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New Pipes and Carb Adjustments

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Old Feb 2nd, 2011, 09:01 AM     #1
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New Pipes and Carb Adjustments

My bike, a 2000 Fat Boy, 4000 miles on the odo, came to me in pristine condition. It has V & H Longshots and was running without baffles. To this admitted novice (40 years since I last rode) it runs very well and has more power than I need. After being on the site several months, I read repeatedly about the need to rejet the carb after changing exhaust and/or breather elements. I noticed that the bike did pop back a bit with deceleration so I reinstalled the baffles. That quieted the exhaust just a small amount and decreased the popping back also. The Boy still runs well although cold natured. Short of tearing into the carb, is there any way to tell whether I'm running lean or rich? Spark plug color? I'm progressing slowly on doing some of my own wrenching but don't want to join the "If it ain't broke, fix it til it is!" crowd. Thanks in advance for any comments/advice.
Ishmael

PS Intake is still stock

PS to the PS Those baffles surprised me in that they are very minimal slip-in tubes with some louvres punched in them. I guess that's all thats required to give some back pressure?
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Old Feb 2nd, 2011, 09:09 AM     #2
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Here's a color chart for the plugs:
Spark Plugs

==================================================

I knew I had this page stored somewhere. Might try this before tearing into it.
Harley Davidson Carburetor Performance Tuning

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Old Feb 2nd, 2011, 10:18 AM     #3
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Re: New Pipes and Carb Adjustments

I understand why you would have to richen up the A/F when running a FI set-up but someone please explain to me why you need to richen it when running a carb.

If you increase the VE on a FI system, your only letting in more air, hense it runs lean and you must instruct the ECM to electrically add fuel. That all makes sense.
But on a carb setup, when you increase the VE your also pulling fuel along with the added air and the A/F ratio should remain somewhat constant. Your not really leaning out the A/F until you have reached the maximum flow rate the jets. If that is the case I understand why you need to re-jet. But are the jets actually max'ed out in regard to flow rate? At best a set of pipes and air cleaner increase VE by 10%. The present jets can't support that small increase?

I have also had Zero success reading plugs with E10 fuel. I have sweep the A/F ratio by 3 full points and it made next to zero change in the appearance of the plug.
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Old Feb 2nd, 2011, 10:29 AM     #4
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Re: New Pipes and Carb Adjustments

Thanks Hoop, my thinking exactly. The bike runs well as is so maybe no digging in the carb is needed. But what is VE? Thanks.
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Old Feb 2nd, 2011, 11:36 AM     #5
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Re: New Pipes and Carb Adjustments

+1 on Hoople's reply. When I first got my carb'd. Dyna, I did a lot of jetting experiments with it. At best, all I accomplished was "feel good". At worst, I got spitting, stumbling etc. Went back to almost stock and got happy again. They will benefit a little from opening and adjusting the idle air mix.
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Old Feb 2nd, 2011, 12:17 PM     #6
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Re: New Pipes and Carb Adjustments

Usually, on my 2000 FXDS(gone) and 2006 sport, Both Carbed bikes, It takes a while to get up to "Running Good Temperature" so it responds, Especially when COOL outside. After about 5 min OR MORE of running/riding(Never idling that long but Riding) IF it doesn't respond on the throttle Up and hesitated a Lot, It may be NOT getting the fuel ratio Needed to run properly.. OR if it Hick-Ups when you first twist the throttle, Too Lean or excel-orator pump not giving enough gas into the Venture..

It sounds like in Your situation, This is Not the Problem, BUT if it does Any of what I have said above,,,,IT needs to be remedied. Get back and Help will be here..

I like the Putting Back of the baffles and Yes that is NEEDED for the bike,,, Just enough back-pressure that HD designed to make it run PROPERLY...

IF it is running without any of the above Problems I would say IT IS good to go..

A little popping on deceleration was Normal on My dyna BUT NOT Loud big Back-fires.

signed....BUBBIE
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Old Feb 2nd, 2011, 12:46 PM     #7
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Re: New Pipes and Carb Adjustments

Quote: Originally Posted by Hoople View Post
I understand why you would have to richen up the A/F when running a FI set-up but someone please explain to me why you need to richen it when running a carb.

If you increase the VE on a FI system, your only letting in more air, hense it runs lean and you must instruct the ECM to electrically add fuel. That all makes sense.
But on a carb setup, when you increase the VE your also pulling fuel along with the added air and the A/F ratio should remain somewhat constant. Your not really leaning out the A/F until you have reached the maximum flow rate the jets. If that is the case I understand why you need to re-jet. But are the jets actually max'ed out in regard to flow rate? At best a set of pipes and air cleaner increase VE by 10%. The present jets can't support that small increase?

I have also had Zero success reading plugs with E10 fuel. I have sweep the A/F ratio by 3 full points and it made next to zero change in the appearance of the plug.
As with fi from about 91 the carbs were jetted a wee bit on the lean side also the stock airbox has a fair bit of restriction in it so if you allow more air through the stock jets deliverd insufficient fuel for the air flow so minor jet increase is required
at any throttle position more air goes through the carb with a free flow system than with the stock system
But then i dont really like the cv carb and tend to replace with a mikini hsr as it works better here

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Old Feb 2nd, 2011, 03:56 PM     #8
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Re: New Pipes and Carb Adjustments

To all of you a big "THANKS". I think I'm ok. The baffles stay in and I kinda like that little popping on decel, after all, Its a Harley! No loud backfires. And like Bubbies bikes, 5 minutes of easy riding is all it takes to get it to good running temp. No dying at the stop sign, great acceleration and best of all, give me a lonely country road and listen to those pipes.
Ishmael, almost 65, can you tell I'm enjoying being a senior biker?
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Old Feb 2nd, 2011, 05:19 PM     #9
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Re: New Pipes and Carb Adjustments

The bit of popping on decel is to me normal for un burned gas in the pipes with no baffles, all the carbed bikes were too lean from the factory IMO but adjusting the mixture screw helps a lot Adjusting a CV Carb - Harley Davidson Community (Adjusting a CV Carb)
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Old Feb 2nd, 2011, 05:29 PM     #10
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Re: New Pipes and Carb Adjustments

There is always a pressure drop across the air filter. The better the filter flows, the less the pressure drop. This pressure drop causes a slight vacuum, pulling in more gas. Put on a higher flow filter, and you reduce the pressure drop and vacuum, pulling in more air and less fuel. This is why you can run leaner with higher flow air filter.

Since most exhause is IR(Individual runner) and not a shared system, reversion can also make a difference in what the cylinder sees. And since both intake and exhaust valves are open at the same time during overlap, the carb can actually "feel" the pulses from the exhaust, and this too can change jetting requirements.

(In my racing days I've cured backfiring problems by going longer on header pipes)
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