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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Oma Aika on June 11, 2014, 07:29:34 AM
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When starting our K75, it's impossible to ride when engine is cold. Between 1000 - 3000 it's just coughing and jerking. When warm, it's so nice. It easily takes rpms 1000 - 9000. Is it a typical feature? This one has been like that always =since we bought it July 2013) but after "everything" was adjusted it's been worse cold - but a lot better when warm.
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Have you balanced the throttle bodies and checked valve clearances, Oma?
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Everything should have been done at the service. And it's perfect when warm, better than before. Just the character of the cold engine is annoying.
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greetings oma aika...
you gotts to warm them up... go slow... they will purr for you... then go f-ing crazy... yeeeehaaaaa...
j o
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Curious -- how cold is cold? Mine doesn't do that but it's never really cold here compared to there.
So it idles fine at 1000rpm but sputters between 1k and 3k rpm until the engine warms up? No problems at all at low idle?
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Engine temp sensor comes to mind. Stuck thermostat?
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When my valves are in spec and the TB's are balanced, my K75 takes about a minute or two to warm up enough that I can turn the choke off. It runs smooth right from the start though.
I had serious coughing and jerking when cold for six months until I figured out the throttle bodies and valves.
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The bike is in my warm garage so it's about 20 C. It start immediately, the "choke" can be taken off immediately and the idle is around 1000 rpm. But if i ride without letting it be warm (=wait few minutes idle) the first kilometers are terrible, almost impossible. The temperature sensor should work because if temperature is 25-30 C outside and after riding I let the bike idle for 10 minutes I'll see the red light.
When the engine is cold, it's like it really needs a real choke, I've understood that this choke isn't really a choke?
And as said, after the difficult first kilometers it's nice. Not very much power 1000 -3000 but it's smooth, and on the other end it easily takes rps to the red zone (9000 rpm).
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Could the temp sensor be telling the ECU that the engine is warm, when it is not? The ECU would lean out the mixture. The symptoms sound very similar to the ones on my MG V7. Moto Guzzi's are notorious for being cold blooded, primarily because of the lean mixture. Reflashing the V7's ECU cures the problem. Check the temp sensor, valves and TBs as suggested.
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It sounds like its lean when cold.
Check for vacuum leaks. The crank case vent hose would be suspect.
There should be an adjustment for hydrocarbons at idle. It's on the air box somewhere. That may be adjusted wrong. Tweak it alone way 1/4 turns if it improves give it more.
There are two temp sensors one is a coolant sensor and since your bike is door style AFM it's probably a nub in the front side of the actual AFM, BMW doesn't make it easy but there is a way to fully test the AFM with a VOM. This may actually be a valid test. http://4crawler.com/4x4/CheapTricks/AFM/index.shtml (http://4crawler.com/4x4/CheapTricks/AFM/index.shtml)
Another thing to check is that the fuel pressure regulator is functioning. As you give it throttle the FPR should give it more gas. Again when cold it needs that extra fuel. Once warm you may be getting away without it.
And this seems to always be where I find problems on my bike. Inspect the ECM plug. Take a fine screw driver and scuff the connections. The dielectric grease dried up on mine and I was getting electrolysis caused corrosion. That fixed a lot of issues. The leads for the pump I think is where I was having the worst problem.
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+1 vacuum leaks. I seem to remember a similar issue with cracked rubber bits on throttle bodies on my bike ages ago. Rubber expands when warm so maybe a crack is sealing up once the bike is warm. Maybe try the unlit propane test around the throttle bodies to see if you can find the crack.