I've had issues with my carb lately and could use some advice. My 1993 FXRS has the usual mods of air cleaner, exhaust, cam (Andrews EV3) and single fire ignition, and ran great for years. A year ago or so I had to up the slow-jet to #48 to stop the condition of carburetor backfires just off idle, which I think is a lean condition at that one point of throttle. The #48 also caused a bloated feel of running rich and the smell of unburned gas. I recently pulled the carb off and cleaned it using a new ultrasonic cleaner, installed a rebuild kit to include new vacuum slide, accelerator pump diaphragm and spring, set the float, and re-jetted back to #45 / 175. The needle I've been using is the recommended '88 Sportster issue N65C. And still, the problem persists, idles fine, runs fine, but backfires thru the carb and stumbles just off idle. If I pull the choke 1/2 way out the problem goes away. Does anyone know the main jet needle that was issued for this bike. Would like to go back to that, and try any other suggestions y'all may have. I doubt there's any air leaks since I had a recent top-end by a reputable shop and a new boot on the intake side of the manifold. Original jetting on this bike was #40 / 165, which I know was lean, but ran great at #42 / 175 for years. Thanks.

 

Assuming the accelerator pump is operating correctly and you're leaving the choke part out for the first 2-3 miles on a cold start; you either have an intake leak at the heads or the hose for the VOES / petcock or a bad VOES not letting the timing advance properly. Or, a couple of the tiny, low circuit holes are plugged in the throat of the carb. But a slight leak at the manifold / head flanges would be my first guess and spraying fluid at them won't always show up a leak. It's about as time effective to just replace them and be meticulous going back together.

That cam with free flowing pipes, needs a minimum of 45/175 with the mixture screw way out, like 2.5 turns or more and it should do fine with a 48 at 1.5 - 1.75 out with a 180-185.

But to answer your question, the correct factory needle would be N86F (27184-92) Good luck finding one, just troll ebay and be patient, you may happen on one eventually. I have seen the N86E for sale lately, it'd be really close to the "F" needle.

 

t150vej Thanks for the fast response. While I have the carb off (for the 4th time this week) I will go ahead and replace the VOES and it's hose, and remount the manifold, since I didn't install the current set-up. I also happen to have an N86E in my collection so I'll drop that in too. Those tiny transfer ports under the butterfly and their passages were my main concern, but they are clean now (I hope). I will button it up with 45 / 175 to start, and test with new plugs. For months, riders behind me have complained about my exhaust being gaseous using the 48 / 180 combo. Should I lube or apply anything to the manifold seals or just replace?

 

You know your way around the CV carb. Something to look at since you've made a thorough going of the carb. The manifold gets tired, and sometimes they will never seal correctly. When you press the CV carb on the manifold, it should be tight. If it's easy to get on and off, you will always have a potential leak, even with new seals. I've been told this by a friend who has hundreds of thousand miles on an Evo. I put a light surface lube on the rubber seals of the manifold that butts up against the intake ports, but nothing on the seal that the carb mounts to. The area that leaks is normally bottom part of manifold.

 

You want to leave the flanges loose on the heads then push the carb part way into the grommet. Attach the air cleaner backing plate to the carb and then loosely mount the backing plate to the heads, pushing the carb all the way into the manifold grommet. Then tighten the flange screws. This puts everything in a relaxed (where it's going to run) position. If it's an aftermarket air cleaner back plate, you may need to shim / adjust whatever mounting arrangement you have. Just be sure the carb stays straight and square with the manifold when it's all snug.

As to the burning smell, with the stock engine breathers putting blow-by straight back into the intake and depending on your mileage, you could have excessive blow-by that's burning in the cylinders. That's not uncommon and many guys re-route the breathing system to atmosphere. (you may have already done this with the new air cleaner)
Look at your valves with the manifold off and check for excessive build-up. If you have a small inspection light you can see the piston tops thru the spark plug holes also.

 

Thanks Daven and t150vej, I will re-mount manifold as you guys describe above. The carb-to-intake is a snug fit, but not tight. I have a screamin eagle air filter that vents to the outside atmosphere. My local shop that did the top-end job says, if it were an air leak, it should show signs through more of the throttle range.
I'll have to see if he has the tool to measure the VOES function... my shop manual says the FXR version measures different than the FLT model. FXR= 3.5-4.5 inches of mercury, and the FLT is 5.0-6.0. Will report when done next week.

 

I had a similar problem. Took mine in I got so frustrated. They changed the jets to what the books says and adjusted the carb (S&S) as the book says. They said my float was to low and Installed a new ignition coil.