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Difficult Diagnosis
Blog Date - 03 February 2017
"My bike is running rough, it sometimes doesn't tickover right and stalls occasionally"
"Crap in the injector mate."
"Will that help?"
Sharon's goat impersonation is probably funnier than my joke.
So my bike hasn't been running right for a couple of weeks. On the throttle it behaves although it does feel just a little "woolly" then on tickover it seems weak, too low and variable too. So what is the issue? Could it be :-
- Air idle control valve. Maybe this is sticking. My CBF125 doesn't have a throttle stop screw as the computer has control of a tiny electric motor that can alter the amount of air that bypasses the butterfly valve and the throttle body. With this and also by altering the amount of fuel injected the computer has total control over the idle or tickover. On a cold start the tickover is raised a little then as the engine warms this drops appropriately. Recently the tickover has been up and down, sluggish on cold starts then suddenly revving up more than required. After warm up sometimes it ticks over fine and is snappy away from the lights, other times it bogs down for a second or even stalls as soon as I open the throttle. If the Air Idle Control Valve is sticking or not reacting as requested by the computer this could be the source of my problem
Is my Air Idle Control Valve sticking?
- Worn valve seats. This was the cause of all the nightmares on my CBF250. Infinitely variable tickover, poor performance away from a standing start, massive changes in behaviour from cold to warm engine temperatures and just general under performance. Maybe the CBF125 also has worn valve seats and the computer is doing it's best to manage the tickover? It will struggle more and more as the valve seats get worse.
Reground valve seats sorted out the CBF250 eventually
- Faulty engine temperature sensor. If the computer thinks the engine is cold it will vary the fuelling and tickover to accommodate this. Imagine then the temperature sensor is sending warm signals when cold for a few moments then cold signals when warm for a few more moments. The computer program will keep on altering fuelling and idle air to manage these changes. Of course the engine temperature is not changing all the time so the tickover is rising and falling causing my troubles.
- Poor Fuel...
- Failing fuel pump...
- Failing battery (tenuous but I have my reasons)...
- Failing wires to the computer...
- Failing coils / HT lead / spark plug cap / spark plug
- Dirt or some blockage in the air idle control system or another part of the throttle body
...and so on and so on and so on.
The thing is with any motorcycle from a vintage 1934 Wurstlethorpe Side Valve 450 to a modern R1 some problems are complicated and have several perhaps many possible causes.
OK at least with old motorcycles getting to the engine is a lot easier.
So here are Mr and Mrs mechanically uneducated stood outside a garage or repair shop of their choosing. They have presented their vehicle suffering from "it feels wrong and it keeps on cutting out sometimes". They expect the mechanical engineer to suck air between their teeth, listen to the engine for a brief moment, diagnose the issue immediately, suggest a price to repair the problem and be back on the road later that day.
One workshop believes it to be the carburettor float bowl level is out, they've seen this problem before on this model and last time a quick tweak of the float with some pliers fixed everything right up fine. Another garage thinks the coils are on the blink. The lad down the road assures our hapless couple that the inlet manifold gasket is letting in air. And so on and so on and so on.
"Carbs mate, dead simple easy peasy an awl dat"
Talk to any DIY mechanic and he'll have been through this painful process. Ask any online forum what is the problem with my motorcycle and you'll get 27 different suggestions of which 18 have some logic and plausible thinking behind them. Most vehicle owners will have a tale of garage X that charged them £300 to fix something and the car came back just the same or worse. It is a nightmare!
Is there a solution?
Here's my thinking. If you are lucky enough to have some mechanical knowledge there are 2 things to take into account. Firstly the cost of repair for each possibility and secondly the likelihood of a possibility being true. So in the my case as listed at the start of this missive.
- Air idle control valve. Possible, in fact likely. I can get them second hand off ebay cheap enough, they're easy to fit. It's a contender
- Worn valve seats. Possible, less likely as the bike has been well maintained and the tappets are staying within tolerance. Damn hard job to do, pain in the ass but not expensive. Still, I think this is a last resort.
- Faulty engine temperature sensor. Hmmm...I suspect this would show up on the dash as a problem. Cheap and easy fix though. Towards the bottom of the list.
Probably not the engine temperature sensor.
- Poor fuel. Easy, just refill the tank and see what happens!
- Failing fuel pump. Maybe not, I'd expect problems at high speeds too. Expensive although easy to replace. I reckon that's towards the bottom of the list too.
- Failing battery. The battery is ancient and sluggish in starting these days. Unlikely to be the problem but I'm going to replace it anyhow, it is overdue.
- Failing wires to the computer. Bugger to test properly but it can be done at home and cheaply. Middle of the list.
- Failing coils / HT lead / spark plug cap / spark plug. Second hand parts are cheap. Possible, but I think I'd see arcing out at night and the problem is no worse in the rain. Lower in the list.
- Dirt or some blockage in the air idle control system or another part of the throttle body. Maybe...just maybe...
Have I found a solution? Hopefully. I stuck a large squirt of Redex injector cleaner in the tank 2 days ago and it feels a whole lot better. I'm not outta the woods yet but I'm optimistic. Perhaps it was crap in the injector or air idle control valve or perhaps the Redex had nothing to do with it and the problem coincidentally disappeared at the same time. I can no more prove the Redex helped than I can prove there is or is not a God.
Reader's Comments
Ian Soady said :-
Good advice. I'd add "only change one thing at a time then check".
I refer you again to Mr Pirsig's excellent book which goes into some depth on the issue of fault diagnosis as well as lots of other things.
One of the best bits (see you've started me now) is where Pirsig's mate has a problem with his BMW's handlebar controls being loose however much he tightens up the clamp screws. The clamp turns out to be slightly oversized; Pirsig says "what you need is a shim to take up that clearance".
The BMW owner (who is completely mechanically ignorant) is fascinated by this and starts to get enthusiastic but is horrified when Pirsig fishes an old beer can out of the bin and starts to cut a strip off it with tinsnips. BMW owner: "You're proposing to fix my £10,000 BMW with a bit of old beer can? No way". Pirsig: "It's the perfect material. Thin aluminium, easy to bend and cut and just the right thickness".
The story ends with Mr BMW storming off still with his floppy levers. If he'd gone to his local dealer and they'd charged him £50 for essentially the same thing he'd have been happy.
Have you started to read Jupiter's Travels yet?
04/02/2017 11:26:22 UTC
Ren - The Ed said :-
The problem with myself and reading is that I'd rather be writing, tinkering, riding or socialising. A few folks who read this 'ere bloggy website thingy are surprised I don't read much. Listening to real writers on the radio and TV they all seem to read a lot as well as write so I guess people assume I must be similar.
What will happen is the book will sit around for a while then something will click and then I won't be able to put it down. I had that problem with Zen and the art of Motorcycle Maintenance.
I've got a piece that involves "shimming" coming up.
I'll fix my bike (or my TV or my kitchen sink or my windows) with anything and everything I have lying around. I must admit though the driving force behind my ingenuity and MacGyver-esque bodges is financial rather than making an anti-establishment political statement. I don't like spending money...unless of course it is someone else's money.
As for doing one thing at a time you are quite correct. What happens in reality though is if you've got the tank off you might as well replace the temperature sensor AND the idle control valve...otherwise you've got to take the tank off again and on a bike with fairings this is a pain in the derrière.
04/02/2017 13:25:00 UTC
Sharon said :-
Ah the wonderful Robert M. Persig. I adored reading Zen And The Art Of Motorcycle Maintenance. It is one of the reasons why my Keeway is called Zen. His other book Lila An Inquiry Into Morals is another good read. However as his mode of transport on this journey is a boat it did not have the same appeal as Zen did for me.
04/02/2017 20:13:54 UTC
Ian Soady said :-
I never really got on with Lila despite lots of people telling me how good it was. It may as you suggest have been the non-bike content.
What I really liked about Zen was the way you could read it in many ways. As a straightforward travel story, an exploration of one man's (re)descent into mental disorder, a treatise on how to approach problems using motorcycles as the example, a dissertation on the differences between a "classical" and "romantic" views of the world, a questioning of the "either-or" philosophy and perhaps most important his exploration of the meaning of "quality". And each re-reading can expose new layers of meaning.
I must say however that I probably would not have enjoyed meeting him in the same way that I probably would not have got on with Socrates, another person whose views I appreciate.
05/02/2017 10:21:40 UTC
Liam said :-
I had idling issues on mine. The fuel injector looked like it was full of gold flakes inside. It was the flake in the paint that had reacted with the petrol where the filler cap sits had managed to get past the filter and into the injector.
A 50p large car in line filter stopped this from happening again. You should see how much crap it's caught since installation.
I unfortunately brought the rogue Friday afternoon model. Dodgy gear box since day one, really should of returned it but thought I'd ride through it and it would eventually bed in. Still misses 5th gear and jumps out of 4th and 5th. Riding like you have 6 or more gears until the lever locks is the only way to select 5th.
Fuel pump and injector at 5k. Coil and ECU (they call it the ECM) at 6k. Made my own led rev gauge as old style ECU won't run the rev gauge.
Tip over sensor has been altered to trick ECU into seeing it as it went open circuit too.
At 7k5 cleaning the oil strainer guaze looked like the bed on a lathe. There was a disturbing amount of metal swarf. Always used fully synthetic pro 4 silkolene oil that's changed every 2500 miles and never ran low or overfilled.
Mines not got 12k on it yet. You're doing better than me.
07/02/2017 10:49:31 UTC
Ren - The Ed said :-
Blooming heck Liam sounds like you did get a real Friday afternooner. Did you buy the bike brand new or second hand. I guess even if it was second hand it was low mileage.
If you look around the site you'll see my story of ownership. Major problems have been clutch basket and alternator stators. Otherwise it's been the usual chains, tyres, oils and brake pads.
07/02/2017 11:01:19 UTC
Liam said :-
Brought it new, my mates sons broke clutch basket and like all of them burnt the stator out.
I'll get round to fitting that one I wound at some point. Work has been mental at the minute with over time coming out my ears.
I thought about selling the bike but can't ethically let someone else get lumbered with the thing. If I'm honest in the listing I'll get sod all for it. 3 years old in April.
I'll just keep running it until it breaks in half.
07/02/2017 11:41:36 UTC
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