Heavily undulating idle!

[lemppari]

Riding home from work, the RM started coughing at lower revs but accelled without a hitch. When I stopped at a traffic light, I noticed that the idle undulated like an old diesel truck. With a bit of choke applied, the engine runs evenly at 1600. Without the choke, opening the choke slowly results in sputtering at 1300-1600 rpm.

 

Taking off the spark plug caps one at a time briefly showed that both cylinders get fuel and spark, the idle was static at 900 rpm. WTF is going on?? The bike stood out on its' side stand in rain today, so could this have something to do with the TPS??

 

Valve clearances were checked 2 weeks ago, as was the TPS voltage and TB balance. Come to think of it, as I rode the bike 2 days ago the last time, I noticed it ran a little rougher but I attributed that to significally colder weather, the temperature dropping 20 deg centigrade from the previous week!

 

As my LM I is also drydocked, I'm confined to pedalling so PLEASE somebody, where do I start looking?????

[Tom M]

The first thing that I'd look at is the throttle body boots. Are they tight and free of tears? I don't know if the RM has an electric petcock but if it does that would be worth checking too. If those are OK I'd let it dry out and see if the problem corrects itself.

[Cliff]

Valve clearances were checked 2 weeks ago, as was the TPS voltage and TB balance.

If you've recently been tinkering then perhaps something wasn't done up sufficiently. You should revisit those things and check again.

[guzzimeister]

Valve clearances were checked 2 weeks ago, as was the TPS voltage and TB balance.

If you've recently been tinkering then perhaps something wasn't done up sufficiently. You should revisit those things and check again.

 

Hi

 

symptoms are due to the engine running lean. Number of reasons:

- leaks in the TB rubbers. This can sometimes be detected by spraying WD40 around the TB rubbers, the engine idle will increase slightly. But pls note that the leakage that will affect idling is often so small this won't show anything. Make sure you you check the rubber BOTH sides of the TB. The ones to the air filter can degrade badly before they affect anything but when they do they will produice this symptom. The ones beyween TB and cylinder are absolutely critical and a tiny leak will give the symptoms you describe

- TPS set slightly low, try 175mV at true idle ie throttle stop screw wound completely out

- throttle body spindle seal leak. Difficult to fix because it's hard to buy the spare seals but easily corrected with a Power Commander richening the mixture in the bottom third of the TB opening range (I'm doing this). Alternatively, the bodgers route is to set the true idle TPS value to say 200mV which will richen things up right through the whole range

 

I suggest you try these out in this order. I guess it runs OK from cold and gets worse as it warms up ie as the mixture leans out? Please note it's not unusual for the TPS position to shift if you have not tightened up the retaining screws tightly.

 

Hope this helps

 

Guzz

[lemppari]

Valve clearances were checked 2 weeks ago, as was the TPS voltage and TB balance.

If you've recently been tinkering then perhaps something wasn't done up sufficiently. You should revisit those things and check again.

 

Hi

 

symptoms are due to the engine running lean. Number of reasons:

- leaks in the TB rubbers. This can sometimes be detected by spraying WD40 around the TB rubbers, the engine idle will increase slightly. But pls note that the leakage that will affect idling is often so small this won't show anything. Make sure you you check the rubber BOTH sides of the TB. The ones to the air filter can degrade badly before they affect anything but when they do they will produice this symptom. The ones beyween TB and cylinder are absolutely critical and a tiny leak will give the symptoms you describe

- TPS set slightly low, try 175mV at true idle ie throttle stop screw wound completely out

- throttle body spindle seal leak. Difficult to fix because it's hard to buy the spare seals but easily corrected with a Power Commander richening the mixture in the bottom third of the TB opening range (I'm doing this). Alternatively, the bodgers route is to set the true idle TPS value to say 200mV which will richen things up right through the whole range

 

I suggest you try these out in this order. I guess it runs OK from cold and gets worse as it warms up ie as the mixture leans out? Please note it's not unusual for the TPS position to shift if you have not tightened up the retaining screws tightly.

 

Hope this helps

 

Guzz

Thanks!

Already checked for leaks and more than a few connectors and the relay bridge today. Then started the engine and voilá! With the choke on it runs perfectly, dying out completely when the choke is off. Definitely running lean and yes, the TPS seems to have wound itself slowly to the end of the adjustment slots. Only myself to blame, I must have left the torxes a bit loose when adjusting the TPS a few weeks ago

 

Henri

[lemppari]

Valve clearances were checked 2 weeks ago, as was the TPS voltage and TB balance.

If you've recently been tinkering then perhaps something wasn't done up sufficiently. You should revisit those things and check again.

 

Hi

 

symptoms are due to the engine running lean. Number of reasons:

- leaks in the TB rubbers. This can sometimes be detected by spraying WD40 around the TB rubbers, the engine idle will increase slightly. But pls note that the leakage that will affect idling is often so small this won't show anything. Make sure you you check the rubber BOTH sides of the TB. The ones to the air filter can degrade badly before they affect anything but when they do they will produice this symptom. The ones beyween TB and cylinder are absolutely critical and a tiny leak will give the symptoms you describe

- TPS set slightly low, try 175mV at true idle ie throttle stop screw wound completely out

- throttle body spindle seal leak. Difficult to fix because it's hard to buy the spare seals but easily corrected with a Power Commander richening the mixture in the bottom third of the TB opening range (I'm doing this). Alternatively, the bodgers route is to set the true idle TPS value to say 200mV which will richen things up right through the whole range

 

I suggest you try these out in this order. I guess it runs OK from cold and gets worse as it warms up ie as the mixture leans out? Please note it's not unusual for the TPS position to shift if you have not tightened up the retaining screws tightly.

 

Hope this helps

 

Guzz

Thanks!

Already checked for leaks and more than a few connectors and the relay bridge today. Then started the engine and voilá! With the choke on it runs perfectly, dying out completely when the choke is off. Definitely running lean and yes, the TPS seems to have wound itself slowly to the end of the adjustment slots. Only myself to blame, I must have left the torxes a bit loose when adjusting the TPS a few weeks ago

 

Henri

 

The RM purrs like a cat after readjusting the TPS. One could say that the mixture was a bit lean, 160 mV precicely. On idle with the rod connected! Basic mechanics, really, one should tighten the screws properly....

 

Henri