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Message started by Tony on 09/21/05 at 08:39:32

Title: Need help with carb/backfire
Post by Tony on 09/21/05 at 08:39:32

I am having trouble getting my carb tuned right. I have an '05 S40. I have already performed the White Spacer Mod and replaced the main jet with a 155. I installed both a Sportster Muffler and a K&N air filter. No matter how I adjust the mixture it seems to backfire whenever I shift or when coasting down to a lower speed. The poping gets worse when putting back pressure on the engine such as coasting down a steep hill. I started the mixture at 2 turns out and adjusted both ways using 1/4 turn intervals. Do I need to change the Pilot jet as well?

Title: Re: Need help with carb/backfire
Post by Dynobob on 09/21/05 at 09:54:43

The first thing I would do would be to make sure you have no exhaust leaks. Replace the crush gasket where the header pipe connects to the cylinder if you've loosened it at any time. Seal the muffler to header pipe connection with Permatex high temp silicone. Make sure you get the high temp for exhausts.

Popping on deacceleration is due to leaness in the slow mixture screw / pilot jet. You don't need to go to a bigger pilot jet unless you screw the slow mixture screw out alot (4 turns +) and still need more richness. I think at 2 turns out you should be fine. That's about where mine is set with the stock pilot jet. Turn the scew out a bit more and see if that helps with the deacceleration popping.

Title: Re: Need help with carb/backfire
Post by mmm63 on 09/22/05 at 10:08:05

Hello - I have a 05 boulevard 650 and it has been in the shop 3 times so far for such backfiring that it shakes the bike. I also backfires about 8 times per day. The shop tells me that there is nothing else they can do about it due it being a single cylinder and all single cylinder bikes do this. Does anyone else have this problem with there suzuki single cylinder??

Title: Re: Need help with carb/backfire
Post by Paladin on 09/22/05 at 10:28:04

Fixing the Backfire. AFAIK, the dealer is not allowed to do so legally.

http://suzukisavage.com/cgi-bin/YaBB.pl?board=tech;action=display;num=1104205157

Title: Re: Need help with carb/backfire
Post by Savage_Rob on 09/22/05 at 10:34:47

A Savage backfiring? Hmmmm, let me think if I've ever heard that mentioned before.....

Title: Re: Need help with carb/backfire
Post by torque on 09/22/05 at 11:31:11

Savage_Rob wrote:

A Savage backfiring? Hmmmm, let me think if I've ever heard that mentioned before.....

ROFLMAO! ;D

Title: Re: Need help with carb/backfire
Post by mmm63 on 09/22/05 at 13:12:34

I just joined this site and asked about my 05 backfiring. I have got replies like they never heard this before and roflao and I don't get it. Is the backfiring common or what. I am being serious that this is a big problem for me. It has caused me to wreck once all ready. I was going around a bend on a gravel road and it backfired and shook the bike and down I went!! I have a friend who has the same bike and hers never backfired once!

Title: Re: Need help with carb/backfire
Post by torque on 09/22/05 at 13:26:07

ROFLMAO (rolling on floor laughing my as$ off) there are around 1000 posts covering this topic just look back a couple of pages.

damm it. ::)

Title: Re: Need help with carb/backfire
Post by Savage_Rob on 09/22/05 at 14:04:39

Better yet. Do a search. This site's search function works well. Just remember to set it for more than the default of 7 days back. I usually use 500 for mine but for a topic as well covered as backfiring, 60 should do it. Paladin's post above should've explained a lot if you click on the link and check out the post it leads to.

Title: Re: Need help with carb/backfire
Post by Tony on 10/02/05 at 18:34:38

OK, I know I have the same old question again but:

For some reason I cannot seem to get my carb tuned correctly with the K&N air filter. I have already done the spacer mod and installed a 155 main jet. Backfires are constant at a throttle down, including shifting. I reinstalled the stock filter and the bike runs great with little or no backfire. I searched the old topics and it apears i have done everything. Do I need a bigger jet or a different pilot jet?

Title: Re: Need help with carb/backfire
Post by Savage_Rob on 10/02/05 at 19:01:39

I wouldn't go to a bigger jet. I have the K&N direct swap air filter and a MAC muffler and the 152.5 is doing very well for me. One of the prime causes I've had for backfiring has been exhaust leaks. Make sure you don't have any between the cylinder and the header or between the header and the muffler. There are gaskets for both connection points. That's not to say you couldn't have a problem somewhere else but it's a fairly easy thing to fix and, at least for me, was the primary cause for problems with backfiring.

Title: Re: Need help with carb/backfire
Post by DavidV on 10/02/05 at 19:28:19

And don't snug the header-to-head bolts when the bike is warm. Very bad.

I'm running the same basic setup as you. The backfiring was mild with the Sportster muffler. I just got an occasional shut-down huff or some putter on decel. The big bang was gone after the 155 jet & white spacer mod. Going to a Screamin' Eagle muffler didn't change it much. Now it pops a little during shifts - no big deal.

You should definitely look for a loose exhaust connection.

And welcome aboard!

Title: Re: Need help with carb/backfire
Post by Tony on 10/03/05 at 03:40:07

I verified that I have no exhaust leaks. What I find confusing is that when running the stock filter everything runs great!

Title: Re: Need help with carb/backfire
Post by Savage_Rob on 10/03/05 at 06:05:25

Tony wrote:

I verified that I have no exhaust leaks. What I find confusing is that when running the stock filter everything runs great!

I don't want to harp on this too much but I do want to emphasize it. I did not think I had an exhaust leak either but I did have one between the cylinder head and the header pipe. Because of the way the header is recessed into the cylinder head, you may not see any soot or feel a leak. The gasket ring inside can become misshapen with loosening and tightening of the header. It's less than $4 at RonAyers (see part #2 (http://www.ronayers.com/fiche/300_0271/muffler/muffler.cfm)) and it's worth having a spare anyway. I went without changing it for a while because I saw no evidence of a leak and was frustrated with the backfiring. I even removed it and looked at it. The problem was that I didn't know how much different it was from a new one until I had a new one to compare it to. Just my .02. Good luck.

Title: Re: Need help with carb/backfire
Post by lancer on 10/03/05 at 09:45:00

Tony wrote:

********

Tony, you have provided the information needed for the fix in what you have already stated..."backfires with the K&N .....does not backfire much with the stock air filter".
What this tells you is that you are running LEAN with the K&N, because the K&N flows much more air which leans out the fuel/air ratio. When you put the stock filter back on, it does not flow as much air which makes for a richer fuel/air mixture.
So, in order to use the K&N (which is preferrable) you need to compensate for the extra air flow, and the way to do that is to provide more fuel...in the pilot circuit...so you need to go up a size on the pilot jet.

This does assume of course that there are no air leaks (as stated before) and that you are correctly tuning the pilot jet adjustment screw.

Keep in mind that a main jet change affects 3/4 -full throttle.
A white spacer or clip position change on the needle affects 1/4-3/4 throttle.
A pilot jet change and screw adjustment affects idle-1/4 throttle...AND THIS IS WHERE THE BACKFIRING ON DECELERATION ISSUE COMES FROM.

***Note that I said "throttle position"...not speed or rpm. Throttle position is what changes where the slide is in the carb. You will find that almost all backfiring on deceleration occurs when the throttle is at or near the idle position, and this is when the carb is operating in the pilot circuit...regardless of the mph or rpm.
The problem is caused by an incorrectly jetted/tuned pilot circuit...and the FIX must be within the same pilot circuit.

Title: Re: Need help with carb/backfire
Post by Tony on 10/04/05 at 04:12:11

Lancer, I was guessing there was a chance that this might be the case as it seems to run perfect when the old filter is in place. I have never played with the inside of the carb though and am apprehensive about attemtping the pilot jet change. The spacer mod was done at a local shop.Do you know what the stock pilot jet size is, or whatI should consider going up to?

Title: Re: Need help with carb/backfire
Post by lancer on 10/04/05 at 10:13:40

The stock pilot jet is #52.5, and going to the next larger jet...a #55, should take care of the pilot circuit problem for the stock carb.

The float bowl is the bottom of the carb and is held on by 4 phillips head screws (most riders replace those with allen head screws..about $2 at the hardware store).

Turn the carb over on its' side and take the float bowl off (it is easier to just pull the carb from the rubber mounting flange and the rubber filter tube).

With the float bowl off you will see the main jet in the very middle. (the stock main jet is a #145, and if that has not been changed then replace it with a #155) Next to the main jet is a tube like shape, look down inside and about 3/4" down you will see the small pilot jet. Use a "small" screwdriver to remove it and replace with the new pilot jet.

Then put the bowl back on, put the carb back on the engine, start it up and let it warm up for several minutes. Then readjust the pilot screw and reset the idle.

Keep in mind that the jets are made of brass and the carb is aluminum so be careful not to damage threads and such. Very snug but not HARD tight.

Title: Re: Need help with carb/backfire
Post by Kropatchek on 10/05/05 at 01:41:00

lancer wrote:

Keep in mind that the jets are made of brass and the carb is aluminum so be careful not to damage threads and such. Very snug but not HARD tight.

And a correct fitting screwdriver.

Greetz
Kropatchek ;D

Title: Re: Need help with carb/backfire
Post by Tony on 10/05/05 at 04:14:57

Thank you for the help. I am going to have to wait now until the weekend to do this. I am in the middle of a major floor replacement in my living room, and my wife says no bike till this its done (I cant argue with her).

Title: Re: Need help with carb/backfire
Post by alwaysuphigh on 05/31/13 at 13:15:19

i had the same annoying problem. finally one day, i went to start her up. she flooded so bad gas puked out of the breather tube. of course that means the crankcase was now full of fuel. i took the time to pull the carb off, and found all the jets were clogged. also, the choke shaft on the inside of the diaphragm area was covered in gunk. i soaked the carb overnight in denautured alcohol, remved the jets and cleaned them. i had to shove (carefully) small gauge wire thru them to open them up.
also, i re jetted the them with slightly bigger pilots.
put her back together and she fired right up. i have been riding ever since with great compression and no backfire. also, i changed my oil to 20/50. i talked to a savage guy who says these bikes like that best.

hope that helps!

Title: Re: Need help with carb/backfire
Post by Dave on 06/02/13 at 04:15:35

717C67716963656078797778100 wrote:

i changed my oil to 20/50. i talked to a savage guy who says these bikes like that best.

The Savage may like 20W50 best when it is really hot out.....but the bike runs well on 10W40 just the same. A lot of us are using Rotella T with is 15W40.