04 Fatboy Bogging on hard trottle
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From: Jonesboro, AR
04 Fatboy Bogging on hard trottle
I have an 04 FLSTF with stage 1 from new purchase Bike sat for a year due to back injury. Over that time I would start it and ride to get oil up to temp. I now have an issue with the bike bogging on hard throttle. Drained gas, changed plugs, wires, had CV carb rebuilt at local shop. Have Screaming Eagle pipes from new. Motor has never been opened up. Changed primary and secondary jets up and down. Also new air cleaner, battery load tested and fine. Bike has been in shop for 8 weeks and they cannot get it from bogging. Once it goes it goes. If you roll on the throttle slow it is fine. I do not have a Harley shop near that does service. Any thought's or suggestions would be appreciated! I am thinking it has to be electrical?
Dave Adams
Dave Adams
Last edited by Fatboy@2004; Jun 30, 2024 at 11:20 AM.
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From: San Diego, CA
I have an 04 FLSTF with stage 1 from new purchase Bike sat for a year due to back injury. Over that time I would start it and ride to get oil up to temp. I now have an issue with the bike bogging on hard throttle. Drained gas, changed plugs, wires, had CV carb rebuilt at local shop. Have Screaming Eagle pipes from new. Motor has never been opened up. Changed primary and secondary jets up and down. Also new air cleaner, battery load tested and fine. Bike has been in shop for 8 weeks and they cannot get it from bogging. Once it goes it goes. If you roll on the throttle slow it is fine. I do not have a Harley shop near that does service. Any thought's or suggestions would be appreciated! I am thinking it has to be electrical?
Dave Adams
Dave Adams
The clues in your description would seem to be that it sat for a year. That could negatively affect the fuel system.
Who did the carb rebuild?
It is possible to just swap out carb parts and leave some hard deposits/gunk in the pathways/channels of the carb. I know a few people who will strip a carb body bare, then put it in an ultrasonic cleaner to get all the hard gunk/deposits out when rebuilding a carb... especially if it was old, and/or sat for awhile..
Who tuned it?
Was the OEM EPA plug removed from the carb to allow access to the mixture screw? Changing jets without adjusting the mixture screw won't work well...
There is a process for tuning the CV40 carb. It involves adjusting the mixture screw, then letting the performance tell you if you need a pilot, main jet, or needle change. But the process always begins and ends with the mixture screw. Having owned and replace a couple Keihin Butterfly carbs on my shovel heads, I am a fan of the Keihin CV40.
Here's a good site for instructions, guides, and parts on the CV40 carb:
https://cv-performance.com/instructions-guides
If it were my bike, I would go through the fuel system start to finish.
I would start with checking the tank to make sure there is no peeled lining material or other debris flosting around that can block the petcock.
If you still have the OEM vacuum petcock, I would inspect, rebuild, and/or replace that.
I would check the fuel line from the tank to the carb for interior delamination that could affect fuel flow. Maybe just replace that section of hose as maintenance. (use 1/4" I.D x 5/8" O.D. premium fuel line)
I'd revisit the carb rebuild. Checking for missed blockages in the passageways and pay specific attention to how the float was set.
Then I would give a tune...
Not being there to put hands on and hear for myself, that's about all I can offer at this point..
Keep us posted....
Last edited by hattitude; Jul 1, 2024 at 08:41 AM.
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From: Jonesboro, AR
Fatboy@2004
Thanks for the reply. Drained the tank and inspected it and it looked good. Always kept it full. Carb was done by Big Bore Bikes in Jonesboro, AR..It was untrasonic cleaned. Vacuum pump was replaced with rebuild. Guy said he has done 100's of CV's and has not had this many problems.Mechanic feels jets were too big ans he has tried several variations, but they are original size from purchase. I will have them replace all fuel hoses and see what happens?
Regards,
Dave Adams
Regards,
Dave Adams
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From: Pennsylvania
Once it goes it goes. If you roll on the throttle slow it is fine
1. Need to revisit the carb and the accelerator pump parts to ensure all passages are clear & clear.
2. Make sure all rods and mechanisms are functioning correctly and all the parts are in the correct locations.
3. Make sure the accelerator jet nozzle is facing the correct direction and is squirting fuel when the throttle is twisted.
4. With the air filter off, petcock on, the carb charged with fuel, and the engine turned off, you should be able to see fuel squirt into the carb throat when the throttle is twisted.
5. Make sure the vacuum slide is operating correctly, you should be able to push it up with your finger and not feel any sticking and then letting it go it should smoothly return to bottom.
Last edited by CoolBreeze3646; Jul 1, 2024 at 04:02 PM.
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From: College Station, TX
Is the bog on rapid acceleration from low speeds? Or WOT after it gets up to a certain speed?
If it's rapid acceleration from a stop or low speeds then CoolBreeze3646 has some good suggestions. If it bog on WOT at higher speeds or under demand when fuel requirements are highest, then I'd suspect not enough fuel flow to meet the demand.
I believe there is a strainer in the tank at the petcock hole. You can remove the screen when the petcock is removed. But older ones can be difficult to remove in one piece because the plastic breaks down over time. If there is an inline (in the fuel line) filter, I'd likely remove it or replace it with a new filter. And as hattitude suggested, look closely at the petcock itself. If it is vacuum controlled, I'd replace it with a good quality manual petcock.
Paul
If it's rapid acceleration from a stop or low speeds then CoolBreeze3646 has some good suggestions. If it bog on WOT at higher speeds or under demand when fuel requirements are highest, then I'd suspect not enough fuel flow to meet the demand.
I believe there is a strainer in the tank at the petcock hole. You can remove the screen when the petcock is removed. But older ones can be difficult to remove in one piece because the plastic breaks down over time. If there is an inline (in the fuel line) filter, I'd likely remove it or replace it with a new filter. And as hattitude suggested, look closely at the petcock itself. If it is vacuum controlled, I'd replace it with a good quality manual petcock.
Paul
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From: Jonesboro, AR
04 Fatboy
Sorry for late reply. Been out of town. Bogs at any speed on hard throttle. Going home tomorrow and will go to shop and discuss next steps. Vacuum pump was replaced. Have manual petcock. Will pull and check screen and check all fuel lines.
Dave Adams
Dave Adams
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Road Captain
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From: Spokane, WA
What on earth is a vacuum pump doing on your motorcycle?
Seriously though, it sounds like accelerator pump or fuel inlet, is the float set correctly?
If you have a weak spark due to a bad coil it can bog when you open the throttle.
Seriously though, it sounds like accelerator pump or fuel inlet, is the float set correctly?
If you have a weak spark due to a bad coil it can bog when you open the throttle.
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2nd Gear
Joined: Jun 2024
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From: Jonesboro, AR
04 Fatboy
I probably misidentified. I believe it is the vacuum slide in the carb.. I am not doing the work so I do not know if the float is set correctly, but the problem is the same pre and post carb rebuild. I am going tomorrow to talk to the mechanic and maybe P/U the bike and work on it myself.
Dave Adams
Dave Adams
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Joined: Sep 2008
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From: San Diego, CA
Just FWIW...
The CV40 carb has both an accelerator pump and a vacuum slide....
It's easy to mix up the terms if you are not familiar with the CARB.
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