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Takes long to warm up?

rafalc

CB750 Enthusiast
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1973 CB750. How long does yours take to warm up?

With a cold start, I keep the choke fully open for about a minute, then close it. At this point I have to adjust the idle screw probably about a whole turn in order to keep the RPM around 1000 without the bike cutting off, oil pressure gauge shows 60-70. I need to wait close to 10min before the oil pressure at idle drops to around 30 at which point I can back off the idle screw to where it was without the bike shutting off.

If I don't wait and attempt to ride before it is fully warmed up, after giving it some throttle, the RPMs jump to 4-5k and stay there.

Is this normal? I assume this has something to do with the carb? Mybe something with jets being clogged?



The other cb750 in the garage (1978) does not require this and idle adjust screw doesnt have to be turned at all. It takes 1-2 min to warm up at which point idle RPMs are correct and it is ready to ride.
 
I would go through and do a complete tune...valve adjust, adjust points, set timing, sync carbs, compression test, check for vacuum leaks at the carb boots. The early carbs it is normal to have to play with the speed screw as it warms up. The late carbs have accel pump and also have a fast idle built into the choke.
 
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