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Old 05-10-2016, 01:25 PM   #1
2008G29Green
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Default 2008 Yamaha G29 Backfiring

Hello Everyone,

I'm new to the forum and recently bought a 2008 Yamaha G29, gas. I've done some work to it, bought it from a local dealer used. It ran fine for three weeks and now I'm getting a BAD backfire after revving up and letting it coast (especially down hill) it won't backfire until I hit the accelerator pedal again (even slightly) then BAM! The dealer adjusted the governor down (getting 22-23mph top end speed) and it was running great for a while, now this problem is persisting for the last few days.

Based off of what I've read on this forum and consulting the Yamaha official service manual, I've compiled what I currently believe to be the best course of action troubleshooting the issue. Put this together for everyone's benefit but please feel free to share an edit/opinion if you think something should be higher on the priority list or if something is amiss here. Thanks for advance and hopefully this is pretty close to correct!

1. Throttle plate in the carb not closing completely when accelerator is not depressed, (like when coasting) Adjust cables to accelerator pedal (under floor access panel) to ensure there is slack and not too tight.
2. Throttle plate in the carb not closing completely at idle – too much fuel, running rich and leftover fuel is combusting in exhaust chamber and/or muffler (loud bang). Adjust air mixture screw on carburetor?
3. Air leak (bad or poor seal) causing engine to run lean (too much air). Check airbox bolts (4), especially the (2) that hold down carb to engine intake. These should all be tight and properly torqued.
4. Air leak (bad or poor seal) causing engine to run lean (too much air). – check/replace carb gaskets to A. airbox to carb & B. carb to engine intake
5. Back down governor to a slower speed and lower RPM. Opened (no) governor can sometimes cause backfiring
6. Muffler too loose, check muffler bolts and check/replace header gasket between engine and muffler
7. Carb needs to be adjusted with screws to run more/less lean – adjustment screws, adjust and test mixture
8. Carb needs to be completely replaced – new carb and gaskets
9. Needs a new muffler overall, replace muffler and gasket
10. Engine needs a valve adjustment? described in service manual and this link: http://www.buggiesgonewild.com/gas-y...ackfiring.html
11. Replace spark plug – already new
12. Change oil, ensure proper level and oil is clean - fresh
13. Ensure fuel is fresh, non-ethanol, with proper proportion of fuel stabilizer and system cleaner (similar to SeaFoam)
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Old 05-10-2016, 06:50 PM   #2
smallblock450sl
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Location: Tacoma Washington
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Default Re: 2008 Yamaha G29 Backfiring

Does the throttle shaft "alway's" return to fully closed position? Did "someone" turn the throttle stop screw in? People now rent golf car fleet cars and know how to tamper with them, had a couse that they would grab cable #2 at the carb and give it a "yank", cinking the cable and not alowing the throttle shaft to return to fully closed position. Incorrectly adjusted valves can cause back fire also.
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Old 05-17-2016, 02:05 PM   #3
DakotaEight
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Default Re: 2008 Yamaha G29 Backfiring

Maybe your jet is dirty?
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Old 05-18-2016, 10:05 AM   #4
2008G29Green
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Default Re: 2008 Yamaha G29 Backfiring

Update, I've tried what seems like everything I've listed above! The throttle plate is closing fully when there's no pressure on the accelerator pedal (even did the flashlight test several times). Carb was totally taken apart, cleaned and inspected. Tried adjusting the mixture screw but that doesn't really move much or make a difference. The seals and bolts are all good from the airbox and to the muffler as well. The fuel is fresh and it has a new spark plug and engine oil. I'm now going to try completely replacing the carb. Going to try an aftermarket one from ebay first (the OEM one is $200+ compared to $40 for an aftermarket). If that doesn't work then it's going to have to go into the shop for the valve check/adjustment process as that's one of the few things left and I don't have the tools to do it myself.
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Old 05-18-2016, 07:01 PM   #5
smallblock450sl
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Default Re: 2008 Yamaha G29 Backfiring

Take off the "rubber" cover between the muffler and engine. Check to see if the nuts are tight, blown exhaust gasket or if the flange or header tube welds are broken.
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Old 05-19-2016, 09:21 AM   #6
2008G29Green
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Default Re: 2008 Yamaha G29 Backfiring

Thanks for the tip, I will try that as well!
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Old 07-25-2016, 05:43 PM   #7
Monterey
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Default Re: 2008 Yamaha G29 Backfiring

Were you able to resolve your backfiring?
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Old 07-26-2016, 08:11 AM   #8
2008G29Green
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Default Re: 2008 Yamaha G29 Backfiring

Not totally. It got better after a new factory carb and several hours of tweaking/tuning but i'll still get a good pop occasionally. Not nearly as bad as it was originally and the frequency is 20% of what it was originally but it's not totally gone. Part of it is just how i drive it now, knowing to let it rev down a hill and not hit the gas pedal until i'm almost stopped to avoid the backfire
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Old 10-24-2019, 07:36 PM   #9
dgt
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Default Re: 2008 Yamaha G29 Backfiring

I have a 2010 G29 that started backfiring very badly this week when coasting down a steep hill that I travel down daily when using the cart (from parking lot at marina to docks) - the backfire would happen right when I pushed the gas pedal at the bottom of the hill. I could actually replicate the backfire by pressing on the gas while coasting down the hill - it would backfire each time on command.

Thanks to these forums and cgtech's statement that "most all backfires on the g29 are from an air intake leak or exhaust leak (paraphrasing), I looked for any such leak.

I found 3 of my carburetor gaskets had blown out or cracked - some worse than others. This is Item 4 in the list above provided by the OP. This allowed to much air in when coasting thus causing the backfire. I did a temporary fix with gasket maker since I'm 6 hours from anywhere that would have a gasket and confirmed that this fix stopped my backfire problem. It did. So I'll pick-up new gaskets and replace next trip, but the cart is now usable without scaring the crap out of my dogs riding with me and the people of the docks.

Thanks OP for the general list of items to look at on this forum, and the specific statement from cgtech of the first two things to look at when our Yamaha's are backfiring. -Doug
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