DRZ400SM - FCR 39

[arbakken]

So, the good news! I just bought a 2005 DRZ400SM. It has stage 1 hotcams, pro circuit t4 exhaust, holes drilled in the side of the filter cover (instead of 3x3 mod? don't ask me) and a FCR 39 carb. And it was professionally installed and tuned! I absolutely love riding the thing, it's the most fun I've had on 2 wheels. It seemed like it rode really well when I test rode it, but after a week of riding it around, I can tell the carb isn't quite adjusted right. So, to figure out my baseline and see what jets and such were in it, I took it out.

 

So, the bad news! It's the wrong fricking carb. It's a FCR 39 alright, but it's got the fixed bell, the throttle hookups are all messed up (I'm not honestly sure how they installed the cable on the push side). So this also means that the main and slow air jets will never be right. It was kinda jerry rigged in there with radiator hose. Here are pics, I think its from a yzf450. (I don't know why some are sideways... thanks photobucket)

 

 

I do have the stock carb, but... well... no. So what are my options? Buy the correct carb i guess. Does the TT FCR 39 MX kit have the hot start and air cutoff valve? Is there any reason I wouldn't want both of those things? Can that kit be adjusted properly for 4500 ft with above mods (replacing holey side cover with proper 3x3 mod)

[Craigo]

The OP in this thread may be able to help you out with a bell adapter...https://www.thumpertalk.com/topic/1089064-old-fcr-carb/page-2#entry11672473

He has the same carb.......as with his, your carb won't have a main air jet, just the fixed open hole...

Jetting =

for 4,500K with 3x3 mod, open pipe

155 main jet

OCEMP needle, clip 3

45 pilot jet

O ring mod with wire

2 turns fuel screw

 

 

[arbakken]

Another question: Can I mill off the intake bell to take a removable (proper) bell? Are the air jets located in the intake bell? Does anyone have pictures of the proper fcr with and without intake bell attached? Pics of intake bell?

 

I'm already assuming I can mill off the cast throttle cable tower and bolt on a proper cable mounting bracket.

 

Thanks!

[OverSquareEng]

Another question: Can I mill off the intake bell to take a removable (proper) bell? Are the air jets located in the intake bell? Does anyone have pictures of the proper fcr with and without intake bell attached? Pics of intake bell?

 

I'm already assuming I can mill off the cast throttle cable tower and bolt on a proper cable mounting bracket.

 

Thanks!

 

The air jets are in the carb itself under the intake bell, not inside the intake bell.

[arbakken]

The OP in this thread may be able to help you out with a bell adapter...https://www.thumpertalk.com/topic/1089064-old-fcr-carb/page-2#entry11672473

He has the same carb.......as with his, your carb won't have a main air jet, just the fixed open hole...

Jetting =

for 4,500K with 3x3 mod, open pipe

155 main jet

OCEMP needle, clip 3

45 pilot jet

O ring mod with wire

2 turns fuel screw

 

So, I cracked open the carb, and here were my settings:

158 main jet

OCEMN needle, clip 3

45 pilot jet

O ring mod (but fell off)

1/4 turn fuel screw (red, aluminum, assembled incorrectly... screw, washer, spring, oring)

100 pilot air jet

72 some other jet (starter jet? slow jet?)

 

so, that's interesting, huh?

[arbakken]

The OP in this thread may be able to help you out with a bell adapter...https://www.thumpertalk.com/topic/1089064-old-fcr-carb/page-2#entry11672473

 

Well, I decided to help myself. Busyness delayed it for a month, but I made a thing:

 

 

 

I have a lot of trouble half-assing things, and this thing was kind of a pain to make. I'll upload the drawing later in case anyone wants to follow, but it pretty much requires a CNC mill to mill out the off center hole. The rest was easy on a manual lathe. I'll let the RTV dry for a day and install this weekend. I'm also adding a OCEMP needle and a flexjet, and I 'fixed' the holes in the side cover of the airbox and cut the correct hole in the top. I can't wait!

Edited July 11, 2014 by arbakken

[Stuwy123]

I understand the reasoning for the holes for the main air jet and pilot air jet but why wouldn't you oversize the hole so you can take the jets out.

I just made a straight adapter, crude but effective.

Check your leak jet. If the carb came off a yzf450, you'll have the wrong size leak jet. Get a #35 from sudco.

I'm in the same boat. Trying to get the most performance out of this carb.

I ended having to pick up a handful of jets (main, pilot, and leak) and needles. I haven't received all the parts but I'll keep ya posted. I like to try to fine tune carbs to get the most out of them. This fcr carb should be more of a challenge then the stock mikuni.

[Stuwy123]

I took the pilot air jet of my carb and ended up with some serious popping on decel.

Nothing too bad but compared to the almost zero popping with the pilot air jet in.

[arbakken]

I understand the reasoning for the holes for the main air jet and pilot air jet but why wouldn't you oversize the hole so you can take the jets out.

I just made a straight adapter, crude but effective.

Check your leak jet. If the carb came off a yzf450, you'll have the wrong size leak jet. Get a #35 from sudco.

I'm in the same boat. Trying to get the most performance out of this carb.

I ended having to pick up a handful of jets (main, pilot, and leak) and needles. I haven't received all the parts but I'll keep ya posted. I like to try to fine tune carbs to get the most out of them. This fcr carb should be more of a challenge then the stock mikuni.

 

The holes ARE oversize so I can take the jets out! Which one is the leak jet, is that one in the bowl?

[arbakken]

Check your leak jet. If the carb came off a yzf450, you'll have the wrong size leak jet. Get a #35 from sudco.

 

Mine is a #55

[Stuwy123]

Gotcha. Just the slightly blurred pic makes them look small.

And now that I'm not half asleep I can see what you mean by the off-center bore.

Pretty fancy piece.

 

The bike will run with the carb as is. It won't be 100% but it'll run and you'll feel the boost in power (low end and top end).

I would suggest getting a RD Racing flexible fuel mixture screw or at least an adjustable fuel mixture screw.

These FCR carbs really need to be tuned with the mixture screw.

 

You can run the fuel petcock on "PRIME" if you didn't buy the vacuum port nipple ( P/N 13685-29F00 OEM Suzuki Vacuum Port Nipple).

It works. You won't have reserve if you run on "PRIME", you will have the entire tank at your disposal without having to switch to reserve. 

[arbakken]

Gotcha. Just the slightly blurred pic makes them look small.

And now that I'm not half asleep I can see what you mean by the off-center bore.

Pretty fancy piece.

 

The bike will run with the carb as is. It won't be 100% but it'll run and you'll feel the boost in power (low end and top end).

I would suggest getting a RD Racing flexible fuel mixture screw or at least an adjustable fuel mixture screw.

These FCR carbs really need to be tuned with the mixture screw.

 

You can run the fuel petcock on "PRIME" if you didn't buy the vacuum port nipple ( P/N 13685-29F00 OEM Suzuki Vacuum Port Nipple).

It works. You won't have reserve if you run on "PRIME", you will have the entire tank at your disposal without having to switch to reserve. 

 

Lol, the pictures are pretty blurry. I took them when I was half asleep!

 

I already bought and will install a RD racing flexible mixture screw. I know it will help because the old one was installed incorrectly and only 1/4 turn out. The bike already has a vacuum port nipple on it. What will the leak jet do?

Edited July 11, 2014 by arbakken

[arbakken]

So, I finally got it installed, and it was kind of a PITA. It does fit, but barely. The thing freaking rips now, and seems to run perfect. I suspect the main jet is a tad bit large, but barely. I'm sure most of the ridability gain was due to the mixture screw and the settings it is now at, but it runs great!

[arbakken]

Bumping my own thread. Bike runs good, but I've always kinda thought it was a bit rich. I had just nominally set the flex jet 2 turns out previously. I went through the idle mixture screw adjustment procedure, and with the screw all the way in, the bike still doesn't stumble. Might be richer than I thought. Is the leak jet the culprit? Pilot jet too big?

 

It's worth noting (probably) that I've never once used or needed the choke...

Edited August 26, 2014 by arbakken

[Craigo]

No reaction to fuel screw turned fully in, go to next size smaller pilot jet

[arbakken]

No reaction to fuel screw turned fully in, go to next size smaller pilot jet

 

Just one smaller, or a couple?

[Craigo]

Just one smaller, or a couple?

 

1 size smaller should be sufficient 

[Stuwy123]

Glad to hear the carb rips for ya.

Same here.