87 R80RT issue

87 R80RT 20k miles, original carburetors, and parts.

Recently tuned up, spark plugs, air filter, re-torgued heads, valve adjustment, and carb sync etc., fuel line.

I'm having an issue and hoping the "Diagnostic Gurus" can point me in the right direction. My issue is from idle, taking off in first gear the engine "shutters" or "shakes", once the RPM's are above say 2K it smooths out.

Any suggestions what to look at would be greatly appreciated.

thanks

73516

Does it bog down or just shake? If there is a loss of power then I would suspect a fuel delivery issue, specifically the idle jet...but definitely something in the carb. If it just shakes but no loss of power, then id suspect a deeper problem in the engine. Con rods, bearings, something along those lines is out of balance but smooths out at higher frequencies.

its kinda like a really rough idle as you increase the throttle. As it get higher in RPM's all seems well. Once you get up in RPM, it'll run right down the road.

73516

It really like it bogs down, then get better when I'm able to get it up in RPM's.

73516

My couple of thoughts... You may have an issue with the idle circuit. There are three regimes on the carb - idle (up to about 1/4 throttle), needle (1/4 to about 3/4 throttle), and main (3/4 throttle to WOT) - and you transition from one to the other. It might also be that you didn't really get a good synch. Synching the carbs includes the cable tension and is usually done at about 1500 to 2000 RPM. This is where differences in vacuum have a more prounced effect. Once you really get the butterflies open, any differences side to side begin to diminsh unless it's hugely off.

Kurt

I need a little further explanation of the "idle circuit", please. Also, once I'm able to get the RPM's up something over 2k, things smooth out. With that being said, what component would you suggest needs to be looked at in the BINGs. I've ordered rebuild kits, to include diaphragms, and needle valves.

thanks
73516

73516 -

Read through this article on the Bing carbs...there are some good visuals there:

http://www.omnilex.com/public/bmw78/cvcarb.pdf

Since you're having trouble coming off idle, I think the cables are not pulling evenly and you have mismatched vacuum during this period. Not knowing how you synched the carbs, which includes the cables, I'd have to suggest that's an area to investigate.