Honda C90 wont spark

[Madgooner2017]

hello all

i just recently got a old honda c90 off my grandad who has had it sitting in his garage for a good couple of years i know a little about motorbikes but not much about this one. As it came without a ignition key i have bought a new one and it has all the same colours as the wires inside the bike so i just connected all the same colours and hoped for the best.....

I flicked the ignition on and tried to kickstart it but nothing ive looked on youtube how to fix this but not sure later i looked at the spark plug wire and kicked the bike to see if it had a spark but nothing i dont know what to do about this

any help would be amazing thanks.

[ThatDippyTwat]

It's been stood for years, it's not going to fire right up.

You need to make sure the plug has somewhere to ground out to, or you won't see a spark. Hold it next to the hole it goes into (making sure not to knock any crud into the hole), and see if it sparks then. You would be surprised how many people just hold it in midair then declare it dead. You may well need someone to help you while you kick it over if you are not a contortionist.

[Teflon-Mike]

First of all, get a bit of oil down the bore.. pour it in through the spark plug hole, and work the engine over for a bit on the kickstart 'gently' to lube up the moving bits, before you do ANY more and risk stuff breaking or siezing.

Next; handbook will give a list of 'routine maintenance', and provide the mileages it should all be done at, or the time interval... "Whichever comes first"... so, if sat for years, go down that list and do EVERYTHING.. cos its likely long past due... AND it'll eliminate variables come fault finding.

Sparks? If its an older C90, good chance its a points ignition. dont even BOTHER to try getting the thing running, if it is, until you have swapped the points and the condenser... bits should be pretty cheap, but you may need to buy a rotor puller to get the generator rotor off to get at them... worth having though and usually only a tenner or so.

Ignition systems are a peculiar bit of electrickery; the clever bit is the coil, which gets 'energised' when a voltage is put accross it; then when that voltage is removed, the coil reacts to the change in voltage with a reverse voltage, proportional not so much to the size of originally applied volts, but the speed the volts change; hence instantly breaking teh circuit to remove volts on the primary winding creates a HUGE reverse voltage to oppose that change, and that in tern is amplified by the turns ratio on the secondary winding, like a conventional 'transformer' to make the mega-volts needed to make the spark jump accross the electrodes of the spark plug.

Points then are the switch that makes the spark happen, turning 'off' the volts accross the coil, and they are rather notoriouse for needing constant cleaning and adjustment as the contacts corrode or pit.

Again, long layup, they are likely in pretty dire state; buying new and replacing them, then ensures they are good, and act of fitting sets them up to the book to work as they should.

Condenser; is basically a large electrolytic capacitor that is coupled across the points, when they are closed, there's no voltage difference across its terminals so it stays discharged; when the points open, it sees the voltage accross the points and gets charged by them, so that the current doesn't try and 'arc' jumping teh points gap rather than the electrodes in the sparkplug! Useful things, but a bludy pita when they start to fail! and they tend to when they are old, and or unused. AND they can go either way; closed circuit, effectively bridging the points so whether they open or not, coil doesn't see the current turned off and don't spark the plug. Or they go open circuit, and don't accept charge and electric can start jumping the points, and you get weak and erratic sparks if any at all. And sometimes they just cant make up their mind!!!!

Again, penny part, swap it out, eliminate variables.

Couple more checks/precautions I would make; would be to remove the coil and clean the earth pints to the frame, laid up, likely to have rusted so not got a good earth; likewise the earth point between engine and frame.

And I'd probably drain the petrol, and flush the fuel tank, remove and strip the carb and clean, and refit with fresh petrol.

BUT... from experience renovating a C50 for No1 son maybe a dozen years back, engine would be near the bottom of my list of priorities.

These things have a pressed steel and pipe frame and forks, that can be rather prone to the old tin worm. I'd be paying particular attention to the forks and swing arm and the rear pressings, nibbing back anything that looks like a blister and stripping back hard anything that showed rust stain, and making sure the metal was sound.

Wheels, similarly wire spoke steel rims; they rot from inside the rubber; I'd be pulling the tyres off, tweeking spokes and tapping and shaking the rim, to assess whether they were good; ISTR having to track down a replacement for No1 sons.

Switches ISTR were pretty typical old honda, and quite nice in that they could be stripped down and cleaned up in the contacts rather effectively; BUT that tin work rot issue was a nightmare on earth points.

Ignition is also switch 'off' by making a circuit to short circuit the coil to earth.. check your new ignition switch contacts carefully; I have bought a couple of the CB125's that have proved to be of Chinese oragin and slight variants on the original honda with the 'make to kill'' turnie offie wire routed externally to the multiway connector.

BUT, if you struggle to get sparks with new points and condenser, look for that circuit being 'earthed to kill' elsewhere.

Other advice? Buy the Tappet Lock-Nut box-spanner: 07908-GE00200 -> £7.33 @ Dave Silvers & Tappet Adjuster Key: 07708-0030400 -> £3.80 @ Dave Silvers . (Prices correct last time I looked quite some time ago!

Absolute GODSEND on the little lay down single C90 motor and derivatives to get in at the damn things through the ruddy inspection caps!

A cheap pair of feeler guages, you dont mind spoiling, robbing out, I think it's the 0.05mm blade (but check the manual!) and 'cranking' at the tip, and possibly slimming down a bit in the width on a bench grinder to more easily get through the inspection hole, is also a good call.

Removing exhaust tappet inspection cap also dumps all the oil out the motor!!!! So drain oil before doing tappets, and you may want to find a way to rest the front end of the bike over the back of a garden bench or something to make it easier to see in the ruddy holes!

All the best... have fun with it!
____________________
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?'

[Madgooner2017]

thank you all so much for the advice i will be sure to be doing everything you guys suggest as its better than me just attempting to do it myself