Hi all,
I hope someone might be able to offer me some advice on an on/off starting problem i have with this 1991 Honda CBR600FM.
Firstly, a bit of history on the bike, it is a Spanish 1991 model which was imported to the UK in 94 and owned by my father from ~'04 until he didn't use it any more and it was laid up for about 3 or 4 years. I picked it up, had the carbs cleaned up and had been using it as a daily commuter in London for about 18 months with little issue.
I then moved to Norway with it and have been having intermittent starting issues. The bike is now not used year round and spends winters tucked away, the first year in a non-heated garage with the battery removed (i didn't remove fuel or put in any additives, which i know i should have) but it continued to start afterwards though with the same issue. It also sounded like it was running on 3 cylinders, so since then i have swapped out the ignition coils for other used ones from the same model and year and had the solenoid go pop, so have had an after market one of these in. The starting issue kept happening but i used it when i could through the warm months. I had the bike away in a heated garage last winter with a mechanic to perform a large service so it should have been stored optimally.
This year is has fresh tyres, chain, sprockets, battery, spark plugs, oil, air and oil filters, and apparently also a new solenoid again, i know this is a common issue but i didn't expect to need a new one so soon. So this year it has a lot of fresh bits in, and the mechanic said it seemed good to him once he gave it back to me and now it starts maybe 50% of the time i want to use it but started all the times he tried it.
The bike will often start and hold very low revs and then cut out. I can try it give it some throttle, but anything over a tiny amount will cause it to instantly cut out. Sometimes it will run for a minute or two as i warm it up and gear up and then cut out and then occasionally it will not fire up at all.
Then, the other 50% of the time it works perfectly, no issues whatsoever. I use it for work sometimes and if it has started in the morning then i have never had an issue with it starting again in the afternoon (touch wood). And sometimes it will not work like above, then a couple of hours after it will work absolutely fine as though nothing is wrong even though i have just left it alone and done nothing. I have wondered if it is a temperature/humidity related thing but cant notice any link there.
I am now using a fuel additive in the tank to try to clean any gunk off of the carbs in case it is possibly a fuel delivery issue, but haven't noticed a considerable difference yet after 3 or so tanks.
Does anyone here have any suggestions for what could be the cause or any reasonable lines of enquiry. I have already dropped a lot of money this year on this bike which i didn't really want to but a lot of required things all came up at once unfortunately, so any ideas for what i could check myself would be very much appreciated!
Thanks,
JordanInNorway

 

I'd start with doing a compression test, 4 new plugs, a fuel filter then check breathers and ventilation including the fuel cap vent.
Then check carb diaphragms for pinhole punctures, get it running and spray wd40 or similar around carb to cylinder rubbers and carb joins etc to see if there is any air leaks.
Get hold of the multiplug on the ECU and unclip it and plug it back a few times and any other electrical terminal plugs same procedure on relays etc, on my 600fk it had previously had a alarm removed badly leaving some dodgy wire joints behind giving connection troubles.
Get a Honda works manual off e bay then test engine pulse coils etc all these tests are covered in the original factory manuals for sale on e bay if you can't do it your mechanic should be able to.
The problem could be anything but as an old employer once told me the engine needs compression, fuel, air and a spark that's it we myself included always fear the worst and look too deep sometimes and the simple things like a bad HT lead or a duff plug can be overlooked. Hope this helps a bit good luck AL. (ps does sound like fueling or air restriction to me)

 

What he said, start with the simple stuff, I do suspect that it will be dirt in the carbs.

 

Thanks, I'll have a look at my manual and have a go on a nice dry weekend and ask my mechanic if he can do any of the bits i haven't been able to. Cheers guys!