| Author | Message | ||
     Zackxb12s |
Why does my bike huss or lag when i nail on the gas from an idle? | ||
| Boney95 |
Read "My" The 08 Issues thread below. Has to do with the large throttle body. | ||
| Ochoa0042 |
its got to get going, i've dealt with it by feathering the clutch, not a issue to me | ||
| Iamarchangel |
Because... why would you do that? Think old school. You've just asked the fuel system to skip two or three steps. Idle to main without needle or other jets just creates a lag. Same with the ECM, you've just asked it to skip several stages and inputs that it still needs for smooth acceleration. If you're standing beside your bike, any engine, and doing this, it will lag. On a small engine, it won't be so noticeable but it'll be there. On a bigger engine, it's more noticeable. On a bigger engine on a cold day, it will stall and foul the plugs, and once you make the connection, you won't try to do it anymore. If you're at a light, stop sign or drag, you'll use your clutch which is there to help get past the lag. If you have a lag from idle to quarter throttle, or quarter to half, etc., then you can work it out. See xopti on that. Blame Newton. | ||
| Point_doc |
Why does my bike huss or lag when i nail on the gas from an idle? Another consideration is the LARGE amount of rotating mass in the primary drive especially attached to the crank. It takes time to spool up mass. Read thru this link... http://www.badweatherbikers.com/buell/messages/327 77/446812.html?1238190565 (Message edited by Point_Doc on March 29, 2009) | ||
| Jraice |
+1 to everything so far... If your trying to launch I was shown by my dealer that you can just ease the throttle up to bring the rev's up a bit, perhaps to 2,000rpm and then let the clutch out and hit the gas harder... It shouldnt lag then. My 09 does this also but for regular riding I have not found it a problem, as soon as the clutch starts to engage the engine works just fine and the throttle response for a normal take off is perfect. | ||
| Xbrfirebolt |
Another consideration is the LARGE amount of rotating mass in the primary drive especially attached to the crank. Why is it that Harley's big twins don't hardly have any lag? | ||
| Jraice |
I am pretty sure it comes down to fueling in the big picture. Other things contribute but a lot of it is the characteristics of a twin, large rotating mass and fueling. Just be smooth on throttle application! | ||
| Xbrfirebolt |
Jraice, I too believe fueling is the whole problem. The earlier XBs didn't have the problem with the flat spot off Idle, and not all '08s have it either. I know my dealership did allot to try and fix it, but it's still bad. I've learned to ride around the problem most of the time, but every once in awhile it will bite you in the ass. It can be a safety problem. | ||
| H2owerker |
"Why is it that Harley's big twins don't hardly have any lag?" I'm just grasping at straws here... I'd imagine that has to do w/ the overall design of their engine. Specifically the heads that are designed for power lower in the RPM range, while our bikes are a little more high-strung. The idle around 950RPM is more a matter of practicality or comfort. Who wants to sit at a red light idling at 1500RPM where our cam timing/valve duration begins to 'work'. Zackxb12s As Jraice implied try altering your launch technique. If what you're describing is a misfire when you 'whack' the throttle...consider doing some data-logging, and alter the fuel/ignition map or have someone else do it. (Message edited by h2owerker on March 29, 2009) | ||
| Steve_mackay |
The earlier XBs didn't have the problem with the flat spot off Idle Yes they did. Just not as pronounced I think. I've not ridden an '08+ bike that has a severe off idle problem however. The 10 or so XBs that were on the demo fleet didn't have a problem. I'd imagine that has to do w/ the overall design of their engine. Specifically the heads that are designed for power lower in the RPM range, while our bikes are a little more high-strung. You are absolutely correct. It was explained to me by someone FAR smarter than I on these things. The XB head is by far the best flowing head that HD has EVER produced. But, it's also the worst idling. So that transition from idle to throttle will sometimes have problems. This is even MORE pronounced if the engine isn't warmed up. | ||
| Old_man |
Many carburated bikes have a second throttle controlled by engine intake vacuum to alleviate this problem. | ||
| Jraice |
Anybody noticed a difference after adding an exhaust? I was shown a used XB12 (2008) with a D&D muffler and dont recall it stuttering quite as much, you could make it stutter but it didnt happen as readily... But anyways I have not found it to be a safety problem at all on my bike, if I know I need to pull out quickly I will ease on the gas to get the motor spinning, even just 100-200RPM higher then idle and can go just fine. I only notice it when bliping the throttle with clutch in. | ||
| Pkforbes87 |
It was explained to me that the ports in xb heads are larger which allows more volume of flow at higher rpms, but the large ports allow for less precision at low rpm operation. | ||
| Etennuly |
Have you ever seen a dragster take off from an idle? Car or bike, door slammer or top fuel, they all rev up before launching. Most right to the upper mid range as they let out the clutch. Same principal. A loaded diesel truck needs to have the rpms brought up a percentage before taking off it. Powerful race engines that are cammed and tuned to run at 8000+ seldom idle below 2000 rpm. Compromises are what make a powerful engine streetable. You may need an electric motor. Only problem is.....those take time, however little, to spool up also. | ||
| Andymnelson |
What differences are there between a 2003 XB head and a 2007 XB head? | ||
| Andymnelson |
"What differences are there between a 2003 XB head and a 2007 XB head?" Come on...someone here knows, I'm sure of that! | ||
| Old_man |
I was not aware of any difference in the heads. Nothing that I can remember being published about any change. | ||
| Froggy |
I don't recall any differences either from 03 to 07. Possible a revised part or two, but no spec sheet changes that I know of. | ||
| H2owerker |
"What differences are there between a 2003 XB head and a 2007 XB head?" In 2003 they were exclusively bolted onto 984 v-twins, by 2007 the 1203cc was introduced into the line-up. I'm under the impression that the heads are the same. The crank and pistons were changed to alter the displacement via stroke length. So they are using heads designed principally for short stroke engine, and using them on one w/ a larger displacement thereby altering the power band and reaction to throttle input. (Message edited by h2owerker on March 30, 2009) | ||
| Andymnelson |
"I don't recall any differences either from 03 to 07" That's what I was thinking. Steve_M said: "It was explained to me by someone FAR smarter than I on these things. The XB head is by far the best flowing head that HD has EVER produced. But, it's also the worst idling. So that transition from idle to throttle will sometimes have problems. This is even MORE pronounced if the engine isn't warmed up." And many others have hinted at the heads being some kind of problem....but my '03 does not have these issues. Seems like it would point us to fueling issues as the cause of the off idle stumble? | ||
| Xbrfirebolt |
I've not ridden an '08+ bike that has a severe off idle problem however. Like you said not all have the problem. I think some people here don't understand that point. My son and I both have '08 models. His doesn't have a problem with the flat spot off throttle, yet mine has it severe. So don't tell me it's just "how I turn the throttle". It has to be in the fuel map in the ECM. I don't see Buell making it any better here in California. | ||
| Andymnelson |
See I'm not even sure it can be blamed on fuel maps- because of what you just stated: some have it and some do not. There are bikes on both sides of the fence that have the same maps! Do you and you son have the same maps loaded into your ECMs? | ||
| Xbrfirebolt |
Do you and you son have the same maps loaded into your ECMs? No, plus mine had the new flash in April or May of last year. Mine was built in Aug. of '07, his was in Nov. of '07 I think. | ||
| Fast1075 |
One of the differences between "Harley" and Buell is CAMS...the harley has more trapped volume at idle compared to the Buell with "hotter" cams...develops a tad more cylinder pressure. |
