Well schucks... that Sportster Seat/Tank lift mod sounds pretty cool. Getting to the plug that easy peasy would be a dream. I also own a Sportster and can attest to how much more comfortable the more firm seat is.

Unfortunately I'm not quite sure what the issue is. It "pulsing" like that would sound like a petcock issue off of top of the head forum go to knowledge. But clearly you've replaced that and that's typically not under load.

Is your clutch slipping perhaps? Granted that's typically pretty noticeable.

I can't imagine the exhaust leak causing it. I have a Dyna as well.. I can't get the exahust leak to go away despite everything but applying a sealer and welding. (I hear the sealer causes a nasty mess, the slight puff and occasional backfire don't bother me enough to mess with the goo) I ever tried the crush can method. Guess I'm not precise enough.

Is your battery putting out good voltage?

I'm just stabbing here, as I'm not really sure.

Is the "pulsing" worse when the engine is cold?  Does it go away if you accelerate.....and feel worse when holding a steady cruising speed?

If so......You may be slightly lean at the 1/8 - 1/4 throttle setting.  Mine did that until I raised the needle slightly, and it richened up the mixture over the entire range.  I ended up dropping a main jet size after doing so.

One way to get some actual data on your situation, rather than just guessing about symptoms is to use a vacuum guage.  Use the port on the carb that used to be for the line to the old petcock, temporarily hook up a vacuum gauge, and go for a ride.  See what the needle is doing when you feel the unevenness.  If it moves exactly with the unevenness, then you most likely have something happening with mixture and/or intake leaks, etc.

It won't tell you exactly what is wrong, but at least you'll eliminate a few things or narrow it down, anyway.

You'll need to put a restriction of some sort in the line between the carb and the gauge so the the vacuum seen by the gauge is not the thump thump thump of our big 650 single, but more of a slow leak.  The size of the hole should be large enough to allow the needle to react quickly, but not so large as to have it moving with each thump once you get past about 2000 rpm.

Wake:  I wouldn't suspect the clutch since I only have <4,500 miles.  Also, it isn't noticeable under acceleration.  The battery is a brand new mini AGM that I installed about a month ago.  No issues with it so far; just adapting to having a lot less AH.

I mentioned the exhaust leak because I understood it makes tuning difficult to impossible.  I was under the impression that it causes a lean condition, which I thought might have an affect on this feeling.

As for my fuel filter: it's just a generic cheap-o paper element filter from Autozone.  The arrow (which you can't see in the pic) points in the direction of fuel flow, so I'm fairly certain it's installed right.



Here's a pic of my robber stopper tank lift.  I just drilled a hole in the middle and installed longer bolts.


Before I go out and buy a vacuum gauge, I'm going to test for intake leaks.  If I have a leak, I suspect it would be where my cone goes into the rubber tract.



I shaved down the inner lip of the stock throat so that the cone could fit all the way in.  I then cut the clamp portion off of a large hose clamp and used the remaining ring of steel as a spring.  I inserted my new spring inside the rubber boot of the cone filter to give it support.  I then placed the whole boot inside the stock throat and used the stock clamp to hold the thing together.  It seems to work fairly well so far.  It'll come off if you tug on it hard, but I expected as much with now kind of locking lip or ridge.

I'll check for intake leaks later today.  Gently spray some carb cleaner around the edges, look for surging, right?

P.S. I just realized that my description of my intake mod might be confusing.  Pics to come later this afternoon.

I initially thought that the fuel filter might be too restrictive, but it's the same style that has been posted in the tech section for proper installation of a filter.  I did a flow test, and fuel seems to flow just as regularly with the filter as without.  However, I didn't take any official measurements.

I added the fuel filter, welded the exhaust, and modded the intake about 2 weeks ago.  I only added the raptor and tank lift yesterday.  I started noticing the problem about 10 days ago.

I've been busy all afternoon, so I'll go test my intake now.  Might ride without the filter just for gits and shiggles.

Also, I meant to ask:  I noticed that if I snap the throttle and let go, RPM dips below idle speed before returning to normal.  This is less noticeable with a properly set idle, much easier to tell with a low idle.  Is this because we don't have an accelerator pump, or is this a symptom of something else?

Well, my intake is a lot better than I thought it was.  Definitely no leaks.  However, the "spring" that's in the cone seems to have burnt edges...    Not sure how that is even possible.  Valve gap and timing are all good and set, just checked it last month.

FWIW, I'm currently at 2 turns on the mix screw, 55 pilot, 152.5 main, and white spacer is shaved to 0.64.  SE Dyna muff and K&N cone on the stock throat, as mentioned earlier. Lean condition in the needle jet circuit certainly sounds plausible.  I'll wait until I get that exhaust leak fixed so that no more of my tuning is in vain, and I'll probably still go get a vac gauge just to plug it in and see.

Thanks for the input guys.

Gyrobob wrote on 10/08/12 at 06:37:37:


Before getting a vacuum gauge, check that the vacuum port on the carb (mentioned by Gyro, above) is plugged up good and solid.  Here's how I did that when I installed my Raptor petcock several years ago:





I squirted some RTV into the tube before folding it.  The tube was the OEM vacuum tube.

If you get an air leak here, it could cause the symptoms you are experiencing.