Hey everyone,

I am having a carburetor problem. I have a Keihin CV Carburetor on my 88 Twin Cam 2006 Road King Custom. When I bought it, the dealer installed a Stage 1 kit with V&H slip ons. The jets that they replaced were 48 on the low jet and 195 on the main jet. I have know idea what the stock jets were.

From the beginning, when the engine is hot and the choke is already completely in, I'll be sitting at a stop light and give it a light throttle and sometimes it coughs. Sometimes it coughs so hard that it kills itself. I changed out the exhaust to Rinehard True Duals and it doesn't make any difference.

What are stock jet sizes for a '06 Road King Custom 88 Twin Cam? Obviously I have a lean condition at idle going on. Do I need to increase the 48 low end jet, use a different needle, lower the clip on the needle to get a richer condition? Please help me out some of you old time harley carb gurus.

Thanks,

Mark

 

Stock should be 45/190...Jetting may not be bad, but try to shim the needle...Whats the idle mixture screw at?

 

I drilled the plug cover out of the idle mixture screw about a year ago. Think I ended up with about 1-1/2 turns from seat. I've tried several turn settings that didn't help much.

BTW, plugs look real good. Slight tan on 13,000 miles.

 

Curious. I have drag pipes, and have no problem with my rk custom (with a carb) I have been toying with the idea of getting a thunder slide kit, and playing with a few different needles, but I want to get a few different needles, and can't find a kit that has several different sizes of needles... Any of ya'll out there that once had a carb, if you still have your old needles, I will be happy to take them off your hands... I did not do my rejet, although I wish I had tried it... I just do not know what to do, but want to learn... Any good links out there???

 

Hey PT, the TS kit does work, but mileage suffers, badly. if you want quicker throttle response and don't care about mileage, it will perform somewhat better than an un-modified carb... been there, done that
I'm back to a basically stock set-up, my RK ain't a hot-rod, it's a hwy cruiser....

 

Stock jets should be 45 and 190.
You could shim the stock needle with 2 #4 machine washers and see if you're getting closer.
I did this and it just wasn't quite enough , then went with the old sportster needle (in my signature).
The sportster needle ( with no shims) worked for me , but some say it's a bit rich for a carb with an accelerator pump.
Make sure your idle speed is at 950-1050 (hot) and make sure the accelerator pump "does work" this could also cause your problem.
This combo worked for me , and should get you close.
Also make sure the dealer didn't drill the slide or use a screaming eagle slide spring , this could make things a bit worse.
I tried the screaming eagle slide spring and it made things finicky , so I run that stock.
Change one thing at a time and give each change a few hundred miles so you can feel the difference and check the fuel mileage change afterward.
Fortunately it won't cost much money , and will be time well spent when you're done.
Good luck.
Mick

 

Take your idle screw to 2 1/2 turns out, and replace the stock needle with a needle for a 1988 1200 Sportster. The taper on the Sportster needle is different to compensate for that year 1200 not having an accelator pump. This should solve the problem.

Your jets sound just about right for the modifications you have.

Bill

 

I put the Mikuni 42 on my 99 and I love it. throttle response is great and it rips now.

 

I did this on my '04 Dyna as well, big difference. Its a flat slide carb, more performanced based, easier to tune, just a much better carb.

 

Hey there, not too many of us Carb folks left anymore. I feel like a red headed step child
They had the carb off so now you need to make sure something else did not get jacked up before you concentrate on mixture and jets.

Very first thing I would do is make sure they did not leave any lines off the carb such as the petcock vacuum line. This will do it almost everytime.

Check to make sure there are no other vacuum leaks. WD40 or something like is a pretty good detector. You can spray it around the manifold and seals while its warmed up and idling properly.

Make sure the enrichener **** actually goes all the way in and there is a little stem still showing behind the ****, indicating it's in and there is a little bit of travel left.

If you verify all this is fine then start with the idle mixture screw. Hopefully they already removed the cap. First, find out where it currently is,count the exact turns as you turn it in until it's lightly seated, then count the turns as youback it out until it's where you originally started. Write this down somewhere just in case. Should be around 1-1/2 to 1-3/4 turns out. Try opening the screw (CCW) 1/16 of turn at a time and see if your cough goes away. Very, Very small adjustments. This idle screw will affect midrange cruising as well as fule mileage, the adjustment is very sensative so go slow and test after each adjustment.

If it takes more than 1/4 - 1/2 turn and your still not right then it's time to play with the insides (jets).

The previous owner of my bike had modified the carb so much it wasn't funny. It spit and coughed so bad it was embarrassing. Fuel mileage was so bad that I could barely get 100 miles per tank and I better be looking hard for a gas station.

Rather than spend the time and money to go back and replace the slide, spring, and then get it jetted properly I decided to go a different route. I finally got tired of all the cough and put a HSR42 on it and now love the response and no more freaking cough, and fuel mileage went way up 27 to 40. When I crack the throttle she jumps as in INSTANT response! Flat Slides are awesome for throttle response and low end.

I ran the CV's before and they aren't bad carbs, but too many people out there now days have mods and kits that can really jack them up. Most of themleave HDare lean on idle from the factory, and maybe just a "tad" lean on the needle but generally not by much.

The idle circuit has a big roll, not just at idle but as well into mid-range RPM. A little adjustment there goes a long ways and this is where I think it's important to change "1" thing at a time and tune them in instead of making 2,3,4 mods at once then trying to figure out where you went wrong.

Warning, if you ever even consider the HSR itwas a snap to install, unless you have cruise control. Even with the "adapter kit" there is all kinds of stuff to drill, grind, and fabricate.