PDA

View Full Version : '71 R50/5 newbie carb question

ebeeby
03-13-2006, 04:52 PM
My '71 R50/5 with 18,000 miles develops a fast idle (2,000 rpm) when the engine reaches operating temp. Throttle return to idle also slows way down. I pulled the pistons to clean for varnish (carb cleaner and a rag) as well as the piston throats - still same problem. Doesn't happen on a cold or warm engine - just once it gets to operating temp.

Are my throttle springs bad? Do I need to hone the piston throats or piston?
jdiaz
03-13-2006, 05:49 PM
How is the exhaust valve clearance? Won't tight clearances sometimes affect idle return when hot?
20774
03-13-2006, 05:51 PM
How about your advance unit? Is it possible that it's sticking in an advance position, or the return springs have gotten weak? If it's never been off, possibly you should remove and lube it sparingly at all the contact points. Careful tightening the 10mm nut that holds it on...it doesn't need to be that tight and snapping if off will ruin your day.

Kurt in S.A.
20774
03-13-2006, 05:53 PM
How is the exhaust valve clearance? Won't tight clearances sometimes affect idle return when hot?

I wondered about valves, too, but I thought that tight valves would result in a rough idle or even trouble holding idle. Nonetheless, yes, check the valves, too, just to rule them out.

Kurt in S.A.
flash412
03-13-2006, 05:58 PM
Spray WD-40 on the intake manifold while the bike is idling and see if it speeds up. If it does, your manifold is leaking.
lkchris
03-13-2006, 07:19 PM
Set throttle cable slack and balance carbs with engine hot--this takes 10 miles riding.
dlearl476
03-13-2006, 08:18 PM
I'd check Flash and Ikchris' (free) suggestions first, then springs.

I'd suspect you have one tight throttle cable.
88bmwJeff
03-13-2006, 08:34 PM
One thing comes to mind in addition to what's already been said. Occasionally this can be caused by adjusting the carbs before the bike/engine is fully warmed up. If that's not the case, I go with a sticking advance mechanism. Check out the following website for better information.

http://w6rec.com/duane/bmw/advance/index.htm
ebeeby
03-22-2006, 09:39 PM
I think it was not hot enough when the carbs were adjusted.

After re-adjusting on a hot engine, the problem seems to be resolved.