CV carb jetting
Thread Starter
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Road Warrior
Joined: Apr 2018
Posts: 1,347
Likes: 820
From: Moneta, Virginia
CV carb jetting
97 FLHR: kerker slip on mufflers with stock headers, Screaming Eagle air cleaner, Screaming Eagle ignition, EV13 cam.
My gas mileage has deteriorated bit by bit through the last 3000 miles or so, and I recently noticed a sluggishness with throttle response and overall performance. (Felt very rich and the plugs were a bit sooty at the base of the ground prong, mufflers a bit sooty, and started getting backfires on de-acceleration)
In checking things I uncovered intake leaks at all three seals. The diaphragm had a hole, and the slide needle clip had come off.
I took the carb to a local Indy to install a V-Twin carb kit. He says he set the needle and mix screw to midpoint.
This carb had been re-jetted in 97 when the bike was new and has always performed nicely. I vaguely remember the slide spring being changed to a lighter version at the time. I thought the diaphragm material seemed thinner than what came in the kit too.
The jet sizes seem a bit weird; 45 and 150.
I havent reinstalled the carb yet, but just wondering if I should change out that main jet before reinstalling the carb. Im not sure which spring he reinstalled or if there is a difference.
Any input from you tuners is appreciated.
Oh yeah, Im not drilling a hole in my pipe for an AFR... lol
My gas mileage has deteriorated bit by bit through the last 3000 miles or so, and I recently noticed a sluggishness with throttle response and overall performance. (Felt very rich and the plugs were a bit sooty at the base of the ground prong, mufflers a bit sooty, and started getting backfires on de-acceleration)
In checking things I uncovered intake leaks at all three seals. The diaphragm had a hole, and the slide needle clip had come off.
I took the carb to a local Indy to install a V-Twin carb kit. He says he set the needle and mix screw to midpoint.
This carb had been re-jetted in 97 when the bike was new and has always performed nicely. I vaguely remember the slide spring being changed to a lighter version at the time. I thought the diaphragm material seemed thinner than what came in the kit too.
The jet sizes seem a bit weird; 45 and 150.
I havent reinstalled the carb yet, but just wondering if I should change out that main jet before reinstalling the carb. Im not sure which spring he reinstalled or if there is a difference.
Any input from you tuners is appreciated.
Oh yeah, Im not drilling a hole in my pipe for an AFR... lol
Grand HDF Member
Joined: Nov 2009
Posts: 4,315
Likes: 1,663
From: Tampa
That is weird. My 1200 Sportster when tuned took a 180 main, unless it's a Dynojet kit, they have weird jetting numbers. OEM Keihin jets are metric equivalents. IE: a 150 main is 1.5mm in diameter.
Backfiring on decel is a lean condition, not rich. Are you saying all the weird symptoms were from the air leaks and loose needle?
Overall, how does it run?
Ya know what you need to install?????
Backfiring on decel is a lean condition, not rich. Are you saying all the weird symptoms were from the air leaks and loose needle?
Overall, how does it run?
Ya know what you need to install?????
Seasoned HDF Member
Joined: Jan 2015
Posts: 16,013
Likes: 7,137
From: Sandy Eggo's North County
Check your needle jet tip. The aluminum needle erodes with the use of ethanol laced fuels, over time. Compare it with a new jet needle (of same size/contour). If it's ANY different, replace it.
I can post a pic of a worn needle if you want.
I can post a pic of a worn needle if you want.
Thread Starter
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Road Warrior
Joined: Apr 2018
Posts: 1,347
Likes: 820
From: Moneta, Virginia
That is weird. My 1200 Sportster when tuned took a 180 main, unless it's a Dynojet kit, they have weird jetting numbers. OEM Keihin jets are metric equivalents. IE: a 150 main is 1.5mm in diameter.
Backfiring on decel is a lean condition, not rich. Are you saying all the weird symptoms were from the air leaks and loose needle?
Overall, how does it run?
Ya know what you need to install?????
Backfiring on decel is a lean condition, not rich. Are you saying all the weird symptoms were from the air leaks and loose needle?
Overall, how does it run?
Ya know what you need to install?????
I wont know how it runs until I put it back together.
popping when you let off the throttle doesnt tell me much, it could be rich or lean. It feels rich, but Im nooo expert!! And yeah yeah Ive heard, theres only one accurate way to know!!!
Ill look up the dynojet kit info... might be what was installed 22 years back.
Grand HDF Member
Joined: Nov 2009
Posts: 4,315
Likes: 1,663
From: Tampa
I guarantee decel popping is lean. Most likely from the air leaks you already found.
Button her back up and let us know how things are running. I'd advise a thin layer of oil on the intake seals as you install them. I've had them pinch and create leaks.
Button her back up and let us know how things are running. I'd advise a thin layer of oil on the intake seals as you install them. I've had them pinch and create leaks.
Thread Starter
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Road Warrior
Joined: Apr 2018
Posts: 1,347
Likes: 820
From: Moneta, Virginia
I guess Ill put it back together and run her up the road. I may never know if she was rich or lean.
I was hoping for input on that 150 main. I would think that would make it run rich, but she ran for 21 years and 90k Miles without any issues. Maybe Im overthinking things.
Grand HDF Member
Joined: Nov 2009
Posts: 4,315
Likes: 1,663
From: Tampa
Considering I've used the AFR meter you're resistant to install on multiple bikes, every time I've heard decel pops it was lean and the throttle was closed so.... 
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Seasoned HDF Member
Joined: Aug 2008
Posts: 5,081
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From: Ohio
http://www.dynojet.com/pdf/8105.pdf
https://www.jpcycles.com/product/404...or-rebuild-kit
Dynojet jets have different threads for the DJ emulsion tube and won't interchange with the stock jets, nothing else different. The V-Twin kit is only showing a rebuild set up, not a tuning kit. If it is a Dynojet kit the jets will have DJ before the number stamped on them. You need at least a 185 main jet in there, 45 low if completely stock or a 46 which is harder to get.
You need to put the carb back on with the repairs, a new set of plugs in it and attack one thing at a time, most likely the items you found wrong was the issue. The only other odd thing that can cause a rich condition is the diaphragm in fuel petcock having a hole in it pulling fuel through the vacuum line if you have the automatic shut off petcock. You can check it with a hand pump vacuum with a gauge and see if it holds a vacuum.
Popping on decel is a lean condition igniting left over gases in the exhaust by excessive exhaust heat, stay with Mr Bastards recommendations and put it together, you have a known good fuel delivery system and then can adventure out from there.
https://www.jpcycles.com/product/404...or-rebuild-kit
Dynojet jets have different threads for the DJ emulsion tube and won't interchange with the stock jets, nothing else different. The V-Twin kit is only showing a rebuild set up, not a tuning kit. If it is a Dynojet kit the jets will have DJ before the number stamped on them. You need at least a 185 main jet in there, 45 low if completely stock or a 46 which is harder to get.
You need to put the carb back on with the repairs, a new set of plugs in it and attack one thing at a time, most likely the items you found wrong was the issue. The only other odd thing that can cause a rich condition is the diaphragm in fuel petcock having a hole in it pulling fuel through the vacuum line if you have the automatic shut off petcock. You can check it with a hand pump vacuum with a gauge and see if it holds a vacuum.
Popping on decel is a lean condition igniting left over gases in the exhaust by excessive exhaust heat, stay with Mr Bastards recommendations and put it together, you have a known good fuel delivery system and then can adventure out from there.
Last edited by 1997bagger; Sep 8, 2018 at 10:34 PM.
Thread Starter
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Road Warrior
Joined: Apr 2018
Posts: 1,347
Likes: 820
From: Moneta, Virginia
I put it back together and shes running great. Starts easy and idles correctly.
I have an occasional pop on de-accel, but not at full throttle. It happens when Im puttin 30-45 mph, accelerate through a sweeper or up a small incline, then ease off the throttle. If Im running high rpm and cut the throttle, theres no pop.
Next time out, Ill fiddle with the mixture screw... Ill try backing the screw out 1/4 turn or so to richen her up a bit and just see.
Its funny how a bikes performance will decline gradually and you dont notice it. My bike hasnt run this strong in years.
I have an occasional pop on de-accel, but not at full throttle. It happens when Im puttin 30-45 mph, accelerate through a sweeper or up a small incline, then ease off the throttle. If Im running high rpm and cut the throttle, theres no pop.
Next time out, Ill fiddle with the mixture screw... Ill try backing the screw out 1/4 turn or so to richen her up a bit and just see.
Its funny how a bikes performance will decline gradually and you dont notice it. My bike hasnt run this strong in years.