sv650s K5 won't idle when petrol isn't a full tank (running rich)

[Blackie]

Good evening! Thank you for letting me join the forum.
I'm having problems with my bike and I'm hoping someone will know what may be wrong.

I have a 2005 SV650s which has ran perfectly for 15 years until this idling problem.
This bike is standard except for a Delkevic slip on that was installed 5 years ago. It ran 3 years with no problems after this change was made.

I have a problem where the bike now has issues idling without stalling. This has been going on for 2 years now, though admittedly covid meant I haven't been out on the bike so much.
This seems to only happen when the tank is getting lower on fuel. It runs well with a full tank, then after a bit, it's a pain in the neck. (after filling it while on the side stand, the problems start around 35 miles used from full.)

Issues experienced when fuel is lower:

• The engine seems to run rough, almost raspy, like the bike has a cold.
• Every now and again it runs ok for a couple of junctions, then it goes to crap at the 3rd.
• It won’t idle most of the time, with the revs lowering to 900 max, causing it to konk out.
• I can often smell fuel.
• The bike runs a bit "farty"(? lol), maybe even a little jerky, in first and second gear / lower speeds.
• When I'm out on the open road, the bike runs well. I'd say around 30mph+ it runs fine. I couldn't bet my life on it, but I don't think there is any difference to it's upper speed peformance compared to before this problem.

Other observations:

• The bike seems to run rich, there is a layer of soot inside my exhaust. It never used to run rich like this and I never used to smell fuel.
• With a full tank the bike idles at the correct 1400 revs.
• It feels like the bike runs progressively worse as the fuel goes down.
• I might be imagining it, but the bike sound is worse and feels more front of the bike when its low on fuel and having problems vs more central & rear of the bike when the tank is full. This might be complete nonsense! But it's the feeling I get, so mentioning it incase it's significant.

Things I've done to try fix it:

• I changed the easier fuel filter but this made no difference.
• The bike got worse after a year, to the point where I'd run it 70mph for a few miles and when I came to a junction after this, the bike would just DIE and it'd take 2 or 3 attempts to get it running again, having to rev the heck out of it to stop it continously stalling. I changed the spark plugs, which were quite sooty, and this seems to have stopped this high speed / bad stalling problem (but not the overall idling problem).

My dad is wondering if it's the TPS sensor that needs replacing. Unfortunately TPS sensors are around £100 each, which is a lot to spend on a guess.
Any clues where to start?

Any guidance would be amazing. Thank you.


(**** FIXED - IT WAS A DUFF BATTERY ****)

[Bibio]

ageing battery, spark plugs, Rectifier/Regulator i would say are the three main contenders to look at first. i had pretty much the same symptoms last year and it turned out to be a duff battery even though the battery took a charge.

less common is the ignition and the Rectifier/Regulator connectors and the mantels in the injectors.

you can check and roughly adjust the TPS without the engine running.

[glang]

I think if it was TPS, or any electronic component, you would get the FI warning light and code which I take hasnt happened?
It seems to be more a mechanical type problem like a fuel or air leak. How many miles has the bike done and do you know if the maintenance schedule been followed?

[Biker Biggles]

I had something similar on a different bike some years ago. The bike was running rich all the time and it was caused by a faulty temp sensor which was telling the "brain" it was running cold so it was constantly in cold start mode.

[Blackie]

Originally Posted by Bibio

ageing battery, spark plugs, Rectifier/Regulator i would say are the three main contenders to look at first. i had pretty much the same symptoms last year and it turned out to be a duff battery even though the battery took a charge.

less common is the ignition and the Rectifier/Regulator connectors and the mantels in the injectors.

you can check and roughly adjust the TPS without the engine running.

Thank you for the reply
I never thought of the battery. I usually change it every 2 or 3 years, but things have been a bit slack due to covid spoiling my fun. This problem has been going on 2 years now. Would a poor battery cause the bike to run rich also?

I'll get a new battery just incase, it's due a change anyway. Cheers!

[Blackie]

Originally Posted by glang

I think if it was TPS, or any electronic component, you would get the FI warning light and code which I take hasnt happened?
It seems to be more a mechanical type problem like a fuel or air leak. How many miles has the bike done and do you know if the maintenance schedule been followed?

I only get an F1 warning for 1 reason, when my bike ignition turns on and it's in gear and on the stand. This started after we removed the alarm, but it's no biggie.
There is no other warning. Are SV's quite intuitive for errors on electrics? I read I can run a diagnostic check on it but didn't know if this was something worth taking further or not.
(I'm not used to vehicles that tell you what's wrong )

I did assume it was an air problem. The bike has only done 16k and has been garaged nearly all its life.

[Blackie]

Originally Posted by Biker Biggles

I had something similar on a different bike some years ago. The bike was running rich all the time and it was caused by a faulty temp sensor which was telling the "brain" it was running cold so it was constantly in cold start mode.

Thank you for your reply
Hmmmm... well it starts ok whether full tank or not, and quietly warms up before the revs drop. The bike does smell a bit fuely all the time though, regardless of how full the tank is. Do you think this would come up with a diagnostic test?

Krikey, this is what gets me with bikes. There could be so many blooming things at fault LOL. And it takes trial and error with numerous cures, to finally get the problem solved.

[Adam Ef]

Does it happen when the bike is cold as well as hot?

[Blackie]

Originally Posted by Adam Ef

Does it happen when the bike is cold as well as hot?

Hard to judge because I don't run the bike cold cold... I wait for it to reach 40c.. and as its warming up it idles at higher revs anyway. In saying that, I think I remember seeing it idling at 1400 / 1500 revs the other day while warming, where it should probably be more.
When I do take away at 40c and the tank is lower in fuel, it does the same crappy idle though, yes.

I've gotten really good at keeping the throttle on a little at junctions!

[Adam Ef]

Ok. Just trying to work out of it's an electrical resistance problem exagerated by heat, which it sounds like it isn't if it does it relatively soon after starting too.
I'd be looking at fuel filter, injectors and air lines, air filter. Also double check your TPS before doing anything to rule that out to start with.