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No Cost DR650 Jetting Upgrade – Phase I -Backward Tuning

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Well I thought I would share my jetting experiment in an attempt to pay back in a small way for all the great information I have picked up on this site. This is going to be long and different than the conventional wisdom so please bear with me. But in the end, I have much more power than stock, smother running engine and today, I got 52 MPG when I filled up after some easy back road riding. And the best part is it was all free. OK free if you don’t count my time.

The bike is a 2008 DR650 with about 4,000 miles when I started and the only other performance mod so far was grinding down the weld in the exhaust pipe. (Another great free mod!) I am in Florida near Orlando so the elevation here is just above sea level.

OK first off some of my theories:

1) The biggest thing holding the DR650 engine back is the air box.

2) The next biggest issue is the jetting. – Nothing controversial so far.

3) The larger the air box opening, the lower the pressure drop from carb vacuum and the larger the jets required to maintain correct AFR. And more airflow needs more fuel.

4) Trying to tune by throttle chops and plug color with modern gas is a complete waste of time. Worked good back in the day on our 2 stroke MX bikes but not with modern 4 strokes and modern gas. The gas burns too clean and there is way too little difference between a little rich and a little lean for my eyes to see anything. My plugs always come out gray until WAY to rich or lean. By the time I can see something on the plug, I already know the issue by the horrible way the bike runs.

5) As you jet toward too lean, you will notice performance issues long before you damage the engine. (unlike the old 2 strokes) Most amateur tuners (like me) are afraid of burning up the piston so they inevitably end up on the too rich side. The bike runs fine but gas mileage sucks. The best needle position is the lowest (leanest) that will run clean with no surging or roughness at low RPMs.

6) A correctly jetted bike with mods should return about the same MPG as a unmodded bike when driven at the same power level. Maybe even better. Yes it can make more power and if you ride it wide open a lot mileage will suffer. The biggest problem is that it is hard to ride slow when the bike is running so good!:smirk:

7) The engine will run well enough to feel about the same to the rider over a wide range of Air/Fuel Ratios (AFR). This makes it very difficult to get spot on by seat of the pants tuning. Especially with the overlapping zones of control between the main jet, needle, and pilot jet. The only way to be really sure is with an AFR meter with a wideband O2 sensor. (Phase II) But you can get close by using the testing methods listed below.

8) For the main jet, the best size is the one that gives max power.

9) The Stock needle will work just fine if shimmed correctly. It has almost the same profile as the KTM and Factory Pro. See: http://www.thumpertalk.com/forum/garage.php?do=viewattachment&attachmentid=35683 But with the air box open, it needs a big shim. A washer or two will not get it done.

10) The most critical tuning for MPG is the needle setting at about 1/8 to ¼ throttle because that is where we spend most of the time as we cruse down the road. It should be as lean as you can get it and not experience drivability issues like surging.

11) It is much easier to tune the air box to the main jet than to tune the main jet to the air box!

OK enough theory. Let’s talk about the air box.

The stock set up with the snorkel has an opening area of only 1.5” Sq. Just removing the snorkel increases the area by 83% to 2.75” Sq! I drilled four 1” holes in the top of the air box. See picture. IMG-20110420-00064.jpg

Each hole is equal to .78” Sq. (that Pi R Squared thing) .This way I can cover or uncover holes to control the open area and indirectly the vacuum developed in the carb. Each additional open hole (1 to 4) adds progressively smaller percentage increase to the total opening area. That is the first hole adds another 28% for a total of 3.5” Sq. The second adds 22% more for a total of 4.32 “ Sq. ,and the third, 18% for a total of 5.1“ Sq. , and the last 15% for a grand total of 5.75”Sq.

Bottom line is that this setup give me a quick way to adjust air flow for testing with from 1.5 to 5.9 Square inches of opening. And it does not require removing anything but the seat, and having a roll of duct tape to adjust.

Yes you can open it up even more by removing the entire top or cutting more or bigger holes but at this point I can open it almost 4 times bigger than stock so I think we have reached the point of diminishing returns. And I want to be able to tune it.

Now Jets;

The stock Jet is a 140 if remember right. I happen to have a milling machine, numbered drill bit set, and some old jets so I just drilled one out with a #53 which should be about a 152 Mikuni. I don’t recommend this DIY jet drilling but it worked for me. Also as I am adjusting the air box opening to match the jet, it is less critical. Interesting I ended up going up one drill size while tuning and the next size up is a common 1/16”! That should be about a 157 Mikuni by my calculations. But I am getting ahead of myself. For sane people, you can just pick up a 155 or 157.5 Mikuni or both.

Main Jet Tuning

This is the first step and the most critical. For this jet we are looking for the max power at full throttle. A dyno is the best way of course but this is my free method. For start I shimmed the needle to .150” while I tuned to the main jet (just a WAG to get it in the ball park) . I picked a section of country road near the house with no cross roads, driveways, blind spots, and very little traffic. I picked two markers about 1/10th mile apart. This is not critical except you need two clear markers near the edge of the road so you know exactly when you pass them (Sign, Poll, . . .) . The idea here is to measure the WOT acceleration over a short distance in one gear without getting into a dangerous situation. I started in 4th gear at dead on 50 MPH as I passed the first marker, snapped the throttle wide open and measured the speed as I passed the second marker (around 75 or so). Adjust the marker or start speed if you find you are running out f RPM before you get to the second marker. Simple easy and repeatable. Now repeat with one, then two, then three, and finally four holes uncovered. You can make the adjustments quickly on the side of the road or nearby parking lot. Leave the side panels off and you just need a 12 MM wrench and some tape. Record each end speed. If you find you were a little off on start speed or if traffic shows up, no worry, just do it over. You should see one setting that gives a faster final speed than all the rest. That is the correct setting for that jet. With my jet drilled to #53, I got the best time with only hole opened. I then went to the 1/16” drilled jet (about 157 Mikuni) and repeated the test. This time I got the best time with 3 holes open (and the snorkel removed). The bike was running WAY stronger than stock. Snaps the front wheel up in first and if I catch it just right, pulls it up in 2nd for a nice long power only wheelie! :cheers:

Needle Tuning

I used the great information in MX-Rob’s classic Needle thread and a lot of guess work to come up with the initial setting of .150”. My shims are a combination of fiberglass tubing cut to length and small washers for minor tweaks, placed between the clip and the plastic washer. The bike actually ran fairly good that way but MPG was just over 43. I dropped the shim to .130” and things got better. So I tried .100” it seem to run good except it wanted to surge at very low throttle cruse and felt rough below 4,000 RPM. Still strong and good MPG but I could pull in a little choke at a low RPM cruse and it would smooth out so a little lean. I ran it that way for a long time trying for best mileage but it was a bit too lean. So I ended up back at .130 and now the bike runs sweet.:thumbsup: And so far I seem to be getting even better mileage but I was particularly well behaved on the last tank! Not normal. :bonk:

Pilot jet

This should be just the normal adjustment drill. I don’t have Jessie’s extended adjustment screw so it is a bit of a PIA. For now I have it set to 1 ½ turns out and it seems to be fine. I will fool with it in stage II.

So there you have it. Cost to implement, Zero dollars. Satisfaction of having a much stronger smother running bike. Priceless. :lol:

So I should be happy and leave it alone now right? Not! The engineer in me will not let that happen! On to phase II! Now I want to know how well this process worked and how close I got the ideal AFR. And do I want to play with needle tapers? Can I find more “free” power? So I ordered an AFR meter with wideband O2 sensor. (So much for free tuning!:thumbsup:) It should be here this weekend. Once I get installed and sorted out, I will post the results.

Hope you all find some of this useful. OK Flame away!:lol:

John

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Whew! Now that's a post!:thumbsup: I read through that and got most of it. I'm a noobie on the stock BST carb, but I am studying it and the air box mods. Got a spare BST-40 on hand with jet kit. I only need another DR650 to tinker with.:thumbsup: I pulled the snorkel out of my 09 DR and it runs great. It's gonna stay stock; would'nt want to mess anything up, hence the search for another used DR. For me it was a good read, and looking forward to your next post with the AFR meter. I don't have the bucks for the FCR/pumper carb, but having an extra stocker and jet kit is enough for me to learn about it and save up for another DR. Rather have a whole extra DR650 on hand than a high dollar carb (though all I've read about the pumper carbs is that it blows away the stock BST). I'm not in a hurry and love riding the stock DR:ride:

rc.

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Great post!!, am I right in thinking you've only got one clip position on your needle?, my DR is a 92/93 model and there are 5 clip positions so I assume I can just move the clip.

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The US DR650se's don't have the adjustable clip. Pretty much the rest of the world does.

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+1 on what NordieBoy said.

Thanks, for the kind words Guys!

RC, if I understand your post, you have the snorkel removed but have not shimmed the needle. I would expect that with the snorkel removed you would find it would run much better with about a .040" shim (small washer or two). Unless you are at high altitude, the bikes normally come lean in the mid range from the factory and removing the snorkel should make it even leaner. But the main comes a little rich so you should not need to change that. Don't worry about messing things up, shimming the needle can only make it richer and will not hurt the motor in any way. In fact, it should make it run smoother and stronger as well as cooler. All good! And it is easy to do because you don't have to remove the carb to get to the needle. Just loosen the front and rear clamp and rotate the carb enough to remove the cap. One trick is to take off the tie wrap that holds the throttle and choke cables to the frame just above the head so you have enough slack to allow the carb to rotate. If you don't see an improvement or if MPG takes too big a hit, no worry, just take the shim back out. No harm no fowl.:thumbsup:

Well my AFR meter just got here so I am going to get to work welding in a bung and then I can hook up the AFR meter and see how it works !! :thumbsup:

John

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Interested to see your results. Based on a combination of some dyno work and seat of the pants, I am running a bigger main, DJ 160, and lower needle, second from top, than most people. Which I think is similar to your philosophy. My bike is stock with the exception of the open airbox and DJ jet kit mods.

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Hey jaeger22, yes, I pulled the snorkel out last year. Earlier this year I put it back in and it started running rough; sputtering at idle, low speed and all the way to highway speeds at 75-80 mph. Pulled it back out and it runs fantastic. I don't know why. It made it through the hot Arizona summer just fine last year. I don't really want to mess with this stock bike, that's why I bought the extra BST-40 to study with the BST Bible in pdf. Also, that's why I'm saving for a used DR. I'm tempted to just r&r the BST and swap it out with the pre-jetted (155 main) carb and drill some holes in the airbox top. However, I'm not real comfy tinkering with a great running bike. Also apprehensive about touching the stock carb. Like I said in the other post, I'm not in a hurry. Love riding this 09' just as it is. I'ts a blast and I (being a WAY newbie to m/c carbs) just don't wanna mess with it. :thumbsup: My goal is a used DR to make my tinker toy! Still learning. Thanks for your good info. The pennies are adding up every week, and hopefully I'll be able to pick up a used DR sometime this year. :thumbsup:

Ride safe.

rc

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RC, I hear you, if it is running that good I would not want to mess with either. Just ride that puppy! :thumbsup:

Is is strange that it now doesn't want to run with the snorkel in it now. The only things I can think of that would explain that is high altitude or a dirty air filter. Either would make it run rich and then lean out with the removal of the snorkel. But every bike is a little different and the bottom line is that your setup is working for you so it is all good.

I got the AFR meter installed last night and took a quick ride. I am very pleased with the install and the first ride results were interesting and surprising. :thumbsup:

I will post install writeup with pictures soon. Also first readings. Hope to get some experimenting in this weekend.

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Well I got the AFR meter yesterday and got it installed by just after dark last night. It was too late to do more than a quick check out ride. Here is what comes in the box:

IMG-20110422-00068.jpg

I wanted to install the sensor in the header for a couple of reasons. It may be more accurate there but mostly because I plan to do a GSXR pipe mod some time I the near future and did not want to have to do it all over again. The problem with putting it in the header is that the header is only 1.5” in diameter and the bung for the sensor is 1” in diameter. So it could cause a significant restriction if you just drill a 1” hole and weld the bung protruding into the header. The tip of the sensor is only .4”. So I decided to drill a ½” hole in the header and round the face of the bung (fish mouth) to make it fit snug to the header. Then I brazed it on the outside on the header aligned with the hole. I hope these pictures help make it clearer.

Hole drilled in header.

IMG-20110422-00070.jpg

Side view of bung with the sensor installed showing how much it sticks out of the fish mouth.

Oviedo-20110422-00076.jpg

Header and bung ready to weld (Braze in my case)

Oviedo-20110422-00072.jpg

Installed sensor.

Oviedo-20110422-00077.jpg

Gauge in heat mode

Oviedo-20110422-00081.jpg

Gauge with engine running .

Oviedo-20110422-00082.jpg

So I only had time for a very short ride last night but enough for some quick initial impressions.

First the AFR gauge works great! The readings jump around a fair amount (like 12.7 to 13.2 and all points in between) but you can mentally average the readings as you go. This is normal from what I see looking at Youtube and what I remember from a similar set up I installed on a DR-350 a couple of years ago. Second the tuning method above worked as far as it can go. That is WOT was in the 12.5 to 13.2 or so range consistently. So the “tuning the air box to the jet by timed runs” thing worked.:thumbsup: At least for me in this case it did. Also the 45 MPH steady cruse (my other key tuning point) was right around 13.5 which is about what I was looking for.

The shocker was how wildly if varied off of those points! :jawdrop:Idle is 12.5 to 13.2 or so. At just above idle, at a very slow steady cruse, it when to around 10.5 to 11.2 or so. Way rich. Then it was right on the 13. 5 or so I was looking for at around 45 steady in 5th, but it got much leaner as I slowly increased the speed, to around 15+ at 55 or 60. I did not expect that. I thought I was too rich above my low speed cruse. Just goes to show it is very hard to tell what is going on by the seat of the pants. At least for me it is.

My first impression is that I need a faster taper on the needle. Maybe Dynojet is on to something with their fast taper needle. I thought it has way too much taper but now I may have to re-think that.:thumbsup:

I still need to do a lot more research and testing before I jump to any definite conclusions.:cheers:

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Excellent, excellent work! :thumbsup: I am surprised those AFR sensors have come down to the $200 range. Did you get the 3ft sensor cable or the 8 footer?

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I got the 3' cable. What they call the "power sport" version. Still had to roll up about half of it under the tank so I am glad I didn't get the long cable version!

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Looks good...

I am considering the LM-2 AFR meter.

Nothing to install permanently so you can use it on multiple bikes and also have no electronics to wack in the dirt.

As long as the cycle has no cat you can use the venturi effect sensor clamp to mount it to the tip of your exhaust can.

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Yes that LM-2 looks like a nice unit and includes data logging. But I think they all use the same Bosh O2 sensor with the same mounting requirements. I don't think the plug in to the tail pipe adapter (that you can get for any of the systems) will work for the DR at least not in the stock muffler. I would like to have gone that way but could not see a way to make it work. The tail pipe is blocked just a few inches in and the prob needs to go in much deeper. Let us know if you find a way to make it work.

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I think it would work with my FMF Q4. There is a baffle in there. If you pull the spark arrestor you can see it down there a ways but I think it's far enough in for it to work. On the Ducati the CF pipes have no baffle.. The existing bungs are to small in diameter for a wideband sensor.

My stock head pipe broke because a hanger on the muffler broke and it vibrated enough to snap the weld at the head flange.

I am glad it did actually. The Q4 is so much lighter atleast 15lbs lighter and nicer sounding. As soon as shorai batteries are back in stock I will get one for the DR and shave off another 5lbs.

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Nice job on the installation, looks good. Am I right in thinking that the AFR meter confirmed what you knew already? Seems that your timed runs with a fixed main jet changing the number of airbox holes covered/uncovered was on the money.:thumbsup:

rc.

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Well I did some more testing and for the most part I am happy with the results. I only recorded steady speed readings for now and have not played around much with dynamic response. It is a little lean at high speed cruise but not as bad as I first thought. I saw mid to upper 14's at 60 and 65. As speed goes up the main jet starts having more influence and the AFR gets better until at around 75 and up. and with WOT, it is at 12.5 to 13.

Basically the process worked and got me close to the jetting I was shooting for with improved performance with minimal or no money invested. So, is it close to as good as a pumper, or fuel injection? Not a chance! :smirk: But those mods are very expensive. Definitely worth it to some but I am thinking that for many of us that don't race this mod is a fun way to add a little extra snap without investing a lot of $. And if it doesn't work out, just put it back to stock. Nothing is hurt as long as you don't run it super lean and burn it up. But you will know if it is that lean because it will run like crap.

The AFR meter answered a lot of questions but opened up even more. :thumbsup:

Two things surprised me. First the stupid pig rich readings just above idle in low gears. Like when you are putting around the neighborhood in second gear 15 - 20 MPH. I am getting readings or 10.5 to 11!:cheers: Why, I have no clue. Idle is high 13.5-13.8. (Actually a little too high for idle I think.) And with just a little more throttle than the rich area, it is running back in that same range. But in between with the throttle just cracked, it is super rich. I can't even think if a way it COULD do that. But it does. And it does it 100% of the time not just once in awhile. However it feels fine. Without the AFR I would never know. :thumbsup: So do any of you have a theory on what could be going on there?

The other thing is how inconsistent the readings can be. Like cruising at 50 to 60, most of the time the readings are in the 13.7 to 14.5 range. Then I turn on a different road. come back up to speed and see 12.5 to 13 for a while. Next road, back to normal. Later in the day it got windy and some times it would start to see reading up around 16 at the same speeds. Then back to normal. It seems like small changes like road grade (even here in Florida) or head or tail wind may be having a big effect due to the change in load. The really frustrating thing is that we can only guess at what the #$@# slide is doing! It is all sealed up inside and just does what it wants to. We can't see it or directly control it. Makes me wish for EFI! :bonk: (I may have go read Rob's EFI thread again. . . )

I played around with opening and closing the 1" holes in the air box. (very quick and easy to do) The number of open holes (1 to 4) had a very strong influence on the WOT main jet reading but much less on the part throttle needle readings, and none I could tell on the idle readings.

Ride safe!

John

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So do any of you have a theory on what could be going on there?

The end of the stock needle is very blunt. I think a more needle-like needle would smooth out the transition between pilot and pilot+main. Also, I heard you can soften the pilot/main transition by swapping the pilot jet for one with bleed holes (?)

But you may not want to "fix" that because the it may just be designed that way.. less like a needle, more like a cork.. to compensate for the lack of accelerator pump. The fat spot is your AP :thumbsup: Before you change needles, I would look at how the mixture is doing as you open the throttle at different rates of whackage. It may be rich with gradual throttle openings, lean with sudden openings, and you may already have the best compromise the BST can offer.

.. The really frustrating thing is that we can only guess at what the #$@# slide is doing!

Yes, would you please repeat all this great experimentation with the FCR carb so that I might buy one and copy your setup? :thumbsup:

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The end of the stock needle is very blunt. I think a more needle-like needle would smooth out the transition between pilot and pilot+main.

I am thinking that is the wrong end of the needle. It is the top part of the needle that is in the jet at idle. But I think you may be on to something with the pilot jet. I seem to remember that the pilot jet system has several paths to the main carb body, some before and some after the slide with the air correction screw only affecting the after the slide part. I will have to think about that and do some research. Hurts my head :thumbsup:

But you may not want to "fix" that because the it may just be designed that way.. less like a needle, more like a cork.. to compensate for the lack of accelerator pump. The fat spot is your AP Before you change needles, I would look at how the mixture is doing as you open the throttle at different rates of whackage. It may be rich with gradual throttle openings, lean with sudden openings, and you may already have the best compromise the BST can offer.

Yes I am thinking along the same lines. I do see a very short duration lean event when I quickly snap the throttle open. I assume this is the "just off idle bog" that so many have talked about. If I fix the pig rich low speed will it make the bog worse? Could be. So you may be on to something again, they may have set the carb up to be rich at low speed to help the CV cover up some of the bog.

All this gives me a lot of things to play with, research, and test. I am having a ball playing with my new AFT toy!:thumbsup:

Yes, would you please repeat all this great experimentation with the FCR carb so that I might buy one and copy your setup?

Love to! Please send me your FCR carb and I will get started ASAP. I can probably get it back to you in a year or two.:cheers:

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