Yamaha Sport ATV Forum

carb "backfire"

This is a discussion on carb "backfire" within the Yamaha YFM350 Raptor/Warrior ('87-Present) forums, part of the Performance /Technical category; I know something similar was addressed a month or so ago but...My wife's 97 Warrior just developed carb backfire after sitting over the summer. To ...


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Old 11-15-2009, 03:33 PM   #1
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Default carb "backfire"

I know something similar was addressed a month or so ago but...My wife's 97 Warrior just developed carb backfire after sitting over the summer. To date I have cleaned out the carb (several times), replaced the rubber 'O' ring at the carb/manifold, adjusted the air/fuel mixture screw from 0-2.5 turns out, replaced the manifold and 'O' ring at the cylinder and still the backfire. When the bike is idling and it backfires, it will die most of the time. If the bike is being ridden no real issues until you come off the throttle. Could it be the valves are way out of adjustment?
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Old 11-16-2009, 07:52 AM   #2
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hmmmm im not sure what would cause it to start doing it from just sitting... i would typically say "clean the carb" but you swear its clean.... you also you checked/ replaced the next items on the list..... OH I KNOW! how about bad gas?... the only other thing i can think is the valves grew carbon on them and arent sealing tight, if that is the case then you just gotta run it like you stole it and blow the carbon out
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Old 11-25-2009, 08:28 PM   #3
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Default "Carb Backfire"

Quote: Originally Posted by bomber315 View Post
hmmmm im not sure what would cause it to start doing it from just sitting... i would typically say "clean the carb" but you swear its clean.... you also you checked/ replaced the next items on the list..... OH I KNOW! how about bad gas?... the only other thing i can think is the valves grew carbon on them and arent sealing tight, if that is the case then you just gotta run it like you stole it and blow the carbon out
I have the same issue. Had it for awhile now even before getting a ton of motor work done but I will stick to pertinent stuff here. It is strange and every time i think I got the right item replaced I fire it up and... the darn thing still does it.

I have replaced both the intake and exhaust valves and seals. New tapits that will be adjusted again here in a few more hours of riding. New carb boot. Even replaced the carb! New gas, new air cleaner, now I even have a different exhaust on it.

Fire it up, darn thing still does it. I have a 96 Warrior and it runs like a three year olds nose. Can anyone shed some light on this. It is honsetly driving me crazy, and I feel like "any backfire of any type could potentially harm my motor" and I put a lot in to that motor :(
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Old 11-26-2009, 09:28 AM   #4
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in both your cases, how do the plugs look? are you guys sure enough gas is flowing from the tank?
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Old 11-27-2009, 05:50 PM   #5
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Plug is brand new, after about 20 minutes of run time, it is black, not wet or oily. Also the carb has actually been replaced, and both carbs same effect., I got good gas flow, It screams with acceleration, but like at an idle you can notice the "carb backfire" remember this isn't popping out the exhaust it is like it is popping back in to the carb.
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Old 11-27-2009, 05:53 PM   #6
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It has also been bored, over sized piston, rod crank / rod bearing ... honed, and a new after market CDI box on it and a lot more. Only thing that changed is the amount of power and response I have now. Because with all of that I still get the "carb backfire" I honestly think it is doing it just to agitate me :)
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Old 11-27-2009, 09:36 PM   #7
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hey mark,
if your plug is black even after 20 hrs, it's too rich. plug should look light tan at end. sounds like you need less fuel or more air or more exhaust flow. try drilling a few large holes in the airbox lid. or back off the airscrew 1/2 turn. what jets are you running?
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Old 11-28-2009, 06:24 PM   #8
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Quote: Originally Posted by 366warrior View Post
sounds like you need less fuel or more air or more exhaust flow.
I am going to pick more air... Exhaust good and clean :) I have extra large fuel lines and I think it gets plenty of gas so maybe I will equal it out with some more air?

I am going to do two things:

First I am going to find out what jets I am running and then get back to you because it might make a difference in the adjustments you recommend.

Second thing is I am going make a few air box mods.


I will throw some pics on of the mod if it is any good.
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Old 11-29-2009, 10:17 PM   #9
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yeah good idea... lets us know what jets are in there.... dont got drilling in the airbox just yet.... also check what the fuel screw is set at
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Old 02-07-2010, 12:09 PM   #10
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Mark, did you ever figure out the problem?
This is the same thing mine is doing.

warrior popping.... help
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Old 02-07-2010, 05:07 PM   #11
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Thats what mine is doing took it to the shop and he said my carb was shot so im putting the carb off my z400 on it
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Old 06-06-2015, 02:53 AM   #12
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...what happened? Enquiring minds want to know? The stock warrior carb comes with a "one size fits most" 145 jet, depending on altitude, higher a person is, less air there is; therefore less gas is needed to make the machine run...RIGHT!!! Apparently, we are supposed to change jet, put in new plug, warm up bike, RUN IT WIDE OPEN THROTTLE THROGH THE GEARS ITO HIGH GEAR ...AND THEN IMMEDIATELY SHUT IT OFF, pull the plug (I would let it cool off a minute or two), "read the plug" compare it to the "ideal" plug picture in Chilton's manual or online and keep going down until...it starts..."pinging" and/or gets the exhaust red hot (that's bad=TOO LEAN=SCORES CYLINDER N PISTON SKIRTS/RINGS) A $10/ HF TEMPORATURE GUN IS WELL WORTH THE INVESTMENT...u can use it to see if your soup is hot enough to eat and not burn your mouth ;) someone put a LOUD PIPE ON MINE, must've put a bigger jet in it, it would backfire through the exhaust on gettin OFF "the pipe" VERY ANNOYING. Too much fuel not being burned in combustion chamber, igniting in exhaust when it sucked in air on deceleration. Factory jet solved the backfiring through exhaust. Now, plug is BLACK!!! TOO MUCH GAS, ask mechanic, "if it came with 145 jet from factory and it runs RICH HERE AT 3600', how many jet sizes should I go down?" I'm sure his answer will be...140, 135, 130, 125...until the plug comes out tan like the picture in the book. The jets on E bay are like $7/each or jetsrus.com $3/each +$7/ s/h (might as well get ~ jets at a time to justify the s/h cost at jetsrus.com?, y/n?) trial n error, its not that hard/time consuming to take carb off warrior...i have milk crate to sit on, music, tools RIGHT THERE n cold beverage handy in the shade. A well versed person could do it in...an hour? Faster with portable electric spinner. Get Chilton book, read it, it has picture, guys do well with pictures. I use yellow highlighter in it as I read as I cannot remember...anything...even if I read it 3x. C.R.A.F.T can't remember a fng thing. Backfire through carb on decel? That would be annoying...BUT IT RUNS LIKE A STRIPPED @$$ APE? Timing issue? Timing light on spark plug n watch for the "T" on THE MARK on the flywheel in the timing window? Problem above my pay grade, need another opinion. I seen people squirt some water into car carbs to try to get carbon loose. THERMAL SHOCK it is called COLD WATER HITS HIT CARBON/METAL, SHOCK IT, MAKES IT CONTRACT FAST AND...CRACK!!! DONT PUT COLD TAP WATER IN OVERHEATED ENGINE AND START IT OR...CRACK...HEAD/ HEAD GASKET/ BLOCK. Leave car and come back later to get it whenvits cool or, AS IT IS RUNNING WITH GLOVES ON STAYING CLEAR OF SUPERHEATED WATER, POP THE CAP, LET IT "BREATH" TILL IT CALMS DOWN A BIT, TAKE CAP OFF, SLOOOOWLY ADD COOL WATER TO THE SYSTEM...STAYING CLEAR IF FILL POINT AS IT MIGHT "burp" superheated water all over you=SCALD=HOSPITAL W/2nd degree burns...3rd degree burns=skin grafts? I digress
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