Recently purchased a 1988 R100RT that had been sitting in a garage for the last 20 years (unfortunately with fluids not drained). It has 62,000 miles on it. Have drained the fuel tank, added new fuel lines, rebuilt the carbs, added new spark plugs and BMW spark plug wires. Spark appears to be strong (blue). Float levels look good. Runs great above 2500 rpm, but below that, it begins missing and at normal idle (1,000 rpm) it seems like one cylinder is completely missing out. Smoothes out immediately with a twist of the throttle and has excellent acceleration. Suggestions?
Welcome Aboard !
The jets most prone to clogging due to storage with aged fuel are, of course, the smallest ones. The smallest jets are for the idle circuits. Fuel metering is so fine for idle that cleaning the jet without gouging the finely machined surface is almost impossible, therefore replacement is HIGHLY recommended. Luckily, this is a screw-in jet easily replaced by only removing the float bowl.
> First step. Pop the float bowl off and look for a tiny brass jet, typically a #45. It can be reached and replaced from the float area when the bowl is removed.
> Second. Your symptoms tell me that although the carbs have been cleaned, some smut remains. Highly suggest you use a name brand fuel with cleaners* AND supplement that with a carb cleaner such as StarTron. Maybe 1/2oz per fill up, until the bottle is finished.
* See the Top Tier Fuel web site. https://toptiergas.com/
Issues may also be related to....
> Air filter
> Old, hard intake hoses
> Pin holes in diaphragms
> Wrong type spark plug wires or aging plug caps
> Tight valve clearances
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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