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Unmodified DR650 running extremely rich

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I just picked up by 1st DR650 and it is running extremely rich. From what I can tell the only mods are: FMF 2 exhaust, removal of snorkel, and the choke cable has been replaced with a manual choke knob that screws directly into the carb. (brass with black pull knob)

I smell gas all the time, and anyone riding behind me tells me that the exhaust fumes are awful. I pulled the plugs and they are totally sooted up. When cold, it starts up easily without the choke. It seems to run well and it pulls strong, but the fumes are unbearable. Have not driven enough to determine gas mileage.

I pulled the carb and disassembled it - found stock jets, and no problems. I am completely stumped as to what could be wrong.

Paul

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Is it possible that the float valve is sticking OPEN so that the carb is constantly flooding while running?

With STOCK jetting, it should be running lean, not rich!

Choke installed properly? Mixture screw present?

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Most likely the problem is the 2 o-rings that seal the float assembly into the carb body. They shrink with age and allow fuel to flow past the float valve. This is a relatively common problem and easily fixed.

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Most likely the problem is the 2 o-rings that seal the float assembly into the carb body. They shrink with age and allow fuel to flow past the float valve. This is a relatively common problem and easily fixed.

+1 on the "O" rings. I keep a spare set on hand. Buy the from ProCycle unless you have a good source for metric as SAE will not work.

Also pull the cap at the lower front of the air-box and see if gas has puddled inside. I leave the cap off as any air entering will be filtered. To me it's a fire safety issue.

Bruce

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Guys, thanks for the tips. Now that you mention it, the Pull type choke was threaded into the carb body very loosely. I was able to unscrew it by hand. Hmm.

Also, the O rings which seal the float assembly to the carb body had a lot of white reside on them. I cleaned them up and lubed them with O-ring lube, but I will get a new set to be sure.

Really appreciate the help. This is my first dual sport - I have never done any off-road biking before. I am 60 and just loving it. You CAN teach an old dog new tricks!! :smirk:

Again, thanks for the help.

Paul

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OK, I replaced the O rings on the float assembly and the main O ring seal on the float chamber, put in an extended length idle mixture screw, and checked everything else to make sure it was all stock. Also put in a new remote choke assembly and a pair of hot plugs. Put it all back together, and nothing has changed. The exhaust still smells like gas, as you can smell gas at idle.

The idle mix screw was originally at 1 3/4 turn out, and that is what I set it back to during re-assembly. After starting it and warming it up, I then started turning it in some more. As I turned in it the revs kept going up, then it finally rolled off. It is now at less that one turn out - but I still smell gas at idle and in the exhaust. The inside of the exhaust is heavily coated with soot.

There does not seem to be any fuel coming out of the float camber vent tube, so I don't think the float bowl is flooding - but maybe its too subtle to notice.

Anyone have any ideas?

thanks,

Paul

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There does not seem to be any fuel coming out of the float camber vent tube, so I don't think the float bowl is flooding - but maybe its too subtle to notice.

On a DR650 with the stock carb the float bowl can flood w/o gas on the floor. That is a problem with the carb design, the float bowl vents into the intake so raw gas ends up in the intake. It puddles in the lowest part of the airbox, which has a drain but it is capped stock. Also rinses the oil off the filter as it runs through. To be safe pull the cap to be sure there is no gas in there other wise a fire danger. I have drain as much as a cup out! I now run mine with the cap off as it is before the filter.

Did you use OEM "O" rings or at least metric? SAE (inch) will not work well at all, I've tried.

If that's not the problem I'm out of ideas as the idle circuit is fairly simple.

Bruce

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BDM,

Thanks for the response. I will remove the float bowl and float assembly, then replace the float needle today. (At least I don't have to remove the carb from the bike - I should just be able to rotate the carb to get to the float chamber.)

This has to be the problem, as I have verified everything else. I didn't realize that the fuel overflowing out of the float bowl would go back into the carb intake. Why would anyone design a carb like that?

thanks and I will let you know how I make out.

Paul

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Only carb I have every seen like that. The only hose off the float bowl is the drain hose.

I'm also not impressed by the 'O" ring/float/float needle valve design either, again only carb I have seen like it.

I keep a spare set of "O" rings on hand as you never know when they will get hard and crack with todays fuel formulations.

I can think of a couple of things which can cause the idle to go lean, but going rich is odd if it's not float related.

If it have been very rich or flooding check/change the engine oil as it can become contaminated with fuel.

Bruce

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Check the float adjustment and check to see if there is any pin holes or fuel inside the float.

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If all is good with the carburetor, then look at you're exhaust, a clogged muffler, or bent or kinked header/down tube would cause this.

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Only thing not mentioned yet could be a heavily worn needle or a likewise half-destroyed needle-jet, letting way more fuel pass than intended.

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Only thing not mentioned yet could be a heavily worn needle or a likewise half-destroyed needle-jet, letting way more fuel pass than intended.

+1 The BST40's needle chafes against against the needle jet something fierce.. out of line by design :smirk: That combined with the bobbling of the vacuum slide could have worn out the needle and needle jet. Might as well replace them if you have to go back in.

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I read that another possibility was that fuel from the petcock was leaking into the carb through the vacuum line - so I disconnected it and capped the petcock line and the vacuum line. No difference, but when I unplugged the vacuum line, revs went up about 500 and it ran smooth as silk - just more proof that it is way too rich. I then put everything back together.

Next I screwed in the idle mixture screw all the way and it still ran well at idle.

I will replace the entire float assembly tomorrow as I cannot buy just a float needle from the dealer - I'll be happy to spend the $70 if it fixes the problem!

Paul

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Working on my carb problem again. I have ignored if for the summer, but just completed a 3 day 500+ mile ride through Vermont with my 2 sons to view the hurricane devastation (and to ride some of the closed roads) and I only got about 30MPG and anyone behind me said my fumes are unbearable. Since my last post I replaced the float assembly and, again, no improvement. My idle fuel screw is now totally closed, but it still starts easily without ever choking it, and it still runs rich at idle.

I am about to give up and try to get a carb from someone who upgraded to something else. I don't know what else to try.

Paul

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By the way, I looked at the needle and needle jet - everything looks new. Only 7500 miles on the bike. Next time I open it up , I will take a closer look. Heck, I 'll just replace them as I am not sure how to tell a good needle jet from a bad one.

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By the way, I looked at the needle and needle jet - everything looks new. Only 7500 miles on the bike. Next time I open it up , I will take a closer look. Heck, I 'll just replace them as I am not sure how to tell a good needle jet from a bad one.

I wouldn't be surprised if the difference isn't visible to the naked eye...the needle comparison thread by mxrob (found in the faq) touches on this a bit. I couldn't tell you which of the 68 pages it's on though! :thumbsup:

I will be curious to see your results. I miscalculated my economy in the past, and it now looks like I'm averaging low 40's:banghead:...and that's prior to my jet kit install...haven't finished a tank of fuel on that yet, but I'm not holding my breath...I'm guessing/hoping it will end up being a float related thing for me...

http://www.thumpertalk.com/forum/showthread.php?t=467615

Good luck!:smashpc:

Kev

PS - The info on the worn jet was posted up sometime around the first week of April (2007)...

Edited by kevsie1
add info

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You should start with the float adjustment if you are not sure that it is dead on. It will cause this. My buddy had a brand new totally stock 2009 DR650 that got poor mileage and smelled of gas. His float setting was off for some reason. We adjusted it and it fixed it. If the float height is perfect than I suggest you replace the jets as they could have been drilled out. If all this fails put a pumper carb on it. You will be happy you did...

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Recently I had a similar experience with my dr650. Do a search on my name and you will find the thread. I too had to run the bike with the fuel screw all the way in. What I or actually one of the guys on here observed was I had the wrong pilot jet in the carb. Mik carbs take two types of pilot jets. Both will fit but in my case the bike ran pig rich even though the jet was stamped with the correct number. Be sure you pilot jet has one hole through the middle and that’s it. The others that fit and will work also have holes in the sides. I went from 31-33mpg to 43-47 now.

jets.jpg

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You've probably already done this, but assure that the snorkel opening is clear of any obstructions, such as a strap from a strap on seat cushion. Assure that the air filter is not blocked, wet, or over oiled.

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