Cold start and fast idle revs?

[bad_hat_harry]

Hello all,

Well, winter has arrived here in the UK - first snow down south in October in 70 years - brrrrr....

 

I have a cold idling problem with my 1150 twin spark RT. When stone cold the bike struggles to idle, with the revs spluttering around the 1400-1500 mark, even with the cold start (choke) lever held out to the start position. When left to rest at the fast idle setting, it drops even lower and usually stalls unless I keep a bit of throttle on. Once warm, the bike runs fine.

 

Is this just a case of undoing the lock nut on the choke cable adjuster at the handlebar and twiddling the adjuster? If so, what do your bikes rev to on cold start and fast idle settings?

 

I have checked my Clymer and it talks about a gap between the locknut and adjuster, but no reference to engine speeds at either cold start or fast idle.

 

For info:

- Valve clearances checked

- TBs balanced

- Warm idle stable at 1100

- New battery

 

Any help would be most appreciated!

 

Thanks

 

 

[AndyS]

...I have a cold idling problem with my 1150 twin spark RT. When stone cold the bike struggles to idle, with the revs spluttering around the 1400-1500 mark, even with the cold start (choke) lever held out to the start position. When left to rest at the fast idle setting, it drops even lower and usually stalls unless I keep a bit of throttle on. Once warm, the bike runs fine.

 

Is this just a case of undoing the lock nut on the choke cable adjuster at the handlebar and twiddling the adjuster? If so, what do your bikes rev to on cold start and fast idle settings?

 

I have checked my Clymer and it talks about a gap between the locknut and adjuster, but no reference to engine speeds at either cold start or fast idle.

 

For info:

- Valve clearances checked

- TBs balanced

- Warm idle stable at 1100

- New battery

 

Any help would be most appreciated!

 

Thanks

 

 

The fast Idle lever seems to be doing exactly what it's meant to do. - I wouldn't look there.

 

Have you checked the air temp sensor that plugs into the top of the air filter housing?

 

Andy

[T__]

Hello all,

Well, winter has arrived here in the UK - first snow down south in October in 70 years - brrrrr....

 

I have a cold idling problem with my 1150 twin spark RT. When stone cold the bike struggles to idle, with the revs spluttering around the 1400-1500 mark, even with the cold start (choke) lever held out to the start position. When left to rest at the fast idle setting, it drops even lower and usually stalls unless I keep a bit of throttle on. Once warm, the bike runs fine.

 

Is this just a case of undoing the lock nut on the choke cable adjuster at the handlebar and twiddling the adjuster? If so, what do your bikes rev to on cold start and fast idle settings?

 

I have checked my Clymer and it talks about a gap between the locknut and adjuster, but no reference to engine speeds at either cold start or fast idle.

 

For info:

- Valve clearances checked

- TBs balanced

- Warm idle stable at 1100

- New battery

 

Any help would be most appreciated!

 

Thanks

 

 

 

 

 

Harry, might be an easy fix or could be a pain to find..

 

First off what weight & type of engine oil are you using? If the engine oil is a real thick Dino type it can cause enough engine drag cold to hinder fast idle.. (maybe try a lighter engine oil)

 

Are you holding the clutch lever in during the cold start & first few seconds of the cold start idle? If not try that.. (removing the cold transmission internal drag can really aide cold start/cold idle until the engine clears up & pulls clean)

 

What is you fast idle RPM on a hot engine? If too low set it up a little..

 

One thing I have seen work for a cold start & stall is to hold the fast idle lever all the way up during starting,, then once it starts use the R/H twist grip to blip the engine a couple of times to clear the engine faltering.. Usually a couple of blips & they will then cold idle OK..

 

Are you getting full fast idle with the choke lever held all the way up (cold engine)? I worked on a bike last year that had enough cable drag in the choke cable & splitter box that it would get basic fast idle but the additional lever movement above basic fast idle would not open the throttle plates any farther (only happened on a very cold bike).. The way I found that was to set & hold the choke lever all the way up,, then using my right hand open the throttle with the twist grip then slowly release it back to closed (prior to starting).. If I did that prior to starting it always started & stayed running but if I only used the choke lever (only) it would start & stall.. (new cable & cleaning the splitter box worked wonders)

 

Any possibility your lower spark plug (or plugs)s are fouled? That will flat out ruin a cold start stay running event..

 

As mentioned by Andy look at the AIT (air intake temperature) sensor in the air box cover.. Those things are as reliable as a paper clip & seldom if ever fail but the terminals in the connector are the weak spot & can open up enough to lose contact with the switch terminals.. If that happens the system defaults to about 70°f intake temp..

The system basis most of it’s fueling from the oil temp,, RPM,, & TPS on a cold engine but those are probably pretty good if it runs good when hot..

 

 

If none of the above mentioned things help you will have to dig a little deeper..

 

Try removing the #5 (Motronic) fuse after your last ride of the day (leave out for about 30 seconds),, then re-install the fuse,, turn the key on (do not start) then fully open & close the throttle twice.. That will re-set the fueling computer’s fuel cell learn & 02 sensor learn.. Then start as normal the next morning.. If it starts & stays running better after the above, suspect your 02 sensor is getting lazy or not working correctly.. Does your UK bike even have an 02? If not try the re-set anyhow but it won’t be the 02 sensor if you don’t have one..

 

I presume you don’t have an aftermarket fuel controller on that bike (like Techlusion or such)? If by chance you do try turning that off.. With a fuel controller operational it can force a computer learn offset that can (not will but can) effect cold start fast idle..

 

There is more to add to the list but these are the most common so see if anything in the above points a finger to you problem..

 

 

Twisty

 

[AndyS]

.. Those things are as reliable as a paper clip & seldom if ever ....

Twisty

 

Hey Twisty I must have had a very sheltered upbringing, I only worked in the Armed Forces for 25 years, but I never heard that expression - I laughed.

You have made my morning.

Nice one.

Andy

[bad_hat_harry]

Hi again,

 

Thank you very much for your wise words - it's fantastic when people take the time to share knowledge like this, I really appreciate it!!!

 

I've added some thoughts after your points below....

 

Cheers!

 

 

 

Harry, might be an easy fix or could be a pain to find..

 

First off what weight & type of engine oil are you using? If the engine oil is a real thick Dino type it can cause enough engine drag cold to hinder fast idle.. (maybe try a lighter engine oil)

 

I've just done my first oil change on this bike, and the oil was recommended by my local BMW dealer - it's their own-brand stuff, 20/50. However, this idling problem occurred before that I think.

 

Are you holding the clutch lever in during the cold start & first few seconds of the cold start idle? If not try that.. (removing the cold transmission internal drag can really aide cold start/cold idle until the engine clears up & pulls clean)

 

Not done that, will try it!

 

What is you fast idle RPM on a hot engine? If too low set it up a little..

 

Errrr, don't know - again, will have a look.

 

One thing I have seen work for a cold start & stall is to hold the fast idle lever all the way up during starting,, then once it starts use the R/H twist grip to blip the engine a couple of times to clear the engine faltering.. Usually a couple of blips & they will then cold idle OK..

 

Not tried this either - will have a go!

 

Are you getting full fast idle with the choke lever held all the way up (cold engine)? I worked on a bike last year that had enough cable drag in the choke cable & splitter box that it would get basic fast idle but the additional lever movement above basic fast idle would not open the throttle plates any farther (only happened on a very cold bike).. The way I found that was to set & hold the choke lever all the way up,, then using my right hand open the throttle with the twist grip then slowly release it back to closed (prior to starting).. If I did that prior to starting it always started & stayed running but if I only used the choke lever (only) it would start & stall.. (new cable & cleaning the splitter box worked wonders)

 

Interesting ruse - the choke lever is very stiff, so I'll give this a go.

 

Any possibility your lower spark plug (or plugs)s are fouled? That will flat out ruin a cold start stay running event..

 

Possible, will remove for a check.

 

As mentioned by Andy look at the AIT (air intake temperature) sensor in the air box cover.. Those things are as reliable as a paper clip & seldom if ever fail but the terminals in the connector are the weak spot & can open up enough to lose contact with the switch terminals.. If that happens the system defaults to about 70°f intake temp..

The system basis most of it’s fueling from the oil temp,, RPM,, & TPS on a cold engine but those are probably pretty good if it runs good when hot..

 

I didn't notice any obvious problems with this when I last checked the air filter, but then I wasn't looking too closely so will check again.

 

 

If none of the above mentioned things help you will have to dig a little deeper..

 

Try removing the #5 (Motronic) fuse after your last ride of the day (leave out for about 30 seconds),, then re-install the fuse,, turn the key on (do not start) then fully open & close the throttle twice.. That will re-set the fueling computer’s fuel cell learn & 02 sensor learn.. Then start as normal the next morning.. If it starts & stays running better after the above, suspect your 02 sensor is getting lazy or not working correctly.. Does your UK bike even have an 02? If not try the re-set anyhow but it won’t be the 02 sensor if you don’t have one..

 

Funnily enough, this has happened recently anyway. I've fitted a new battery and did the throttle twist twice after re-connecting the battery. One follow-on question based on your notes - should this be done with the engine at normal operating temperature?

 

I presume you don’t have an aftermarket fuel controller on that bike (like Techlusion or such)? If by chance you do try turning that off.. With a fuel controller operational it can force a computer learn offset that can (not will but can) effect cold start fast idle..

 

Nope - no Techclusion or other black boxes fitted.

 

There is more to add to the list but these are the most common so see if anything in the above points a finger to you problem..

 

 

Twisty

[Doom]

Don't rule out a bad stick coil on the primary plugs. That was my problem.

[T__]

Harry,

 

Funnily enough, this has happened recently anyway. I've fitted a new battery and did the throttle twist twice after re-connecting the battery. One follow-on question based on your notes - should this be done with the engine at normal operating temperature?

 

Engine temp isn’t important but it must be done with the choke in OFF position..

I am saying to do it again after a days ride as that will clear the computer BEFORE the next morning’s start up.. If it starts & idles better the next morning that will tell us something..

 

Interesting ruse - the choke lever is very stiff, so I'll give this a go.

 

That is the same thing I found on the one I worked on (a verity stiff choke lever)

 

 

Any possibility your lower spark plug (or plugs)s are fouled? That will flat out ruin a cold start stay running event..

 

Possible, will remove for a check.

 

If you find a fouled or non functioning spark plug make sure the coil is operating as it should.. An easy way to tell if all plugs are working is to discontent one coil connector (careful they break easily) on a cylinder & the engine should still run on the other,, if it doesn’t the other plug isn’t firing..

 

Twisty