could accidentally do wheelies at the lights

[N cee thirty]

Sure you're not a fat bastard and its struggling to haul your arse?
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[VultureZ1300]

LOL. Not quite a fat bast,just 13 stone, sons a measly 10 stone and it's no better with him on it.
O well on gum tree it goes,can't be bother to mess around with the thing.

[smegballs]

[bladerunner]

Just to check....you are revving the nuts off it with the throttle wide open in each gear sent you? Should be able to hit 60 happily with you on board on the flat!
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[VultureZ1300]

Hello. Turns out the problem was over gearing,the rear sprocket was several teeth undersized,it's quicker in third than than in top.
Cheers for the replies.