I rode 4000 miles from New Mexico to Costa Rica. Engine started running rough and loosing power. Found a Suzuki dealer in San Isidro and we discovered the air box full of fuel. We cleaned the air filter and replaced the fuel filter. The valves and timing checked out fine. The plugs (#10) were yellow so we replaced those with new #8's. (That is what the mechanic said works best here). I then rode it another 60 miles and it was fine but when I went to start it a couple days later the engine would not turn over more than a half a cycle or so. I once again found the air box full of gas. It seems to me like there is a valve problem to cause the fuel to back up but timing and valves both checked good and it ran fine after my visit to the mechanic. Any ideas? Do I need to replace the carb jets for sea level? I rode along the coast all through Mexico, Guatemala, El Salvador, Honduras and Nicaragua without issue. I am here for a couple weeks most likely and there is a Yamaha dealer nearby but I have time and if I can save money and fix it myself that would be nice.

Update: Tried starting it again, and it seemed electrical, starter cut out. Light comes on fine and it is a new battery. I fiddled with the wiring for the starter a bit without really doing anything and it then turned over fine but required lots of gas to fire up cold even with the choke on and it took a couple tries to start. Low idle even with choke on required gas to keep it from stalling. I only ran it a minute or two. Any ideas?

Based on the experience of my DR 350 :
The float bowl may be overflowing due to fault O-ring on needle valve assembly. The o-ring fits to the 'brass' needle valve seat.
There are another couple of o-ring in float bowl which are probably worth replacing while you're in there.
Otherwise .. maybe the float or needle valve may be sticking.

Having said that I'm puzzled you didn't see the fuel spilling out via overflow.
I'd also check the engine oil to see if fuel has leaked past piston rings.

I just discovered that the overflow hose from the top of the carb is routed to drain into the air box. Don't know why. It is beginning to make sense now. I will take off the carb and look at it and reroute the overflow tube to keep from filling he air box. Thanks for the help

Jeeez man, I hate to hear this.

I HOPE for your sake ... that you haven't "hydro-locked" the motor. It's likely the reason it won't turn over is because crankcase & cylinder are full of fuel. In this condition you can bend or break a rod. The DR is tough, so there is hope. When crankcase and cylinder fill up with fuel and you attempt to crank it over ... thousands of pounds of pressure are put on the rod ... but it can't move because the liquid (fuel) won't allow it. Something can break. Very sad if it does.

I'm betting your crankcase is FULL of fuel (mixed in with oil) If this is the case ... do not ride the bike in this condition, even if it will run. NOT GOOD. Oil thinned with fuel offers little protection from wear.

As mentioned above ... it's the O rings in the float bowl area. Specifically the float needle valve. (little rubber tipped thing at bottom of float bowl that cuts off fuel flow when float bowl is FULL. When this little rubber tip is worn ... it no longer stops fuel ... and either (or both) air box or crankcase fills with fuel.

It's a simple repair on the BST40 Carb. Order the O ring kit from Pro Cycle or find O ring kit elsewhere. The rubber hose that goes into air box on the DR650 should be the Crankcase breather hose. (very hard to plug back into air box)
If crankcase fill up with fuel ... it will then pump it into the air box. There is a drain on air box. Use it ....OUTSIDE!

Now drain oil, add FRESH oil after Carb is fixed. (a two hour job max) Restore rubber hoses to correct locations.

TIP: On DR650 Always SHUT OFF fuel at tank when parked for the night. This way, at least your crankcase will not fill with fuel if an O ring or Float Needle goes bad.

DR Carb O rings need replacing (typically) on older bikes ... no matter mileage, at about the 5 year mark or sooner. Other parts on the BST40 can also wear out over time/use. I just replace my OLD Carb with a near new Used one off the forums. I'm on my 3rd Carb now, have TWO new ones (under 1000 miles) in reserve. If stored DRY (in zip lock bag) they are good for decades.

Good luck getting back on the road. Speak up if you have more questions or go onto DR Riders forum.


PS: Carb fuel overflow hose should be routed down past shock linkage to ground. Only should leak fuel in this case ...
or when bike is on it's side.

Great info thanks.

It appears the O rings were the problem and we are trying to locate new ones now. That may be a problem since they don't stock parts for this size bike in CR since few people ride them. Will change oil and hope there is no damage to the rods or anything.

Molly Dog, I owe you several s. Your diagnosis was right on. I replaced the O rings and changed the oil and as you suspected the crankcase was full of fuel. It is amazing how one tiny little part can have such a tremendous impact on the whole machine with potentially disasterous affects. Any other gotchas about this bike I should be aware of?

Good news that you found an O ring kit. What happened to you is fairly common on carb bikes like DR650's. Certain new fuel additives also speed up O ring deterioration.

As I think i've mentioned ... you should sign onto the DR Riders forum. Helpful bunch there who know a lot more than I do.

Other common DR650 issues to address:
1.NSU bolts need to be loc-Tited (under clutch, easy fix)

2. Carry spare pulse coil (AKA Pick up coil) about $35 on aftermarket

3. Cush drive rubber inserts, replace ($65 set) before long journey or insert bits of inner tube between spacers to tighten up the fit. Smooths out drive feel, very nice.

4. start with NEW chain & sprockets if possible. (JT make affordable and good ones. Worn chain/sprockets #1 problem issue with travelers. (Pay a little now ... or pay A LOT later)

5. Add in line fuel filter, clean petcock filter and flush tank.

6. HID or LED headlight. DDM Tuning HID kits are $25 ... 3 times brighter than stock 55W headlight ... and HID only draws 35W.

7. Go to Pro Cycle on line ... very good with shipping and help/advice on the DR650. One stop shopping for everything DR650.

Er, can I have a pint too - if you're going to the bar? Cheers.

You got it 2-wheels.

good analysis MollyD sure you know this bike .
It is always useful to look at specialized fora : these guys are good
in FRANCE there are
drmania for all dr , with serious builders and experts
400drz for the drz , very wise ( but younger !!) too
used both, very helpful

Thanks ex- Xt,
You can find A LOT MORE DR650 information here:

www.DRRiders.com

or here:

the DR650 thread | Adventure Rider