Backfires when you try to rev up engine, It backfires and pops whenever I try to rev engine in gear or out of gear then shuts off, will crank and idle with no problem.

Hi there,

Have you check the valves and the valve gaps?? Sometimes but not always having the wrong valve gaps can cause backfires. Have you also tried tweaking the carburetor to try and improve the idle??

Could be short or faulty switch .look around for bare wires touching metal.,ext ext., test switches., maby battery to low to run bike as well... charge it or get new one .,.try them , and we can go from there

Try changing the spark plug. A bad plug will drive you nuts.

Check for vacuum leaks. Spay starter fluid around intake,carb base, etc., while engine is idling, listen for change in engine idle.
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fast idle start usually indicates an air leak somewhere.check carburettor bolts are tight and engine head bolts are tight.try that first

Try checking the ignition timing,then the valve timing. Should take care of your prob.

Two things, not enough gas coming through the carberater or a vacuum leak

Main jet in carburetor partially plugged? Has it been sitting a while, probably varnish from old gas. Clean carburetors.

check fuel flow and check spark at spark plugs

According to an "ATV Rider" 2009 article, "When the Grizzly was introduced in 1998 as a 600cc machine, the top was blown right off the displacement wars of the time."
It was replaced in 2002 with Yamaha Grizzly 660, an even bigger engine derived from the well-established all-terrain vehicle (ATV) Yamaha Raptor 660R.
Grizzly's 660 cubic centimeter (cc), four-stroke, liquid-cooled single overhead camshaft, five-valve engine performs well in open country, but sometimes it causes serious problems for owners.
Before you call a Grizzly dealer, however, trying a few tricks in your garage can save you a lot of time and money.

Check the fuel level.
Locate the fuel meter indicator on top of the multifunction display.
If it does not work properly, open the fuel tank, and push the Yamaha 660 Grizzly side to side.
Ensure the fuel is not contaminated by water or rust.
If you have not driven your Grizzly 660 for a long time, drain the tank completely, and fill it with a fuel tank cleaner.

Check fuel hoses for cracks or leakage.
The hoses should be soft and simple to bend.
Replace those that show any sign of wear.

Check the compression.
Screw a compression tester into the spark plug hole, and press the electric starter button.
If no compression exists, contact a Yamaha dealer.
Wipe wet or dirty electrodes with a dry cloth.
The spark plug gap should be checked regularly

Correct the spark plug gap.
Measure the gap with a wire thickness gauge.
If necessary, adjust it to 0.8mm using a screwdriver or replace the spark plug.
Use only a Yamaha-specified spark plug.

Check the Yamaha 660 Grizzly's battery.
Operate its electric starter.
If the Grizzly starts quickly, then its battery is in good condition.
If the engine turns slowly, check the battery lead connections, and you may need to change the battery.
If the engine still does not eventually start, your Grizzly is beyond home repair.

Carb is gummed up

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