First airhead, new to me 77 R100S. Had to get reacquainted with carbs, points, etc. Idle speeds up when I screw in the right idle mixture screw. Plugs show it's running very rich. I searched, unsuccessfully. What could be the prob?
1. We assume here that you've popped off the float bowls and made sure all the jets are clean and everything is free of any kind of storage mung. The new ethanol fuels collect mung, scale and yucky gunk (these are all highly technical terms us pros use) at an amazingly fast rate. This will tend to clog the smaller jets (idle) first.
2. If the carbs have ever had doses of really strong carb cleaning solutions, then you may find that the o-rings on the jets need replacing.
3. Scot is correct. Carb settings are done after everything else (timing, plugs, valve clearances, etc) is verified to be correct. I chased poor idle for several days before someone reminded me to adjust the valves. It makes a huge difference.
Hope this helps. 🙂
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks, guys. Yes, I did adjust the valves, check timing, go for a fairly long ride, etc., before trying to adjust the idle mixture. It runs fine but right cyl spark plug is sooty black. I'll get into the carb next to check for mung, scale and gunk!
It runs fine but right cyl spark plug is sooty black.
Different color plugs could be caused by several adjustments...
• The enrichener (choke) may still be slightly ON as stated above. When the lever is in the OFF position, reach your finger down to the carb body and see if you can push the lever on the side of the carb slightly more. If the cable didn't push it to the extreme limit, then you need to readjust the cable.
• Use a vacuum gauge or home made manometer to balance the idle speed on both cylinders to 1000 RPM. Then while still connected, use it to balance the throttle cable pulls at about 1500-2000 RPM.
See.... http://www.650ccnd.com/mano.htm One 12 ft long piece of hose, doubled over, strapped to a yard stick, and filled with red ATF.
I'll get into the carb next to check for mung, scale and gunk!
Oh man, you have no idea what this awful ethanol fuel will do to your entire fuel system if you allow fuel to sit in any part of the system for several weeks. Sometimes I think my entire work life is spent cleaning carbs !!
All the best.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
OK, trying to order a carb rebuild kit. Trying to find the model number. It's supposed to be stamped on a web shaped area between the top and the socket, toward the engine, on the outside of the carb. Either I'm blind or . . . Believe it's a 40mm CV (has domed top).
Speaking of carb rebuild kits. Any vendors recommended?
Thanks for all the info!
The numbers are stamped on the RH side of the carb body, on the web that is on the top side, next to the rubber intake manifold. Therefore, they are best viewed on the RH carb. The numerals are only about 2mm (0.080") high, and you'll need to 1) clean that area, and 2) may need magnification in order to see them. (See attached photo)
Apparently, from my brief stint in BMW land, BMW does not offer "kits". Instead the parts are sold individually. The float bowl gaskets are rather delicate, and I would advise keeping 2 extra on hand. Also, I found my original float needles had taken a 'set' and showed a deep indention on the viton tip, and therefore needed replacing to get good fuel sealing.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks! Found the EUBMW, listed in the Links, has kits for sale at 1/2 dealer cost (for those who have them) and 1/4 that of BING Agency International, also listed in the Links.
Oh wow ! I had never looked at the Links section. Thanks for the great tip on EUBMW !!
🙂
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
That mixture screw, if I remember correctly, controls air, not fuel.
Scott -
I believe this is a "pilot screw" rather than a "mixture screw". If not mistaken, air enters and a "pilot jet" sets the fuel to air ratio. Then the mixture passes through the pilot screw which sets the volume of the mixture allowed to enter the engine.
Don't hold me to that, but that's what I've always understood.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Apparently, from my brief stint in BMW land, BMW does not offer "kits". Instead the parts are sold individually. The float bowl gaskets are rather delicate, and I would advise keeping 2 extra on hand. Also, I found my original float needles had taken a 'set' and showed a deep indention on the viton tip, and therefore needed replacing to get good fuel sealing.
This information is not correct. My bad. BMW tends not to, but Bing does offer kits for the 40mm CV... 13 11 1 336 902 at $69 each from BMW Max, or EUBMW for $28.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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