02 Grizzly 660 Backfires

More than likely that new carb is the issue. Did you fine tune it or did you just install it and ride on?
What kind of carb was It? A factory OEM carb or a Chinese eBay special.

Try adjusting the pilot needle (Idle Air Screw) 1/8 turn at a time. See if it improves.

It is a factory Mikuni Yamaha carb. Cost me a pretty penny over the cheaper Chinese ones( I bought one of those but it ran badly so I junked it). I just installed the new factory carb and rode on, I thought these came pre-set to factory specifications. After riding some more today on the bike it didn’t maybe 3-4 times in about 2 hours of riding time. A backfire would mean it’s running lean, so just adjust the air/fuel screw out?

That's good that you got a factory carb. Money well invested. You need to find tune it, that's all.
Adjust the pilot needle. Out to richer, in too lean.

Definitely a higher quality carb all the way around over the Chinese copies. The adjustment must just be slightly out, only backfired twice in today’s ride which was a little over an hour of run time. Once the snow clears from the blizzard we had and I can get the bike back to my garage I’ll see about adjusting it. Btw, these bikes are amazing in snow compared to anything else I’ve driven.

If you find adjusting the pilot needle does not cure the issue, you'll need to adjust the clip on the main jet needle. Move it down to enrichen, up to lean. Most clips are in the center position from factory.

Where’s the main jet clip located? Also how do you know when it would be time to adjust the clip? I don’t think I’ve come across that yet.

Subzero said:

Where’s the main jet clip located? Also how do you know when it would be time to adjust the clip? I don’t think I’ve come across that yet.

Click to expand...

It's not a main jet clip...It's the main jet "needle" clip.
You'll need to pull the vacuum slide out the top of the carb. The needle will come out with the slide. Remove the needle from the slide and you will see a small c-clip on it, with several (usually 5, some have only 3) different areas to position it on the needle. Moving the clip down lifts the needle for a richer mixture. Lowering the does the opposite.
All stock bikes on stock carbs that I have worked on have always had the clip on the middle position.

How far can the pilot jet be adjusted before I need to switch to the adjusting the main? I read that a stock bike like mine should be at about 2.5 turns out from lightly seated.

Adjusting the pilot and adjusting the main are 2 separate adjustments. You don't run out of one then start adjusting the other to compensate.

The pilot needle and pilot jet are for 1 circuit, while the main jet is for a different circuit.
The pilot circuit is idle and low rpm. The main jet circuit is mid to high rpm.

The pilot needle stated turns out is a starting point. Every different bike can be a different adjustment. They will only be off a slight amount though. That's why I say you only make adjustments 1/8 turn at a time.
Now there does come a point that you may need to change out The pilot jet. Although I have never seen a completely stock bike require changing of the stock jets in a stock carb.

Have you verified the jets in your new carb are the same size of jets that were in the old carb that you removed? That might be your issue.

Thank you, the bike runs well currently other than the occasional backfire so I’d hate to cause it to run worse by adjusting it wrong. I’ll try adjusting the pilot jet first and if it has to go over a half turn out then move on to the main. The jets should be the same- both carbs are stock.

bake fire issue

Hi there had something similar happen on my 04 grizz after pulling carb out, in my case at some point the spark plug boot got just alittle loose maybe putting plastics back or something and caused that issue. worth a quick check , 4500 miles plus and still tear'n it

Got the bike back to the shop and checked for I take leaks and that the spark plug boot was on correctly. Ended up slightly adjusting the idle up and turning the pilot jet up about 1/8. Doesn’t backfire unless you ride it so next time I go out I’ll have to wait and see what happens. Thanks for the help