I have a 06 Streetbob and it seems to be running a little rough (at least I think it is).

I live in Colorado and am wondering if the elevation (6500 ft above sea-level) might be causing it to run a little rich (or lean).

Any suggestions as to how I could make it run better without spending a mint?

Thanks

 

I've read here in this forum that the HD's are set up lean from the factory but, the increase in elevation from sea level to 6500 should no dout richen you up (make the situation better not worse). I think that the ecm will try to lean you up a bit but not enough to make any differnce (but I'm a rookie). I'm located in northern New Mexico running around at the same elevation as you are and my bike seem to run great. May have to go see you dealer? I can also tell you that I've had to lean my dirt bikes up comming from 4000ft to the 7000-9000ft elevation I us it at here in NM.

 

I think I will give the dealer a call and see if they can take a look at it. It is supposed to be cold this week so it might have to wait until I thaw out.

 

I live not to far away from you, in rockrimmon. Yes, the altitude plays a huge role in fuel mixture and cylinder pressures. As ambient air pressure drops, fuel ratio would increase, making the mixture richer. They are lean to begin with, so you should be pretty close right out of the box. The closed loop system should be able to compensate here. But, if you've done some mods, that all changes. Popping and backfiring are the usual symptoms of a lean condition.


Did you buy yours at PPHD? They should have recommended the correct tune for this area.

 

Yes, I got it from PPHD.

It doesn't pop or anything when I decelerate but it seems like it hesitates at low speed. It also runs pretty rough when you first start it up until it warms up. I haven't done any mods to it yet and have about 130 miles on it. Maybe it needs to break in more? I don't know because I have never owned a brand new bike before.

 

I would continue to ride it (not today, of course). Let things settle in a little. The rings are probably not fully seated yet. If it's still the factory tune, it's probably a little rich. When cold, it's even richer. On car EFI's, the computer "learns" over time and multiple cold starts. Don't know if the HD system does.

If it doesn't smooth out, take it back and let the techs work on it. Could be something as simple as a bad plug or faulty sensor.

 

Correct me if I'm wrong here but in fuel injected engines this is not supposed to be a problem as there are mesurements of air mass entering the inlet plenum that by default accounts for variations in air density (by adjusting air volume presumably). Not sure for Harleys but from memory there is a mass airflow sensor located behind the throttle body for other vehicles.

Have alook at this Fuel Injection for some info.

 

That would be true if this were a mass air system. But it's not, it's a speed density system.

Speed density is the most simple of EFI. The computer measures two parameter - rpm and throttle position - and feeds fuel according to a look up table. Think of a spread sheet with rpm at the top and TPS on the side. The computer assumes the density of the air, which we all know is affected by temperature, altitude, humidity, etc. So the mixture is usually pretty close, but rarely dead on. But it's close enough and with carefull tuning you can make it work really well. Far better than any carb.

Then you add the O2 sensors, which is a huge leap in technology. The computer uses the same speed density table to send the signal to the injectors. But that signal gets modified based on the O2 sensor readings to correct for variances in the system. That will correct for altitude changes, humidity, temp etc. But it's limited. In stock form, the computer can only adjust by about 10-12%. So the look up tables need to be fairly accurate to begin with. The trick with these systems is to ignore the O2 sensor input, and tune for best ratio at most cell points. Sounds a lot more complicated than it really is. I tuned the EFI in my car in about an hour on the road. Newer systems - like the Techlusion - need no operator tuning. It uses a true wide band WEGO sensor and does the tuning itself. Very slick. PFM.

A mass air system doesn't really use a map like you see in speed density. It reads the mass of air coming in to the engine, rpm's, TPS, BPS, etc, and calculates the currect injector pulse. Much more comlicated and expensive. Also, much more difficult to modify for performance. Big changes require a new mass air sensor ($$$). Changes later require another sensor ($$$). The injectors are matched to the sensor, so you have to change them, too. Look what you have to do with a Mustang. Most newer cars are mass air, but many newer trucks (Dodge) are still speed density.

All EFI systems get modified in a third and fourth dimension as well . If the air temp is below 40*, use a differant table/calculation, if head temp is above 240* use a differant table/calculation, etc. All those mods are to improve cold starts, emissions, driveability, etc.


Whew, that was rather long winded wasn't it? Didn't mean to ramble like that, sorry.

 

That's not ramble that's solid information. Great post mate.

I did say I could be wrong, and I was.

Good to finally get the Low down.

 

Im Newbie,but got to ask. How do you calculate what your A/F mixture is ? I have an 07 bike with PC111 usb,SE Ariflow,Vance and Hines Big Radious Drag Pipes. Downloaded the correct map bike runs great,but am cuorious how to determine the current A/F mixture ?