Exhaust valve, poor cold starting 1200

[Engineer]

My 2018 1200GS Rallye TE recently developed poor cold starting, the revs would rise on starting and then immediately drop back and stall. I had to hold it on the throttle for 30 seconds or so before it would idle reliably. This only happened when the bike was stone cold.

The exhaust valve was stuck - silencer off, freed it up, greased it - cold starting now good.

Anyone else noticed this?

 

[Robbi]

No, i have a 2001 RS 1150 GSA

 

[Daffy]

Me neither on my Husky or R1200c

 

[GreatScot]

I've never been anywhere near you or your bike so I haven't noticed it either.

 

[Geekay]

I don’t think those things are related. My exhaust valve has been seized (open) for years and no issue with cold starting.


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[oblertone]

Exhaust valve is a very specific part; you’d have thought an engineer might have known the difference

 

[Engineer]

I don’t think those things are related. My exhaust valve has been seized (open) for years and no issue with cold starting.


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That's what I always assumed but the coincidence made me think that maybe there was a connection - as it shuts during starting.

 

[Engineer]

Exhaust valve is a very specific part; you’d have thought an engineer might have known the difference

All parts are very specific what do you mean?

 

[malcopopolo]

Time to part X and buy a 1250

 

[malcopopolo]

if he valve is closed for to long - surely the bike will stall at some point a sit cannot remove exhaust gas

 

[knutk]

When I read this thread, it strikes me that perhaps some of the gentlemen in her posting perhaps should do their homework and read up before posting condescending ass-hole comments.

What used to work on older bikes is not necessarily valid for new ones.

The thing is: @Engineers post is indeed relevant.

The strict requirements for the Euro-4 and and Euro-5 means new ways of controlling the engine compared to older bikes.

A cold engine requires a richer fueling than a warm engine.
While this used to be simply a matter of richening up the fueling, the newer emission regs. interfers at all stages of running an engine to a much higher degree than for pre Euro-4 engines.

By closing the exhaust flap, a backpressure will be built in the exhaust flow. This means that when the exhaust valves opens and the pistions try to empty the cylinder for burned gasses, the backpressure caused by the exhaust flap will reduce the flow, and some of the unburnt gasoline (a result from the less efficiency of a cold engine) will be kept in there and be burned on the next stroke. This again allows for the ECU to add slightly less extra fuel to the cold engine and thereby less pollution.

If the flap does not close, this will result in a too lean mixture for the engine when cold, and this corsponds to the symptoms @Engineer described.

 

[dean0n0]

Quite a difference between a exhaust valve and a flap valve in the exhaust.

 

[Daffy]

When I read this thread, it strikes me that perhaps some of the gentlemen in her posting perhaps should do their homework and read up before posting condescending ass-hole comments.

What used to work on older bikes is not necessarily valid for new ones.

The thing is: @Engineers post is indeed relevant.

The strict requirements for the Euro-4 and and Euro-5 means new ways of controlling the engine compared to older bikes.

A cold engine requires a richer fueling than a warm engine.
While this used to be simply a matter of richening up the fueling, the newer emission regs. interfers at all stages of running an engine to a much higher degree than for pre Euro-4 engines.

By closing the exhaust flap, a backpressure will be built in the exhaust flow. This means that when the exhaust valves opens and the pistions try to empty the cylinder for burned gasses, the backpressure caused by the exhaust flap will reduce the flow, and some of the unburnt gasoline (a result from the less efficiency of a cold engine) will be kept in there and be burned on the next stroke. This again allows for the ECU to add slightly less extra fuel to the cold engine and thereby less pollution.

If the flap does not close, this will result in a too lean mixture for the engine when cold, and this corsponds to the symptoms @Engineer described.

You haven’t really thought your theory about the exhaust flap holding some of the fuel back for the next stroke have you.

 

[malcopopolo]

My flap is stuck open and does not stall EU4

Although i run AXFIED which make the fueling sublime - this flap has stuck open prior.

The flap is solely for noise emissions - no other reason!

 

[Engineer]

When I read this thread, it strikes me that perhaps some of the gentlemen in her posting perhaps should do their homework and read up before posting condescending ass-hole comments.

What used to work on older bikes is not necessarily valid for new ones.

The thing is: @Engineers post is indeed relevant.

The strict requirements for the Euro-4 and and Euro-5 means new ways of controlling the engine compared to older bikes.

A cold engine requires a richer fueling than a warm engine.
While this used to be simply a matter of richening up the fueling, the newer emission regs. interfers at all stages of running an engine to a much higher degree than for pre Euro-4 engines.

By closing the exhaust flap, a backpressure will be built in the exhaust flow. This means that when the exhaust valves opens and the pistions try to empty the cylinder for burned gasses, the backpressure caused by the exhaust flap will reduce the flow, and some of the unburnt gasoline (a result from the less efficiency of a cold engine) will be kept in there and be burned on the next stroke. This again allows for the ECU to add slightly less extra fuel to the cold engine and thereby less pollution.

If the flap does not close, this will result in a too lean mixture for the engine when cold, and this corsponds to the symptoms @Engineer described.

Thanks - a great explanation, I was thinking along these lines and was hoping someone else had experienced the same issue. What you describe makes a lot of sense to me, a humble Electronics Engineer

 

[spoonz]

I think what knut might be getting at is that exhaust servo valves are often used to trap exhaust gasses on a cold start to speed up the heating of the cat. That results in the cat dealing with hydrocarbons that would otherwise be expelled before the cat was hot enough to function as intended if heated by an open exhaust.

If your exhaust servo valve is stuck open that cold start cat heating won’t happen in the way intended so maybe that has a knock on effect on the fueling. The lambda will pick it up and maybe lean off the mixture enough to stall the bike. After a few start ups, you have a hot cat and off you go.

 

[knutk]

You haven’t really thought your theory about the exhaust flap holding some of the fuel back for the next stroke have you.

It's a bit of the same principals that you use if you tune a 2-stroke engine with a pipe.
If you cone the pipe 'wall' you spread the performance band over a wider rpm range, whereas a flat wall will give a heavy kickback at a narrow rpm-range, and outside this narrow rpm-range the engine will be much less powerfull.

In a 4 stroke, the flap will make some of the half-burned exhaust bounce back in/keep it from escaping, and it ads to the fresh air/fuel mix.
This means that in the very beginning, a Flap that does not close will cause the cold engine to go a bit lean. Then, within less than 30 seconds, if the lean condition still exists, the O2 sensor has warmed up and starts to report back to the ECU that the engine wants a tad more fuel, and then the engine will run just fine.
It's not about performance. It's about noise and pollution. Keeping the exhaust flap nearly closed will also contribute to a quicker warmup for the CAT.

My explanation here is very simplified, but it boils down to that the exhaust flap will indeed have an effect on the fueling when starting a cold engine.

 

[Geekay]

That's what I always assumed but the coincidence made me think that maybe there was a connection - as it shuts during starting.

I’m not sure this is the case - it goes through a cycle when you turn the ignition, but,I think, returns to fully open at start. Hence the rather “explosive” startup sound.

I’m still saying (despite the explanations) that the flappy valve is u related to your starting and I’d ask when the plugs were last changed.


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[spoonz]

I’m not sure this is the case - it goes through a cycle when you turn the ignition, but,I think, returns to fully open at start. Hence the rather “explosive” startup sound.

IÂ’m still saying (despite the explanations) that the flappy valve is u related to your starting and IÂ’d ask when the plugs were last changed.


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Lots and of owners have had bikes with stuck open valves and don’t seem to report startup issues as far as I can see. So in general your probably right, but plenty of weird stuff happens with motors. You get a car with an egr valve and associated pipe work so blocked it’s amazing it got down the road but gave no indication until it failed an emissions test. Yet another the same model runs like a dog and throws codes for a bit of minor clogging by comparison.

if engineer wants to validate the possibility of the valve as the cause he could stop the valve from closing again and see if it still starts, assuming nothing else has changed ( had a service since etc)

 

[Engineer]

I’m not sure this is the case - it goes through a cycle when you turn the ignition, but,I think, returns to fully open at start. Hence the rather “explosive” startup sound.

I’m still saying (despite the explanations) that the flappy valve is u related to your starting and I’d ask when the plugs were last changed.


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Hmm I’m sure it stayed closed (after I’d unstuck it) when I turned the ignition on and was looking at it with the silencer removed.

I did consider the plugs too as I am now at 22,000 miles, service booked for 28th March.