Advice sought

At the risk of public humiliation, I'm seeking the advice of this collective crowd. I know enough about old BMWs to be dangerous, but I'm smart enough to know I don't know much.

I have 1966 R50/2. Fully restored, stock 6v system. Has run beautifully for me for years. Have owned it since 1986. But I've let it sit for the last 18 months. Just put a clean, newly lined sport tank on it. Then attached and finally aligned my Steib S500. Added fresh gas (non-ethanol), and pulled the pilot and main jets to clean them.

She starts and purrs wonderfully. Running thru 1st, 2nd and third gears with no issues. But in 4th, around 45 mph, after about a minute or so she'll start acting up. The symptoms are like fuel starvation. Dying, surging, hesitating, surging, running smooth, then losing power. Downshifting doesn't help. It has occurred on mainly on flat, level roads and is not happening specifically on hills or curves.

I pull to the side of the road, and she is purring like a kitten. Wait 30 seconds, take off again. Get up to speed, 4th gear, 45-50 mph, and in a bit it starts again.

I'm planning on pulling both carbs and thoroughly cleaning them (not just the jets). My questions is should I be concerned about the timing advance? Is there anything else that might be contributing to this issue (beside not riding her enough?) I've never had this issue riding her solo. Is there anything that attaching the sidecar could affect that would be causing this?

My first hypothesis is something is blocked in the carbs, besides the jets. The second check will be the points, and timing advance.

Any suggestions? I am all ears.

Jeff
Petersburg, Va

I certainly would take a closer look at the carbs...hopefully nothing from the tank relining is affecting things. Do you have some in-line filters? I find it a comfort to look down and see that fuel is flowing to the carbs. Also, could help filter out any debris.

Try popping the gas cap...maybe the cap is not venting.

It's worth checking the timing...easy enough to do with the timing light, although you'll need a 12v source for the light. Be sure that the timing does indeed advance. It's possible that the weights are not moving out to create the advance curve.

Adding a sidecar does put strain on the driveline. Note there is a transmission for sidecar specific use...I believe that the 1st gear is a different ratio. Not sure about the final drive, if that needs to be different as well.

Another thing that a sidecar does it mess with airflow to that side of the bike. It could be getting hotter and maybe fouling out the plug or maybe boiling the fuel, but I would think that you would probably notice something out of the ordinary.

Also, check the filter built into the fuel petcock (assuming your bike has such).



Mine didn't always look that clean.

20774 said:

I certainly would take a closer look at the carbs...hopefully nothing from the tank relining is affecting things. Do you have some in-line filters? I find it a comfort to look down and see that fuel is flowing to the carbs. Also, could help filter out any debris.

Try popping the gas cap...maybe the cap is not venting.

Click to expand...

Will check all that. I cleaned the tank myself prior to having it resealed and painted. I also took apart and cleaned the petcock while I was at it. I can pull the two lines into the tops of the carbs, and when I turn on the petcock they piss gloriously. No issues from tank to carb.

20774 said:

Adding a sidecar does put strain on the driveline. Note there is a transmission for sidecar specific use...I believe that the 1st gear is a different ratio. Not sure about the final drive, if that needs to be different as well.

Another thing that a sidecar does it mess with airflow to that side of the bike. It could be getting hotter and maybe fouling out the plug or maybe boiling the fuel, but I would think that you would probably notice something out of the ordinary.

Click to expand...

I have learned that, but finding a sidecar final drive is very difficult. Even more so to pull the transmission and have the 1st and 2nd gears changed. But you are correct, 1st gear really is a challenge to get going. Right now it is only a nice day and special occassion ride, but I should do the correct sidecar gearing if I'm to make this car permenant.

jeff