Boxerworks.com

Hello all, I just recently purchased a 1973 BMW 50/5.
Everything is fine with it except while I am riding it and shifting through the gears 1st 2nd and 3rd are very responsive rpm and throttle/acceleration wise. When I shift into 4th gear I get decent acceleration until about half throttle then the bike starts to get sluggish in throttle response. I can only get up to about 60mph. Any thoughts or ideas on what could be causing this? I haven’t done anything to the carbs yet.

Sorry, can't even begin to help you without a roadtest.

"everything is fine" "very responsive" "decent acceleration" "sluggish"
These are all VERY subjective terms and totally depend on what you're used to riding.
A stock r50/5, well tuned, tops out at only 80-85mph in top gear (maybe 90 downhill with a tail wind on a really good day).
Just to keep things in perspective, any modern jap 250 will blow it away in the real world.

The only useful advice anyone can give you without trying it first is to do a full tune-up and see if things improve for you...
Check all the following:
Compression
Valve lash
Plugs
Points and condenser and timing
Air filter
Clean carbs

SORRY

One thing at a time. You are running 3rd gear all the way out before shifting into 4th?

Do a compression check. Make sure you don't have a nest or restriction in your airbox. Next make sure your timing advance weights are free. If you have not found a problem by then, do that full tune-up that was suggested. I'd leave the carbs for last. They are simple slide carbs right?

Yes… running 3rd gear all the way. I will start looking per your suggestions. Thank you for the information/reply.

Yes, they are slide carbs.