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07 grizzly 700fi runs rough,black smoke out the exhaust

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Hi everyone how are you.I have a 2007 yamaha grizzly 700efi .One day out of nowhere my atv started to run really rough.turns over fine but i need to press the throttle for it to start and hold it here and there so the atv does not stall out.it does not stay idling.its really choppy at low revs and as i press the throttle it gets better almost normal in high revs.i have the original exhaust and i drilled out the baffle in it for better flow and i also installed a stealth exhaust.stealth exhaust is a extra exhaust and it acts like a silencer.i also noticed lots of black smoke coming out the exhaust. i had this set up for 3-4 years with out a problem till about a year ago. i tried lot of things like: new spark plugs,different spark plugs,new k&n filter,ignition coil,adjusted the valve clearance,swapped ecu,checked all fuses,took stealth exhaust off,drained old gas and put new gas in,and so far had no luck the atv is not showing any error codes.if anyone can help that would be great,thank you.

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Based on what you have described, here is what the manual says could be the problem(s). I hope this helps you.



● Improperly returned starter plunger

● Loose pilot jet

● Clogged pilot jet

● Clogged pilot air jet

● Improperly adjusted idle speed

(Throttle stop screw)

● Improper throttle cable play

● Flooded carburetor

Electrical system

● Faulty spark plug

● Faulty CDI unit

● Faulty pickup coil

● Faulty charging/rotor rotation direction coil

● Faulty ignition coil

Valve train

● Improperly adjusted valve clearance

Air filter

● Clogged air filter element

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You are most likely having an injector issue.. It's prolly dirty and wil need cleaned out with injector cleaner .. If not it's your throttle position sensor that's bad .. Hope this helps

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I appologize, CK may be right, I was looking at the wrong manual. Heres the info from the correct manual:


Electrical system

• Faulty spark plug

• Faulty ECU

• Faulty crankshaft position sensor

• Faulty ignition coil

Valve train

• Improperly adjusted valve clearance

Air filter

• Clogged air filter element

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