FCR 37mm Carb Jetting Recommendations on Warrior

[dcg4403]

My OEM carb is toast and after a lot of review I've decided to convert it to the FCR 37mm carb. My quad is pretty much stock except for the air box and Quad 4 exhaust system.

Can anyone running something similar give me some starting points for jetting? I'm not even sure what sizes I should order.

 

[fknboss]

Start high and hope its rich. 185 main or 190 might end up being 165 but its impossible to tell you where to start. So many factors come into play. Pilot jet id start at 48 you might end up with a 45. Make sure your carb is at factory setting before jetting go backwards til rich bog stops then you can fine tune it.

 

[Venom]

Also time the AP, mine was way off the gas jet started to late

 

[dcg4403]

Also time the AP, mine was way off the gas jet started to late

Maybe a dumb question but what is "AP"?

 

['00 WO-YA!]

Accelerator pump. Honestly I don't think I can be much help with the 37mm, I've never used it, only the 39 and my setup is far from stock.

 

[dcg4403]

AP = accelerator pump (got it). I see some people recommend plugging the leak jet entirely or performing a "O-ring mod". I'm going to run it stock & go from there.

Here is where I'm going to start based off the reference points below:

155 - 160 main is a good starting point.
Pilot of 40-50 (I'm going 45)
Leak jet of XYZ? (most YZ owners like 55-60 (smaller) but stock is ~100 depending on year, so I'm keeping it there initially)
Running the stock needle jet which is year dependent. I will drop the needle clip down one notch from YZF250 stock.

Reference points:


1) For others here is what I've found (but have not tried) as a good starting point for 250-375cc motors using 37mm FCR from a aftermarket supplier:

Main jet: #160
Main Air Jet: #200
Slow Jet: #45
Slow Air Jet: #100
Jet Needle: OC-EMR
Throttle Viv. Cutaway: 1.5
Needle Valve Seat: 3.8
Float Height: 9mm

2) I also found an owner of a DR350 that installed the 37mm FCR and his settings were (he did say he felt the AP needed was creating problems as his carb was stock on a DR400)

"Subsequent testing and a #48 pilot ran better, leaning the needle slightly from EMN to EMR gave smoother low-end, and a bigger main #158 increased top-end"

3) 1993 dr350-435 stage 1 ported, opened up intake to mach id of fcr 37mm drop in cam air box mod stock pipe opened up.

fcr 37mm carburetor crf250 transplant.

160 main
45 pilot
100 main air
ecyr needle 4 clip
70 leak jet
2 turns out fuel screw alumminum

4) On a DRZ400:

i installed a 37MM FCR off an 05 KX250F and it is much improved on the bottom and i'm very happy with the way it turned out. i had to fabricate a sleeve to fit on the airbox side of the carb and i also fabricated a velocity stack that fits inside the sleeve to eliminate turbulance problems Eddie said i would have around the pilot air jet(pilot air jet is a 100), but the bike runs well. i'm at sea level, have the 3x3 mod, a SS Yosh RS-2, K&N filter. i'm running a 160 Main, 40 Pilot, 2 1/4 turns on a ZipTY extended fuel screw(not recommended, get the Keintech) and an EMN needle, clip 3 from the top. i have virtually no decel pop, and the bike pulls very hard on the bottom and will still hit 100MPH on the flat with my fat ass(210lbs) sitting straight up in the air. It will work and unless you've experienced a 39, i believe you will be very pleased with the increase performance over the stock CV carb.

5) On a VOR 400en

my jetting is
170 main
45 pilot
70 leak
OBEKP needle 5th possition from top
pump timing standard crf 250 settings

6) KLX300

I'm running,
54 Pilot (I'm getting fade once the engine warms up, may need a 55 or 56)
155 Main (160 would prob be good)
OCDVR Needle. (3rd clip down)
200 Air Jet
1.5 Air Screw
2.7 Mix Screw

7) KLX300

'm currently using the following jets riding at 2500':

Main = #160 (I think its a little rich and may drop it a size or so, I'm getting black soot on the exhaust pipe)
Pilot = #38 (might be a little lean - see mixture scew setting)
Pilot Air = #100
Mix screw about 3 turns out
Needle clip 3 down from the top using the stock needle from an 05' Yz250F carb. OLEM-R I believe.

 

[Venom]

my leakjet is a #40 i folowed mvvette advice (i had a #60) a 40 leak jet gives you a longer stream of gas when bliping the throttle but it also can become to rich you must know if your bog is rich or lean.

 

[offroadrider12]

First off, in order to get accurate recommendation on a ballpark for jetting we need to know the letters stamped on the needle. Needle taper will have a very drastic effect on the size of your main & pilot jets. Needles with the 3rd letter of D for example OBDVR are a relatively lean needle. Needles with a 3rd letter of E are a richer & steeper taper and make nice power, but use more fuel. I'm not sure how all yamaha & honda needles compare. Some are very similar to the OCEM_ series needles but vary in clip positions.

When I had my 525EXC I ran an OCEMN needle in clip position #5, while it ran well in #3 it made substantially more power and hit harder in position #5. Your results may vary.

The KTM carb was a GEN II FCR and did not have a leak jet. I performed the "BK" mod to adjust the pump squirt. The same can be done with a leak jet. Realistically you want an accelerator pump squirt from about 1~1.5 seconds in duration. As for the O-ring, it increases the intensity of the pump squirt. It makes for a rather noticeable, difference however over time the o-rings can stretch out and not have as good of an effect. There are companies that sell stiffer aftermarket springs which keep the parts inline, just as the o-rings do.

It would also be helpful to know your location, elevation, and supporting engine modifications.

Also, I suggest not getting to caught up on a slight amount of popping on deceleration. A properly tuned fuel screw and pilot jet will exhibit a slight amount of decel popping unless your FCR is one equipped with an Air-cut-valve. (Many WRF bikes had them, YZFs didn't.)

There is an excellent write up from a man named Dave Hopkins on other sites on how to set up a FCR carburetor. I suggest reading up on it.

 

[Gen1Pat]

Yeah for those of us that have put the 39mm on our bikes, it has been a big learning curve!