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MattHman

Quiet exhaust and power loss w/ minor elev. change

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I bought my first motorcycle a few weeks ago. A DRZ400 sm with 6100 miles. Its got an RS-2 with spark arrestor, 3x3 mod, although it’s more of a 3x4 mod, for whatever reason. I’m assuming it’s been jetted since it seems to run pretty well other than the issue I’m having. The bike always starts right up with choke, and sometimes without.   

When I go to the nearby twisty roads and reach an elevation of around 1300 ft the bike gets noticeably quiet and loses power. I’m typically at 200 ft above sea level, which is similar to the original owner who had the work done. Unfortunately, I’m not in contact with him since I’m the third owner. The bike is pretty loud down here at 200 ft. To the point where I’m a bit concerned for my neighbors. By the time I reach 1300 ft, it sounds like a scooter, and stays that way until well after I have returned to my typical elevation.  From what I have researched on TT, going up in elevation makes the bike run richer, but an increase of 1100 feet should not cause such a noticeable difference in performance. This is probably a jetting issue right? I’m considering either re-jetting the BSR36, or just getting an FCR39, which I would eventually do anyway.  Is there anything I can do to troubleshoot or should I just go ahead with one of those options?

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These motors are jetted pretty lean from the factory and if you don't know for sure that the carb has been rejetted from what you describe the PO may have slapped on a free flowing pipe and did a 3x4 and not necessarily rejetted the carb at all.That would make the bike run way lean and down on power when going uphill.Sea level jetting should work fine until about 4-5,000 ft elevation.

As a test you may want to install the rs2 spark arrestor and tape off the 3x4 hole in the airbox and take it for a test ride and see how it does.If it runs better it will confirm it's too lean.Otherwise it's best to pull the carb out and write down the jetting(main,pilot,needle,clip position,turns of the fuel screw,float height,etc).

Edited by bumtarder

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I taped up the hole, tried to start the bike and it didn't start. Then it dawned on me that there should be at least some kind of opening, otherwise the motor is getting no air, right? I peeled off a third of the tape, didn't start. All the tape. Didn't start. In the end I had to open up the throttle to start it. I think I flooded it. Anyway, the airbox should have some kind of opening right? Roughly how big should it be to replicate a stock airbox?

 

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Correct me if Im wrong (I live in the flat part of Ohio) but doesn't an engine run richer as you go up in elevation? Taping the box if it is already rich, would aggravate the situation.  I'm going to put my chips on that it is on the verge of being too rich at sea level and 1100" is just enough to push it over the edge.

Instead of taping up the box, remove the airbox door and see what happens.

To answer your question about the box, yes, the engine has to be able to take in air in order to run.  

It's hard to remember but I think the stock opening is something around 1.5 x 2.5 with the snorkel removed.

There is a possible cheat to tell if it was jetted without opening up the carb. The JD kit comes with Allen heads to replace the JIS screws on the float bowl. An adjustable fuel screw or the brass plug being removed are good indicators too.

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14 hours ago, ohiodrz400sm said:

Correct me if Im wrong (I live in the flat part of Ohio) but doesn't an engine run richer as you go up in elevation? Taping the box if it is already rich, would aggravate the situation.  I'm going to put my chips on that it is on the verge of being too rich at sea level and 1100" is just enough to push it over the edge.

 

Dude I was so hoping you were finally going to be wrong; alas, you are correct again. Hahaha.

But, it takes a ton of elevation difference for a bike to go from running to not running. I live at 1500' ASL and have my bike jet for that elevation, and because I live at the base of the San Gabriel Mountains virtually all my off road rides take me to 5000' ASL or higher and my bike never struggles to start. 

Edited by ptgarcia
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1 hour ago, ptgarcia said:

 

Dude I was so hoping you were finally going to be wrong; alas, you are correct again. Hahaha.

But, it takes a ton of elevation difference for a bike to go from running to not running. I live at 1500' ASL and have my bike jet for that elevation, and because I live at the base of the San Gabriel Mountains virtually all my off road rides take me to 5000' ASL or higher and my bike never struggles to start. 

And there you have it. Sadly, the pain and joy of having elevation screw up the tuning is a problem I may never experience. 

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I went ahead and put an FCR39 MX kit in, w/ JD jet kit (Red needle #4 groove, #160 MJ, #42 Pilot, 2 turns fuel screw). Bike runs great, but the volume changes are almost identical to the stock carb. When I get to the same spot on my daily ride up the twisties, I notice that the bike is a whole lot quieter. I'm at a loss. It's so weird. I don't think the bike performs worse, just quieter, and I'm curious what the cause could be. I do have the spark arrestor in, and I wouldn't be surprised if Yosh muffler hasn't been repacked since 2013.

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51 minutes ago, MattHman said:

I went ahead and put an FCR39 MX kit in, w/ JD jet kit (Red needle #4 groove, #160 MJ, #42 Pilot, 2 turns fuel screw). Bike runs great, but the volume changes are almost identical to the stock carb. When I get to the same spot on my daily ride up the twisties, I notice that the bike is a whole lot quieter. I'm at a loss. It's so weird. I don't think the bike performs worse, just quieter, and I'm curious what the cause could be. I do have the spark arrestor in, and I wouldn't be surprised if Yosh muffler hasn't been repacked since 2013.

Your ears may be blocking up at a certain elevation.

Or the ambient surroundings may change at that particular point and be soaking up the sound.

Pics please.

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18 hours ago, Tony Wyp said:

Your ears may be blocking up at a certain elevation.

Or the ambient surroundings may change at that particular point and be soaking up the sound.

Pics please.

The ear thing crossed my mind. I'm not even going up high enough for my ears to pop, but maybe the fact that they don't pop is what causes it. I also notice the difference even with my ear plugs in. The surroundings are an interesting thought. Less objects for the sound to bounce off of or something.

It really sounds like the motorcycle is changing, but who knows, it could be as simple as the environment's effect on the sound. I'll probably just put it in the back of my mind for now, and ride some hills in other areas to see how the engine reacts. 

Pics of the area? 

 

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1 hour ago, MattHman said:

The ear thing crossed my mind. I'm not even going up high enough for my ears to pop, but maybe the fact that they don't pop is what causes it. I also notice the difference even with my ear plugs in. The surroundings are an interesting thought. Less objects for the sound to bounce off of or something.

It really sounds like the motorcycle is changing, but who knows, it could be as simple as the environment's effect on the sound. I'll probably just put it in the back of my mind for now, and ride some hills in other areas to see how the engine reacts. 

Pics of the area? 

 

Yeah, area pics 🙂

You must be hyper- sensitive to your engine  😀

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