Intermittent problem?

[blossomsowner]

hi.
hoping someone out there with more clues than me has some good ideas about this.
Bike is only running on three cylinders. But not all the time, sometimes it runs on four like it should.
Low mileage rf900. Tonight i went to the nic smith thing, started off on three, about 2km up the road it smoothed out, power on beautifully and ran great all the way there. Coming home again,,,,,,3 all the way running like a pig.

the sparkplugs are fairly new and when swapped around makes no difference.

checked for spark and there seemed to be plenty.

swapped coils around but made no difference. So coils and ht leads are ok?

pulled out carburettors and stripped the offending one loking for blockages or wear........all seems good.

Someone suggested valve problems of some sort.......but surely this would be a constant state.

could it be an ht lead with a fault in the wire?

always same cylinder...........no 3.

any ideas/advice much appreciated

[howdamnhard]

Sparkplug cap or HT leads would be my guess. My bike did the same and previous owner replaced coils to no avail. Check it at night when it's running on three May be able to see the arc). If you listen carefully you can hear if it's arcing (ticking/clicking) sound. May not exhibit fault with tank off when checking so try check it with everything in it's normal position if possible.

[blossomsowner]

thanks for that....will try it and see.
anyone else got any ideas now that I will actually have some time to have another go at getting this sorted.

[kwaka_crasher]

the sparkplugs are fairly new and when swapped around makes no difference.

checked for spark and there seemed to be plenty.

swapped coils around but made no difference. So coils and ht leads are ok?

pulled out carburettors and stripped the offending one loking for blockages or wear........all seems good.

Someone suggested valve problems of some sort.......but surely this would be a constant state.

could it be an ht lead with a fault in the wire?

always same cylinder...........no 3.

How do you know it's #3 that's dropping and only #3? Header pipe temperature? Timing light?

If you're certain it's always the same cylinder (after swapping the HT leads & suppressor caps) and you're sure the #3 carb float isn't sticking closed or the slide sticking, it could possibly be a tight valve but that's unlikely. It couldn't be the ignitor because that would affect two cylinders. It couldn't be a coil because that would also affect two cylinders. It could be a lead or cap but you say the misfire is always #3.

But I would look at hard at the carbs again. Very hard. And the intake rubbers.

[jellywrestler]

i would look again at the carbs. I took the carbs off my RF gave them a tickle up to what I thought was good but I'll admit I had to get in there deeper for a second clean as there's a lot of hidden places.

[MSTRS:Me]

RF900 is based on the older GSXR1100. I had the same symptoms. Was a poked plug cap.

[kwaka_crasher]

RF900 is based on the older GSXR1100. I had the same symptoms. Was a poked plug cap.

If that was the case the misfire would have moved with the cap. In this case the OP claims that it's ALWAYS #3 missing.

[gammaguy]

check where the vacuum feed for the fuel tap is from.if it is number 3(which i think it is)then you have a leaking diaphragm in your fuel tap.you are experiencing a crude form of fuel injection,which makes that cylinder run rich,eventually causing a misfire.

time for a new one.......

[motorbyclist]

Someone suggested valve problems of some sort.......but surely this would be a constant state.

the valve clearances might be such that some valves aren't shutting entirely to make a seal in that cylinder - and this clearance will change as the bike warms up

but this sounds more like a typical carby problem... dare I ask what colour the plugs were when you pulled them out?

[blossomsowner]

ok thanks for the ideas........been a while since I did the swapping lead over thing so will redo and see if cylinder missing changes. other ideas good as well.will try again and see how it goes.
cheers

[MSTRS:Me]

If that was the case the misfire would have moved with the cap. In this case the OP claims that it's ALWAYS #3 missing.

I read he'd swapped the coils about and the plugs. But not the leads.
Whatever, it was the problem mine had. It happened because the design of these engines allows (rain)water to get all over the top of the engine and it tends to sit there, causing problem eventually with the plugcaps.

[kwaka_crasher]

check where the vacuum feed for the fuel tap is from.if it is number 3(which i think it is)then you have a leaking diaphragm in your fuel tap.you are experiencing a crude form of fuel injection,which makes that cylinder run rich,eventually causing a misfire.

time for a new one.......

This too is a viable theory although I'd expect it to do it all the time due to the vacuum not just when hot as seems to be the case. It'd need to be a lot of fuel too.

Simple check though - temporarily pipe a clear tube for the vacuum between the two points, instead of the rubber one, over the tank where you can keep an eye on it. Check for fuel.

I read he'd swapped the coils about and the plugs. But not the leads.

Fair enough. I just couldn't see him removing the leads from the coils to do it.

Whatever, it was the problem mine had. It happened because the design of these engines allows (rain)water to get all over the top of the engine and it tends to sit there, causing problem eventually with the plugcaps.

They must have been aftermarket suppressor caps - genuine generally have an intergrated moulded rubber seal that prevents the egress of water.

[Stone_Duck]

I had a similar problem, which you seem to have covered, No.3 plugged was fouled, are the plugs all the same colour when you took them out? I cleaned the dark one & it ran fine , but replaced the set that week. Also I have found my 95 RF much prefers 95 fuel to 91. Other issue with RF's is setting the float levels in the carbs correctly, I adjusted mine & fuel consumtion went from 15 to 17km/l instantantly. Riffer has a good post on this.

[FROSTY:Me]

have a look at your carb diaphram and whilst looking check the needle

[ManDownUnder]

Ex owner of RF here - many many miles under the belt...

RFs are famous for dropping a cylinder when cold and/or (especially) when wet. It's what they do, probably their biggest fault.

Okay... here's something I've posted a few times


I paid $4750 for a 95 with 45,000 miles on the clock. four and a half years later it's now done 86,000 miles (141,000 kms).

I've found it to be pretty hard on front tyres - it tends to triangulate them, but its got a front-heavy bias so not unexpected. Avon Viper fronts don't last long but the grip is great. I recommend Avon Storm front and rear, however I've had success with Z6s as well and next week I'm putting some Conti Road Attacks on so I'll let y'all know how they work out.

The lack of a fuel gauge is a pain - especially with a reserve that lasts a good 80-90 kms. I get 300kms before it hits reserve and the tank holds 21.5 litres from empty. A real nana might get 400 kms from a tank.

Big problems with the carbs around the 100,000 kms mark. Pay attention to the needle jets and the emulsion tubes they run in - its a problem with Mikuni downdraught carbies - friction as the jet needle slides and it wears the needles and emulsion tubes. I've replaced mine with the carbs from the 135HP MantaRay model, and run a K&N air filter, ignition advance and debaffled exhaust and it flies.

There's a known problem with the alternator cush drive - in some of the earlier models (94, 95) the drive for the alternator failed and they replaced a part to stop it snapping - unfortunately this part only lasts about 20,000 kms so needs to be checked often - and its a prick to get at too. See here on this site for complete instructions on how to fix it.

Don't leave it lying around in the rain because it won't run on four cylinders afterwards. It's a problem with the water either getting into the coils or the low-tension leads just behind the headstock. My solution is to smear Vaseline into the low tension connections as they exit the wiring loom and as they enter the coils. My RF doesn't have any problems starting after sitting in the pouring rain all day. Others have had problems with the spark plug boots but not me, so I'm hesitant to say its an RF problem.
I've also noticed that as the miles get up you get a bit of problems with the electrics to the instrument panel. The wires run through the frame and a bit of chafing here can cause issues with the lights on the instrument panel not working - its an earthing problem - rewrap the wires and it should fix it.

The brakes are non-standard for a Suzuki (Nissin - normally found on Hondas) but they will take the Tokicos from the Hayabusa which apparently is a mod worth doing.

The whole bottom end (with the exception of the clutch) is straight out of the GSXR1100 so its bulletproof. Others overseas have commented on the hardening on 2nd gear going and causing problems but consensus of opinion seems to be that wheeliing the bike while preloading second ain't good for it.

The RF has a steel perimeter frame so in the unlikely event of a bent frame at least it is actually fixable, unlike an alloy frame.

Most RFs have about 125 at the crank, but you can get a lot, lot more. To meet American emission standards in the later models (S2 and later) they did the same trick as on the gixxers - look for the pink wire just under the battery on the gear lever side - more midrange power in 3rd gear if you undo it. You can drill and remount the digital pickup as they will easily take another 4 or 5 degrees of advance. Also, putting in the cams from the 92 GSXR750 will help liberate even more power. With these two mods and a rejet you could get 160HP.

Good for 265km/hr on a good day. Best kept secret in motorcycling..

Mine has just hit 141,000 and although cosmetically it could do with a bit of work, mechanically it's perfectly sound, if you ignore that seal on the front sprocket case that makes the chain a bit icky...

Here's some articles and posters elsewhere on the site.