Not firing properly after not being used for over a year

[kmcbr1000fm]

I have a 1991 Honda CBR1000FM with only 20,000 miles on the clock but it's been off the road for over a year. It starts OK and continues to run once up to temperature and the choke is off, but it sounds like it's not firing on all cylinders and won't "pull" when I engage 1st gear and try to pull away. It's as if there's very little torque. Before I think about sending it to a garage I thought I'd ask if anyone has any idea what might be the most likely problem - and solution. My own thoughts are spark plug problem, or maybe carb needle blocked with dirty fuel..... I can probably manage to fit a set of spark plugs myself, if it's a blocked carb needle or something potentially more significant, it's probably a trip to the garage. Any thoughts would be very welcome.

[MCN]

If the fuel dries out in the carbs it can leave salts and varnishes causing blockage. It may start on over-enrichment of choke then fail with choke off.
Spark plugs don't fcuk up just sitting but moisture can creep into HT leads and connections.
If you can get a hand in you could try to determine which cylinder is dead by removing HT leads one at a time.
If you pull a lead and there's no difference to the engine note (the engine just runs the same) then that circuit is dead or that carb is blocked. You don't need to get into every cyl. You can try and see how many leads you can remove before it dies. It is possible to run on one but lumpy. Then try each cyl. With the others cut out. If you fancy the challenge whip the carbs, open the float bowels and clean out da shit/s.
Or fit a new lead set.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[BTTD]

If you can access the header pipes the cylinder not firing will be the one that doesn't melt the skin off your fingers. Or use a water spray bottle.
Then you can check if it has a spark.

[doggone]

Maybe one of the coils has gone, if you could find which cylinder is not firing - assuming it is that - you can swap the coils over and the dead one will change.
Fairly easy DIY fix to replace.

I'm always sceptical of 'bad fuel' type explanations, a year is not that long depending on storage conditions.

[Matt B]

[MCN]

And
99.999% of water in fuel problems are the cause of water in the fuel.



If it has been sitting with a half tank/less than full the repeated condensation cycles could have allowed 'substantial' water to collect/pool in the bottom of the tank and that may have been drawn into the carbs when started.
(The parts of the tank not submerged 'in fuel' condense water vapour in the atmosphere as the tank 'breathes'. Overtime the droplets will 'drop' into the fuel where it is now trapped and cannot re-evaporate to atmosphere again.

It's why it is best to start a 'stood bike' on fresh fuel.
Not necessarily because the fuel 'goes off' but because half full tanks collect moisture. (Unless sealed).
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Ichy]

[kmcbr1000fm]

Thanks for all the replies. There's a lot of good solid advice and just within a few hours. Some chat fora are a waste of time (I won't name the ones I'm aware of), but this one seems to offer something of real use. The comments about water/condensation in the petrol are of particular interest 'cos the bike has been in the South of France (very hot and very cold) with very little petrol in the tank which would exacerbate the condensation issue. I'll get onto it in the morning and let you know how I get on - I bet you can't wait....

[temeluchus]

Drain the float bowls and slap a gallon of fresh in the tank. Probably run better straight away.
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[Robby]

Temelechus is right. To add to what he said, put a few miles on it with fresh fuel before thinking about pulling the carbs out. They may be filthy, but petrol is a very good carb cleaner and riding the bike is the best way of getting it moving through the carbs.

[kmcbr1000fm]

This morning I did the "water spray test" on the downpipes and also disconnected the spark plug leads one-by-one. Conclusion is that both pots 1 and 2 (far right and 2nd from right when viewed from the front) are not firing. Pots 1 and 2 are supplied by different coils and as pots 3 and 4 are firing it's probably not the coils which are the problem(?) - or could it be? Is it likely that by coincidence the 2 HT leads feeding pots 1 and 2 are defective at the same time? If so, is it possible to replace them without replacing the coils as well as I've tried to loosen the leads from the coil using just my fingers and they seem pretty "fixed". Finally, could I be on the right track or could there be another better diagnosis that doesn't involve HT leads? I haven't done any more "diagnosis" yet as I'd rather tackle it step by step.

[Minty]

I don't know why but my cbr plugs loosen slightly when laid up and then obviously misfires, runs rough etc.

Make sure they are tight. Simple things first.
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[kmcbr1000fm]

Minty - just checked and the spark plugs seem tight.

Also just noticed that the 2 connectors for pots 1 and 2 on the coils are blue whilst the connectors for pots 3 and 4 are black. Don't know if that is usual or might be a sign that those "halves" of both coils are dead(?) Is there a simple way of checking the coils are delivering power to the plugs?

[BTTD]

I've used a spark plug test lead with a funny light thing before. You can also get an arc to the engine block from the unplugged lead. Youtube is your friend for basic tests.

[temeluchus]

If its on the side stand 1 and 2 would get the lions share or water.

Drain the float bowls.

As far as the HT leads go, separate the caps from the leads and check for rot.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[davebike]

Remove and clean carbs modern fuel has short shelf life so fresh fuel as well
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Dave
NC750Xdct + others at work !
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[kmcbr1000fm]

I've now drained the float bowls. The petrol seemed clear, clean and free from water. Unfortunately the draining did not solve the problem. I've also done a check on the sparks. They are probably not the strongest possible, but there is a spark across the gap. The HT leads also look OK. I've noticed that the downpipes of the "problem" cylinders do get hot, but not scorching hot like the other 2. It's as if they're firing intermittently. Also, the engine stalls once I take the choke off. I'm now thinking that it's either a problem of "half" of both coils being defective, or that the carb jets are partially blocked....or maybe something else. If anyone has a view on what's best to do next I'd appreciate it. If I need to get the carbs fully cleaned I'll probably get that done by a garage. I can replace the coils myself.

[Ichy]

Swap the plugs around and see if the problem moves then swap the plug leads around for the shared coil, so swap 1 for 4 and 2 for three ( Im guessing but hopefully you understand what I mean). That should confirm if it is electrical or not.

Next suggestion would be a carb clean.
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[kmcbr1000fm]

Itchy - good suggestion (don't know why I didn't think of it myself). However, I've now swapped the plugs and sadly found no difference. I've also swapped around the HT leads and similarly no difference. I'm now thinking it can only be a pair of half-dodgy coils or perhaps more likely 2 out of 4 dirty carbs suffering from the salt/varnish problem mentioned earlier. I was hoping it wouldn't be the latter as I don't really want to venture into cleaning the carbs myself so it looks like a trip to the garage (on the back of a trailer). It's a good (albeit rather expensive) lesson not to let the bike stand around without "prepping" it first.

[Robby]

Take it for a ride. Get some fuel moving through the carbs, blow out the cobwebs.

If the carbs are gummed up, it is likely to behave better at higher power output. The jets are bigger, so less likely to get clogged.

Do this with fresh fuel.

If it doesn't make a difference, then clean the carbs. I would want to avoid removing the carbs if at all possible. It's of the sort of age where carb removal is tricky, and old enough that the inlet rubbers may get damaged, or just be tricky bastards when it comes to refitting.

[kmcbr1000fm]

Robby, understand your point but as soon as I take the choke off the thing stalls. Equally when I twist the throttle it wants to stall. Put these things together and I can't ride it. Maybe I could try to open the throttle up whilst still on choke and see if that "clears" the jets out???

[Robby]

Give it a go. The longer you play with it (running) the more likely it is to start behaving. Just don't let it sit there ticking over for an hour, you'll boil something.

[davebike]

Blocked idle jets

Remove and clean the carbs
Fresh fuel
____________________
Dave
NC750Xdct + others at work !
[email protected]