Miss fire that clears at higher revs

[Grip]

I'm a first time user of this site so apologies if I appear to struggle with some features.
I have a very low mileage K6 (4000 miles) which I have had for 18 months and has been fine until recentl. It has developed a miss fire which clears at higher revs. I have checked the plugs then 'to eliminate' replaced them. I put new fuel in and added injector cleaner. The sparks are all healthy. I then took the bike to a local guy who was recommended to me. He checked the diagnostics and reported that all readings came back within tolerance when the engine was hot and cold. The coil resistance was also checked 'hot and cold' and found to be ok. Looks like all sensors are ok and no fault codes up. He had to admit defeat. So I am still none the wiser. He suggested it may be a bent or cracked valve or choked up with carbon (with it being low mileage and gentle use). I'm speculative on this and don't really want to start down that road just yet. Finally I'll point out that it gets worse as the engine heats up but it still Miss fires when cold. Any ideas guys?? Thanks

[KiwiCol]

Gidday Grip, welcome to the Org.

Interesting situation you have going on there.  Could suggest all sorts of things, but sounds like they've all been checked anyway.

One for Q or Alphadave or Lord Barmy himself I suspect.

Good luck with it, let us know how it gets resolved.

Cheers. Col

[froudy]

Has the bike been parked up over Winter with a part filled fuel tank?
If it has, then it could well be that the fuel has gone off and you have water in there due to condensation..Just a thought and something else to consider

[gsxbarmy]

I somehow doubt a bent or cracked valve or carboned up. Highly unlikely.

More this sounds electrical. Do you know which cylinder is misfiring or is it across all cylinders? What colour were the tips of the old plugs and were they all uniform in colour?

Can you also be more specific when this started and what you had done beforehand. Had it been standing all winter and since you started it, its now misfiring? Ridden in the rain and now misfiring? What were the circumstances?

As Froudy has said, I would dump all fuel in the tank and start with fresh (use something like BP Ultimate or Shell Optimax when you put fresh in as they have detergents to help "clean" the engine) , but whilst it is all out, just drop the fuel pump to check its not clogged up.

Its possible it could be an HT lead or plug cap breaking down, but at such low mileage, that would be unlucky. Does it misfire when standing still or only when under load

Simple things to check:
- If you have had the tank off, check that the overflow pipe is running freely down the side of the frame and is not kinked anywhere (else you could be getting back pressure in the tank. (Out of interest does it misfire under load, or does it do it when you rev it at a standstill as well - if at a standstill - just undo the tank cap and see if it still does it....
- Take off the LH side panel. Underneath you will see there is a big grey plug. Undo that, spray in some contact cleaner and re-assemble the plug (that plug leads to your ECU)
- Check your earth leads. Its possible you have corrosion under one of them which could be causing the issue
- Take the battery out and lift up the ECU - is it wet? Take the plugs off, spray with contact cleaner and re-assemble.
- At the front of swing arm is a pipe running down from the air filter with a plug at the end. Undo the plug and let any water that may have gained entry out.

See if any of those make any difference, and report back on the questions above.

[Grip]

Thanks for your response gsxbarmy.

Answers to your questions as follows:
1. Old plugs were all in very good condition (not overly carboned up or wet) and even in colour. Sparks all excellent.
2. I used the bike quite a bit after I bought it in July 2015 but just before I garaged it up for winter in late Sept. 2015 it developed this miss fire which has been present ever since. I have hardly used it over the last 18 months partly because of this issue (<100 miles). The previous owner reported that it had literally never seen rain and since I've had it it hasn't seen water in any form. The bike is pristine with no corrosion at all.
3. A complete fuel change was the first thing I tried and has since been tried again (last week). Fuel Conditioner / Injector Cleaner has also been added twice.
4. The Coils 'so I'm told' were checked when engine was cold and hot by the guy who was recommended to me and found to be ok.
5. It miss fires while standing still as well as when ridden / under load.

I'll add that the miss fire initially only occured when the engine was hot but it now miss fires when cold as well but it clears with high revs.
I'm offshore at the moment but will try your other suggestions when I return next week. Much appreciated thanks.

[Mrg]

Hi grip

Not saying this is the problem, but you could check the camshaft sensor  mine was very similar to some of your running problems and mine also started small and got worse along time, and the only way to check is change with another  i.e. Anyone near you to change and see if this is the problem or ,,, buy another so no f1 lights at all hmmmm    Suzuki own are pricey  so if you do need one sort  Suzuki four stroke out bore boat engine as I said it might be it might not but mine was like this and I did nearly all that you did, 

Hope you get to the problem soon

[Mick_J]

Thanks for your response gsxbarmy.

Answers to your questions as follows:
1. Old plugs were all in very good condition (not overly carboned up or wet) and even in colour. Sparks all excellent.
2. I used the bike quite a bit after I bought it in July 2015 but just before I garaged it up for winter in late Sept. 2015 it developed this miss fire which has been present ever since. I have hardly used it over the last 18 months partly because of this issue (<100 miles). The previous owner reported that it had literally never seen rain and since I've had it it hasn't seen water in any form. The bike is pristine with no corrosion at all.
3. A complete fuel change was the first thing I tried and has since been tried again (last week). Fuel Conditioner / Injector Cleaner has also been added twice.
4. The Coils 'so I'm told' were checked when engine was cold and hot by the guy who was recommended to me and found to be ok.
5. It miss fires while standing still as well as when ridden / under load.

I'll add that the miss fire initially only occured when the engine was hot but it now miss fires when cold as well but it clears with high revs.
I'm offshore at the moment but will try your other suggestions when I return next week. Much appreciated thanks.

Mine did that last year but only when hot, checked all the things listed but then I changed the plugs and it's sorted.

[Grip]

Hi grip

Not saying this is the problem, but you could check the camshaft sensor  mine was very similar to some of your running problems and mine also started small and got worse along time, and the only way to check is change with another  i.e. Anyone near you to change and see if this is the problem or ,,, buy another so no f1 lights at all hmmmm    Suzuki own are pricey  so if you do need one sort  Suzuki four stroke out bore boat engine as I said it might be it might not but mine was like this and I did nearly all that you did, 

Hope you get to the problem soon

[VladTepes]

Having never looked does the 1400 have separate high and low speed coils for the stator? 
If so I'd say the low speed coils are shot, if not then I'm out of ideas?!

[gsxbarmy]

It could well be the camshaft sensor. GRIP - do you a workshop manual (if not look in the Downloads - Manuals section) and that should tell you how to check it. If I remember I'll look the section up later.

[Mrg]

hi grip

you might wont to look this up if you have to get a camshaft sensor its a great price

http://www.ebay.de/itm/Nockenwellensensor-Sensor-Nockenwelle-Suzuki-GSX-1400-/302229173085?hash=item465e43335d

[gsxbarmy]

Camshaft Position Sensor testing is on Page 4-31 of the workshop manual

[Grip]

It could well be the camshaft sensor. GRIP - do you a workshop manual (if not look in the Downloads - Manuals section) and that should tell you how to check it. If I remember I'll look the section up later.

That's fantastic gsxbarmy
I have a Haynes manual but your post has made things easier. I have a few good ideas now to try. I'll report back when I return from offshore. Thanks

[Grip]

hi grip

you might wont to look this up if you have to get a camshaft sensor its a great price

http://www.ebay.de/itm/Nockenwellensensor-Sensor-Nockenwelle-Suzuki-GSX-1400-/302229173085?hash=item465e43335d

Thanks Mrg
I will check the that sensor out when I return from offshore. Also, thanks for the eBay link. Could come in handy. I'll report back hopefully with goods news

[BlackAdder]

Did the mech check valve clearances too?  ...just a thought...