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PostPosted: Tue Mar 28, 2017 7:22 pm 
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Joined: Fri Feb 24, 2017 11:48 am
Posts: 14
Location: Fredericksburg, VA 22407
Hello and thanks in advance for any help.

USA VA, 30 ft above sea level 50-70F.

I recently purchased a 2012 dr650 in close to stock condition with 5100 miles. I added FMF power bomb, Pro Cycle silencer, Opened air box, K&N air filter, Pro Cycle jetting kit (150 main). I removed stock fuel filter and added an inline filter.

Tried the 3rd (from top) clip position and way to lean. Massive surging. Needed near WOT to pull cleanly.
Tried the 4th clip and much better, but still lean (surging, lack of throttle response) at low throttle openings (<3/8).
Now I'm on the 5th clip position and it was running very well. Just a crack of the throttle to cruise at 65 mph.
After a about 10 miles, it started running lean again at partial throttle openings, and required much more throttle to cruise at 65 mph. I thought it may have been nearly out of gas, so I filled to the top (2.5 gallons). May be my imagination, but it seemed to run well again, but after another 10 or so miles, was acting lean at low throttle openings again.

I've had a lot of experience with Keihin PWK 2T carbs, but this is my first carbureted 4T. On a PWK, it would be the slide cutout acting in this throttle range, but there don't seem to be specific circuits to tune on BST. I'm also puzzled why the fuel/air ratio would seem to change during a ride unless the engine was getting very hot and leaning out.

Next time I ride, with a cold engine, I'll see if it runs well for a while, then goes lean again. That would lead me to suspect a heat related issue.

Any ideas, thoughts, suggestions where I could look to diagnose this?

Thanks again for any help!

:good:


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PostPosted: Wed Mar 29, 2017 8:13 am 
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Joined: Fri Sep 10, 2010 10:22 am
Posts: 9376
Location: Mackinaw City, MI, USA
Sounds like a possible tank venting issue.

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PostPosted: Thu Mar 30, 2017 1:19 pm 
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Joined: Fri Feb 24, 2017 11:48 am
Posts: 14
Location: Fredericksburg, VA 22407
The stock non-CA gas cap looks fine and I never seemed to have negative tank pressure when I opened the cap.

Rode again yesterday evening. Temperature is 10-15F cooler than previous ride. Issue took longer to duplicate and seemed less severe. It appears to be related to the stock fuel petcock. When the bike goes lean, switching to prime mostly solves the issue. A raptor replacement petcock is heading my way.

I'm also going to raise the level of the fuel in the float bowl slightly. Even when it's running well, it still is a bit lean at very low throttle openings.


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PostPosted: Fri Mar 31, 2017 12:45 pm 
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Joined: Sun Feb 19, 2017 3:00 pm
Posts: 52
Location: North Carolina, USA
USA NC 300 ft 1996 BST40 carb Yoshimura exhaust

The bike was sitting for two years. I replaced the petcock and rebuilt the carburetor with a Procycle kit. I kept the same jet needle since the previous owner said that they had jetted it for the Yoshimura.

So it starts and runs, but not too well. Symptoms:
COLD
Won't start with full choke
On zero choke starts with a couple of turns of the starter motor
While cold when I increase throttle motor stalls
WARM
As it motor gets warm, engine revs easier, but still stalls if throttle is increased a lot
Even when warm, sharp increase in throttle causes motor to stall
Motor idles well when warm, but with some loud popping (don't think it's backfiring, but popping is loud!)

IMO these symptoms are because it's running too rich. Yes, I need to pull the plugs but I think I know what I am going to see. If it is running too rich, what is the best place to adjust throttle mid-range to make it leaner? Or am I not thinking right about this? Many thanks in advance for help! (Sorry if this has already been discussed! If so, much appreciated if someone could point me in the right direction.)


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PostPosted: Tue Apr 04, 2017 4:33 pm 
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Joined: Thu May 15, 2014 12:21 am
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So after being a stock DR rider for 8 years I have finally got around to installing the x40 exhaust and pulling the snorkel. I can't believe how much the bike has pepped up in the low/mid end. I suspect its been running rather rich most of it's life.

I have a dynojet/moose jet kit I picked up a number of years ago. I am inclined to not mess with anything with how well its running now. Should I be jetting at this point? What would I be looking to do if I drill/remove side panel from the airbox?


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