I searched this site and found a few relevant articles. I have a '73 R75/5 that I've been sorting out over the last 2,000+ miles.
I rebuilt the carbs when I got the bike, I believe the enrichers are reassembled correctly. They function as expected [when tested, don't need to use them to start]. Had poor mpg, 33-34 initially with needle in stock position 3. Moved to 2 and improved to 36-37. Now to 1 and 41-42 mpg. No discernible difference in performance other than mpg [no bog or miss, acceleration still ok]. Starts without enricher even with needle in position 1 which surprises me. My mechanic says I shouldn't be able to go from position 3 to 1 without getting too lean. I've also lowered the fuel level in the bowls to around 17-18mm [22-24mm seems to be the recommendation] with no discernible changes in performance of plug color.
Spark plugs get sooty very quickly, seemingly running rich. No discernible oil consumption. Perhaps I shouldn't worry about this but I'm taking a trip away from my home 700' elevation to the Rocky Mtns and will be at 5,000-11,000'. I'm worried about the presumed rich condition causing very poor performance at elevation. I ride 50-100 miles before rechecking plug color, I haven't tried the "run fast then kill engine, coast to stop, inspect.
I've been running Bosch W6D plugs. I'm considering trying NGK BP5ES plugs, which are one heat range hotter, hoping that will improve self-cleaning but don't want to risk running too hot and damaging the engine.
Comments solicited and appreciated.
I'm running all stock jets. 135 main, 45 idle, 2.70 needle. Needle jets and needles are new. Bing 64/32/9&10 carbs.
I have a ‘78 R100 with 40mm Bings. I was chasing a carb issue years back. I wanted to eliminate the enrichment circuit as part of a process of elimination.
I had some multi-colored Dorman vinyl vacuum caps from O’Reilly’s Auto. The smallest vinyl cap, yellow in color, fit nicely over the pick-up tube for enrichment circuit in the front corner of the carb bowl. When you remove your bowl, you will see the pick-up tube extending down. It pulls fuel from a well in the front corner of the bowl, supplying the enrichment circuit. The vinyl cap can go on the tube, and the bowl reinstalled. The enrichment circuit then can no longer draw fuel.
it is not normal for your bike to start without using the enrichment circuit. A bunch of fuel is coming from somewhere.
It is not normal for your bike to start without using the enrichment circuit. A bunch of fuel is coming from somewhere.
I agree. Some thoughts....
• BP7ES plugs should run perfectly in most any Airhead.
• Have you replaced (simply due to age) the plug caps and plug wires ? And if you did, were the wires "metal core" wires ? You must not use the automotive "suppression" type wires on an Airhead.
• Replace the air filter. It can be filled with dirt due to age, or oil due to the sump breather needing replacement. The phenolic disc type breather valve should be replaced with the later style reed valve.
• R75's have the open scoop on the starter cover which is an invitation for mice to build winter nests.... which seriously block the intake air path. Check it while the air filter is out.
• It is a common occurrence for the enrichener valve (a flat disc) to be placed in the wrong carb when both carbs are disassembled at the same time. This is why I always advise users to disassemble 1 carb at a time. Some of these valves are marked LH and RH, but not all. I suggest you remove the 4 screw cover on the side and check this.
• Based on age, it is also time to replace the "float" and "float needle". Bing revised these parts for ethanol fuels, but it's time. It's a great time to check the float levels too.
• Then there's the common stuff we always check concerning torn diaphragms and matching needle protrusion.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
I have a ‘78 R100 with 40mm Bings. I was chasing a carb issue years back. I wanted to eliminate the enrichment circuit as part of a process of elimination.
I had some multi-colored Dorman vinyl vacuum caps from O’Reilly’s Auto. The smallest vinyl cap, yellow in color, fit nicely over the pick-up tube for enrichment circuit in the front corner of the carb bowl. When you remove your bowl, you will see the pick-up tube extending down. It pulls fuel from a well in the front corner of the bowl, supplying the enrichment circuit. The vinyl cap can go on the tube, and the bowl reinstalled. The enrichment circuit then can no longer draw fuel.
it is not normal for your bike to start without using the enrichment circuit. A bunch of fuel is coming from somewhere.
Thanks for the vac cap blocking enricher circuit idea. Did it, bike still started easily cold.
Took enrichers back apart, confirmed they are very clean and properly assembled, now with another set of new gaskets and o-rings. Presumed rich condition is not coming from the enriching circuit.
Jets are stock, clean and open. Air and fuel passages are open.
Float bowl fuel levels are low (18mm) so that shouldn't contribute to rich condition, but hasn't resulted in observable fuel restriction.
Air filter is very clean. Breather is working, dumping oil into right carb intake, but both plugs blacken very quickly. Disc type but I can't get it out. Will get a new gasket and reassemble.
So the bike starts easily and idles well w/o enrichment. That's convenient but "not right". Mileage is decent at 41-42 mpg.
I'll see if the hotter plugs make any difference in plug color. Even if they do it seems like treating the symptom rather than the cause.
And, your needles are still at the first position (leanest)?
Hmmm … what could it be? Air filter is good. You’ve been under the starter cover and there is not a rodent nest in there. So, air supply should be good.
when you rebuilt the carbs, that included diaphragms? Boy, you got me! The fact that it starts and idles with no enrichment - that is puzzling. Where is your idle mix screw? Does the engine respond to turning the idle mix screw?
And, your needles are still at the first position (leanest)?
Hmmm … what could it be? Air filter is good. You’ve been under the starter cover and there is not a rodent nest in there. So, air supply should be good.
when you rebuilt the carbs, that included diaphragms? Boy, you got me! The fact that it starts and idles with no enrichment - that is puzzling. Where is your idle mix screw? Does the engine respond to turning the idle mix screw?
No nests or mess under starter cover or in air filter housing. Yes new diaphragms. Left idle mix is 1 turn out, Right is 3/4 turn out. My mechanic did the initial tuning and I don't mess with idle mix because it's running and idling well. I did make minor adjustment to idle speed & sync'd. I use a TwinMax mostly to sync cables. It's a puzzler.
I probably need to do the run fast/cut engine/stop/examine plugs method rather than reading them when I get home after putting in town the last mile or two.
1. Describe your plug reading method, please.
• You should not be pulling your plugs out on a whim and then judging or tuning anything by what you see. Plug reading follows a highly defined schedule of riding for 5+ miles at a CONSTANT throttle opening (strictly corresponding to a specific jet you are trying to read), hitting the kill switch while at the same time disengaging the clutch so that the engine completely STOPS turning. THEN you can pull the plug(s) there on the side of the road and read the result of one single carb jet range.
• The idea that you can pull a plug at any random time and learn something definite is total BS. That's like glancing at your watch at random times during the day and hoping it's 'going home time'. Sometimes it is; most of the time it isn't. By definition, random readings produce random results.
2. Carburation and fuel mixture are the result of ALL OTHER tuning factors. That is, changing the ignition timing, air filter, ambient temperature, valve settings, etc, etc, all contribute to the final, end result we read on the plugs. And unlike all these other settings (which have FINITE, highly defined settings), carburetor settings are not defined. Carb settings are the result of all the other aspects of engine tuning. That means you cannot simply start tweaking the carb adjustments at any time you choose; every other aspect of engine tuning has to be perfect.
That being the case, I'm wondering how your ignition timing was set. Please describe your ignition timing procedure.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
I've now heard from you and another source about the proper way to prepare to read plugs. Stuff I didn't know and am glad I've been enlightened. Thanks. I've probably been chasing a phantom. Although the starting with no enrichment with needles in position 1 [all the way down] is said to be a potential warning sign... It starts immediately and idles very well. Fuel efficiency is decent at 41-42mpg riding 50-60mph on county hard roads. Was only 33-34 needles in pos 3, 36-37 in pos 2.
My mechanic reset the timing & rechecked points gap when he was chasing a cam seal leak. I didn't ask but I assume he used a timing light.
I'd earlier checked/slightly adjusted valve clearances. So it was properly tuned before I went on the carb adventure.
Have new EME copper wires and 1k ohm caps.
Air filter is very clean, so is breather. Disc type, doesn't do the turkey gobble and is putting condensed oil vapor into right carb intake as it should. I'm not going to try to wrestle it out for replacement, leaving well enough alone for now.
Leaving in a couple days on the Rocky Mtn ride with an old Army buddy who got me into airheads back in '75. We've both acquired bikes like we had back in the day. His a LWB R60/5, mine a LWB R75/5. I'll carry spare spark plugs.
Thanks to all contributors for their thoughts.
Bike sorted and on the trailer. Blast off tomorrow morning!
That's great news !
Ride report when you get back.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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