Any Other Ideas?

[WildBill]

I have a 1997 Suzuki Savage LS650. It backfires on deceleration. I have read much on this and I did try the fix I read on this forum (remove the white spacer). While the bike seems to run better after this mod It still backfires. I thought it was backfiring less but I'm not so sure. While it's not really a big problem (and I can prevent it sometimes with a more gradual slowdown), it is annoying at times. Is there anything else I can try? Thanks for any help.

[intimid8er]

Did you adjust the fuel mixture screw?

[WildBill]

Yes I did but I don't know if it is correct. I turned it all the way in and then out until the fastest idle.

[intimid8er]

Did you readjust the idle screw to compensate also?

[WildBill]

I did. In fact I backed it out until the throttle stop wasn't even hitting it so I readjusted the Idle/air again a little lower. This step in the procedure didn't quite go as I read.

[intimid8er]

So you've adjusted the fuel mix screw....

You've adjusted the idle screw....

You've removed the spacer....

Did you remove ALL of the spacer or a partial amount of it?

[WildBill]

I removed the entire spacer. It did seem to improve performance. Before I could feel some holding back in second and third when accelerating now the acceleration is smooth but the annoying backfire is still there.

[intimid8er]

Do you still have the spacer?

And if so can you cut it in half?

Or better yet...go to Home Depot get some washers with the same diameter. Stack them up to about 1/4 the original height of the spacer. Try that. Keep adding or removing.

If it don't work...then a re-jet is probably in order for you.

[Easy Rider]

Originally Posted by WildBill

I did. In fact I backed it out until the throttle stop wasn't even hitting it so I readjusted the Idle/air again a little lower. This step in the procedure didn't quite go as I read.

If I understand this correctly, with the mixture screw in the best location, it idled so good that the idle speed screw wouldn't slow it down ??

So then you re-adjusted the mixture screw instead to slow the idle down??

If that is true,which way did you turn the mixture screw on the last adjustment?? If the answer is "IN, clockwise", then you might want to revisit that proceedure and make the last adjustment of the mixture screw in the OTHER direction....."out, ccw".

Come to think of it, I don't know for sure which way is lean and which is rich, so which EVER way you did it last time, try it the OTHER way !!

[WildBill]

First I turned the screw all the way in and then I turned it out until it had the fastest idle. Then the idle screw didn't slow it down so I turned the mixture screw in to slow it down a bit. You're saying I should turn the mixture screw back out some?

[WildBill]

BTW I think turning the mixture screw out (ccw) richens it.

You think I should put some washers in to add a little space but not as much as the original spacer. What does that actually do. I do like the fact that it seems to run better with out the spacer but the backfire can definitely be annoying.

[intimid8er]

Originally Posted by WildBill

First I turned the screw all the way in and then I turned it out until it had the fastest idle. Then the idle screw didn't slow it down so I turned the mixture screw in to slow it down a bit. You're saying I should turn the mixture screw back out some?

Easy is right.....

The proper procedure...(I assumed you had researched it thoroughly) is to turn the screw all the way in until flush, and back it out two and a half turns.

Then balance adjust the idle back to where it was originally. Play it by ear as best as you can without hooking up a tach.

Originally Posted by WildBill

BTW I think turning the mixture screw out (ccw) richens it.

You think I should put some washers in to add a little space but not as much as the original spacer. What does that actually do. I do like the fact that it seems to run better with out the spacer but the backfire can definitely be annoying.

It's been found that some of these, require a little bit of tension to work better. Hence, the little bit of spacer. As opposed to removing the entire thing.

[Easy Rider]

Originally Posted by WildBill

BTW I think turning the mixture screw out (ccw) richens it.

OK and the problem that causes the backfire is that it is WAY lean. So if you must adjust it OFF the ideal idle mixture, you should adjust in the direction of RICH, not lean (which is back toward where you started).

I would certainly give that a try before taking the carb apart again.

Stock pipes and air-box ??

[WildBill]

Thanks. Yes everything is stock. One question, when you say turn the mixture screw all the way in until flush do you mean until it stops? That is what I did and then adjusted out.

[intimid8er]

Originally Posted by WildBill

Thanks. Yes everything is stock. One question, when you say turn the mixture screw all the way in until flush do you mean until it stops? That is what I did and then adjusted out.

Yes...then back it out two and a half turns.


Then adjust the idle screw.

[Blade]

I looked at the parts diagram and do not see anything like air injection system like the P.A.I.R. on Suzuki's?. I would check the gasket between the header pipe and the cyclinder head to make sure it is not leaking.

Back fire depending on where it is coming from:

Exhaust:
Air getting in and igniting the unburnt fuel.
Leaking exhaust valve and some flame sneaks by sometimes. Leaking can be caused by out of adjustment on the tight side, bad or burnt valve.

Intake:
Same as exhaust leaking valve.

[diamond_jim]

Originally Posted by Easy Rider

OK and the problem that causes the backfire is that it is WAY lean. So if you must adjust it OFF the ideal idle mixture, you should adjust in the direction of RICH, not lean (which is back toward where you started).

I would certainly give that a try before taking the carb apart again.

Stock pipes and air-box ??

In my experience, backfiring is the result of the mixture being too rich, not lean. When it is too rich, then unburnt and sometimes still burning gases pass through the exhaust valve port and ignite or finish burning when they hit the high temperature of the header pipe. Then the fuel igniting in the header pipe (backfiring) instead of in the cylinder, makes the header pipe a lot hotter causing the header pipe to start to turn blue.

[Easy Rider]

Originally Posted by diamond_jim

In my experience, backfiring is the result of the mixture being too rich, not lean.

Very true. I do NOT believe that is the case with the S40/LS650 however.
I think the sound produced is more of a pop as opposed to a real (LOUD) backfire.

[WildBill]

Actually it was at times a real loud backfire. At any rate I revisited This over the weekend. I didn't put any spacing back as I noticed after removing the spacer it did improve the way it ran. So, I turned the mixture screw all the way in and then backed it out two turns (2 1/2 seemed too much by ear). The backfire seems to have gone away. I have even tried to get it to backfire but it hasn't for two days now. It seems to run generally better and idles better. Thanks to the info I found on this site I think it's running like it should now.

[Easy Rider]

Originally Posted by WildBill

So, I turned the mixture screw all the way in and then backed it out two turns (2 1/2 seemed too much by ear). The backfire seems to have gone away.

Good show!

How long has it been since you put on a new air filter?
When you do, you might need that last 1/2 turn.