650 twin spark - tough starting the morning after

[aesmith]

Hi,

This is something I've noticed a few times, initially I wasn't convinced but it's happened too often now to be coincidence. And I've seen the same behaviour on my old pointy and with the twin spark L2. It seems that if you run the bike for just a few minutes one day, then the next day it will be a bitch to start. For example this Sunday the bike had been sitting for over two weeks. It started immediately when I moved it from garage to shed. I then left it on the Optimate to make sure it was fully charged. Monday morning start was rough as hell with the engine coughing but not catching. In these cases it seems the only way it will ever start if by holding near to full throttle.

Anyone else found this? It doesn't happen if the bike if run normally, or if it's fully warmed up. It's just this scenario of running for a few minutes that puts it in this state. Trying to speculate on the cause could there be part of the cold start mechanism that gets left in a funny state that makes a true cold start difficult?

Thanks, Tony S

[Seeker]

I have a 2016 AL7 SV (21k miles) and it has done that once. I did an oil change, started it for 60 secs to check for leaks and then shut down. Next morning it started reluctantly on one cylinder. The AL7 has the "Suzuki Easy Start" system where you momentarily press the starter and it cranks until it fires, I often wondered what happens if it doesn't catch. The answer is that it stops cranking after about 3 secs.

Incidentally I have a related problem at petrol stations in the winter (air temp about 6°C), if the bike is at normal temp, tank almost empty, I fill it to brim, pay inside with a delay (queue of people) then, on leaving, sometimes it starts on one cylinder. If there's no delay; no problem, if I were to leave it for 10 minutes; no problem.
Unfortunately, it is also unpredictable. Flooded? stuck fuel injector? temp sensor reading wrong? Who knows. Second cylinder chimes in almost immediately and the bike then runs perfectly.

I've had two curvies that would occasionally backfire on first start attempt or sometimes sound like compression was suddenly too high, maybe the pistons end up in a "wrong" position occasionally.

[R1ffR4ff]

Fuel companies change their blends in winter.Any weaknesses in the fuel delivery/Ignition system can get shown up so go through the usual e.g Air-filter/Plugs and connections.

I always have a bit of Redex or similar fuel cleaner in my fuel as this also stops the fuel from decaying which it can be much faster in the cold especially with the 5% ethanol in most modern fuels.

Drop half a bottle of a fuel cleaner in a decent tank full and give the bike a good run.Can work wonders and has never harmed any of the engines I've used on for over 40 years.

Wilkos are still doing a 4 bottle deal for £8.50,

https://www.wilko.com/en-uk/redex-pe...B&gclsrc=aw.ds

[aesmith]

Cheers, I don't see how it can be anything to do with fuel since on Sunday it started right away after standing for two weeks. Then around 16 hours later with the battery freshly charged it played silly buggers.

[R1ffR4ff]

I'd check the fuses for corrosion and any of the large electrical connectors for the same?

[aesmith]

I still struggle to see how that would cause a problem only after a short engine run the day before, but not at any other time.

[garynortheast]

It's possible that you are ending up with condensation in the fuel system if the engine hasn't got hot enough to dry out. The moisture just sits there till you try and run it again.

[SV650rules]

Could be unburnt fuel condensing and basically triggering the hydrocarbon sensor in CAT.

This happens on cars and the fix is to fully press accelerator while spinning engine over, which opens butterfly but if throttle is fully open when starting engine the ECU inhibits fuel being injected and gets rid of unburnt fuel. This is called clear flood mode and should work on any fuel injected engine.

This should allow a normal start to be carried out ( with throttle closed ).

Regular refusal to start from cold can be engine temperature sensor faulty, as more fuel is injected when engine cold, if ECU thinks engine is warm mixture will be too weak to start.

http://diycardoctor.com/clear_flood_mode.htm

[embee]

Two issues can be a play in this situation.
On a "cold" start (any start when the engine is well below its normal temperature) the mixture will tend to be relatively rich, especially during cranking when a "cranking fuelling" value will be used, the cranking speeds are usually too low to get a reliable measurement of air-flow in the conventional sense so a nominal value is adopted until it can actually measure something. Once the engine fires it will usually switch to "afterstart" fuelling where the initial enrichment will ramp down over a few seconds until it reaches the base mapped value for that engine speed, then it will adapt idle speed and fuelling to engine coolant temperature as it warms up.
During the rich phase it will produce carbon/soot, and with a cold cylinder the water in the exhaust gas will condense on the surfaces. This combination can easily result in cold fouling of plugs. If left to start and run unassisted (leave the throttle alone) the plugs will normally cope until they are hot enough to self-clean. Avoid blipping the throttle during the first minute or so after cold starting.
If you stop the engine before the plugs have reached a high enough temperature to self-clean, the next cold start will just compound the wet soot condition and it can easily cause very poor starting.
In the car industry we used a plug foul test where we would do repeated cold starts, blipping the throttle, then stopping. The plug resistance (to ground) would be measured after each start and plotted, the resistance gradually decreases until it reaches a critical value where the spark will track.

This is also where iridium plugs can help, the voltage required to get a spark to jump is reduced compared to a "conventional" plug (the charge is more concentrated at the fine tip) so the resistance to cold foul is generally improved for a given heat rating. Make sure the plugs are the correct heat rating, colder than standard plugs can be a nightmare for fouling.

Try not to run the engine for a short time. If you must, before shutting off hold the speed steady at say 3000rpm for 30sec or so, spark plug temperature rises very rapidly with speed and this will usually get them hot enough for long enough to self-clean. Don't blip the throttle (this just adds acceleration fuelling and makes things worse, hold it at steady speed).

There can be another issue depending on how the ECU works with it adapting to using a running condition to set the next base fuelling value. If you stop the engine before it has a chance to do this it can revert to a nominal default value which doesn't always suit. I suspect this isn't really the case with the SV, but I know my (old) Yaris can suffer from this if I start it when just part warm and stop it again, the next cold start can be a pig.

[Bibio]

you should never start a bike thats laid up. if you do then remove the plug caps and run it from the starter just to circulate some oil.

cant help with the other starting issue. but yes its more than likely moisture on the plugs as water is one of the effects of combustion.

and yes i have also had the same on my twin spark but never had a cause to investigate as its always cleared and run fine so put it down to a gremlin.

if your going to run a bike on layup then always get it up to temp enough to get the fan running.