Carb Tips for 1979-1980 points ignition R65

[montmil]

This from the Airhead Beemers Facebook page:

Question: It was warm out today so my bike (1980 R65) was running great. However, below 50 degrees, It has very little power between 3000 and 4500 RPM. I am assuming it is something carburetor related. Any ideas?

Response #1 from Tom Cutter: 1979 and 1980 R65s were too lean on the needle jet and needle. Don't raise the needle, just go UP one size on the needle jet to 2.68. Stock 1980 R65 jetting SHOULD BE: Main: 145, Needle Jet: 2.66, Needle: 46-241, Needle Position: #3, Idle Jet 45. If you use those specs and it still is flat in the midrange when cold, go up on the needle jet to 2.68. Make sure that your fuel level in the float bowls is 24 mm measured to the center of the bowl on a level surface. Points and timing MUST be right on the money. You can use a dwell meter to set those points-in-a-can very accurately. The dwell spec is 78 degrees, which will read 39 degrees on the 4-cylinder scale on your dwell meter. Set valve clearances at .004" IN, .008" EX.If your air filter is clean and you are running 10W40 semi-synthetic oil (SPECTRO) that little thing will rip.

Response #2 continued from Tom Cutter: Points wear, and the 1979 and 1980 models use different points than all the other models. A lot of aftermarket companies sell Bosch car points for that application, and they do not have a stiff enough spring. Look for white paint dots or stripes on the black points wire INSIDE the beancan. If yours have a solid black wire, replace the points with BMW p/n #12111243969. Look up that part number on the MAXBMW site to see the paint dots on the wire.

Check out Tom Cutter - Rubber Chicken racing Garage

http://www.rubberchickenracinggarage.com/

[Barry]

I'll agree with 79 flat tops being lean on the needle jet and needle. Reading the period road tests confirms they could be weak in the mid range from new. One needle position is a huge change so the usual way to correct it would be a needle jet increase.  

I heard about the point substitutes too. There is a long list of possible alternatives which would be a good thing if it wasn't for the potential issue of points bounce at high revs. It hasn't been a problem for me as I have two genuine BMW sets which with a points amplifier greatly extending their life will likely see me out.

While I'm as anal as it gets when it comes to setting the ignition timing spot on I'm surprised that dwell is as critical as all that.

Greatly surprised and gratified to hear there is one more advocate of thinner oil. I used 10W40 for years and more recently 5w40 not that there is much practical difference between them.