125cc scooter wheezing like an old drunkard

[whiskydeltata...]

Hello,

Can anyone here identify possible reasons why my 125cc scooter won't start?

I've put in a new battery, changed the CDI unit for a new one, and replaced the spark plug.

I've uploaded a video of my attempting to start it on YouTube here:
https://youtu.be/BDdjGZ1woWc

Thank you in advance for any suggestions; unfortunately I'm a complete beginner with mechanics, and yet I am trying to learn more.

Regards,

Dylan

[Baffler186]

What made you buy a new CDI and new battery? Were you having problems before this or did you randomly think that your CDI and battery were faulty?

Did you fill/charge battery properly according to the instructions first?
Are you sure the spark plug was the right one, and did you check the gap?

What's the oil like - have you recently looked at it or changed it?
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Current: 2009 SV650 S, 1990 Kawasaki GT550
Previous: 2009 CBF125, 1998 GSF600, 2004 FZ6 Fazer, 1978 CB400a Hondamatic

[Evil Hans]

Does it start with jump leads?

Does it start with jump leads connected directly to the starter?
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Triumph Sprint ST 1050. And it's Red.

[Fizzoid]

Did the starter always turn so slowly?
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Rogerborg wrote: It'd certainly make it easier to ego-find my own posts on pages, given the number of fags (gay like traps) who insist on putting my name in their .sig

[MCN]

Seized piston or crank or big end,

Has it been roasted? Ran without enough coolant/oil.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[whiskydeltata...]

Many thanks for your replies, folks. My own now will show just how little I know about mechanics.

Baffler186
I bought a new CDI and battery because I read that these may be issues. As they were fairly inexpensive, I thought I'd give them a go.

The scooter has been sitting under a cover for two years and has not been started even once during that time.

I correctly filled the battery but did not charge it as I read online that there would be enough charge to start.

Spark plug is correct. Sorry, what is the gap?

I haven't checked the oil.

Thanks.

[whiskydeltata...]

Evil Hans

Unfortunately, I'm unable to check this as I don't have access to a car.

Thanks.

[whiskydeltata...]

Fizzoid

No, the last time the scooter did start it turned over much quicker.

Thanks.

[Teflon-Mike]

Err..

1/ did the battery you bought have any acid in it? Did you have to fill it.. and remember to?
Post-Office wouldn't/wont deliver a battery with acid in it cos of H&S... they come 'dry'... they should have a seperrate sealed acid pack or three with them so you can fill before use.... the cheaper e-blay specials dont, the acid is another and chargeable item, to make the BIN price look cheaper....
2/ "Dry Charged", as supplied... means that there is a small amount of surface charge on the battery... IF the battery is then filled with acid, and left to settle, you MIGHT be lucky enough, if you have a decent starter to start with, just about get it to crank and catch on that charge...
I would NOT bank on it, and would follow the old fashioned instructions for a new battery...
1/ make sure its full of acid!
2/ TRICKLE charge on a mains bench charger over night before anything else
3/ leave to settle for an hour or so, in order that frothy acid made by charging froths out... THEN check the electrolyte levels as they have probably dropped... top up if needed, and put back on trickle charge for an hour or so.. and repeat
4/ Fit to bike... and use...

B-U-T, if the bikes a lazy starter or been layed up for any length of time, I do NOT start cranking it on a brand new battery.... battery has a rating, probably something in the order of 8-10 Amp-Hours... thats the number of amps it can notionally supply for an hour, or it takes to charge it.... ie; put an 8!h battery on a 4A bench charger, on 'fast' charge or 'full'.. that can supply 4Amps at peak.. battery will only draw that when first put on charge, as it charges the terminal volts will ride and the amps it will draw will drop... so it can take perhaps 12Houirs to fully charge an 8Amp-Hour battery from new on a 4Amp bench charger.

Starter motors suck phenominally more amps than the battery's nominal rating; maybe 80Amps.. which means that with a good battery, fully charged, and a good starter system, thumbing the butto9n with the kill-switch 'off' you can completely flatten one, in maybe 1/10th of an hour, 6min.... or less, as again, as the battery discharges terminal volts will drop, and the amps will be loath to flow, as the acid inside is locally depleted of electrons and effectively 'boils'... so, the cranking will slow down, and you may get more than 6minutes of turning time from it, but it wont be quick enough to get the engine to catch.... secondary phenomina is that the locally boiled electrolyte, left to settle, the battery can seeminly 'self charge' or 'recover' and after being allowed to settle after cranking, can find another burst of cranking amps...

B-U-T.. and this is the critical bit... its called deep-discharge, sucking an enormouse ampage out the battery above its nominal charge or delivery rating... done excesively, that current flow can make the electrolyte and or coatingfs on the plates break down, and redfuce the charge capacity of the battery.. and in pretty short order.. it is NOT something condusive to good battery life, and an old laid up bike witrh a new battery, loath to start can kill that new battery in short order.... dead, flat scrap, shows terminal volts making you think its good, but no matter what you charge it with or how, it wont hold the charge it should, and in worst cases not enough to get even a good starting engine to catch....

Take Note: bike charging system probably only rated at something like 80W, about 5-6amps, 'max' when the engine is turning at perhaps 5ooo rpm or more..... at tick-over revs, 1000 or so, you probably donbt get more than 20W, and that's being supplied to the ignition to keep the engine sparking, then any other electrical equipment thats turned on, like the head-lamps or warning lights on the speedo, BEFORE there is any left to charge the battery back up with.... its enough to top the battery back up after starting, but ONLY if the thing has a decent enough run at charging revs to be able to put back in more than was taken out... and if it would take a higher power bench charger all night to replenish the charge used in 6-minutes of starting-cranking? Leaving the thing running on the patio at tick-over for 10 minutes, or chugging accross town for an hour PROBABLY isn't going to put back all that was taken out.

HENCE... for fault-finding and diagnostics, I do NOT use the bikes own battery... that is taken off, put on the window-sill on trickle charge, and I use a large, 45Amp-hour car battery... I keep specially for the purpose... on bike freindly jump leads... that is it has starter motor guage cable slighty thinner than wot you get in halfrauds but up to the current they have to carry, and with either smaller crocadile clips of a pair of bike battery terminals on the end, that I can clip of bolt more easily and securly to the bike's battery leads, than common car crud....

Big car battery, has the excess of amps in its capacity that it is not so deep-discharged by prolonged or repeated starting, and that much bigger can and will do it for longer, whilst I de-bug the thing finding out whats wrong with it and getting it to catch....

Once I have sorted the bike, and know it will start.. THEN I might put bike battery back on, or even risk a new one, that I can be reasonably sure the bike wont instantly blugger, and I wont kill trying.

DO NOT direct 'jump' from a car. You dont have one, you say so possibly not such a worry, But.. easy to wheel a scoot round a mates.... Car batteries are a dang site larger, they also have a different sort of charging system, and the huge amps that a car alternator can bang out, can fry the electronics and particularly a bikes electronic regulator, trying to regulate the amps it gets from the car alternator. If you must jump from a car, take the battery off the bike, couple it with jumps to the car battery to charge, then re-fit to bike. Safer, and oft easier as ytou aen't trying to get usually enourmouse car sized crocadile clips onto tinyt bike battery terminals, in a fairy-finger sized hole for the thing, 'on' the bike.

Oh-Kay! Thats the battery dealt with....

Next up why wont the thing start? You need three things to get signs of life;
1/ Air/fuel
2/ Compression
3/ Spark

First check is simple, pull the plug out, make sure the metal of the plug has a good earth out of its hole, and crank the engine to see if you have a spark accross the gap.

Next; Stick thumb over spark-plug hole... does air try and push your thumb out the way, suggesting its getting compressed in the cylinder?

Last... when you remove thumb... does it smell like petrol..... of course this is a redundant test of it smelt of petrol before... so wash hands first!

If no spark! Then you need look at the ignition system. And first checks are answringf the silly questions... is the ignition switch 'on'? Is the kill-switch activated?: Is there a stand inhibitor? Is stand 'down'? Is there a brake or clutch inhibitor.. may need to check user book, but some scoots require the brakes to be held in to start. Check, double checl, look for the dummmm and or obviouse first.... before you start ripping of complicated electronic black-boxes randomly hoping that they are mystically to blame!

Next, is there compression... if you get sparks in free air... takes a heck load more volts to make a spark jump the electrodes on a plug when its in a pot of compressed air and petrol in the engine... a spark in free air IS a good sign... but not 100% So, is the plug good? Is gap correct? Is the plug cap properly seated, etc... and you work back from there, to the coil, looking at the HT lead between the plug cap and coil, for signs of damage or posible shorting, or even not being connected coil end! Is it clean, is it dry, etc etc etc.

And does your thumb smell of petrol? If not it aint getting through to the cylinder and even if you have sparks and compresion, there's nowt there to set on fire. Id there a fuel tap? Is trhere fuel in the tank? Is it fresh!!?!

Petrol goes stale with age; the lighter more volatile fractions nautrally evaporate, like perfume or air-freshener... leaves a ticker liquid less want to vapourise or burn.. so drain the fuel, fill with fresh. Check the fuel tap is on, check the fiulter on the fuel tap is free and clear and clean...

And back to compresion... if all else seems good, as said a spark plug can give a spark out the pot, but not in it. So, iof the basics are bottomed, and you need double check this, you need to get a compression tester on it.... this is a guage that can push in or screw ion to the spark plug hole and measure how much pressure the piston actually makes when cranked.... and on little bikes, they are NOTORIOUSELY unreliable......

Your engine is trying to squash just 125cc of air into a 12.5cc combustion chamber to get 10:1 compression ratio.... taking the spark plug out, you have probably 4-8cc's of 'space' it would normally fill, added to the combustion chamber volume, which can make the readings way-off, compared to a car, that probably has a 400+cc cylinder, and 40cc combustion chamber, and the 4-8cc of spark-plug is a fr less significant influence on the ratio..... Use a push-fit compression tester, that rely on how well the rubber fits the hole, and how hard you push on it to even get a seal... they are even LESS accurate or reliable on a little motorbike engine... may give you an idea.. but not a lot more than the rule-of-thumb over the spark-plug hole!

If comprssion low... and bikes been layed up.... good odds that the pistoin rings are gummed ip or rusted in the bore cos of lack of use, and pressure is squashing past them into the crank-case.... just as good odds that the valve clerances have never been checked and the valves not sealing so pressure is going out the way it came in.... and again, lack of use can see the valves and the seats rust and stop them sealing and wast compression.....

So.. basic service ops... check valve clerances!!! And as precaution on a laid up motor, before cranking it.... small squib of oil in the cylinder with the plug out, then crank and work that in, to lube the bore and work the rings free, and you dont have metal rubbing dry on metal when you try spinning it over under load... or it WILL sieze!

And on you go from there... working methodically... getting hands dirty, checking one thing at a time systematically... NOT randomly having ideas that it migt be a black box and randomly changing components on the off-chance, and hoping it fixes the mystery problem!

B-U-T start with the battery... has it got acid in it? Is it properly charged? Has it properly settled? Without that you are onto a looser before you even begin... and trying to run up a laid up bike, and fault find any pre-existing issues, let alone lay up issues, you are REALLY starting from the back of the grid, making life ghard for yourself piddling in the dark.....
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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?'

[Ste]

A bit long winded but that post is helpful and relevant. So much so that a piss take tl;dr version isn't necessary and a word count would be pointless.

wtf has happened? Where is the real teffers?