Hello all, one of our IL members is experiencing a loss of performance with his R75/6. We are looking for ideas. Original owner with an extensive list of experience with his bike. All stock except for a Dyna III ignition. Earlier this year, the owner noted a decline in fuel economy (MPG). Now the bike has trouble achieving a highway speed much over 60 mph, however, the motor revs to 4000 RPM easily in neutral on the center stand. If anyone has experienced this, or has any ideas about it, please let me/us know.
former Airmarshal, IL.
The adage "fuel, fire, and compression" applies... And in this situation "time and amount" are paramount.
Fuel
In Illinois you have a riding season that promotes months of inactivity. First question is, does your pal empty ALL the fuel, or depend upon fuel stabilizers? The method he used in 1980 with leaded fuels no longer applies in 2016 with unleaded ethanol fuels. Everybody knows this, few change their storage strategy. That makes fuel related issues the chief suspect.
▶️ If he didn't buy ALL the fuel in the tank within the last 6 weeks, then pour it ALL into the car and buy all new high octane fuel.
▶️ Remove the float bowls and look for varnish or residue on the bowl and jet block causing the jets to become closed or undersized
▶️ Especially check the smaller pilot jet
▶️ Check the needles for a brown or green coating. Buy new needles.
▶️ Inspect the diaphragms for cracks and holes. Buy more diaphragms.
▶️ Check both petcocks for proper flow
▶️ Replace both head to carb rubber intake hoses
▶️ Check the fuel cap for a clogged breather hole
Fire
▶️ Strobe time the bike at high RPM using the F mark. Since the ignition trigger rides on the camshaft, ignition remains subject to cam chain stretch, even if there is no longer any "points gap" to care for.
▶️ Install new spark plugs. You can't see what stale ethanol fuel does to a plug.
Compression
▶️ Adjust the valves
▶️ Check the compression while holding the throttle wide open. At least 6 good, sharp, fast kicks... Or the electric starter. (With the latter, plugs must be in the caps and laying on the cylinder head !!)
Due to use of ethanol fuels everyone should expect fuel mileages to decrease. I would also venture to say that a lot of carbs are jetted too lean for ethanol, but proper jetting is only going to get you worse mileage. Remember, ethanol was used to reduce the amount of imported fuel, not to improve the fuel quality. If all else fails there is a device called "Color Tune" which has been very helpful to me in really stubborn cases.
Running on the stand is no comparison to running on the road. Running on the stand is a no load situation. Adding the load is the major intent of the dyno. True, the tuning on this particular bike is close, but one or more small items need tweaking.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Allow me to continue in Rant Mode here about the fuel issue....
The shop I work at charges between $60 and $75 an hour. Although I built close to 50 engines last year, 95% of my work continues to be cleaning up after owners who left ethanol fuel in their bikes. (This percentage has been holding for the past 15 years.) It simply staggers my imagination the lengths people will go to hold onto $10 worth of fuel, when I can't even put the bike on the lift and remove the spark plugs for $10 !!
The only proper way to deal with ethanol fuel on an Airhead is to drain the tank completely into a fuel can. THEN... 1) completely remove the fuel cap, or on hinged models... prop the fuel tank lid fully open so the remainder can evaporate, 2) remove both float bowls and set them on the seat for the duration. And finally leave the fuel taps ON. If you don't use the fuel within several weeks, then pour that fuel into your car. Trust me; your car doesn't care half as much about fuel quality as your bike.
I'm telling you, this ethanol fuel is wicked stuff. An invention of the Devil himself. And if stale fuel is your problem, then you're not getting out of any shop for less than $200, plus the pain of finding a trustworthy shop in your locale and delivering the bike to said shop. It's all so preventable with the simplest of steps.
Even if you ride your bike weekly, you need to get in the mode of turning the fuel taps OFF about a block from your house so that the float bowls have been run dry by the time you arrive home.
This applies not just to motorcycles, but any small engines on jet skis, lawn mowers, string trimmers, garden tractors, edgers, blowers, etc, etc.
I hope this saves someone out there some money.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Don Beverage is a genius! He found that the crank case breather tube to the right carburetor intake was compromised and the air filter was oil soaked. He discovered this by taking the bike for a test ride with the intake elbows removed and the carburetors drawing air directly. Howard decided to take the bike to Don after he and I were stymied by the issue.
former Airmarshal, IL.
A lot of those specially bent hoses for the breather are shown as N/A now. Good luck finding replacements.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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