1150 poor running (Surging)

I'm getting a little annoyed with the surging problem at small throttle openings.

30 MPH, 3rd or 4th gear, the bike feels like it's running lean.
This is very annoying when running around town, and especially annoying when instructing kids on scooters for the CBT.

I have tried changing the yellow coding plug for the brown one, but this just moves the problem to slightly larger throttle openings (40MPH in 3rd or 4th).

a friend (also an instructor) has the same issues with his 1150 RT, and we are both starting to dispair. His older 1100RT didn't do it, and my thundercat didn't do it (and that had a race system).

So what's gone wrong here?

It feels like an air leak into the engine, but the throttle response is nice and crisp, pulling cleanly when snapped or rolled open.

I have seen reccomendations to change the TPS setting, but does this not impact on the catalyst?

Any ideas? This fault is spoiling a great bike.

Cheers,

Mike.

Mike,

Mine did this too, and I was getting just as frustrated as you sound. However, I have made changes to the exhaust & air filter which have had the side effect of removing the surging as well as improving the engine response. Firstly, I changed to a K&N filter. This didn't do anything for the surging but made the throttle response much crisper (no improvement to top end power/speed though). Secondly, I removed the catalytic convertor/collector box as it weighs an awful lot and is also v. restrictive. This was replaced by a Sebring "Y" piece from Bracken and this has cured the surging. It took some tightening of the clamps over a period of time to remove the backfires but the system now seems airtight and sounds great. I kept the original silencer for now, but I have ridden one with the full Remus system and it would wheely off the throttle in 2nd gear

HTH,

My 1150 was fine until the 12,000 mile service so they can be OK and it would seem a small change can trigger it off. Since then, tried the plug change and had the valve clearances reset (Hughenden thought it might be due to the need to set clearances when the engine is stone cold). No joy so far. It is coming up for its 18,000 mile service so we will see if there is any change then. Fortunately I don't have to do too much trickling along in 30mph limits.

Paul

This is one thing that I always had issue with. Common belief is that BMW came up with the twin spark to fix the surging issues, but I read about just as much twins sparks as the singles having the issue. In my case it was a weak (or bad) stick coil or coils, that was causing the surge, most of it anyway. My intention was to convert it to single spark just to try it as a troubleshooting, but the bike runs fine so I will probably leave it as a single spark. Of course the assumption is that TB sync is done, that is probably the most important thing (if the bike is fine mechanically)

Few things to try:

Rocker end float
Valve clearance
Throttle balance at idle and where the surging occurs (4000rpm?)
(Check rubber blanks under throttle bodies not split and leaking)
Set TPS a little richer at 371 (mv?)