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Old 02-15-2011, 05:00 PM   #1
vegastele OP
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BST-40 help needed

After cleaning the carb on my 03 640 adventure I can hardly get it to start. It was running good prior to me pulling it out of the bike. The only mod I did was a Stenhouse fuel screw. It will start cold with the choke out but as soon as it starts to warm or I crack the throttle it loads up and dies. Once it runs for a minute it will not restart until cold again. I have tried adjusting the fuel screw setting but cold start with the choke on is the best I can get. There is a throttle position sensor on the opposite end of the shaft there the throttle cable connects. I marked its position before I took it off to soak the carb. Is there a chance I didn’t put back in the same position and this is effecting the timing enough to cause my issue? Any other suggestions?
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Old 02-15-2011, 06:22 PM   #2
gunnerbuck
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I don't think it has anything to do with the TPS...

It sounds like you have a rich condition for some reason...

First thing to check: Make sure the choke/enricher piston on the side of the carb is not hanging up and sticking open... Sometimes cable routing can cause this... If you pull the diaphragm cover of the top of the carb you can see the brass enricher piston in its chamber, now move the choke lever and see if it slides open and closed freely...

Did you move the float height tang at all?

Is the needle jet installed correctly: above clip - nylon washer, below clip nylon washer+steel washer, clip in correct position?

Did you remove the fuel pump and if so are the hoses installed correctly?
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Old 02-15-2011, 06:44 PM   #3
RamMan4x4
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I read about a similar issue on the DR50 TT forum (also uses a BST 40 carb). The fix was to set the fuel petcock to PRI (prime) to refill the fuel bowl in the carb. Not sure if your bike has a similar PRI setting...but I'd be willing to bet its the same issue.
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Old 02-15-2011, 08:02 PM   #4
gunnerbuck
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Quote:
Originally Posted by RamMan4x4 View Post
I read about a similar issue on the DR50 TT forum (also uses a BST 40 carb). The fix was to set the fuel petcock to PRI (prime) to refill the fuel bowl in the carb. Not sure if your bike has a similar PRI setting...but I'd be willing to bet its the same issue.
No prime/vacuum petcock on the 640, instead it has a vacuum operated fuel pump that allows the engine to operate when the tank fuel level gets below the carb level..
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Old 02-15-2011, 08:50 PM   #5
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Fuel and pump lines are correct and not kinked?
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Old 02-16-2011, 12:43 PM   #6
vegastele OP
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Thanks for the replies.
Too rich was my first guess. I tried fuel at half turn increments between 3 to 1 turn out. I will try that again first. Wish I remembered to check how many turns out it was when I tore it down.
Not the TPS. It sounds like the timing is off when it’s trying to start. I’d better at least check the plug.
The fuel hoses are straight. Hoses were never removed from the pump. I will check the chock piston but I don’t think that’s it. I didn’t mess with the clips on the needle.
I did mess with the float position. It looked a little high and I was getting a little gas out of the over flow. I have also had it out of the bike twice to check it aligns with the carb body. Will check again.
I did replace the rubber with a KTM kit. The diaphragm in the kit had wrinkles from sitting in the package. It looked to fit correctly. Could that be an issue?
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Old 02-16-2011, 05:56 PM   #7
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The fuel screw usually sits around 2.5 turns out... This screw and the pilot jet only really affects the carb at idle to 1/8 throttle...

Your float needle may be worn and need replacement, having fuel leak out the overflow can be an indicator of this... When the needle doesn't stop the fuel it ends up flooding the motor and will cause starting issues....

As long as the diaphragm seals properly the wrinkles shouldn't be an issue...
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Old 02-17-2011, 12:31 PM   #8
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The float moves freely and doesn’t appear to have any cracks. What other signs might I see on a worn float? The O-ring on the float didn’t seem that tight and is next on my list. Pulled the plug. It was black and oily. It barely ran with a new plug and the fuel screw at ¾.
When I install the float I hang the weight in the notch at the end of the tab. Then the weight slides up the tab as the float snaps in and the weight centers with the needle valve. Does that sound like a correct install?
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Old 02-17-2011, 12:46 PM   #9
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I was referring to the float needle itself being worn... To be more specific, the rubber tip on the float needle develops a ring groove over time where it sits against the brass seat and no longer fully shuts the fuel off...

Normally, the only thing that really wears on the float itself is the plastic pins that it hinges on... A bob test for float leakage can be performed by suspending it in liquid overnight to see if you have a sinker...

Check your oil level to make sure that fuel hasn't entered the base due to carb overflow... Perform a sniff test and you maybe able to pick out fuel vapor mixed with the base oil.. Also check for oil in your airbox which may of came through the vent...
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Old 02-17-2011, 12:59 PM   #10
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Quote:
Originally Posted by gunnerbuck View Post
Is the needle jet installed correctly: above clip - nylon washer, below clip nylon washer+steel washer, clip in correct position?
Hey - thanks man. I think you've just inadvertently solved my BST-33 problem (Suzuki DR800, dual BST's). I just realised I forgot the bottom metal washer on the needle after rebuilding my carbs. Bike will start, idle, and run, but there's just a really bad stumble below 3000 that couldn't be fixed by turning the screws out.

Sounds logical?
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Old 02-22-2011, 10:29 AM   #11
vegastele OP
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Started over from scratch. Cleaned everything again and reassembled. Now she’s running great.
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Old 02-22-2011, 10:36 AM   #12
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Quote:
Originally Posted by vegastele View Post
Started over from scratch. Cleaned everything again and reassembled. Now she’s running great.

PFM?
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Old 06-07-2015, 06:19 AM   #13
ggstockjr
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DR650 won't start after BST40 rebuild...

Hi inmates, I am a newbie.

Purchased an 06' DR650 with 10.5k miles from someone's porch. It had been silent for a couple of years. It started, but had 4-5L of oil/fuel in crankcase.

After initial eval, decided to replace the fuel petcock and rebuild the carb using Moose Racing kit. Tires, tubes, battery, brakes, filters, fresh oil, fluid flush... the usual stuff with unknown history. After reinstalling the carb, she fired right up! Purred like a kitten, had nice throttle response (Thanks to the BST40 bible page....). SO, I got on my gear a rode her around the neighborhood. Fun! Never been on dirt bike, now I can see the attraction...

...then... poof, she died. Would not start. Cranks, but no fire... fuel all ok, then pulled the plugs to discover no spark! What the hell! I thought this can't be. Then after reading the forum posts, apparently the pulsar pick up coil appeared the likely suspect. Sure enough, it was open (infinite ohms) instead of the 270 ohms suggested. :(

I have pulled the magneto cover only to discover about 2.3L of fresh synthetic oil on my garage floor! LOL! Yes, after more reading I have learned that the magneto is bathed in the crankcase oil!

I have ordered the new pickup from Amazon, and await its arrival. I will be making a gasket from gasket paper (or, if unsuccessful purchasing one on ebay). I will attempt to run the new pickup wires outside the crankcase and make the new electrical connection outside the crankcase. I will let y'all know how it turns out. Probably 2-3 weeks away from affecting the repairs.

I am posting this for several reason:
1. Thank y'all for all of the information on the hundreds of pages. IT has been immeasurable in troubleshooting and confidence building!
2. Sometimes, you can actually have two separate problems causing a similar symptom (in this case, carb issues AND electrical ignition issues).
3. Finally, I look forward to getting out there where the road ends and the journey continues!

Later

GG
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