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General Category >> Rubber Side Down! >> Backfiring and Surging
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Message started by nedelden on 06/18/15 at 19:50:10

Title: Backfiring and Surging
Post by nedelden on 06/18/15 at 19:50:10

When I throttle down, my S 40 backfires. Also, at steady speeds the bike has minor surges. If I keep the choke at half way position the both issues are somewhat better.

The bike is 2005, 9500 miles and no mods from what I know. No doubt it is running lean and hot as both exhaust pipe and Muffler is blue. Pulled the brass plug and backed off mixture screw but still same problem. And the muffler has a hole near the connection to the exhaust pipe.

Title: Re: Backfiring and Surging
Post by bobert_FSO on 06/18/15 at 20:00:55

Classic indications of carb jets too lean. The question now is which jetting circuit is it?

Backfiring may be the idle circuit. Either removing the plug to the idle mix adjusting screw or a step richer of idle jet might help.

I assume the surging is at part throttle. If that is the case, I would try slide needle spacer mod to richen up the mid-throttle range. The link explaining the procedure is on the site here somewhere.

If you get surging or sputtering at full throttle and it gets better by backing off the throttle just a hair, the main jet is too lean.

Title: Re: Backfiring and Surging
Post by justin_o_guy2 on 06/18/15 at 20:31:28

Including year model and miles and any mods done helps.

Title: Re: Backfiring and Surging
Post by Gary_in_NJ on 06/19/15 at 05:11:53

If you are experiencing surging at cruise speeds (50-70 mph) it's your needle circuit. Remove the white spacer under the needle and replace it with 2 #4 ss washers.

Regarding the after firing...learn to love it.

Title: Re: Backfiring and Surging
Post by Kris01 on 06/19/15 at 07:09:05

There are tons of threads around here dealing with how to reject your carb. Plenty of pictures too! It's a simple process. The only hard part is getting the carb out to disassemble it. Don't be afraid to tear into it. We can walk you through it if need be. Once you get the carb out it's about a 5 minute process.

What is your elevation? That's a determining factor in figuring out what jets you need. I'm roughly at sea level and used the stock pilot and the next larger main with a slight change in the washer thickness for the midrange (see signature). The higher up you are, the less air there is so you will need less of a change in jetting.

Title: Re: Backfiring and Surging
Post by justin_o_guy2 on 06/19/15 at 08:52:04

There are tons of threads around here dealing with how to reject your carb.

Now, now, lets not create emotional problems with it. Just get the mechanical stuff done.

Title: Re: Backfiring and Surging
Post by Tomi on 06/21/15 at 15:56:06

4D746F753637060 wrote:

There are tons of threads around here dealing with how to reject your carb.

Fifty Ways to Leave Your Lover?

Title: Re: Backfiring and Surging
Post by justin_o_guy2 on 06/21/15 at 16:33:28

Backfiring and Surging

If not its own chapter, then surely a coupla paragraphs in my autobiography. Friends and family alike have rejected my carburetor.
Sometimes,life just hurts.

Title: Re: Backfiring and Surging
Post by Sonny on 06/25/15 at 15:21:14

I don't *like* the burbling and popping on a backing throttle, but it encourages me to avoid hard engine braking, and loud pipes save lives & etc...

As with any vehicle, there are a lot of ways to ride a Savage from hard to easy. I'm an old guy and I like to take kind care of my engine, brakes and everything when riding. My mill has never seen redline. It's tight and happy. But that's just me, pampering it like a tractor engine. The Savage is capable of savagery, as long as you're willing to deal with the wear and tear and fine tuning.

This is a good time to thank SS dot com for the Raptor petcock, the seat mod, the idle mix screw bidness and other stuff. Great improvements at low cost... sweet!

I do have a fork seal that is not responding to the home made hooked plastic cleaner-outer tool, so I'm fixing to wade into the forks. The riser was dinged on that side by sand or gravel. I smoothed out the sharp pits with emery cloth and I have some nice Bike Bandit accordion boots to put on and stop that from happenin' again.

Title: Re: Backfiring and Surging
Post by 1st2know on 06/25/15 at 15:56:46

42494849404849422C0 wrote:

... And the muffler has a hole near the connection to the exhaust pipe.

Fix this first. Carb tuning and jetting are not going to help you if you have a breached exhaust.

If the problem persists, test your petcock:
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