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Discussion Starter · #1 · (Edited)
In the past few weeks I have been gathering parts and preparing for my FCR 39 install. Now that I have gotten it finished up to my satisfaction the most time consuming part of the whole process was sifting through all the different threads on the project. There is a lot of information on this subject, but it is spread out over so many different threads over the past 5 years that it takes a lot of patience to sift through it all.

I decided to put together a thread of the entire project as I did it to help with some of our newer members that may be intimidated by all the different ways of doing it. I am certainly not claiming this to be the best way to install the FCR, this is just the route I took. I will attempt to reference most of the threads that I got the information from, but I am certain I will forget a few as there are so many.

This project is certainly not as complex as it may seem. The most important thing to anyone thinking of doing this mod is to not get overwhelmed. Do not start this project on a wednesday night trying to rush through it because you want to ride that weekend. Take your time, and be thorough. Do your research and get your parts together before you even pull your plastics off.


To start with, here is a basic list of the parts I used and their approximate costs.

- FCR 39mm - Around $100
-GYTR Jet kit
- (Yfz450 Throttle Cable came with Carb)
- Honda 400ex Thumber - $30
- Honda 400ex Air Intake Boot - $30
- UNI Universal 3"x6" Clamp on Air Filter - $40
- Raptor 660 Fuel Petcock - $15
- 2" Fuel Filler neck - taken from 02 Silverado
- Short piece of 3" Stainless Steel Exhaust pipe
- 5mmx.5 pitch Tap - $16


The next few parts are not always required, but for me they were...
- FCR 39mm carb repair kit - $30
- FCR 39mm Accellerator Pump Rebuild kit - $35
- Tusk Fuel Screw - $15


Start with the carb. The most common FCRs to use are off of either the YFZ450 or the TRX450. I chose the FCR 39mm from an 08 YFZ450. I watched Ebay for quite some time waiting for the right deal. You will notice that the price moves around a lot on these carbs based on how many people are looking for them. They move through ebay pretty frequently, when I first started looking they were going for up around $150 in most cases. Here recently I have seen most of them go for closer to $80. I picked mine up for $88 and it came with the spring mod and the GYTR jet kit and the throttle cable. Here is what the carb will look like right off the YFZ450.



The first step is to tear it all the way down and check the condition on the inside. If you dont at least check the parts over you may never get it to run right because of a plugged chamber, stuck float needle, or in my case... a shot AP Diaphragm



The next step is to get rid of the TORS and TPS cluster on the left side of the carb. Reference to this thread here FCR Carb Mods as it explains step by step how to do it. Very simple if you have a cutoff wheel. Here are a few pictures from mine.

Cut wide and give yourself plenty of room to clean it up with the bench grinder.



Lay the cut out piece on top of the shaft and use a sharpie to mark where you want the shaft cut so that it is flush with the piece.





Plug the holes for both the shaft and the screw and fill the shaft half with metal filler. This is just to keep moisture and dirt out of the bearings on the shaft.



Much cleaner



Also in the FCR Carb Mods thread they explain how to drill and tap your FCR to use the stock idle screw. Be careful to drill the hole straight and not too big. I had NAPA order the tap (5mm x .5 pitch). Heres a picture of my idle screw. Notice the steel wool... my hole ended up too big.



After a few days my carb repair kit and acellerator pump rebuild kit came in and I put in all the new gaskets and o-rings along with the new diaphragm.



Next, dry fit your boots and fittings and leave them clamped to make sure they will fit tight. If you have loose fittings you will have nothing but problems with your bike as air will get by.

For the carb to head boot I used a short section of 2" gas neck filler hose off of an 02 silverado. This is nice because you can cut the boot to any length and angle you need to clear the headstay and keep the throttle cable from kinking.



Then, to go from my new 400ex air intake tube to the UNI clamp on filter I used a short piece of 3" stainless steel muffler pipe. This is also nice because you can get it to any length and angle you need to. I angled mine down a little to keep the air filter from coming into contact with the seat. To connect the crank case breather tube to the 400ex boot I used a 1/2"x3/8" PEX tubing elbow. It is a brass fitting that fit perfectly on both ends, you can find it in your local hardware store. PEX tubing is used as an alternative to copper water lines. You will also need to cut the first ring off of the 400ex boot on the carb side so that it will clamp down onto the FCR.





Next get a base point to start with on jetting. The way I did this was reading through the posts on this thread Jetting Database . Find someone with a FCR with about the same mods you have and around the same altitude and start with those jets. That should get you close enough to get it running, then fine tune it after you can ride it.

The last thing you need to do before you get ready to put the carb onto your quad is decide what you want to do with the Accelerator pump.

In a nutshell... with a carb as soon as you snap the throttle open the engine gets a rush of air but the fuel does not come as quickly and the engine would go lean and bog down. The purpose of the accelerator pump is to squirt a direct stream of fuel into the engine as SOON as the slide opens to keep up with the air. The issue a lot of people have with the FCR carbs is that they bog from a slow idle to WOT when slapped open quickly. This is because the spring on the AP linkage does not move as fast as you can open the throttle so the fuel is not being squirted into the engine quick enough, which can be "fixed" a handful of different ways. This thread on thumpertalk AP MOD goes into a lot of detail about a mod that wires the AP Linkage to the throttle linkage.

Everyone has their own preference on if this mod is for them or not. I decided not to do this mod until I feel I need it. So for now I did what the manufacturer recommends and timed the AP Shot. This is simply done by adjusting the screw on the AP Linkage to shoot the stream of fuel as close to slide as possible without hitting it.

To do this set your gas tank on a bench and sit just beneath it.
- Hook the fuel line to your carb and turn the fuel on
- Hold the carb with the air filter side facing you and turn the throttle with your right hand. You should see a stream of fuel shoot about 6 feet in front of you.
-Turn the screw on the AP Linkage mod out a quarter turn at a time until the fuel hits the slide when you open it. Then turn it back in 1/8 of a turn at a time until the fuel no longer hits the slide when you open the throttle.

Simple enough right? Now youre ready to mount it onto your bike. Start on the head side and work your way back. If you try to start at the air box you will have a much harder time because you have less room to work with at the head. Cut your fuel filler neck to about 2 3/8" and fairly even. Here is a picture of how mine ended up looking after many different cuts and new pieces.



Dry fit your carb onto your head, you want the black plastic cap for the hot start to just barely clear the headstay (top motor mount). I found it easier to angle it slightly to give the throttle cable more room against the headstay and to be far enough away from the nipple on the black crank case breather box to have enough room to get the hose on.

Here is how mine is sitting.



After you get your carb where you want it, clamp it down tight. There are different ways of modifying the stock air box, but I just cut a hole on the upper left part of the air box big enough for the 400ex boot to fit through with the hose clamp around it. You dont want to kink the boot over the frame so you will need to cut the whole as high as you can without having the filter come into contact with the seat. I cut out plenty from my air box and then went back and filled the open space in to get a tighter fit.



I then cut the 3" muffler pipe to the exact length to have the filter sit flush against the 400ex tube. I put a slight angle on the cut to keep the filter from pointing up too high so that it would not hit the seat.



Clamp everything together and tighten it down. Make sure the filter isnt touching anything, check the sides of the air box, the back, and the original filter mounting hump on the bottom of the box.



The throttle cable is pretty self explanitory, just clamp the thumber onto the same spot as the old one and run the cable the same way. Adjust the cable by holding the throttle wide open and then adjusting the cable at the thumber to where the thumber bottoms out in the housing at the same time that the slide is open all the way.

If your jetting is close the bike should fire right up. But youre not finished yet, you wont experience the full upgrade until your jetting is dialed in. Mine was close, my oringal guess was a little rich due to my altitude but finally settled on a 158 main with a 40 pilot and 5th clip on the NCVQ Needle and 3/4 of a turn out on the fuel screw. I will have to order a smaller pilot jet because 40 is the smallest I have but maybe as this filter gets broke in it will lean out on the idle. The Main and needle are perfect though at 4300 feet.

I would recommend this mod to anyone who doesn’t have it yet. I was very impressed with the increased power. It pulls hard throughout the entire range much harder than before.
 

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Nice write up! I think i might be getting another one soon. I couldnt get the bog problem out so i traded it for my bbk.
 

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Nice........how did your idle cable hole end up too big? Wrong tap?
 

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Discussion Starter · #4 ·
Nice........how did your idle cable hole end up too big? Wrong tap?
I believe the tap was right, but I didn't use a long enough drill bit. Once the nose of the drill hit the base of the carb it egg shaped it out.
 

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Discussion Starter · #5 ·
Nice write up! I think i might be getting another one soon. I couldnt get the bog problem out so i traded it for my bbk.
Thanks, it seems to me that if you have everything set up right the "notorious fcr bog" will only happen on the stand. If yours was that bad you must have had other problems in the carb like the the ap timing being too far off, a bad diagragm, or maybe a plugged ap nozzle. You have an awesome quad pulido I think you would really be impressed with it.
 

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Omg this rgt up just changed my mind about putting my fcr on my quad. I have the 40 fcr but I am sure I can figure it out. I was seriously ready to sell it
 

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I believe the tap was right, but I didn't use a long enough drill bit. Once the nose of the drill hit the base of the carb it egg shaped it out.
what scared me is how much you paid for it .way way to much
 

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Discussion Starter · #8 ·
what scared me is how much you paid for it .way way to much
Haha napa had to special order it so I had to pay shipping on it... and that's nothing, fastenal wanted $35 for it.
 

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Nice write up man! This is gonna help me out a lot when I got to do This mod!
 

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i cant even imagine snapon charging that much
 

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yeah they just break in a spot thay you really don't want them to. Talkin from experience
 

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i cant even imagine snapon charging that much
Snap-on doesn't even make that tap... I tried to get one from my dealer... no dice.

I did however find one on amazon for $5-7. Used it and passed it on.
 

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I believe the tap was right, but I didn't use a long enough drill bit. Once the nose of the drill hit the base of the carb it egg shaped it out.
i do understand what happened to you when drilling the hole .my self i took the carb body apart to get a better angle on were the hole has to be. not really recommended because theres a gasket that if damaged its rather expensive to replace.


i would also like to suggest a spring mod to lighten the thumb pull on the throttle
 

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Discussion Starter · #14 ·
Yeah, I noticed that gasket didnt come with the kit. I checked every oem part listing I know and couldnt find any that sold that gasket. I pulled mine apart when I went through and cleaned and found that gasket shrunk. I soaked it in hot water and used some weatherstripping adhesive to make it stick in place while I bolted it back together. As for the spring mod, I believe this carb came with it because there was a heavier spring in the bag with the jet kit. It feels like butter with the 400ex thumber.
 

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Discussion Starter · #16 ·
Awesome, thanks for the link.
 

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Discussion Starter · #17 ·
I ordered a 38 Pilot Jet so I will see if that feels better. I ran a hare scramble today and placed 2nd in the B class :cool:. But I can tell that the pilot jet was still too big, especially when I went up to to 5200 feet for the race. I couldnt turn the fuel screw in far enough to even change the exhuast note.
 
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I egged my hole out when the my drill hit the carb housing. Anyone figure out a different way to make the hole without splitting the carb? I'm guessing just a long drill bit? what about the tap?
 

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yeah go to post 13 . note there is a way to take more of the carb part . just be carful of the gasket .a new one is like $35
 

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I would rather not risk destroying the gasket if I could, was wondering if there was any other way before I removed the half of the carb. (and had to find my security allens)
 
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