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Fellas,

 

I just purchased a 2013 DRZ400SM, I'm new to these forums. I did some searching but it lead to more confusion than anything.

 

I'm having a problem with exhaust popping (backfire) when decelerating. I thought it was normal (from what I read) but it's really sharp and quite obnoxious at times. It just can't be normal, or at least I don't think it is. Also, at half to full throttle it'll have a slight stumble\hesitation, especially when I open the throttle fast. I think this is because of a rush of air into the carb but not sure.

 

I live at an elevation of 5435 ft. The bike is 100% stock, so I think the current jets are 142.5 main jet and a 22.5 pilot fuel jet. Please correct me if wrong on that.

 

Can anyone guide me on how to fix the backfire and stumble at half to full throttle? Should I change the jets or adjust the needle?

 

Many thanks,

 

-bryce

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Crago & Wisconsin are the jetting guru's, they will get you dialed in. 

 

I gave up on the OEM carb and went FRC39 from the TT store.

 

The OEM carb leaves a lot to be desired even with the JD jet kit.

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Your bike is completely stock....100% sure..??....The altitude you are at is more suited to the stock jetting than at sea level...

So I am thinking that the carb may not have the stock needle and main jet...Is it possible to contact the PO to see if they jetted for higher altitude?

If you can't, you will need to physically check what the current set up is...

Edited by Craig-o

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plus 1 on what craig said. check that the 3x3 mod hasn't already been done, it may have been modded but no jetting to suit. try riding it at night and see if the backfire shoots out a small flame, this will indicate the jetting is way too rich

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Alright, so I confirmed that it is in fact still 100% stock. I just bought the bike, it had 0 miles on it.

 

So I thought I would just take it back to them and have it looked at.  This is what they did

 

Technician Notes:

Verified issue, found pilot jet was clogged, cleaned pilot jet/circuit, adjusted needle, no main jets in stock could not rejet at this time, still backfires (Very Minor).

 

I asked them what size mainjet they wanted to install, they wanted to take the stock size down from 142.5 to 130. That's about an 8% decrease and they said this was typical coming from sea level over to the Denver area. I'm a little upset the pilot jet was slightly clogged since it was a new bike but I guess this happens from sitting around?? Luckily, they did not charge me for this work since I just bought the bike but did want to charge me 175$ to do the jetting.

 

I did not want to pay these jokers to simply change the jet, I'll just do it myself.

 

Does 130 seem too small to you guys? I would really hate to run lean...

 

 

 

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So lets follow what they say they did......

 

They had the carb out , cleaned the pilot jet ,re installed it.... 

Wanted to put in a 130 mj ....didn't have one in stock...

so reassembled carb without waiting for a mj to order in..Now want to charge you $175 to remove the carb and fit this 130mj, which they should have waited for ..... :facepalm:

 

Well there are a couple of things i am not happy with..

Firstly their obvious ploy to rip the customer off..by not waiting for the main jet..

How they say they adjusted the needle, as the US models don't have needle adjustment..

The main jet has nothing to do with the backfire on decel..

Backfire is generally related to air air leak in the exhaust system....

Popping on decel is related to the setting of the fuel screw, NOT the main jet...

 

So how is it running now that the pilot jet was cleaned?

 

Ethanol fuel is known to clog fuel jets, use NON ethanol fuel if possible.. 

Edited by Craig-o
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So lets follow what they say they did......

 

They had the carb out , cleaned the pilot jet ,re installed it.... 

Wanted to put in a 130 mj ....didn't have one in stock...

so reassembled carb without waiting for a mj to order in..Now want to charge you $175 to remove the carb and fit this 130mj, which they should have waited for ..... :facepalm:

 

Well there are a couple of things i am not happy with..

Firstly their obvious ploy to rip the customer off..by not waiting for the main jet..

How they say they adjusted the needle, as the US models don't have needle adjustment..

The main jet has nothing to do with the backfire on decel..

Backfire is generally related to air air leak in the exhaust system....

Popping on decel is related to the setting of the fuel screw, NOT the main jet...

 

So how is it running now that the pilot jet was cleaned?

 

Ethanol fuel is known to clog fuel jets, use NON ethanol fuel if possible.. 

 

 

It is running better now, the main jet clog must have been why it had that stumble upon giving it full throttle from a stop.

 

I agree that it seems like a scam to get the customer to come back and spend more money. I'm sure they make a lot of their revenue from the service department. I didn't leave too happy...

 

Yea, all I can get around here is gas with a 10-15% blend of ethanol. Good chance that was the culprit.

 

There is still a backfire but not quite as bad. They mentioned that this carb s a constant velocity carb and that it should adjust itself? I'm curious about going all the way down to a 130 mj, wonder if that would be too lean but I have no way to tell if it's hitting STOICH or not. Could install a wideband, lol, that might be overkill.

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There is still a backfire but not quite as bad. They mentioned that this carb s a constant velocity carb and that it should adjust itself? I'm curious about going all the way down to a 130 mj, wonder if that would be too lean but I have no way to tell if it's hitting STOICH or not. Could install a wideband, lol, that might be overkill.

 

Well ...a vacuum carb does base slide lift on incoming air so atmospheric conditions do have some influence on jetting....

 

If you get any surging or high rpm misfire is a good indicator that your harming your engine by being too lean......

 

I know your  at altitude and have stock air intake, but even still, I am not happy with the fuel delivery of the stock needle..

 

1),,The needle controls mid throttle settings which you mostly ride in...2).Main jet is working at 3/4 to WOT....2 different fuel circuits and must be tuned separately

 

Correcting the main jet is only a part solution, I would be thinking at least a 135mj with your set up..

 

A JD Jet kit with the 3x3 mod would be a worthwhile investment...and would be a total solution... :)

Edited by Craig-o

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I suggest jetting it for sea level and installing an oxygen tank on the DRZ. Hey. ..I bet we could market those. .lol

Edited by GreenHornet450

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Well ...a vacuum carb does base slide lift on incoming air so atmospheric conditions do have some influence on jetting....

 

If you get any surging or high rpm misfire is a good indicator that your harming your engine by being too lean......

 

I know your  at altitude and have stock air intake, but even still, I am not happy with the fuel delivery of the stock needle..

 

1),,The needle controls mid throttle settings which you mostly ride in...2).Main jet is working at 3/4 to WOT....2 different fuel circuits and must be tuned separately

 

Correcting the main jet is only a part solution, I would be thinking at least a 135mj with your set up..

 

A JD Jet kit with the 3x3 mod would be a worthwhile investment...and would be a total solution... :)

I think I'd like to jump straight to the 39MM carb with a 3x3 mod. What jets would you suggest for this?

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What exhaust system are you going to use?

 

That's something I haven't investigated. Would like to keep stock so the sound isn't obnoxious but from everything I've read I'll need to open the exhaust.

 

Any recommendations for good performance and noise control?

 

 

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