Hesitation at 4,000 revs?

[Sullivj]

Having replaced the air filter and plugs, I got to test the bike today.


It hasn't cured the problem unfortunately. There is still a hesitation / flat spot most noticeable around 4,000 revs. When you accelerate hard, it feels like some kind of restricter, holding you back,


Also, I noticed some popping from the exhaust. Most noticeable when you Rev the bike at a standstill, or close the throttle going downhill.


Anyway, it's due an annual service soon, so I'll take it to the dealer, and see what they can find.

[guest2360]

Having replaced the air filter and plugs, I got to test the bike today.


It hasn't cured the problem unfortunately. There is still a hesitation / flat spot most noticeable around 4,000 revs. When you accelerate hard, it feels like some kind of restricter, holding you back,


Also, I noticed some popping from the exhaust. Most noticeable when you Rev the bike at a standstill, or close the throttle going downhill.


Anyway, it's due an annual service soon, so I'll take it to the dealer, and see what they can find.

Defective coil?

[David.]

Anyway, it's due an annual service soon, so I'll take it to the dealer, and see what they can find.

Is the exhaust flow control valve functioning correctly.

[Sullivj]

Defective coil?

Could be RT Man. Is there an easy way to check?

[Sullivj]

Is the exhaust flow control valve functioning correctly.

I found this, so will try it and report back:


According to Haynes Manual to check operation of the exhaust valve, remove silencer, note position of valve in the end of exhaust pipe, then turn ignition ON to actuate the servo, the valve should move through its range then return to its start position. Turn ignition OFF. Hope this helps.

[Sullivj]

I checked the exhaust valve. When I removed the silencer, the valve was between closed and open (normal operating I presume).


Turning the ignition on closes the value, and then it returns to the open position.


I lubed the cables, but it all appears to be working OK.

[johnarthur]

What sort of revs do you cruise at before trying to accelerate through 4,000 rpm?  I found that even though the bike will run happily and smoothly from 2,500 up to 3,500 after a minute or two of this then the hesitation cuts in when trying to accelerate, perhaps plugs getting fouled?  I now keep the revs at 3,500 or higher even though that means using 5th on 60 mph roads, and the problem disappears.

[Sullivj]

In all gears and at various speeds the issue is most noticeable around 4,000 rpm.


My battery is now 5 years old, so I'm going to replace that, just to eliminate it as a possibility. Then I'll book it in to the dealer for investigation.

[David.]

How about giving a fuel system cleaner a go, there's even one with BMW on it, part no. 82140413341.

[guest2360]

Nearly convinced you have a coil,problem but I'm not sure you can confirm it yourself.

[David.]

The Haynes manual says, "In order to determine conclusively that an ignition coil is defective, it should be tested by a BMW dealer equipped with the diagnostic tester."

Does this mean that the coils are removed from the bike & bench tested, might be worth asking the question of a BMW dealer.

[guest2360]

The Haynes manual says, "In order to determine conclusively that an ignition coil is defective, it should be tested by a BMW dealer equipped with the diagnostic tester."

Does this mean that the coils are removed from the bike & bench tested, might be worth asking the question of a BMW dealer.




Tested in situ I think.

[David.]

Have seen a couple of videos & posts on other forums where, whilst the bike is running at idle, the LT lead on each coil stick is disconnected in turn.

The theory seems to be, if disconnecting the LT lead/coil doesn't make any difference to the running of the bike, that particular coil is suspect.

Has anyone else heard of or used this diagnostic technique?

2004 BMW R1150GS Ignition Stick Coils, https://www.youtube.com/watch?v=hMJWr_BdNO8

[David.]

A more scientific approach might be to use an adjustable spark gap tester, https://www.machinemart.co.uk/p/laser-5 ... rk-tester/



Or, check the coil primary & secondary resistances with a multimeter.

The spark gap test sounds the most reliable method, failing that, it's probably a visit to your BMW dealer.

[Sullivj]

Thanks David.


I've run out of time to continue the investigation, so I spoke to the dealer today.


They couldn't book me in for 2 weeks, so rather surprisingly, suggested a local independent, who used to work for them.  I spoke to him, and am taking the bike to him in the next few days.


I'll report back...