39 FCR carb help!

[iski3]

I have a 416 11.1 piston, Full LRD exhaust, K&N, White Bros Ignition. I just replaced the stock carb with a 39 FCR carb. tuning this beast has been difficult. When you start it up, it does puff black smoke, but starts very easy, after a few back fires (tese moters take a while to warm up. It has a HUGH lean spot. off idle is fine, but blip the throttle and dead it will become. I raised the needle as high as it will go and went up to a 178 main and it got better, but still not good. I know it is lean, because if i force the excelerator pump to full, it raps just fine. I have not been able to ride to test top end, and low jetting. Here is how it is set now 50 low speed, needle up all way, 178 high, air jet 1 1/2 turns out, idle speed needle 1 turn out.

Thanks,
HELP:o

[iski3]

Ordered a new needle today, hope it will help.

[NJ300ex]

Talk to Gabe. He has a setup just like yours and he seems to know a whole lot and will be able to help you out.

[iski3]

How do I get a hold of him. I think I met him at a woods race once.

[Sandragggen]

Gabe is the Tech Editor for Extreme Garage at http://www.hondaex.com/ or his personal site http://home.earthlink.net/~gellett/exhaust/index.htm

[RAPTORAZ]

Sound's like you need to adjust the accelerator pump. You're not getting enough fuel when you rapidly go wide open. A friend of mine had a similar problem with his, and this fixed it.

[stevengates45]

anybody tried the Edelbrock carb?

[EX 80]

Might be a dumb question but how is the acceleraor pump adjusted.

[iski3]

Add a heavier spring to make it open faster.

[NVR2L8]

I have similar engine mods as you...416cc JE 10.8 piston, XR400 cam, 39mm FCR, run either a K&N or a UNI filter, but with the stock head pipe and a FMF Powercore Q. My jetting for sea level includes a 52 pilot, needle on the third groove, and a 165 main. With this setup my jetting is dead-on perfect. You should be okay with a 50 pilot depending on your elevation, but I think you're way off with the main jet and needle clip position adjustments.

First of all, you are way lean on the needle. When you raise the clip position on the needle (top position) that's actually the leanest setting for that particular needle. Raising the clip lowers the needle into the needle jet, which allows less fuel to flow past it. Conversely, lowering the clip down on the needle raises the needle in the needle jet, which allows more fuel to flow past it. With the clip on the top position, this is most likely the reason it stumbles and why you have a huge dead spot above 1/8-1/4 throttle. Anyway, if you feel it's running lean between 1/4 and 3/4 throttle, richen that circuit by lowering the clip one notch and see how it performs. With my setup the standard setting for the accelerator pump on the FCR is just fine, and I don't have a stumbling problem at all. Also, given your mods, I'd be surprised if you really need that large of a main.

Here's what I suggest... First, change the clip on the needle back to the 3rd position. Second, if you have a 52 pilot handy, install it. Third, if you changed the spring on the accelerator pump, put the original back on. Install a 170 (or so) main jet. Lightly seat the air screw (the one on the airbox side) and then set it to 2 turns out. Then lightly seat the fuel screw (engine side) and then turn it to 2 1/2 turns out. Now start up the engine and let it fully warm up.

Adjust the fuel screw (engine side) by first turning it out until you notice a decrease in idle speed, and then in until you notice a decrease in idle speed. Note the range between these two points. Find the spot in this range where you get the best off idle response when "slightly" wicking (opening) the throttle. If you end up more than 3 1/2 turns out go a size larger on the pilot, and if you go in less than 1 1/2 turns go a size smaller.

With the needle on the third groove, see how it runs from 1/4 to 3/4 throttle If it feels lean, lower the clip to the 4th position. If it runs too rich on the 4th position, go back to the 3rd position and now look at adjusting the accelerator pump so it pumps quicker. Since I've never had to adjust mine, the only help I can suggest is to call Sudco at 323-728-5407. They've always been helpful when I've called and can probably provide you with instructions/options on how to do this.

Lastly, once you get the 1/4 to 3/4 range dialed in, move to the main jet (3/4 to WOT). The best way I've found to dial in the main is to use a method I call "purposefully over-jetting". Start with a large size main and do a run with the throttle above 3/4 and the engine under load just under the rev limiter--you'll know if you're too rich when the engine blubbers similar to running with the choke on. Also, make sure you can distinguish the difference between the blubbering condition and hitting the rev limiter. Once you know you have too large of a main installed, do a high speed run just under the rev limiter and then do a plug chop by quickly killing the engine and pulling in the clutch at the same time. Coast to a stop, pull the plug, and check the porcelain for a light brown color. Keeping doing these runs and going down in main jet sizes until the blubbering condition goes away and the plug reads light brown--once you get to this point the main is perfect. Also, keep in mind that clean burning fuels will make it very difficult to get a good plug reading. When I jetted mine, I ran a 75/25 mix of 111 octane leaded race fuel to 92 octane premiuim (the lead in the gas will help give you a correct plug reading).

Hope all of this helps...

[JhallettEX]

Great post NVR2L8......My FCR 39mm is on the way and I was really worried about getting in tuned in. It should be no problem now. Thanks, But i do have one questions for you, Will my K&N Jet Kit work in conjuction with my new carb? I know that is is coming with a 50,52,54 and a 165 and 170, Will my lower mains work or will I have to go out and pay new jets. Thanks alot for your help.

[NVR2L8]

When I ordered my FCR through my local motorcycle dealer (who got it directly from Sudco), he gave them my engine set up. It came with a 50 pilot installed and a extra 52 pilot, with a 165 main installed and a bag of extra main jets. I changed the pilot to a 52 since it seemed to work best for cold starting and off idle response...all other adjustments remained the same.

Anyway, to answer your question, the FCR is pretty easy to dial in. I normally run a UNI or a modified stock filter cage set up, but switch to a K&N when I run at the dunes and it still runs great. I'm on the fence when it comes to the K&N letting in dust...I've had dust in my intake tract when running in really dusty conditions. Just remember that changes to the intake side normally affect jetting much more than changes to the exhaust side. Also, the higher in elevation you go the richer your jetting will become. BTW, the pilot jets for an FCR are different than the ones for the stock Keihin, but the main jets are the same. I really doubt that the K&N jet kit would work with the Keihin 39mm FCR...have never tried...and in my opinion you really don't need the jet kit know that you have the FCR. You'll understand once you get the FCR installed and dialed in with your mods...the throttle response is amazing!

[Sandragggen]

NVR2L8...I recently bought a FCR41 from Sparks and set it up for alcohol. I see the fuel screw (closest to the engine, in front of the bowl drain plug), but do not see the air screw (the one on the airbox side) on my carb. Do you think that maybe the FCR39 is different than the 41? Your jetting post is very informative and will follow the steps as stated. Alky jets as you know are much larger than gas jets, but the procedure should be the same for setting it up. I also heard on another site that 1-1.5 hp could be gained by installing the air-filter directly to the carb, losing the air box. The person stated that the stock air tube, if you will, doesn't flow as well as direct filter to carb set up. I'm with you on the K&N filter letting dust into your motor. I bought one sometime back and used it once and only once after finding dirt in the intake track. Good info.

Jay

[iski3]

You hace to unbolt the air horn to get to the air jet. Do you see the two holes on the bottom of the venturi? They leed to the screw. Actualy it is a jet that is adjustable.

[Sandragggen]

Thanks iski3. After taking the bell off there it is.