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Discussion Starter #1
I love my 400, but it backfires. All services are up to date; I clean my own air filter every 1000 miles; I use the best quality fuel I can get. Any suggestions?


Mike
 

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backfiring on the 400

Hi Mike, I'm the other guy on the 400 in Colorado....

Mine doesn't backfire at all, not when I had the stock exhaust, and not
now with the LeoVince exhaust. I have had similar problems once with
an automobile and all I had to do was change the brand of gasoline I
had been using, which at the time was Conoco...I went to a different
quality name-brand gas and the problem stopped. I don't know what
you are using, but you might try changing, and also make sure you
are using the premium fuel.

Just as a side note, my dad worked for Mobil for 17 years, and he
would advise not to mix the different weights of Mobil 1 even though
you can. Runing 10w40 Mobil1 because its Mobil1, would give you
better cold weather protection than if running 5w30 regular oil because
Mobil1 doesn't thicken easily ....I run the 10w40 synthetic in all my vehicles year-round, (but I must confess, if its not at least 50 degrees
out, I won't go riding), anyway.....good choice on your part.

Out of curiosity, where do you live in Colorado ? Good luck on your
backfiring problem.

Gib McKain
K3 400
 

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BACKFIRING

I had the problem for a short time on my 400. It started about 350 miles and left after the 1st service. The dealer said some other Suzuki bikes had the problem and it was corrected by making sure the throttle body closes enough, and check for exaust leaks. It's caused by unburned fuel air mix getting into the hot exaust. Dbl. check your tappits.
 

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Discussion Starter #5
MisterGib,

Thanks for the reply. I have been using either Texaco or Shamrock brand fuels (I wish there was an Amoco station around), and almost always the high octane variety, except for the last tank that I bought, I used 85 octane. It did not backfire as much or as badly with the lower octane, but it was still noticeable. I might take it to another service center just to make sure the dealer did adjust the valves as they are supposed to.

As far as location, I'm in Colo. Spgs'. I know what you mean about not riding at temps below 50, but...I can't help it, MisterGib, I just can't help it. It is so much fun, so smooth, so quiet...Ah....! It makes going to work really fun.

I will heed your word of caution about mixing different weights of Mobil1 oil. Even though the service manual calls for the next oil change at 4000 miles, I'm doing it every 2000; it's worth the investment to me.

Thanks for all the good advice.



Mike
 

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miket said:
I love my 400, but it backfires. All services are up to date; I clean my own air filter every 1000 miles; I use the best quality fuel I can get. Any suggestions?


Mike
Mine starts to hesitates at 1,500 miles occasionally and get worse over time, roughly and backfiring when apply a small amount of twist at handle, near idle and hesitates roughly. Idle at cold start was not in same RPM like before, slighty low, causing some stalling. I go for two options, valve adjustment or dirty throttle body. I remove all the hardware to gain acces to the valves at 6,000 miles and found that i don't have the tool to adjust the valves, so I go for plan 2. With the throttle body cleaned all roughtness and backfiring DISSAPEARS. :D I think that, because this kind of bike has no oxigen sensor, with a small twist of handle, the TPS send the signal to computer to increase inyector pulsation, but there's no enought air to burn this aditional fuel 'cause dirty throttle body, causing hesitation and unburned gases to explode on the muffler, causing this backfire effect. Also, my idle RPM raise again to 1,400 RPM.
 

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One time when I was doing the valves and moved the injector I pinched the 0-ring and had back firing problems. Try replacing the o-ring where the injector attaches to the throttle body and it may solve your problem
 

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My '03 backfires, sometimes heavily, in warmer weather. After repeated ttempts to get it fixed, like some other 400 owners I've just come to accept it as something that comes with the bike.
 

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backfire

I have a K6 with 4000 miles. Mine gives a slight backfire as I'm deaccelerating thru 2800 rpm. Always has done this as I remember, I have not given it much thought as it is minor. I run 87 octane gas and it runs fine on this. Different brands don't seem to make any difference.
 

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Did you do your own service? Make sure the spark plug is in all the way/check the filter and all hoses are hooked up/and make sure all bolts to exhaust are tight. Make sure metric feeler is used, not inches.
scooterjockey
 

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Put standard 87 octane gas and this will help. The problem with high octane fuel is it won't burn all the way in these scooters. Thus leaving raw fuel enter into the exhuast and puddle. When the exhuast gets hot it will cause the fuel to cumbust. This will help.

Other possibilites the compression release is sticking or the valves are to tight.
 

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Ok how about some of you tech guys tell us what those clear tubes are for on the bottom of the left side of the air cleaner houseing? I solved my ruff running poping and stuff when I changed to an irudim plug and cleaned the intake system. put dielectric grease on all the connections. SMOOOOTH now.
Ron
 

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mine runs with 95oct and from time to time do that. 12000 kms (7500m) i cheked the valves my self and i had no need to do anything. i don´t care with that, i think it's "normal"
Rui
 

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easylistener said:
Put standard 87 octane gas and this will help. The problem with high octane fuel is it won't burn all the way in these scooters. Thus leaving raw fuel enter into the exhuast and puddle. When the exhuast gets hot it will cause the fuel to cumbust. This will help.

Other possibilites the compression release is sticking or the valves are to tight.
First, mine is a AN400 with 7,859 miles.
I have no problem with premium fuel (92 octane). On regular fuel(87 octane) have a slight knock problem when going uphills. So, I decide to use 92 octane. It runs smooth and plenty of power. With just cleaning the throttle body it solves the backfiring problem. Fuel is not the problem with backfiring. Air leaks, bad inyector o-rings, and valve adjustments make more sense. Never heard about high octane fuel causing backfiring.
 

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Valves will only cause backfire when they overtight. Spark plugs will not cause backfire unless over carboned. Airleaks won't cause backfires because it will lean the fuel ratio. Back fires are caused by unburned fuel that get ignited in the exhuast system. Dirty injectors can cause it by not getting a spray of fuel, but drip it into the cylinder. Dirty throttle body will cause unstable idle not backfires. I have been a drivabilty tech for 10 years and this is what I do every day.
 

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You are incorrect that vacuum leaks can’t cause backfires because of a lean fuel / air ratio I’ll explain why:
1) A lean running engine can make the exhaust header hotter, and thus more lilky to ignite any unburned fuel.
2) A lean burning engine (if sufficiently lean) may be more prone to misfiring and thus unburned fuel can accumulate in the exhaust system.
3) Unburned fuel will always be present to some degree or another in all engines in all exhaust systems (pre-cat not post cat)) because all engines on occasion misfire and no engine burns all fuel with complete efficiency.
4) It’s more a question of suppressing backfiring to the point of it not being a problem.

It's also untrue that dirty injectors “drip it into the cylinder” what is much more the case is that the spray pattern can become uneven.

It’s also untrue that a sufficiently dirty throttle body cannot exacerbate the conditions necessary for backfiring.

Unfortunately most of your post is incorrect.
 
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