Re-jetting a CV carb

[1996Fatboy]

What's the best way to tell that you have the correct jet installed? I had new V&H's Longshots installed and a Dynojet Thunderslide setup installed. At that point I was still using the factory air cleaner. The bike sounded great when I picked it up and looked even better. To the mechanics creidt he did recommend installing a high flow air cleaner and even recommended a couple of inexpensive types. I recently installed the Arlen Ness Big Sucker. Now I occasionally experience a backfire from the carb when I try to accelerate. If I pull the enrichener out a little bit it seems to respond better. Figure I probably need to install a larger jet. When dyno tuning, do the tech's do this to make adjustments or do they give you a print out with suggestions?

Robert

[94flhtcu]

I'm curious about something. Did you ONLY get the thunderslide? Mine came in a master kit, with some jets, and an adjustable needle. Did the tech give you a plastic box with the extra brass jets in it? It sounds like you had a thoro tech, so he probably sent them back to you, and these are the parts you need. They can be purchased seperately, but if you already have them, there's no need. Seems like there was a good article in AIM on jetting. It's not hard, but is time consuming to dial it in. My advice would be to ask around for jetting suggestions from guys who have the same setup, and go from there. To fine tune your jetting, you'll run the bike at one part of the throttle, pull in the CLUTCH under power and shut it down with the handle bar kill switch at the same time, and glide to the side of the road safely. You'll pull the plugs, and do a plug read by looking at the color on the plug- you could look at yours now- if it's bone white, WAY too lean- cream to gray, just right- fuzzy black soot- too rich. You'll do this for the low speed, intermediate, and high speed functions of the carb. And this is a real simplified description of what needs to be done. Again, it needs to be shut down under power in the rpm range you are checking to get an accurate color, for plug reading.

I'll try to help if I can. Take care!

Don't just run out and try to do it. Look around, ask, read. I think there is some way to look up old AIM articles on this site, but I don't know how.

[1996Fatboy]

Thanks 94, didn't think to check the plugs. My tech did give me the box with the extras plus the old slide and other parts. I don't recall there being an adjustable needle bit then again I didn't see the kit before it was installed. I'll check the plugs this weekend. Is there a certain amount of time I should run each test? Can the jets be changed with the carb on the bike? I could take an assortment and some gaskets along if its a simple procedure.

96

[94flhtcu]

About the adjustable needle- the stock one looks like a nail, with a head like a nail. The adjustable has a bunch of grooves for a snap ring, making it adjustable. I'm confident he installed it.

As for changing the jets carb on, yes, I've done it, but I'm use to working in awkward positions, and this is certainly a tough one. Cross threading one is not an option! Also, gentle tightening here. Don't want to hurt threads.

Another tough thing to do is adjust the idle mixture screw. I will soon get the mixture screw offered by j&p cycles. It's very difficult to adjust the stock screw with a screwdriver, cuz it has to be the right length, and you do it hot, so you probably will get burned. I did until I took an old leather glove and layed it on the cam cover to help cut down on the heat. J&P's screw has a thumb wheel, adjusted by hand.

Do you know what it's jetted at now? Sounds like they didn't do much. Look in the box- stock low speed jet numbers are around 42. The kit comes, I think, with 45 and 48. I'd look to see whats in the box. I'll have to see what I started at, it's written down in the garage. I'll post it tomorrow. If I were you, I'd start at 45 low speed, and stay with the stock high speed. I'll have to see my notes about the needle.

As far as how long to mark plugs, I live in the country, and rode several miles at the speeds I checked it at except for the high speed. I winged it, it's a little rich, and I'll step down one before putting it back on the bike.

Take care, I'll post the needle setting tomorow nite.

Originally Posted by 94flhtcu

About the adjustable needle- the stock one looks like a nail, with a head like a nail. The adjustable has a bunch of grooves for a snap ring, making it adjustable. I'm confident he installed it.

As for changing the jets carb on, yes, I've done it, but I'm use to working in awkward positions, and this is certainly a tough one. Cross threading one is not an option! Also, gentle tightening here. Don't want to hurt threads.

Another tough thing to do is adjust the idle mixture screw. I will soon get the mixture screw offered by j&p cycles. It's very difficult to adjust the stock screw with a screwdriver, cuz it has to be the right length, and you do it hot, so you probably will get burned. I did until I took an old leather glove and layed it on the cam cover to help cut down on the heat. J&P's screw has a thumb wheel, adjusted by hand.

Do you know what it's jetted at now? Sounds like they didn't do much. Look in the box- stock low speed jet numbers are around 42. The kit comes, I think, with 45 and 48. I'd look to see whats in the box. I'll have to see what I started at, it's written down in the garage. I'll post it tomorrow. If I were you, I'd start at 45 low speed, and stay with the stock high speed. I'll have to see my notes about the needle.

As far as how long to mark plugs, I live in the country, and rode several miles at the speeds I checked it at except for the high speed. I winged it, it's a little rich, and I'll step down one before putting it back on the bike.

Take care, I'll post the needle setting tomorow nite.

I'm add adding a Screamin Eagle backing plate on my '03 FXST. Also I want to check or change my main jet. Do I need to completely remove the gas tank to get to the top of the carb? Any special tips? Thanks, Dave

[1996Fatboy]

Originally Posted by dariv1

I'm add adding a Screamin Eagle backing plate on my '03 FXST. Also I want to check or change my main jet. Do I need to completely remove the gas tank to get to the top of the carb? Any special tips? Thanks, Dave

To get to the top of the carb you can pull the tank or just pull the carb. Curious though, you mentioned wanting to change the main jet which is located in the bottom of the carb. No need to remove the top for a jet change.

96

[2003FXDX]

Changed the jets on my bike without complete removal. Just slid it off manifold with cables still hooked up. It's a little tricky but can be done. Changing the air cleaner leaned it out.

[PeterV]

Here's a how to....

Turn fuel valve to OFF.
Remove football air filter cover.
You DON'T need to separate the air filter backing plate from carb.
Remove breather bolts. Capture washers (3 on each side, 2 Large diameter, 1 Small diameter)
Disconnect the choke from housing.
Remove fuel line from carb inlet elbow.
Back off throttle cable jam nut all the way, followed by the adjusting nut.
Remove vacuum hose from inside top of carb.
Wiggle, wiggle....there it is. Carb with cables on yer hand.
Plug intake manifold side of carb with a rag.
Rest is straight forward, whether it's messin with jets(bottom) or needle\diaphragm (top).
On reinstall:
The float bowl screws are crappy! Use the right Phillips screwdriver and DO NOT over tighten.
A little KY (ask the wife for some) or even a dab of light grease around the throat of the carb makes fitting on intake go a lot smoooooother!!!
Make sure throttle cable hasn't jumped out of it's housing (carb side).
This is important: When reinstalling the breather bolts always do so by hand. The washers will get hung up on the threads. Back off bolt a bit, readjust, keep going.
DO NOT REEF ON THE BREATHER BOLTS, they're hollow. Nuff said!
With practice, you can remove, tinker and replace your carb in under 20 minutes!

About them plugs!...
Porcelain color doesn't tell the whole story regarding jetting. Read the base ring of the plug (where the strap is welded on).
Light soot is good.
Bare spotty metal is not.
Neither is heavy black soot.