Carb tuning questions...
Thread Starter
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Road Captain
Joined: Jun 2006
Posts: 723
Likes: 62
From: Cape Cod, Ma.
Carb tuning questions...
For those of you with CV carb experience. I have been trying to get my buddy's 03 Fatboy (carbed) running right after he let it sit too long and then tried to start it. The bike has a set of VH straightshots and the stock air cleaner. The carb was adjusted for the pipes and ran well before. When I got it it wouldn't idle without the choke etc... I pulled the carb and cleaned the crap out of it. The problem I am having now is I can't get ride of a off idle stumble/pop. When cruising and just coming off idle the is an occasional cough. I have tried playing with the mixture screw; going as far as 3 1/4 turns from seated and it still has the cough. Needless to say, it didn't do it before the extended rest period it had. I almost feel that the jetting overall needs to be re-done. 3 turns plus seems like a lot from everything that I have read. Any ideas?? Other than the stumble the bike runs great. Thanks.
Neil
RDMC
Neil
RDMC
Road Captain
Joined: Dec 2010
Posts: 720
Likes: 3
The slow jet may be plugged from old evaporated fuel. Try a new jet of the same size. Also, like was stated the accelerator pump diaphragm may not be sealing. Pull the air cleaner off, hold the slide up and look into the bore whiel twisting the throttle to see if you are getting a good squirt. The accelerator pump nozzle may be clogged as well.
Thread Starter
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Road Captain
Joined: Jun 2006
Posts: 723
Likes: 62
From: Cape Cod, Ma.
Thanks guys for the responses. The fuel pump works good. In fact I kept flooding it while trying to adjust the cables; everytime the throtle turned a good dose of fuel pumped in. As best I could I got all the jets/ports cleaned. The only thing I could get off was the vaccum slide. The throtle cable bracket screw kept me from being able to get the slide cover off. The main jet got cleaned out, so I don't see how the needle could be a problem. I may just have to pull i\the carb off again pull it apart to re-check everything. PITA!
Neil
RDMC
Neil
RDMC
Cruiser
Joined: Mar 2011
Posts: 240
Likes: 0
From: Royal Oak, MI
Sounds like it needs a new slow jet. Seeing as that nothing has been changed other than it sat I'd just get a replacement of the same size and one size bigger and see how that works. Also, did someone take off the air cleaner or something else? If it was put on with a bad seal or something that lets in too much air it could make it lean (like not putting the center bolt in that holds on the cover but also seals a hole).
After I did a stage 1 on mine it ended up needing a 48.
After I did a stage 1 on mine it ended up needing a 48.
Thread Starter
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Road Captain
Joined: Jun 2006
Posts: 723
Likes: 62
From: Cape Cod, Ma.
Sounds like it needs a new slow jet. Seeing as that nothing has been changed other than it sat I'd just get a replacement of the same size and one size bigger and see how that works. Also, did someone take off the air cleaner or something else? If it was put on with a bad seal or something that lets in too much air it could make it lean (like not putting the center bolt in that holds on the cover but also seals a hole).
After I did a stage 1 on mine it ended up needing a 48.
After I did a stage 1 on mine it ended up needing a 48.
Neil
RDMC
Cruiser
Joined: Mar 2011
Posts: 240
Likes: 0
From: Royal Oak, MI
I had a 45 stock in mine, and after adding the pipes and intake it'd pop/cough off idle, but would idle no matter how much I backed out the mixture screw. I then put in a 46 slow jet and could get it to run fine off idle, but would idle for a minute then sputter and die. The 48 fixed everything, but my mileage sucks now (probably need to turn the mixture screw back in, but it runs great).
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Road Warrior
Joined: Jul 2006
Posts: 1,532
Likes: 7
From: Rochester N.Y.
My last bike 2006 FLHT carb , I got to run very nicely for around $20.00 worth of mods.
The engine was a stock 88 with a Ness Big Sucker and V&H Classic slipons.
The best combo I ran was
#48 pilot jet
# 27094-88 jet needle (sportster)
# 180 main jet (stock)
I had tried a bunch of different parts , but these worked together the best.
A #46 pilot was the first mod , but wasn't quite rich enough for my combo.
I tried different main jets , but the stock 180 was the best combo all around.
I tried shimming the stock needle with machine washers , but the sportster needle was the final best combo.
This gave me 45-50 MPG and all around nice throttle response.
It will at least get you very close to what you will need.
Mick
The engine was a stock 88 with a Ness Big Sucker and V&H Classic slipons.
The best combo I ran was
#48 pilot jet
# 27094-88 jet needle (sportster)
# 180 main jet (stock)
I had tried a bunch of different parts , but these worked together the best.
A #46 pilot was the first mod , but wasn't quite rich enough for my combo.
I tried different main jets , but the stock 180 was the best combo all around.
I tried shimming the stock needle with machine washers , but the sportster needle was the final best combo.
This gave me 45-50 MPG and all around nice throttle response.
It will at least get you very close to what you will need.
Mick
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Thread Starter
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Road Captain
Joined: Jun 2006
Posts: 723
Likes: 62
From: Cape Cod, Ma.
Mick,
Thanks for the input. I assume the pilot jet would not need to be changed as much with a stock airbox on it. I have to pull it apart again to see what it has inside and go from there.
Neil
RDMC
Thanks for the input. I assume the pilot jet would not need to be changed as much with a stock airbox on it. I have to pull it apart again to see what it has inside and go from there.
Neil
RDMC
Road Warrior
Joined: Jul 2006
Posts: 1,532
Likes: 7
From: Rochester N.Y.
Actually Neil , the most problematic part of the throttle range is the bottom 1/3 from idle to 1/3 throttle.
This is where the EPA invokes most of it's control over the emissions.
The stock main jetting is actually rich enough for almost any build you can do with the stock carb , as you can't run full throttle all day.
I actually started my carb mods when the bike was new and bone stock.
I was looking to clean up the spot from idle to 1/4 throttle which would "puff" sometimes and the idle was up and down slightly (lean).
I removed the pilot screw limiter and it didn't give me enough fuel even at 3 turns out.
I then went to a #46 and it almost did what I needed , but I was near 3 turns out again.
I then went to a #48 which was a bit much with the stock setup , but the best so far.
I then added the V&H straight cut classic slipons , which really breath and it was about perfect.
Remember at idle , a huge air cleaner makes the least amount of difference of any throttle position.
After I added the Big Sucker filter , I had to richen up part throttle to mid throttle as the air filter allowed more air than the stocker could.
So stock , the leanest the bike will usually be is at idle to 1/8 throttle if it's bone stock.
I ended up putting the #45 stock jet in my kids sportster which came with a #44 and it ran better also (a freebie).
Any mod which enhances the proper running of the engine will also improve fuel mileage until you go slightly richer than you need to make it proper.
Mick
This is where the EPA invokes most of it's control over the emissions.
The stock main jetting is actually rich enough for almost any build you can do with the stock carb , as you can't run full throttle all day.
I actually started my carb mods when the bike was new and bone stock.
I was looking to clean up the spot from idle to 1/4 throttle which would "puff" sometimes and the idle was up and down slightly (lean).
I removed the pilot screw limiter and it didn't give me enough fuel even at 3 turns out.
I then went to a #46 and it almost did what I needed , but I was near 3 turns out again.
I then went to a #48 which was a bit much with the stock setup , but the best so far.
I then added the V&H straight cut classic slipons , which really breath and it was about perfect.
Remember at idle , a huge air cleaner makes the least amount of difference of any throttle position.
After I added the Big Sucker filter , I had to richen up part throttle to mid throttle as the air filter allowed more air than the stocker could.
So stock , the leanest the bike will usually be is at idle to 1/8 throttle if it's bone stock.
I ended up putting the #45 stock jet in my kids sportster which came with a #44 and it ran better also (a freebie).
Any mod which enhances the proper running of the engine will also improve fuel mileage until you go slightly richer than you need to make it proper.
Mick