Just bought a new 2013 72 sportster. It had sat at dealer 3 years, just never sold. Has 25 miles on it. Runs perfect every where but throttle slightly open. Has a pretty good surge only at that point. Idles perfect. Feels like a lean condition but plugs & exhaust look rich. Could bad gas maybe cause this?

 

What you describe sounds like a lean surge. Not surprising since these bikes are set up very lean. What is strange is that the plugs look rich. I would fill with fresh gas, add some Seafoam and even change the plugs, they're cheap enough. Ride through a couple tanks of gas and see if it improves.

 

Thanks nevil, I,ll drain the tank today & refill. Had already changed plugs & seemed a little better. I think that the bike had been started & moved around the dealership quite often but never really ran to clean it out. I think that's why the plugs look as if it was rich.

 

Did the dealer sell it as new? If so, tell them it's surging and they need to fix it. Let them go through the bike and clean it out before you start spending your time and money on it. Just my two cents.

 

Nevil
It is one of the fourms BIGGEST myths that Harley sets their bikes up lean. I'm not trying to pick on you however I will use your post to bust this myth. First off why would any manufacture set something up lean to fail.....doesn't make sense. Contrary to popular belief on these forums there is NO SUCH THING as an EPA map.....thats like saying I have a
3/4 race cam....????????. Yes the afr is set around 14.5:1 in a no load situation, (say around 30 to 70 kPa) however once the ECM sees 80, 90, 95 ,100 kPa the fuel gets to be pretty darn rich....mater of fact it's too rich for my liking. The problem I see is most people see that 14.5 afr area across most of the fuel table and think the bike runs there all the time, but in reality you can be at 25% throttle and be in the 95 kPa column of the map, so now it is out of closed loop and dumping fuel in the cylinders. Several of Harleys maps are in the 12.5 to 12.8 to 13.0 afr when it's out of closed loop...........so............these bikes do not run lean when under a load, they are set up to get good mileage in a NO load area.
Again I am not out to embarrass you Nevil of upset you.....I just used you thats all....lol....lol
By the way what part of Pa are you from? I grew up just south of Pittsburgh in a little town called Monongahela.
Doc

 

I didn't call it an EPA map, but it might as well be. It seems that the only way the MOCO can make the bikes pass government guidelines is to set them up the way we get them. It can't be the ideal way to do it since most of us (if not all) seem to experience a real power and response gain when the bike is tuned to run richer in areas.
When stock, my Street Bob ran hot, surged and had decel pop. Once I installed the ThunderMax the difference was night and day. And nowhere does it run close to 14.7:1 AFR.
Your numbers may be correct, but for me they are just numbers and I don't know enough to challenge it. All I know is that running a map that would be illegal for a dealer to put out has made my bike work like I expect it to.
This is my first EFI bike. When I had bikes with a carb (or carbs) there was no point in re-jetting them to run richer in stock form. That's because there was no federal mandate for the manufacturers to conform, so they set them up for the owner's benefit. And for the most part they ran like they were designed to. So those days are over, I get it.
No hard feelings, that's why it's called a forum.
Anyway, I live in the southeast part of the state, close to the Delaware line. I do have a brother in Tampa.

 

Good argument about passing the Government guidelines Nevil, however AFR is not the way the MOCO passes. The Moco has a certain amount of hydro carbons or emissions they are allowed to burn, or dump into the atmosphere, to pass the Gov. standards..........the way this is met is not by leaning out the fuel, it is met by choking off the air. The MOCO uses a restricted air filter and restricted exhaust. The principal here is simple....less air through the motor is less emissions into the air. Now when you, and most everyone, changes the exhaust and air filter kit you are allowing MUCH more air to flow through the motor (air pump).....this is why you feel a power increase when you do change these items. Now that there is more air pumping through the motor the AFR is much leaner because, unlike a carb, the ECM is programed to deliver only the amount of fuel it had previously mapped to the restricted motor.....now you are lean and need MORE fuel to link up with the air you just put through this motor. Now after this motor has been modified and more fuel has been added the power has surged upwards, BUT NOW, you are a EPA violation.......in my business I am here to make you the BEST EPA violator I possible can......lol.
Remember, less air through the pump is less emissions and a passing grade from our wonderful government. Yes with adding more fuel more power will be felt in a slightly modified motor, but, even in a highly modified motor an AFR of 14.5 isn't lean is a no load situation. Even maintaining 14.5 AFR is a modified motor will take more fuel to maintain that 14.5 because there is more air going through the motor....more air, more fuel is needed......now you FAIL the government guidelines.
Doc