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Carb noob

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So I've worked on quite a few cars, but everything I've worked on has been fuel injected. Now I have a DRZ400 obviously with a carburetor. The previous owner supposedly installed a keihin 39mm (IIRC) FCR carb. I know it's a keihin and seeing as it's a DRZ400-S which should come with some other brand of Carburetor, I'm assuming he did some kind of swap, but I don't know anything about them. I don't know if it's an FCR, or if it's 39mm or 40mm, or what. I do know that I installed a K&N Filter and a straight through exhaust, and it has a big bore 440cc kit, and it is backfiring a bit on deceleration. I'm thinking I'm gonna have to re-jet the carb, but I can't just order a jet kit for the stock carb. Can anyone tell me how to find out what carb model I have? Here is a picture (The numbers appear to be 2S21 OOTJ27)

20141004_123226.jpg

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It is a FCR 39, pirated off another bike. You need to look in it to see what needle, pilot, main jet you have.

Your decel pops are because you no longer have a muffler. Loud accelerating, loud slowing down.

 

You'd be better off with a foam filter and not the pleated cotton K&N (which is a street only filter)

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Also check your muffler packing the decel pops are louder when the packing is almost gone. Decel pops are are fairly normal by the way I'm not sure why people get excited if the bike runs properly. Going up on the pilot usually helps but may not even be necessary. But it will still pop just maybe a little less.

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It is a FCR 39, pirated off another bike. You need to look in it to see what needle, pilot, main jet you have.

Your decel pops are because you no longer have a muffler. Loud accelerating, loud slowing down.

 

You'd be better off with a foam filter and not the pleated cotton K&N (which is a street only filter)

 

Thank you, now I know it's an FCR carb. The decel pops Im talking about aren't just the pops the new exhaust makes, it's actually backfiring. For the K&N, I am riding only street right now, I have supermoto wheels and tires on it. I have saved the foam filter, so I will use that if I swap out to the dirt tires for a weekend off the pavement.

 

Also check your muffler packing the decel pops are louder when the packing is almost gone. Decel pops are are fairly normal by the way I'm not sure why people get excited if the bike runs properly. Going up on the pilot usually helps but may not even be necessary. But it will still pop just maybe a little less.

 

That would be a good suggestion, but the exhaust is brand new. I bought it brand new, and installed in on Thursday. Part of the reason I'm thinking it needs re-jetting is that it seems to hit a flat spot where it doesn't matter how much more throttle I give it, it does not make a difference. I haven't taped out my throttle positions to see exactly where it is, but it's somewhere between half and 3/4 throttle, probably closer to 3/4 where it does not have any more to give. So I'm wondering if maybe the pilot jet is a little small which is causing the decel backfires, and it might need a slight bump in the main jet to get rid of that early top out.

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Thank you, now I know it's an FCR carb. The decel pops Im talking about aren't just the pops the new exhaust makes, it's actually backfiring. For the K&N, I am riding only street right now, I have supermoto wheels and tires on it. I have saved the foam filter, so I will use that if I swap out to the dirt tires for a weekend off the pavement.

 

 

That would be a good suggestion, but the exhaust is brand new. I bought it brand new, and installed in on Thursday. Part of the reason I'm thinking it needs re-jetting is that it seems to hit a flat spot where it doesn't matter how much more throttle I give it, it does not make a difference. I haven't taped out my throttle positions to see exactly where it is, but it's somewhere between half and 3/4 throttle, probably closer to 3/4 where it does not have any more to give. So I'm wondering if maybe the pilot jet is a little small which is causing the decel backfires, and it might need a slight bump in the main jet to get rid of that early top out.

 

Yes that should give it a good shot. It's also easy enough to change or redo at will.

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You probably need a larger pilot jet for that decell BF, but you could try lowering the needle clip one position first. Needle will probably help the hesitation. +1 on loose the K&N, get a uni or such. Change one thing at a time.

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So now the question is, what jets do I buy?

 

You have to find what's in there, what's wrong, and go from there. You can also order an array of jets. Rocky Mountain has good prices and you can get a good handfull of jets for $30 or less. If time is a big concern, just order 4 or 5 of each, in single steps richer than what you have. Costs less than the kits that don't work. Get the $3 third party jets, they are good.

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You probably need a larger pilot jet for that decell BF, but you could try lowering the needle clip one position first. Needle will probably help the hesitation. +1 on loose the K&N, get a uni or such. Change one thing at a time.

 

 

You have to find what's in there, what's wrong, and go from there. You can also order an array of jets. Rocky Mountain has good prices and you can get a good handfull of jets for $30 or less. If time is a big concern, just order 4 or 5 of each, in single steps richer than what you have. Costs less than the kits that don't work. Get the $3 third party jets, they are good.

Thank you for the suggestions, when I get time, I will pull the carb, check what jets are in there, try the needle clip adjustment, and if that does not do enough, then I will order up a few jets. 

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No problem! Be sure to use a screwdriver that fits the slotted jets real well, or the soft brass slot strips right out.

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