idle backfire and stall - Yamaha ATV Forum
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post #1 of 6 Old 01-12-2019, 10:12 PM Thread Starter
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idle backfire and stall

Hey guys, I'm not new, but it's been along time. Unfortunately I don't remember my old info so i started a new account.
Anyways, this is it. I haven't rode much in years. Literally. A couple times every couple years. SO here's my latest dilemma. I have an '05, stock except YMF full exhaust, carb jetting and slight air filter kit. The last time I had her out a couple years ago, she ran great. Had to go thru the carbs, put in some fresh fuel, new battery, but she ran great. She been sitting again and I have some new friends where I live now that are wanting me out there, so here I go. Drained the tank, pulled the pet-cock, re-sealed it, cleaned the tank and screens. New battery, disassemble carb cause fuel was just running out of overflow tubes, and a new plug. Got her fired up, will idle great for a minute or so and just cut out. Fires right back up and will do the exact same thing. I was wondering if it's fuel, so when it died, I shut the fuel off, opened both bowl drains and plenty of fuel came out. As it was running, I noticed there seemed to be alot of fuel coming out of the needle jet on the right side, but IDK. I'm thinking I just may need to put a whole new kit in the carbs, but i cleaned EVERYTHING. Gently passed air thru all the passages and can see clear thru all the jets. Am I missing something or is it that plain?
Thanks in advance for any help
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post #2 of 6 Old 01-12-2019, 11:41 PM
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did you get the right and left carbs mixed up? check to make sure the cabs are well seated in the boots and there are no vacuum leaks.
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post #3 of 6 Old 01-13-2019, 08:31 AM Thread Starter
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I don't believe so. I'm pretty anal about things and kept the carbs in orientation to the engine as I rolled them around like dice. Did not check for vacuum leaks, tho it didn't seem to idle like it had one. I'm not wondering if just the years of sitting in AZ heat just didn't cause issues with the needles and jets now that i got the moving again. I was researching rebuild kits, jet kits and the such last night. What I found was "new" carbs for these things are incredibly inexpensive anymore. I may just buy one for this one just to see, and if it works, I'll buy 2 more. One I'll keep in the house, the other I'll jet for my '01 686
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post #4 of 6 Old 01-13-2019, 09:35 AM
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i would not waste the money on a set of cheap carbs. the carb bodies dont generally wear out. you have about a 50 50 shot at them being junk out of the box and you will just need to rejet anyway. i have seen them with undrilled passages, all kinds of issues. you dont gain anything. it could be float level and it flooding out when its idling but not super likely. my guess is it is just cranky from sitting. if you are confident you dont have a vacuum leak in the boots and the carb lids before you tear them out again try running some sea foam through it. if it was me i would fill it with premium ethanol free fuel, mix in the liquid seafoam into the tank (i double the amount in the instructions but that is up to you), pop the top on the air box and remove the filter, get it running and warm as best as you can and use the spray seafoam to start cleaning the carbs. it should smoke cough and puke but it will start to loosen any of that bad fuel up and then take it to a local track (some place you wont have to push it far if i am wrong) and run the crap out of it. i bet by the end of that tank your issues will be solved. and then dont put any more of that crap fuel in your machine. if the seafoam does not help i would get good rebuild kits for the stock carbs you could have a leaky fuel valve or a pitted/worn jet from the alcohol. ethanol fuels are really hard on the brass parts
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Last edited by cory52000; 01-13-2019 at 09:37 AM.
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post #5 of 6 Old 01-13-2019, 11:13 AM Thread Starter
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Yeah, i'm still at odds as to what I'm going to do. However, I ripped the carbs out again. Took them all apart just to see. This time, I paid a little closer attention to things. Found one of the O-rings for the air screw was torn. Also, realized the main jet seals are flat and have no pliability. As mentioned, fuel fuel tank was emptied and cleaned thoroughly. So I'm going to get a fresh over-haul kit, tidy them up and try again. It's frustrating when parts aren't readily available. The intake boots are still pliable, but I'm sure the seals are flat, so I'll order those as well.
I'll keep y'all posted, but if anyone has any other ideas, chime in. It seems like a lean stall.
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post #6 of 6 Old 01-20-2019, 11:58 AM Thread Starter
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SO here's an update. I ordered a rebuild kit from AllBalls. Wasn't going to spend the extra money piece mealing parts from Yamaha. Much to my surprise and liking; the AllBalls kit had a new design flost needle and seat. The seat is stainless steel with a fuel screen. A little extra protection can't hurt, especially when you found the in tank fuel valve screens laying in the bottom of the tank. Anyways, got carbs assembled and bench set, installed and fired her up. It's in the low 50's so 'choke' was necessary. As it ran for a couple minutes, slowly took choke off, adjusting idle RPM as needed. Choke all off, idle set, seems to be OK. No backfire and stall currently; knocking on wood. Will still need tuning, but need to get out and ride. Tuning will be a challenge with all the different elevations here, but i'm further ahead than I was. Now to either ride more often again or sell her. Riding gear don't fit so well anymore. Apparently I got fat! LOL!
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