So I have 03 soft tail that i just rebuilt the cv carb on. Got low idle and start tuned perfect. Bike runs and revs great.awsome low end power But here's the weird part after a good wide open throttle through a whole gear the bike acts like it's out of gas. I gotta pull the choke out till it comes back to life again. I can ride the bike all day long just cruising around. But as soon as I keep wide open for a gear or 2. Anyone have any ideas?

I'm kinda leaning on at wide open throttle the petcock has no vacuum so no fuel flow. Then off the throttle for min or choke the fuel bowl fills back up and all is good.

 

I think your on the right track...

There is a recent post here in the carb forum on how to modify your petcock so it no longer needs vacuum to operate. After modification, it will act like a normal non vacuum operated petcock. It would be a good diagnostic tool to modify yours. There are a few ways to modify them. The easiest way is the next paragraph below.

I just took my "spare" vacuum petcock apart so I can answer this post, and while some might say it's better to replace the petcock with a non-vacuum style (and I agree), all you need to do is remove the petcock (after you drain the tank) then remove the 4 screws in the back, you will see the diaphragm and spring. Relocate the spring on the petcock, so it pushes the diaphragm open instead of closed. Instead of the spring being closest to the vacuum port/nipple move it to the other side of the diaphragm so the spring pushes away from the seat.

Easier done than said...you can always test it using a piece of hose and blowing thru the fuel flow nipple to see when you have the spring in the right spot. In pre-modified position, no air will flow when the petcock is turned to the on position and post modified, air will flow (of course when lever is in the "on" or "res" position). Remember this is the fuel nipple I am talking about connecting a piece of hose to and not the vacuum nipple.

The only down side is you should turn the petcock lever to "off" after you shut down the bike for any length of time. Something us guys who ride with "pre-vacuum" petcocks have learned to do since the beginning of time. YD

 

I might be able to shine some light on this.

Back a few years ago I had a 2006 Sportster with a 1200CC conversion in San Diego. (Location is important here, lotsa long hills) Same carb, same petcock as you've got. One day I was heading S on the 15 from Temecula when I just started going up a really long hill and I needed reserve. Considering traffic, I kinda **** myself a bit when the bike just lost power but I'm still vertical so that's good. Anyway, switch to reserve and here's what happened:

Power....stall......Power......stall..........POOO OOOOWWWWEEEEEERRRRRR.........stall................ .Then full power and away I went. That was over about a quarter mile, still going up the hill.

My speculation is that the petcock didn't fill the carb fast enough. The heavy throttle and long hill was drawing lots more gas than flat roads (not unlike your WFO example above) and drew fuel out of the carb faster than it would be replenished. I ended up switching to a Golan shortly after, with no more issues. Yea I gotta remember to shut the damn thing off every time but how's that any different than mikey-mousing the OEM one to work without the vacuum?

 

always that possibility but you did say you rebuilt the carb so, need to check your work. cruising around, you are barely on the main circuit but when you demand power, that main sucks a lot of fuel and if the float was not set right, a 1/2" opening petcock cannot keep up. a lot of people mess up by taking out the anti-vibration spring play on the needle. carbs are diff, some measure drop, some float up and flange measurement and some at an angle, always check the fsm.
some carbs also have diff needle & seat sizes for diff flow rates so make sure you did not drop size if you replaced them.

 

Thanks for the fast replys. When I rebuilt the carb I put exactly the same size jets back in it. Got the screw about 1 1/2 to 2 turns out. And runs perfectly fine other than the issue up top. I'm gonna pull the pet **** today and flip the spring around and then take a ride if the rain holds off.

 

Just wanna thank you all from the great reply. I fixed the issue. I flipped the petcock spring around and reset the float height and bike runs like a top!!!

 

Thanks for the follow up!