The problem I have been having intermittently is with idling and occasionally stalls when warm. I think I have it nailed, time will tell. There is a caveat for at the end for other troubleshooters - read and learn.


Heres the story so far:

Got it over a year ago and was warned it ran badly and needed a carby rebuild. The seller started it when I went to look at it and it ran perfectly (on nice fresh fuel and a well charged battery).

At first I had no issues, seemed to run great, apart from a really annoying rattle when cold and with the choke on - just the usual cam chain tensioner issue. I decided the carbys are fine.

Of late, I have noticed an annoying idle problem - it idles, but (intermittently) about once ever 2-3 seconds, there iss a brief dip and uptick in idle speed.

After last months club run, I rode home on a fast straight road and when I got to town I noticed it was worse than normal and was stalling out at traffic lights unless I kept the throttle slightly open. There was also a really bad hesitation and flat spot between about 1800rpm-2800rpm.

I removed the resistors from each plug lead and cleaned the ends as they looked dull and possibly not making the best contact with the plugs. After this it seemed to run better when testing in the garage. All was well on a test ride during the day and didn't have a problem going to/form work. After another long run, I noticed the same problem (though not as bad as before).

Reading this forum and ebay, I decided that the coils/leads might be worth changing and the stick coil mod thread caught my interest. As price to swap the coils and leads for a COP/stick-coil setup was less than replacing with original items, I ordered a set for $AU72 delivered from Florida, USofA.

Advice from others suggested valve clearances ought to be eliminated as a possible source, so reference to the appropriate thread here helped on that front. My bike now has a ticking noise it didn't before (one valve clearance a tad too loose), but I found the idling problem still absent even after 100km today. Then at our lunch stop today the bike stalled when I pulled into the car park.

It was only when I got home later and decided to do some immediate troubleshooting of another issue (minor rear light issue) that I realised the missing piece of the puzzle. When I put the bike in the garage, I usually switch off the headlight. I often ride without the lights on, but usually remember at some point on the open road.

The bike idles perfectly well with lights off, or with parking lights on. With headlight on, it runs a bit rough and stalls out, the flat spot also only seems to be there with the lights on. No issues with charging system

So the alternator is doing its job, as is the regulator. Grounds are not a problem as all lights work OK and it starts perfectly. I am pretty certain the initial diagnosis that the coils/leads are the issue is accurate and am happy that the spark comes good once primary voltage to the coils gets above a certain threshold. Old/weak coils are my top pick.



The moral of the story - when troubleshooting pay attention to EVERY variable, forgetting to verify whether lights were on, or any other loads were on the electrical system caused me to question whether I was making progress or not.

 

You checked your voltage whilst running under load ?

 

Stick coils installed and working. Not taken for a ride yet (bad weather ATM), but runs OK both with and without headlight on.

I didn't exactly follow the stick coil mod thread - I made a neater/smaller wiring loom so it just connects directly to the existing 3 pin plug at the left front of the engine.
By disassembling/modding the CBR600F4 loom I only used 3 solder joints so less risk of failure/corrosion. It even has wire colours that match up to the main harness connector.

Voltages:
13.8V at idle
12.2V with headlight on, then rises to about 13V if light switched off.
14.1V at 2,000rpm light off
14.4V headlight on, 3,000rpm.

 

Hello UNM,

please let us know how it's working now. I'm in particular interested in your problem because I got one almost the same.
In order to check the valves and CCT, it is necessary to remove also the coils. When the job was done , and reconnect all back the engine now runs very badly. I got sparks only on cylinder 1, 2 , sometimes 3 and nothing on 4. I measured :
- primary coil resistance between terminals 4-4.3 Ω (manual values 2.5-3.2 Ω) - could this be the issue?
- resistance between spark plugs caps 25 Ω (manual values 21-27KΩ)
Also cleaned the 3 pin electric plug you mentioned above.

Never thought about cleaning the plugs so this will be my next step.

I hope you don't mind telling my problem on your post, if you do, I'll shush myself.

Thank a lot, Razvan.

 

razvancc, I don't know if it will be any help, but I used bicarbonate of soda to clean the three pin connector to the main harness. Did a great job applied as a paste with a toothbrush and then washed off.

As your problem is with sparks on cylinder 3 and 4, it does NOT sound like the coil itself. Each coil fires two cylinders (one coil for 1&4, other for 2&3).

By 'manual values' I assume you mean the values listed in specifications section of the service manual. I suggest you check if your meter shows any resistance at all when touching the test leads together - sometimes it reads slightly high so you need to take this amount off any measured value.

The lack of resistance in the plug leads is odd - perhaps you are missing the original resistors, but worth checking and cleaning the resistors anyway if they are there. To do this, pull off the plug lead and look into the cap - you should see a slot which can take a largish screwdriver. Unscrew and remove the resistor (about 10mm long, 2-3mm diam). Mine were stuck due to age so I used a slim screwdriver to wiggle them loose, then managed to pull them out of the cap with tweezers. Cleaned them with 1200grit paper and reinserted with the tiniest smear of dielectric grease. Also make sure the plug leads are well seated on the plugs. You can disconnect the leads from the plug cap and trim a tiny bit (1-2mm) off the end, if there is a poor connection there, it might help.

TBH, it is an odd one if the bike was running OK before you did this and the poor sparks are only on 3 and 4.

Good luck. If you can source coils and a harness, it is an easy job to upgrade. I don't know how reliable it is long term, but haven't seen any complaints from others. I'd recommend it rather than replacing with original components. Total cost was about US$50, you might get something shipped within Europe for less as I am in Aus and that affects shipping costs.

Edit: just occurred to me, you might be able to swap the plug leads around between the spark plugs as they are similar lengths. Swap leads between 1/4 and between 2/3. If the fault moves, you know it is in the plug lead or cap.

 

Thanks a milion for all the help! After following your suggestions, finally realised it's no electrical issue. So, no problem with the sparks, I got them on all four cylinders. I think the real problem is that I didn't correctly synchronised the intake camshaft afte the valve adjustment and cct clean up , thus very bad engine behavior.
Well, a proper motorbike service will take care of that and maybe, a nice racing set of spark plug sockets and cables.

How about your CBR?

 

I had a wee test ride and did things to the old lad that should not really be done.

Once I took the chill off the cam chain and verified it was running OK without choke, I switched the headlights on and idle was stable, I then tried giving it wide open throttle from 1100rpm in third and it pulled evenly. Not huge amounts of power as you would expect, but before the mod it would be extremely lumpy and would quite likely need clutch slip. I also tried corners in a higher gear than was wise, still quite stable.

Don't know if this is any better than a new OEM coil, but it satisfies me.

Top marks to whoever first thought of upgrading to a COP setup.