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TL;dr version, the bike runs fairly smoothly when cold, but as soon as it warms up there's a really bad misfire/backfire when the engine is put under any sort of load. What does this sound like?
Hello, I'm pretty new here and I'm just bringing a '97 1100GS back into operation after what appears to be a fairly significant layup. The fuel in the (original) tank was disgusting, there was plenty of rust, the fuel pump filter sock was choked with fine rust and bits, so I've replaced the pump and filter. Most of the fuel pipes were tie wrapped rather than clamped, and many of them were perished almost to the point of splitting. Throttle cables were all sticky, the fast idle cable wouldn't return, etc etc, so I've replaced them all too.
Anyway, I got a replacement tank, re-plumbed everything, filled with fresh fuel and took the bike out. It started easily enough, and settled down to a ridiculously high idle (1800 or so). Smoothish at idle, but under any sort of load it just stuttered and surged and if put under a lot of load the revs build veeeerry slowly in the lower gears, but with lots of popping in the airbox and a backfire or two if held at sustained high throttle in a higher gear.
Today I set the valve clearances and rocker end float, nothing was too far out apart from the exhaust valves a 'tad' on the tight side on one cylinder but broadly correct. Balanced the throttle bodies, again they weren't far out, but the air screws were way too open leading to the high idle.
I had some very weird behaviour once I dropped the idle down at first: the engine would idle very smoothly then every second or so it would appear to do a massive misfire and then recover, but it was doing it far too regularly for it to be a simple misfire, it was as though the engine management was trying to pull the idle down by cutting the fuel or something. As I went around the engine to troubleshoot anything misplaced, it settled right down into a smooth idle.
So I've adjusted the throttle cables, the air screws, and the engine was running beautifully and smoothly, and revving cleanly off load. I couldn't take it out for a test there and then as I had other things to do. This evening, I took the bike out, it ran pretty smoothly when cold (I could accelerate through the gears without any misfires/stuttering) but as soon as the first dash appeared on the RID/temp gauge it started misbehaving under load again.
[edit] I also forgot to say I notice that it was missing/surging when engine braking from a reasonable speed in a lower gear (so putting it under deceleration load, if that makes sense).
I'm tempted to say it's ignition, but what do people think? It's my first BMW boxer, so whilst I've got tons of experience with Japanese bikes of all ages, I'm not used to the foibles of these yet.
Hello, I'm pretty new here and I'm just bringing a '97 1100GS back into operation after what appears to be a fairly significant layup. The fuel in the (original) tank was disgusting, there was plenty of rust, the fuel pump filter sock was choked with fine rust and bits, so I've replaced the pump and filter. Most of the fuel pipes were tie wrapped rather than clamped, and many of them were perished almost to the point of splitting. Throttle cables were all sticky, the fast idle cable wouldn't return, etc etc, so I've replaced them all too.
Anyway, I got a replacement tank, re-plumbed everything, filled with fresh fuel and took the bike out. It started easily enough, and settled down to a ridiculously high idle (1800 or so). Smoothish at idle, but under any sort of load it just stuttered and surged and if put under a lot of load the revs build veeeerry slowly in the lower gears, but with lots of popping in the airbox and a backfire or two if held at sustained high throttle in a higher gear.
Today I set the valve clearances and rocker end float, nothing was too far out apart from the exhaust valves a 'tad' on the tight side on one cylinder but broadly correct. Balanced the throttle bodies, again they weren't far out, but the air screws were way too open leading to the high idle.
I had some very weird behaviour once I dropped the idle down at first: the engine would idle very smoothly then every second or so it would appear to do a massive misfire and then recover, but it was doing it far too regularly for it to be a simple misfire, it was as though the engine management was trying to pull the idle down by cutting the fuel or something. As I went around the engine to troubleshoot anything misplaced, it settled right down into a smooth idle.
So I've adjusted the throttle cables, the air screws, and the engine was running beautifully and smoothly, and revving cleanly off load. I couldn't take it out for a test there and then as I had other things to do. This evening, I took the bike out, it ran pretty smoothly when cold (I could accelerate through the gears without any misfires/stuttering) but as soon as the first dash appeared on the RID/temp gauge it started misbehaving under load again.
[edit] I also forgot to say I notice that it was missing/surging when engine braking from a reasonable speed in a lower gear (so putting it under deceleration load, if that makes sense).
I'm tempted to say it's ignition, but what do people think? It's my first BMW boxer, so whilst I've got tons of experience with Japanese bikes of all ages, I'm not used to the foibles of these yet.
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