jerking and surging : V-Twin Forum: Harley Davidson Forums

rotton1 · 04-07-2007, 05:50 AM

At low RPM my bike has a surging, jerking action, at mid to high RPM it's fine. In 1st and 2nd gear it's more noticable but I can feel it in 3rd and 4th also. It did it a little before the build after the pipes, a/c and carb rejet but is more so now. It kinda sucks riding in slow traffic. On the highway this build kicks ass and I love that part but I still want it to run a little smoother in slower traffic. Any idea what's the cause of this and or solution. I talked to a guy at the shop that did the build, not the owner or builder but he really didn't know why it does it. Any help would be appriciated.

Aloha,
Jimbo

O'Rork · 04-07-2007, 06:32 AM

You've got a very good engine recipe. The reversion from the pipes is most likely the major contributor to the problem you're experiencing.
Now that you've gone to a higher performance cam shaft and bigger valves this reversion is even more pronounced. You can try tuning the reversion to a minimum by
decreasing the pipes' outlet ability to suck air in backwards during RPM when the engine is "not on the cam". At very high RPM's reversion is not so much a factor, as the time between exhaust pulses is very short so the influx of air and the shock wave rebounding off that air up the pipe, backwards minimizes. Don't be surprised that a perfect tune exhibits a noticable stutter at 2,200 RPM and below, during steady throttle ops.

Now if someone would chime in with a bonified way to tune ground pounders, you'll be on your way to a great tuning experience.

Once you get the reversion to a minimum, you can move on to tuning the air/fuel ratio at all stages of the Mik42 and getting the ignition lead set to where the build with the fuel you're using, likes it.

GRock · 04-07-2007, 11:58 AM

You sound like you have "lean surge". Richen up the low speed circuit and you should feel it clear up.

rotton1 · 04-07-2007, 05:29 PM

O'Rork, GRock
Thanks for your help.

GRock, I'm going to attempt to do this myself so could you explain what I need to do to get it done. Sorry I never went inside of a carb before, just changed them out and had someone else do all the adjustments. I wanna be able to do it myself so I don't have to take it to the shop for every little issue.

Aloha,
Jimbo

WVRDKING · 04-07-2007, 05:48 PM

rotton1:

Till GRock gets back to ya, there's some great reading material here:

http://www.mikuni.com/fs-manuals.html

petrock · 04-07-2007, 06:35 PM

I'd first check the simple stuff first before diving into carb modifications/adjustments. More often then not, this kind of thing is either a loose rear belt, loose primary chain, or your clutch needs adjustment. I had the same kind of issue on my ride and it was the primary chain. Adjusted it, and everything cleared up just fine.

rotton1 · 04-07-2007, 08:54 PM

WVRDKING, thanks for the info.
Petcock, rear belt is ckecked and tight, clutch was adjusted but not the primary chain. I will check that first before trying the carb. I was looking in thr repair manual and it says "upward (not total) free play in upper strand should be 5/8-7/8in." Whats the difference in upward free play and total free play?

petrock · 04-08-2007, 09:50 AM

Quote:

Originally Posted by rotton1

Whats the difference in upward free play and total free play?

"Total free play" is the distance between the chain pushed all the way down and pushed all the way up. "Upward free play" is just the distance between the chain at rest (i.e. normal/level) and pushed all the way up. Do a search, there is a handy little tool you can buy for $15 to help with this measurement. I bought mine a while ago and it works great.

Hillside · 04-08-2007, 10:19 AM

Quote:

Originally Posted by rotton1

At low RPM my bike has a surging, jerking action, at mid to high RPM it's fine. In 1st and 2nd gear it's more noticable but I can feel it in 3rd and 4th also. It did it a little before the build after the pipes, a/c and carb rejet but is more so now. It kinda sucks riding in slow traffic. On the highway this build kicks ass and I love that part but I still want it to run a little smoother in slower traffic. Any idea what's the cause of this and or solution. I talked to a guy at the shop that did the build, not the owner or builder but he really didn't know why it does it. Any help would be appriciated.

Aloha,
Jimbo

The pipes are really giving you a big rasberry. If you insist on staying with those chrome plated pieces of tubing,then we can offer a band-aid for them.
We manufacture an exhaust venturi, that goes in the tail of the pipe, and should straighten it out. We use 'em in-house, when tuning, and sell 'em to other outfits, that tune also.Hope this is of help.

rotton1 · 04-08-2007, 02:56 PM

Thanks for the explanation Petcock. Where did you get that tool from, that would probably be more accurate and alot easier.

Hillside, I know your right and am trying to convince myself that I could get use to the look of a 2-1 if I can find one I like, I just like the look of the 2-2 more. I know I losing alot with it but for now I guess I'm just trying to make it work as best I can. You mentioned you have a band-aid solution to my 2-2 handicap, I have thunder monster baffels in it now, is it the same principle? If not I am intrested, can you give me a little more info. on it, price, installation, how I could get a set, ect. Thanks.

Aloha,
Jimbo

duhast · 04-08-2007, 04:26 PM

Cool tool.

http://www.liot.ca/Primary_Gauge.htm

rotton1 · 04-08-2007, 04:58 PM

Thanks duhast.

Aloha,
Jimbo

petrock · 04-09-2007, 05:03 AM

Quote:

Originally Posted by rotton1

Thanks for the explanation Petcock. Where did you get that tool from, that would probably be more accurate and alot easier.

No problem. Its petrock, not petcock, by the way. :-)

I got the tool from http://www.liot.ca/Primary_Gauge.htm. Works great.

rotton1 · 04-09-2007, 05:21 AM

Sorry about that petrock, no disrespect intended,just old eyes playing tricks on me and thanks, I just ordered one today, seems to me you can't go wrong for $20 for many years of use. Again I apolagize bout the name and thanks again for all your help.

Aloha,
Jimbo

Hillside · 04-09-2007, 06:05 AM

Quote:

Originally Posted by rotton1

Thanks for the explanation Petcock. Where did you get that tool from, that would probably be more accurate and alot easier.

Hillside, I know your right and am trying to convince myself that I could get use to the look of a 2-1 if I can find one I like, I just like the look of the 2-2 more. I know I losing alot with it but for now I guess I'm just trying to make it work as best I can. You mentioned you have a band-aid solution to my 2-2 handicap, I have thunder monster baffels in it now, is it the same principle? If not I am intrested, can you give me a little more info. on it, price, installation, how I could get a set, ect. Thanks.

Aloha,
Jimbo

You made mention of Thundermonster Baffles. I am thinking that the restriction is not enough. Don't want to sell you something you alreay have. What size is the smallest part of that baffle?