While traveling in the 70 mph range on the interstate I experienced what I can only describe as "running out of fuel" when I increased the throttle to pass a slower truck. The engine would act as though it was out of fuel and continue to run erratically until the throttle was backed off. It would then run normally. There seems to be a binding of the throttle just before this occurs. This binding acts as though there is a worn spot where the throttle normally stays during normal side road acceleration. The binding point is not reached while riding side roads but can be detected with the bike shut off. Could this be a slide/diaphram or needle jet problem? It was also suggested that it could be a tank venting problem. Any ideas would be welcome. Thanks
Thanks Scott
I will start with the easiest and progress to the carb rebuild if necessary. I will let you know what I find.
We still need a year and model to get more specific.
Scot covered a lot, but he's going on your diagnosis of not enough fuel entering the carb. An air leak or a clogged up main jet causing a lean burn condition will result in the exact same engine response. A clogged up air filter will allow too much fuel into the engine. At higher speeds it's almost impossible to distinguish too rich from too lean.
• When was the last time the intake rubber hoses were replaced ? If you have never replaced them, then that would be cheap insurance and an easy job to complete.
• Have you checked for the presence of the manometer plugs in the Bings ? Maybe someone balanced the carbs and then forget to replace the screws. OR, if you have the "balance hose", maybe that hose has a crack or hole in it.
• Has the bike sat for a period longer than 4 months with ethanol fuel in the tank and carbs ? Then the needles could have corrosion or varnish on them, or the main jet could be clogged with similar scum. At 70mph wind is the primary load on the engine. A lean condition might not show up at 45 because there's simply no load on the engine.
• When was the last time you replaced your air filter and checked the air box and starter cover for mice nests ?
• At the risk of retracing Scot's footsteps, damaged diaphragms is a common occurrence. Ethanol fuel is death to the older plastic and rubber parts. Period OEM parts were simply NOT designed to work with ethanol. Replacing every rubber and plastic part is not a bad first move.
Additionally, as per Scot... remove the twist grip from the handlebars. The chrome on the bars and the cast alloy grip have an immense affinity for each other. You MUST keep a good layer of grease on the bar to keep the galvanic corrosion at bay. This is especially true if you wash your bike OR ride in the rain. Greasing the chain and gear set is somewhat secondary.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
OK - I measured the gas flow through the fuel filters and it met or exceeded the criteria for fuel flow. Also, I followed the instructions for the gas cap modifications and drilled another hole in the cap. I tried spraying carb cleaner around the hoses with the engine running and didn't notice any change in rpm. The bike is an 82 R100 RT. I noticed again today that running at 65 mph for a period of time and then quickly increasing speed to 70-75 causes the problem to occur with the engine stuttering until I back off on the throttle. I cannot tell by quickly looking at the fuel filters if they are dry or full. Is a carb rebuild on the winter project list? Thanks in advance for the helpful hints. JB
You either have an blockage inside the air filtration track, or a fuel metering issue. Without answers to the 5 questions I posed to you 12 days ago, that's as far as I can go.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Hi Wobbly
Air box and filter checked out OK, manometer plugs are in place, rubber hoses to and from carbs are fine. Fuel filters are clear and allowing proper amount of fuel to flow.
Based on the above, what is the most likely cause - diaphragms, main jet, or needle? Also, when you stated that at 70mph wind places the most load on the engine. Does that mean that the wind is making the engine work harder and requiring more fuel to maintain rpm ?
When rebuilding carbs, will I need to order all internals or only specific parts based upon visual. I am not sure if these carbs have been rebuilt as I am the 3rd or fourth owner. Thanks again for your help
JB
Based on the above, what is the most likely cause - diaphragms, main jet, or needle?
JB - The most likely cause is hidden in the answer to my question #3: History of the bike. Has it been in constant service, or was it once stored. Have you just acquired it ? Have you owned it for years ? YOU have to supply the requested information because frankly my Lucas-powered crystal ball is on the fritz again.
Also, when you stated that at 70mph wind places the most load on the engine. Does that mean that the wind is making the engine work harder and requiring more fuel to maintain rpm ?
Yes. That's what "load" means. If it wasn't for the friction of moving through air, then we'd all be driving at Mach I and getting 900 mpg.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Wobbly
Regarding question #3. I have owned the bike for two years. When I purchased the bike from the PO it needed a lot of mechanical work but it started and ran fine. I dont have any prior history regarding storage, rebuilds or general maintenance. During the two years that I have owned it , it had never been on the interstate above speeds of 65 until recently and was ridden mostly on back roads. Everything has been reviewed, renewed or replaced where needed except for the carbs. Also as of late, I am experiencing quiet popping through the mufflers when backing off the throttle when coming to a stop. I have tried adjusting the air mixture screw to no avail. any ideas?
Thanks again for your help
JB
Also as of late, I am experiencing quiet popping through the mufflers when backing off the throttle when coming to a stop. I have tried adjusting the air mixture screw to no avail. Any ideas?
Lean on idle circuit. Carbs need cleaning.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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