I need some help diagnosing a problem.

Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

So this morning i set of to work like every other normal morning on my honda nxr 125but after about a mile and a half it seemed to bog down and loose power. Then at a set of traffic lights it cut out and wouldnt kick up, so i bump started it and it seems to be missfiring and only running when i put on full throttle and whilst this is happening it throws some blueish smoke out the back. If i let go of the throttle it will stall. My first thought was that a gasket might have gone but upon phoning my mechanic (step-dad =p) he said the crank shaft might have gone.
The engine is a CG variant.
Any ideas as to what you guys think it would be is welcome as it is my only way to get to work from home.

P.addy · Red Rocket Joined: 14 Feb 2008 Karma :

Well...he sounds like a fantastic mechanic. Wink

Checked your spark plug and oil recently?

Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

The oil has been changed about 2 weeks ago the spark plug was cleaned on the same day. Hes a great wanabe mechanic;)

Nope. · World Chat Champion Joined: 17 Feb 2011 Karma :

Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

Who am i to question a 50 year old mechanic hehe Wink

i cleaned the spark plug and put it back in, the bike started after 2 kicks but only lasted about 5 seconds. The whole time black smoke pouring out the exhaust. The spark plug seems to be getting wet.

Also i dont have a compresion tester.

P.addy · Red Rocket Joined: 14 Feb 2008 Karma :

Is the plug black as fuck?

Compression test on the cheap, remove spark plug and put thumb over the hole. Get someone to kick start it with ignition off and it should try and blow your finger away from the hole.

Its its black smoke (I'm guessing blue really) then its probably burning oil, which means compression will be a little low.

Get that checked, also get valves checked.

If you are close to Maidstone in Kent, I'm more than happy to have a look.

Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

Yeah it was black before i cleaned it. iv just checked the compression with my thumb and it blows air out through the hole no matter how tight i press down. the first time i checked i accidentally left my ignition on and a fireball flew up my arm :S.

Unfortunately i live in Huddersfield, Yorkshire.

Nope. · World Chat Champion Joined: 17 Feb 2011 Karma :

Stonefly · Scooby Slapper Joined: 17 Jul 2011 Karma :

Sounds like a burned out valve to me
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Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

The only tools/equipment that i have is a big socket set, toolkit that came with the bike, some feeler gauges and a spark plug brush :/

To add insult to injury it broke down 100 yards from my local bike shop which is shut on Wednesdays :S

The oil has burnt down about a quarter of the way down the dip stick in 2 weeks.

nightshaddow · Nearly there... Joined: 18 Feb 2008 Karma :

Usher4566 · Spanner Monkey Joined: 29 Apr 2011 Karma :

Rings gone .do compresstion test .get them halfords ,motospares,eBay ( cheapest).or whip head off and take a look because I think we can confirm from the smoke thY its ducked
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Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

so whatever it is, im going to have to somehow get a lift to work this week cause its not going to be sorted tonight xD

Johnser · Renault 5 Driver Joined: 19 May 2011 Karma :

probably one of the above issues but just check your choke isnt jammed on or that the airfilter hasn't disintegrated into the carb.

Ariel Badger · Super Spammer Joined: 02 Dec 2006 Karma :

Clean the carb. White smoke oil, blue smoke fuel.
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bodger · Nova Slayer Joined: 18 Apr 2012 Karma :

As Ariel Badger says-
If the smoke is black and the plug is wet is sounds like rich mixture, so the carb needs strippng and the fuel cutoff valve checking.
If the bike was running alright previously its very unlikely you have a problem with the engine.

Nope. · World Chat Champion Joined: 17 Feb 2011 Karma :

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

I like how everyone is instantly jumping on the engine rebuild bandwagon, without considering the alternatively.

It has oil in the engine, and has had oil in the engine the whole time. Rings don't suddenly wear out - they either go very gradually over tens of thousands of miles, or they snap. Snapping a ring is unlikely.

Likewise, burning out an exhaust valve is unlikely.

Simple things first:
1. Make sure it has fuel.
2. Make sure the spark plug hasn't unscrewed itself.
3. Charge the battery.

If none of these things help, then clean the carburettor.

These are the cheap fixes that don't require buying tools. A possibly problem going by the symptoms could be a sticking float or a bit of shit stuck on the needle valve, leading to a very rich mixture.

Nope. · World Chat Champion Joined: 17 Feb 2011 Karma :

Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

The bike is made by Hero Moto-Corp of Brazil. Yes there has been oil in the engine the whole time, but it has either lost or burnt down a 3rd of it in the last 2 weeks since i last checked it.

The bike was running perfectly before it stopped, if anything it was running better than usual with not so much as a caugh. The spark plug was the first thing i checked, it was jet black and very wet but after a clean it had a nice bright spark after testing it.

Also when it stopped running it felt alot like it ran out of fuel, so i put it onto reserve just incase which made no difference (it has 3/4 of a tank full)

nightshaddow · Nearly there... Joined: 18 Feb 2008 Karma :

the engine has burnt apoximatly 400ml of oil in 2 weeks?

my cb (26 years old ) and the por (chinese crosser with cg rip off engine) havent lost that much since i owned them even with the cb's oil leak,

if it is a knock off cg engine the chances are no matter where branded it will be chinese with the engine number prefix of 156/157 fmi

i would remove the rocker cover (3x 10mm bolts) and look at the 2 valves maybe even post a pic of what you see, the engines (of which i have had 3 with no trouble) are renowned for dropping valves
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Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

The bike is a Brazilian Honda made by Hero Moto-Corp which works/worked for Honda. As for as i know though Honda supplied the engine as it is the Brazilian made XR125. Il take a look under the rocker cover and inform you of what i find.

Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

just took off the rocker cover and everything seems to be fine, valve spaces are to the correct tolerances, nothing is cracked/broken and it is all full of oil, so its either the carb or the piston?

Also if i am to check the barrel, is there any guide for a CG engine for taking it apart properly? and do i have to loosen the valves to do so as i dont want to ruin any timings.

bodger · Nova Slayer Joined: 18 Apr 2012 Karma :

Unless you were caning the bike on your way to work I cant see how you could have damaged the the engine
Dont start stripping the engine before you check the basic things first. Such as stripping and cleaning the carb.

Tuffers · Scooby Slapper Joined: 29 Oct 2011 Karma :

I had just set off from some traffic lights and was slowing down with the traffic, at max i was at half revs which is why its so confusing to me, it looked like it ran out of petrol but it wouldnt run unless i bumped it and what would have caused the blue smoke if it is the carb :s