Carb question 71 R50/5

[jdvorchak]

Some folks have been following my revival of a really nice shape 71 R50/5 that had been sitting for 20 to 30 years. I got the engine put together, but had to buy two Bing carbs off of eBay. The had mismatched idle and mains so I mixed and matched parts from the old carbs to get the proper idle jets and high speed jets. Now they were virtually taken apart and put together by me. I have the floats set per the clymer manualn and preset the mixture screws 1 1/2 turns out. The idle speed screws I have no idea where to set them so I just guessed where they just start to lift the slide and maybe 1/2 turn more. All passages and circuits are clean so I'm confident the carbs are at least in a functioning starting point.

I tried to test fire the bike and it did pop and run but only on the left side. Some more fiddling with the fuel delivery from my IV gas tank and now both are getting the bowls full. I can coax it up to a good 2k to 3k rpm and both cylinders are running but it sounds lean to me. Now I have not put the air tubes or air filter in yet. So my question is do these old Bing's need the air tubes and factory air filter to run right? Some intake resistance?

Thanks in advance.

[Kurt in S.A.]

Don't know if it is the same for the /5 bikes but I think so. I was helping a guy work on his R51/3. We took the air horns off and did some adjustments. We'd then take the bike out to see how the bike performed...without the air horns. Never could get things right. Finally put the air horns back on and the bike improved dramatically. I think the air horns/filter are important for proper operation.

Kurt in S.A.

[Bamboo812]

Yep, the guys who mount velocity stacks always have to re-jet the carbs...

[jdvorchak]

thanks guys. I kinda thought that when I got it running it sounded lean. I have the carbs set the way I want them now so I'll put the air horns on and a brand new air filter. The biggest problem I have is trying to run new fuel line through that hole in the right side. The old hose is still holding up well but I bought some brand new BMW hose. Hate to go through all this work and have that hose fail 2 weeks down the road. I'm thinking if I put some baby powder on the cloth fuel line covering that it should slide through there more easily. If not I'll try wetting it down with some alcohol and see if that slicks it up.

I'm still running it on the IV as the tank still needs cleaned but I did get the new petcocks so fuel delivery should not be a problem. Need to pick up two inline fuel filters but that's not a real problem until I'm ready to mount the tank.

[jdvorchak]

Well it turns out I had the floats set incorrectly, per Clymer. What a surprise huh? Anyway I pulled the carbs and set the floats the way I thought they should be set, like I was working on a Honda or Kawi. Tickled them for a long 2 seconds and it fired up on both. Some playing back and forth with the mixture and idle speed adjustments and it starts, idles smooth and take the throttle. Now I need to replace the points and get to ignition timing as it sounds a little retarded on timing but not by much because it does start relatively easy. Nowhere from idle to 3k rpm did I see any marks in the timing window with my pro timing light. They just kinda went by too fast. Probably also needs new advance springs. But that ignition timing issue is for another post subject.

Once again thanks everyone. The air horns and new air filter did help a lot.

[wookie]

A quick and dirty way to thread fuel line thru the air filter chamber is to use a long, skinny screwdriver to guide the hose thru. ( A straight, stiff piece of wire will also suffice.)

[jdvorchak]

Actually what I ended up doing was use my pliers to crimp and twist the line from the outside. Once I had about 3 or 4 inches through I just pulled on the other end.