700 SXr Backfire

T

TimSRX

New member
Joined
Feb 26, 2008
Messages
56
Location
Kentwood, Mi
Late last year my 700 SXr developed a little backfire problem. When I would slow down from any speed, say above 40, and then hit the throttle, it would backfire. I would let it idle down and would be fine. This past weekend I started it up for the first time, it would idle fine, but when I hit the throttle to take it off the trailer it would backfire really bad. So I took it off by hand, cleaned the carbs, and would do the backfire thing it was doing last year. Looks like when the RPMs are around 5000 and I let it drop to below 3000 and then hit the throttle, it backfires. I was hoping the carb cleaning would take care of the problem, but it obviously didn't. Any ideas?
 
A backfire is caused by something being lean. Sounds like it is in the mid range somewhere. Did you move the needle's at all? Maybe they are set too lean? I have a 600sxr and i clean the carbs every pre-season because it usually will backfire bad the first run of every season.
 
The only thing I touched in the carbs were the jets. The pilots were pretty clogged from sitting all summer and one main was a little dirty. I haven't touched anything else. I also pulled the plugs and none of those show being too lean, they all have a nice dark brown color to them.
 
I could be wrong and hopefully one of the engine experts will chime in because i am not. A backfire is caused by to much gas usually caused by a stuck float or improper adjustment. The excess gas is expelled out the exhaust and ignited by the hot pipes causing the loud pop and sometimes flames. Check your floats and go through your carbs again. I would say to much gas not lean. Any other help guys?
 
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It could be what you decribe but here are the symptoms of a lean condition.

Lean Symptoms:

•Poor power output
•Hard to start when cold - requires excessive choking.
•Lengthy warm-up required.
•Runs better (but not good as it warms up)
•Spark plugs overly clean..with no deposits or slight glazed appearance
•Rough, erratic idle that drifts toward higher rpms than expected based on the setting of the curb idle screw. Sometimes a lean condition will cause a "hanging" idle that is slow to settle down to set idle speed.
•Backfiring
•Sluggish...hesitates when the throttle is opened, then recovers (often accompanied by a slight backfire)
•Vague throttle response
•Surging at steady throttle cruise operation
•When fully warmed up, runs better when choke is applied.
•Engine runs hotter than normal. Headers can turn cherry red in extreme cases!
•Temporarily removing air filter element makes the engine run worse.
•Unusual "sucking" noises in the intake area.
•Runs better as you climb to higher elevations
•Slight back-firing on deceleration. This normal tendency is controlled by the air cut-off valve(s) operation. If the air cutoff valve(s) is working properly and you still have backfiring on deceleration, something is causing a lean condition.
 
TimSRX said:
Late last year my 700 SXr developed a little backfire problem. When I would slow down from any speed, say above 40, and then hit the throttle, it would backfire. I would let it idle down and would be fine. This past weekend I started it up for the first time, it would idle fine, but when I hit the throttle to take it off the trailer it would backfire really bad. So I took it off by hand, cleaned the carbs, and would do the backfire thing it was doing last year. Looks like when the RPMs are around 5000 and I let it drop to below 3000 and then hit the throttle, it backfires. I was hoping the carb cleaning would take care of the problem, but it obviously didn't. Any ideas?
Click to expand...

You say that you had to pull it off the trailer. Does this mean that the sled was backfiring so bad it would barely power itself. You might have a problem with the tors. Sled will idle fine but not rev high enough to engage clutch. Sometimes if an intermittent problem it could cause backfiring while coming back on the throttle like after a corner.
 
I pulled it off the trailer due to the sound of the backfire. It was quite loud, I didn't want to damage anything. After I cleaned the carbs that initial backfire was gone (when trying to accelerate).

I don't think I am running lean, the plugs do not show signs of being lean. And last year it was not running hot nor was performance less than before. Could I unplug the tors ad see if that is the problem? I thought I have read where people have unplugged or bypassed it to rule it out... Thanks for all the ideas fellas!
 
tors was my backfiring issue on my sx600r just undo the the two wires going to the carbs and the two coming from the harness hook them together if it works get your tors switch fixed
 
ryan2001sx600r said:
It could be what you decribe but here are the symptoms of a lean condition.

Lean Symptoms:

•Poor power output
•Hard to start when cold - requires excessive choking.
•Lengthy warm-up required.
•Runs better (but not good as it warms up)
•Spark plugs overly clean..with no deposits or slight glazed appearance
•Rough, erratic idle that drifts toward higher rpms than expected based on the setting of the curb idle screw. Sometimes a lean condition will cause a "hanging" idle that is slow to settle down to set idle speed.
•Backfiring
•Sluggish...hesitates when the throttle is opened, then recovers (often accompanied by a slight backfire)
•Vague throttle response
•Surging at steady throttle cruise operation
•When fully warmed up, runs better when choke is applied.
•Engine runs hotter than normal. Headers can turn cherry red in extreme cases!
•Temporarily removing air filter element makes the engine run worse.
•Unusual "sucking" noises in the intake area.
•Runs better as you climb to higher elevations
•Slight back-firing on deceleration. This normal tendency is controlled by the air cut-off valve(s) operation. If the air cutoff valve(s) is working properly and you still have backfiring on deceleration, something is causing a lean condition.
Click to expand...


I never gave a lean condition causing backfire any thought. Did some googling and read up on it and it turns out most backfire problems are from lean conditions. Great info, thanks. Ya learn somthing new everyday! Tim Looks like ya got some good starting places. That pesky torrs could be it too. Start with that seeing thats the easiest.
 
TimSRX said:
I pulled it off the trailer due to the sound of the backfire. It was quite loud, I didn't want to damage anything. After I cleaned the carbs that initial backfire was gone (when trying to accelerate).

I don't think I am running lean, the plugs do not show signs of being lean. And last year it was not running hot nor was performance less than before. Could I unplug the tors ad see if that is the problem? I thought I have read where people have unplugged or bypassed it to rule it out... Thanks for all the ideas fellas!
Click to expand...

Yes, you can by-pass to rule out. There are 2 wires coming from your carb rack where the throttle connects. Unplug both and then plug them back into themselves. Basically, you'll end up with the 2 wires on the carb rack connected together and the 2 wires that lead to these wires, connected together. Hope that makes sense. Normally if its not working its an adjustment problem and its not recommended to disconnect as it is a safety feature. Check the link below for adjustment if you find this to be the problem.

http://www.totallyamaha.net/forums/showpost.php?p=365043&postcount=18
 
Never thought of the TORS, could be that also but like the guys said, unhook the wires and hook them together and that will tell you if that is the problem. Also, to tell if you're running a little lean, you need to put in new plugs if you really want for the plugs to tell you what is going on. Used plugs won't change much unless you can run it in a lean state for awhile, long enough for them to cook off the nice brown color.
 
When i first got my sxr i had a nasty backfire as well and went thru plugs like no tomorrow..i switched over to yamalube and a thourough carb cleaning and pre season cleaning each year..no more backfiring.
 
Thanks for the ideas everyone. I will try to bypass the tors first since I can do that without taking anything apart. If that is not it I will start tearing into it and see where I get. I hope it is something easy!!
 
bluewho said:
Try adjusting your throttle play first.It sounds like it is to tight.






.
Click to expand...
Yes ...definately adjust the throttle play first... make sure you have a lil' bit of slack before it pulls the linkage up! sometimes when you take your carbs off you can get the throttle line kinked or rerouted a lil; funny. check it !
 
I may play around with the throttle play this weekend. I can't remember, when I did the carbs of my sleds this past weekend one of the sled's throttle cables was tighter than the other sled, I just can't remember which one it was. I will work on it and let you all know what I find out.
 
Well, yesterday I was able to work on the sled. I backed off the throttle cable so there is a little slack when at idle and the backfire is gone. I think the only way to really test it is to get it on the trail and work it. Let's hope that was the actual fix.
 
I had an issue which sounded like backfiring, but it was due to my exhaust donut being worn and it was leaking between the exhaust manifold and the pipe.
 
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