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Discussion Starter #1
Ok Folks - first minor or possibly major problem with my 03 650:

I am having minor and very occasional cough or intake backfire on low speed throttle closing. And more seriously, the low speed, 1/4 throttle low speed cruise (around 35mph standard drive maode), is feeling slightly rough, or 'hitchy".

THe idle is not lumpy, and accel seems good at open throttle. Indeed, the more the throttle is open, the less apparent the problem is. But that low-mid power band is not right.

The best way to describe this to another 650 owner is thus:

You know that this bike normally feels that it is 'ahead of the throttle' even at low-mid setting (35mph ish), it gets there easily and and faster than you thought at very small openings. But now my 650 feels, 'behind the throttle, slight surging, not smooth at that low-mid seting and feels as though I have to twist a little more. This problem also is exacerbating the dirve train lash, which is no joy on the 650 even when working 100%.

My feelings as to what might be wrong, your opinions are important to me:

1) I think my high speed run for 20 mins at 100+, may have vibrated the throttle body mounts loose on one side, creating a very slight air leak at the manifoild side.

2) the Throttle body synch might just be off enough to create this low speed problem. Again caused by the 'thunder run'.

3) bad fuel, water contamination. I have tried a full can of dry gas injector cleaner. W'll see what happens.

4) Semi-clogged injector one side. Semi-loaded spark plug - but idle is smooth.

Well that's it.

This type of problem is one that a dealer will never fix under warranty, as it is too subtle, and too hard to diagnose.

Anyone with similar experiences regarding this failure mode, or any ideas on how to troubleshoot or investigate this, I would greatly appreciate your input.
 

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Hi abm

Just this past week I have noticed an occasional small backfire as I roll off the throttle when coming to a stop . It doesnt do it all the time and just started in the last couple of days. Mine still idles well at 1000 and rolls on to the power just as smoothly as it always has. Can't say I've noticed any problems there.
However I did notice a slight surging while cruising at 110-115 km/h. I watched the speedo and the tach and it didn't show this surging but I could feel it. I actually thought it was (may still be) wind gusts, as its been very windy up here all week. I will keep my eyes and ears open and take better mental notes knowing that there may be a problem. Thanks for sharing abm.
I guess this is a good case of sharing any feelings you have about your machine. Maybe others are as well but nobody is speaking.
 

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Discussion Starter #3
allwalk said:
Hi abm

Just this past week I have noticed an occasional small backfire as I roll off the throttle when coming to a stop . It doesnt do it all the time and just started in the last couple of days.
However I did notice a slight surging while cruising at 110-115 km/h. I watched the speedo and the tach and it didn't show this surging but I could feel it. I actually thought it was (may still be) wind gusts, as its been very windy up here all week. I will keep my eyes and ears open and take better mental notes knowing that there may be a problem. Thanks for sharing abm.
Yes, my backfire, or rather intake cough, is very infrequent, and only on abrupt throttle close. As you may know, some bikes have this as a feature from new.

Im not going to freak out about this, but I do think its possible that injector synch or the intake manifold seal might be compromised. I hope it is a synch issue.

Lycheed - help!!!!
 

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Not an Expert but...
My bike has done this on rare occasions since new, but it's more frequent now at lower RPM's when I quickly let off of the throttle. I've had similar symptoms on previous V-twin bikes. It's a fuel mixture glitch where it backfires through the throttle body. Sometimes referred as "sneezing" usually, caused by a lean condition and or a vacuum leak.
I've been too busy riding now at 3500 miles since Feb to check into it.
 

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My 650 (5200 miles) also does this minor backfire on closed throttle occasionally - more of a slight cough than a backfire. I never really noticed until I put the aftermarket exhaust on, which made it more audible.

My V-Strom also does this occasionally. May be a characteristic of Suzuki FI?
 

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I have noticed it to, just a bit on my 650, usually after a long run.
My 400 had it bad @ 500 miles. The 600 check up took care of that, and didn't have the problem ever again (traded it @ 3,000 miles). The dealer said some models do it more that others.
He found it's caused by unburned gases igniting in the hot exaust.
I am guilty of not going over my bike as well as I should, too busy working or riding. But it may be just a matter of checking ALL the bolts for tightness, espically at the exaust area. Check to make sure the throttle closes as it should, and there is no exaust leak @ the manifold.
On another suzuki forum, they found vacume line for the pollution controls caused it.

Hope it helps more that confuse.
 

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Discussion Starter #7
GOT MUCH BETTER

Well folks:

It seems the phantom mechanic showed up last night while I slept, for the problem is all but cured. Maybe it was the fi cleaner that I added yesterday, and the new tank of gas, but problem solved for now.

Thanks, most sincerely for all the repsonses; you have proved again that this is a great place for the Burgermaniacs to congregate.
 

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Discussion Starter #9
Scutour said:
Coughing..Sneezing..Backfire...

This burg's got a Cold :D
I think it is more than possible that one can get a bad tank once in a while. Just bad gas.

It happened to me years ago on a disreputable yam 650. When it started right after fueling, I didnt even realize nor think that it could be the fuel.

why, because the bike was such a rat I thought it must have been something to do with its internals. It made so many funny noises that I didnt know If I was comming or going.
 

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backfire

I know on my suzuki intruder 1400, when I got it brand new, it would back fire on de-celleration. What was causing it was fuel mixture was too lean. I had the dealer richen it up just a bit, and the backfire went away.
 

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I also have this backfire once in awhile but noticed that I was getting it when I burned gas that had a little enthanol in it (BP). Once a switched to Sunoco or Mobile without ethanol (Not posted at the pump anyway) the problem seemed to quit. I have tried different octanes of gas and found mine runs best at 89 rather than 87 or 93 (94 at Sunoco).
Just my 2 cents!
 

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Fuel

I would recommend a tank of Chevron Supreme. It will get rid of
the deposits. After that, try it and see if the problem continues.

The consistancy of fuel these days pretty bad. I can't get my
truck to idle on Arco fuel. I gain 5 mpg with Shell. Chevron
seems to be pretty average, but cleans out the deposits.
 

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An occasional slight backfire is pretty common with twins and singles - rare with 4 cylinder engines. At least that has been my experience with the various bikes I have owned. I don't worry about a slight "pop" every now and then. My V-Strom does it more than the Burgman - part of the "character" of the beast....
 
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