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1996 Yamaha Big Bear - Fouled Plug


ChristerLun

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I am about to buy a BB 350 -1996 that have a starting problem, but they change spark plug and then all is fine until next time, not sure how often but it sounded like it was common. Sparkplug gets black.

They drive it mostly short times, water to horses and back. Might it be only that reason"?

What would worst case scenario be?

They also got a flat tire so they bought one new tire, on 4wd I learned that is a big no no.

What do Big bear say about that? Lets say other tires is half worn.

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the plug is turning black because its running rich, higher fuel to air ratio. you could adjust the air/fuel mix screw and check air filter and vent lines to remedy. maybe run some carb cleaner through it too.

the tire isnt a big deal, unless it is a different size, i think you have 25" stock tires, if you run bigger or smaller, it would damage the 4WD system ,,, but if it is same size, you are good to go

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Thank's that was quick! :)

They have had it to a shop once a year for maintenance, they have not found any fix for it. Not sure if it was a good shop or how hard they tryed. But they told seller to inform of the plug when selling...

As long as it is no potentially "big" problem I am calm.

They said it stalls when cold if they leave it running, but cold engines can do that. Not sure how sensitive these are.

I have 2 hours in car to see it, otherwise I should have been there for a test drive already to see for my self.

Yes, it is stock tires so then it's no worry I guess, they belived it was original, the owned it for 10 years.

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Might it be oil fouling? Oil leaking in from valves or piston ring = engine rebuild?

Will I surely see blue smoke then?

Other way to see problem easy? Well, cant start to tear it a part before buying it, might not even pull plug...

It just hit me that they told me of spark problem 3 times, might they know that it needs more work then harder riding and want to keep their back free. Just got suspicious...

edit:

Just saw last post: Yes 350, valve tweaking like adjusting or pull top and change seal?

Edited by ChristerLun
Just saw last post
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Fouling could be from running cheap plugs -ie running to wally world and picking up a champion that "fits" rather than the correct NGK - also air filter/box could be packed with critter nest - that'll cause it to run rich and foul frequently (I always put a screen into the intake snorkel behind the tank to keep critters out).

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Hi again, was there yesterday and looked at it. 2 owners, last one for 10 years.

Engine did not feel good, smoke smelled very much burned engine oil. Dip stick smelled like exhausts. Runned bad om idle, but ok on some rpm. Trivetrain felt good.

Moss was growing on skidplate, for real!

Very black smoke, snow got black after 3 seconds, I smelled burned oil for the rest of the evening. Engineblock was leaking oil in middle, carburator was rusty (all steel items), well everything steel was rusty. Shifting gears was easy, some times. Pull starter was stuck, lights was flickering, cut wires was hanging and so on.

Drivetrain felt fine anyway, must be sturdy...

There was no deal ;)

They said afterwards they didnt now from time to time if it was going to start or not when they tryed.

Thank you for all answers!

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  • 1 month later...
you could use a hotter plug in it too to help burn away the fouling ... your plug should be an NGK D8EA and the hotter plug would be a D7EA ... the valves might need a tweaking too ...

this is the 350 model??

Hey Oxi-Black, I own a 1998 Big Bear 350 4x2 with a similar spark plug issue. I recently pulled out plug and she is BLACK. It is a NGK D8EA. Heres some background info; I installed a snorkel on her a couple years ago and raised the carb needle one notch and it ran alright until the stock muffler rusted out completely. I upgraded to a DG RCM ll slip on exhaust and bike ran only so so. It backfired when I would punch throttle and sputtered a little when I would be creeping thru a watery mudhole. I rejetted the carb. The bike ran great and was very peppy. Exhaust no longer backfired. After a long ride the hot motor would sometimes stall out when I would creep thru a watery hole on trails. Bike has sat in my shed for MONTHS and I recently went to drive it and it runs like crap. Its hard to start, doesnt want to stay idling, and if I drive it up an incline it stalls. It also stalls if I punch the throttle. I went to drive it up my trailer ramps and it kept stalling. I changed the spark plug for new one. I test drove it and same result. I immediately removed plug after 10 min of riding and its already getting black. ANy ideas? DO I need to rejet carb again? I thought I had it dialed in perfect but now it runs like crap. The stalling when I go uphill is really weird. If u need to know the size jets I replaced the stock ones with, Ill have to find the paper I wrote it down on. I did this months ago and cant remember the Jet sizes. I plan on cleaning the carb since it was sitting for several months with no use. I live in FL so this bike never sees severe cold weather. ANy help is appreciate bro.

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I think I`ll have to pull out carb to examine it. I once had trouble with the float sticking and the carb used to get flooded and pour fuel out of overflow line. Maybe float is sticking again? Its just weird the bike runs pretty solid from low throttle to 3/4 throttle, but when I punch WOT it stalls out and when I drive bike on a steep hill it stalls out. Does this sound like the carb is being flooded with gas? I`m no carb expert but I have taken the thing apart several times since I`ve bought bike, so I`m familiar with the components. I think my next ATV will be EFI for sure. LOL! :confused:

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