CG125 cdi 'black box'

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

bike recently stopped in traffic and I have been unable to start it since! I think it's an electrical fault, I have fuel to the carb and the plug is wet after I've kicked it over a few times.

The bike is a 1999 cdi model with electronic ignition, kick start.

I've tested all the electrical components, hit coil, pick up coil etc and got good readings within the ranges stated in the manual. Only thing I don't seem to be able to test is the sealed black box of electronics (cdi box?). I have a spark when I turn the engine over but it seems quite rapid, I was only expecting to see 2 or 3 fat sparks?

I've seen a few of these cdi boxes on eBay but not for my year of bike. Does anyone know if they are very specific? i.e. would a later electric start box fit my earlier kick starter? I'm sure I read somewhere that a CB125 box would work but they're twin cylinder no?

If anyone has any advice on this or even if you think there's something else I should try first I'd be very grateful.

Nobby the Bastard · Harley Gaydar Joined: 16 Aug 2013 Karma :

My experience is that it's almost always not the cdi at fault.
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Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

Cheers, I've brought it inside and put it on a radiator (the CDI box not the bike Very Happy

) I'll see if that makes a difference. This all started after I left the bike out uncovered in the rain all night. Any ideas where else I could try?

Nobby the Bastard · Harley Gaydar Joined: 16 Aug 2013 Karma :

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

Thanks mate..... You've been a great help

Anyone else have any ideas?

carpe_diem · Trackday Trickster Joined: 28 Jul 2016 Karma :

Nobby the Bastard · Harley Gaydar Joined: 16 Aug 2013 Karma :

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

mudcow007 · World Chat Champion Joined: 01 Feb 2012 Karma :

To make the bike go, you need fuel, air and spark

Plug is wet - so you got fuel

Unless you done something really stupid, you should have air - what is the filter like?

Have you tried replacing the plug?

Plug cap/ Lead?

When you are trying to start it are you kicking it or 'leccy starting it?

Battery voltage/ age?

Kill switch?

Side Stand switch?

Start with the basics first

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

Hi, yep I have fuel and air, cleaned the air filter, drained a good bit of fuel through the carb and plug is wet. It's a kick start.

I've tested the HT coil and all the wires from the pick up coil to the cdi unit. Everything checks out. Is there any way of testing the cdi unit?

Do you know if these are very specific to bike year?

Battery voltage is good, horn sounds when ignition on and all lights working. I don't have a kickstand, do you know if there are any other interlocks I should be looking for?

Cheers for your help Smile

pulling my hair out trying to fault find this!

B0ndy · Spanner Monkey Joined: 25 May 2015 Karma :

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

Thanks, ideally I'd like to swap over the CDI unit with one from a working bike to see if it's the problem. Someone at work has a later model electric start bike hence my query about compatability. I'm going to check over all my connections this afternoon, give everything a good spray with WD40 and try again. Replaced HT coil, lead and plug. Still no joy, I really don't want to shell out on a CDI box without being certain it's the problem! Smile

Anyone in the Frome area with a Honda CG125 with CDI?

Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

First check is always the plug for sparks; then damp, then carb, the compression.

You checked the plug; you got a spark; it's damp.. WHY in hells name do you keep re-visiting the same thing over and over, after its checked 'OK'?!?!?!

If you got a spark, you got a fucking spark!!! what are you hoping a new CDi will do the one you got currently isn't!?!?

A new spark plug probably wouldn't go amis; you can get pretty useful looking sparks in free air that dissapear in the cylinder when that air is compressed to 10x atmospheric and theres rather a lot more molecules between the electrodes for it to pass through; but, that'll be the plug, not teh CDi.

CG has a self exited ignition, too. It's seperate from the rest of the electrics; one winding in the generator does nothing but make electric for the sparks; depends on the engine spinning to make it, so on an e-start bike if the starter's lazy it can striggle to spin it enough to make enough electric for a good spark. Kick-start tends to be a bit lazier than e-start and so can take a bit more oomph to get it delivering enough electric to make sparks, but you are getting them off a kick, so you are getting them off a kick; ONLY notion that may effect it is that its a damn site easier to kick a bike over with the plug out with not compression against the piston, so you could be getting more spark kicking to test than you do kicking to start... BUT you are still getting a spark! Try a new plug.. and kick it harder, try bumping in 2n'd gear.

CDi ignition is fixed timed, so should be little chance that the spark is happening at the wrong time; so apart from the spark plug, you have pretty much eliminated the ignition system as the cause of your problem.

And dont matter how much you would LIKE it to be somethiung 'simple' that can be fixed by twiddling a wire, fiddling with a switch, or plugging in a new component..... if its all checked out, its all checked out!!! Look elsewhere!

Rule of thumb compression test. Stick your thumb over the plug hole, and see if you can hold it there while some-one else kicks the engine over.

If you can.. you dont have any compression..

Get the manual; follow basic service procedures... particularly for tappet adjustment and I recommend if you haven't got'em buying the Honda Tappet tools from Dave silvers to make it easy and avoid rounding tappet squares or chewing tappet lock-nuts.

That aught eliminate posibility that tight tappet clerances are holding a valve open so you dont get any compression.

If that doesn't improve matters; THEN you need to start looking elsewhere, and do possibly a propper compression test on a guage.

A Kickstart or duelstart CG aint going to be any spring chicken, and will either be high mileage, likely to have worn its bore and rings beyond, or it'll have been layed up for long periods, rings gumming in the piston grooves, again, likely to give poor compression and excessive bore wear; good chance it needs an overhaul and a rebore or re-barrel.

Could be tired old head gasket has 'gone' or the head has warped so gasket don't seal; but they both still need to the top end stripping and overhauling, and symptom is the same in a low guage reading compression test.

BUT that is where you go after checking you got sparks and juice in the pot....

I SUSPECT, that a new spark-plug and a tappet tickle / basic service, and you'll find the thing springs into life with a hotherto unobserved zest, though...

But, you have checked the sparks, and got'em; at the moment there is absolutely NO reason to suspect that the bludy CDi, probably THE most reliable part of your motorcycle is in ANY way 'suspect'.. so why persist trying to blame the bludy thing?!?!
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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?'

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

OK, thanks for all of this. I'll stop going round in circles with the ignition system then!

I ended up down that cul de sac because it just stopped running in traffic.

Already changed the plug so this afternoon I checked valve clearances, a little tight but some play, adjusted them to the correct gap.

Did a compression check and it seems pretty low, albeit with a cold engine and my compression gauge doesn't have a thread small enough so had to use the rubber 'push on' adapter.

I got 80psi, manual says between 140 - 170psi warmed up.

So it looks like I need to start stripping the top end then?

It started first time every time before this problem, do you think I would have seen a gradual drop off in performance and increasing difficulty to start if it was a worn engine?

Would it more likely be a blown head gasket?... or a burnt out valve?

I guess either way I ain't riding my bike again for a bit! Fuck.

Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

How did it behave when it died in traffic? Did it just stall at tickover, did it feel like it was running out of petrol for a minute beforehand?

The bike clearly started ok that morning, then died and didn't want to restart. It is unlikely to be something really terminal.

The bits I would look at are:
1. Plug - which you have done.
2. Idle adjuster slipping - should still start on choke with a hint of throttle.
3. Water in the fuel. Particularly if it had been washed or got wet for the first time in a while the previous day. Drain the carb and look for water.

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

You're right, I need to get a grip here Sad

Thanks for all your advice, I'll go back to the carb and see how that goes.

Water in fuel? I drained a good jam jar out the bottom of the carb and no signs. I'll pull the carb and try a bit of fuel squirting, thanks for that. Like you say need to start element ing some variables.

I need a beer

symonh2000 · Crazy Courier Joined: 20 Feb 2005 Karma :

Not had a CG125 CDi unit fail, but I did have one fail on a TZR125

So although it is unlikely, I wouldn't completely rule it out if more obvious checks don't solve the issue.

The issue I had was first a loss of performance, on one ride. The next day it wouldn't start at all with no sparks with the plug removed and resting against the cylinder head.

After checking everything I got a replacement CDi and all was well again.
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Four strokes is two strokes too many.

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

So whent through checks on the fuel stetem again. I've removed and cleaned the carb and following Teflon-Mikes advice, tried squirting fuel into the inlet. Nothing.

Removed the head tonight, the valves look like they have a lot of build up on them, as does the crown of the piston. There doesn't seem to be any obvious damage or wear. See pics.

If they've uploaded!

Could the fouling on the valves cause lie compression, gasket looks ok.

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

Second pic

Petemate · Trackday Trickster Joined: 13 Nov 2015 Karma :

Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

A 'bit' of carbon build up?!?!?!?!?!?! Struth!!!
Yeah! - COULD BE! - the problem has been revealed - made too soon!

That carbon has got to have come from somewhere though.. hasn't it?Its been burning oil a while, that has.
Oil gets in the pot to get burned from one of three routes;
1/ HeadGasket failure no sign of tracking on your head, though, so more likely....
2/ Valve Guides, worn or stemseals shot
3/ Rings / Bore - ring snapped/ bore worn / scored.
4/ All of the above!

Overhaul the thing.

Get a chinky barel kit; it'll be as cheap as a rebore & piston.
Head might scrub up if you strip it and soak everything in oven cleaner; lap the valves and fit new stem seals; but if it needs more than that, then it's probably as cheap to get a new chinky head off ebay, as get the valve seats recut, face skimmed and new guides pressed in.

There's hope for it; that lot wont be 'too' expensive; wont be a five quid five minute fix; but could be done in a weekend for around £100 and it'll put more life into the thing than it had when you got it, so worth the doing.
____________________
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?'

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

Cleaned up the head and valves and lapped them. I've ordered a new valve stem oil seal, exhaust only, the inlet didn't seem to be fitted with one.

I was going to pull the barrel off this evening to have a look at the piston and rings before I order a kit. Are these Chinese kits OK then? I've seen one on e-bay for my year for 40 quid!

Any tips on reassembly (I've not done this before), obviously new top and bottom gasket. Any other bear traps I need to watch out for? This is turning into a bit of an epic job but at least I'm learning a bit about bike mechanics!.... and like you say it should put some life back into it for a bit

Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

Mat_ryall · Derestricted Danger Joined: 15 Oct 2016 Karma :

Thanks for your advice on all of this, very much appreciated.

I've now removed the barrell and it all looks a bit shitty Sad

Inlet side is badly scored and the top two rings are stuck and worn flush, bit of a chunk out of the edge of the cylinder too.

I'll order a kit....

Only problem is I can't get the old piston off, I've removed the two circlips but the gudgeon pin won't budge. I've heated the piston, given it a 'tap' while wedging the conrod with a bit of timber and moved it about a quarter of an inch, won't move any further.

Piston is rotating on the pin, pin is stuck in conrod. If that makes sense.

Not quite sure what to do next, maybe make something out if a bit of threaded rod to push it out?