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Old 07-17-2008, 07:46 AM
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Default XR600 Help please!!!!

I own a 1986 XR600 which I use mostly for trail riding, however it does not get much use. Last weekend about an hour or so into my ride I noticed it began to backfire at approximately 1/4 throttle. I normally ride two strokes and my buddy told me that some backfiring is normal for fourstrokes. (Whether this is true or not I don't know) It was running great up until that point. I parked it and let it cool off for a bit then started it up hoping that the problem mysteriously went away, but it didn't. I then began to troubleshoot. My first guess was a problem with the jetting, so I took both carburetors off and disassembled them. In doing this I found that one of the jets (I believe it was the main jet, sorry I am still new to the repairing side of bikes) was clogged with a tiny speck of dirt / sand. I blew it out with compressed air then proceeded to clean as much of the carbs as I could with carb cleaner and let them soak. I was optimistic that I had fixed the problem. Monday I put everything back together only to find that I did not. It still starts no problem and the first 1/4 turn of the throttle rocks, but after that it backfires continuously until I let the throttle back. An ideas? Could it be something with the valves / cam timing? I Purchased a manual for the bike on tuesday so hopefully it will be here today. I just put new sprockets/ o-ring chain / tires / graphics on the bike so I am hoping that this problem can be fixed fairly easily and inexpensively. The bike sat in the garage for 10 years until this past spring when I decided to get it going. Other than the usual maintenence stuff I have not done a whole lot to it, as I haven't used it that much. (It is really more of a back-up bike) I usually ride a YZ250 which is not running right now either (pleae see my thread about this bike in the 2-stroke yamaha forum if you think you can help me troubleshoot this bike) so as of now I have nothing to ride which all of you know absolutely sucks. Please help!!!!
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Old 07-17-2008, 08:16 AM
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Default Re: XR600 Help please!!!!

When your talking about backfiring are referring to small pops or fire breathing booms? My 400 did this constantly when I let off the gas but they were just little pops on decel. From my understanding, (so anyone correct me if I'm wrong) this is just extra gas left over from letting off the throttle and is burning off and is pretty normal. It would be a good idea just to check your valves. I believe they are the "tappet" type of adjusters and are real easy to check. Another thing. When you had the carbs pulled apart, did you clear out the pilot jets? If they are "restricted" this would be more of the cause then the main jet.

-Kevin-
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Old 07-17-2008, 08:40 AM
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Default Re: XR600 Help please!!!!

They backfires are more "pops" than fire breathing booms. However, they are continuous. Anyhting more than 1/4 throttle produces them and it just feels like the bike is "gasping" for air and something is just "off". When I took the carbs apart my uncle ( who is a small engine repair man so I assume he knows his stuff) and I cleaned out all the jets and they all seemed to be good. I apologize for the lack of technical terms in my descriptions, like I said I am fairly new to repairing bikes. What do you mean by restricted? As for the valves, the manual should be here soon so adjusting them should be outlined in there correct? In the meantime could you explain simply how to check them? If not no biggie, I am just anxious to get riding again. Thank you for your help!
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Old 07-17-2008, 09:15 AM
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Default Re: XR600 Help please!!!!

When you were talking about the back firing I assumed you were talk about letting off the gas and it was popping on deceleration. If its popping on acceleration thats a different story. Your pilot jet controls your fuel delivery at about 1/8 to 1/4 throttle. After that your needle and main come into play. Being that your have a 2 carb setup I'm gonna step away a little as I don't want to lead you down the wrong path. I'm not sure if the carbs need to be synchronized like the Banshees do. I'm sure someone who understands the dual carb setup will pipe in soon.

I would wait for the manual to come in, as there is more detail in that literature then what I can come up with. In the meantime, recheck the jets and see if something is clogged in the pilot. Soak the jets for a couple hours in chem dip or something along those lines. I find it easier just to get new jets if the ones in the carb are suspected of clogging. Another thing, pull your tank and clean it out real well. Pull the petcock, clean it out and check the passageways. The only reason on doing this is to make sure your not re-introducing any dirt or grime back to the carb. Sorry I couldn't be more help.

-Kevin-
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Old 07-18-2008, 09:23 PM
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Default Re: XR600 Help please!!!!

Ok I will check that and let you know how it goes. Thanks again for your help!!
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Old 02-09-2009, 09:28 PM
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Default Back firing thumper!

Greetings fellow XR lover/hater!!
A buddy of mine had a very similar prob with his XL600r (same motor)
The problem turned out to be a simple problem with the spark plug cap being burned inside!! Sounds stupid but those caps are a complicated little mother with a resister internally mounted that gets fried if there isn't perfect contact with the plug!! May not be your problem but if it is they only cause about
$20.00!! Give it a shot and let us know!! The way to tell is by looking inside the cap for black charring!! Good luck O.XR.D.
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Old 04-01-2009, 07:07 PM
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Default

Sounds more electrical than fuel to me.
Replace the plug and check the lead and coil with the specs in the book.
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