SuzukiSavage.com - Print Page

SuzukiSavage.com
/cgi-bin/YaBB.pl
General Category >> Rubber Side Down! >> Pilot jet size?
/cgi-bin/YaBB.pl?num=1150860014

Message started by wild one on 06/20/06 at 20:20:14

Title: Pilot jet size?
Post by wild one on 06/20/06 at 20:20:14

I've read alot of the posts on rejeting and our infamous backfiring issue. Ive done some of the mods but still backfire about 20% of the time when upshifting from 2-3 and 3-4 gear and also when engine braking. Currently I have a sportster muffler (which I love), 1/2 spacer, 152.5 main and the mixture screw set at 2.25 turns out. I know it's set a bit rich because I don't need to use the choke to start it. Just hit the starter and she starts right up and doesn't die. Last I checked the spark plug it looked fine. No carbon. I don't think there are any exhaust leaks. I'd really like to eliminate the backfire completely. Should I try a bigger pilot jet? I see many here go with the #55. According to the model year there should be a #52.5 in it now.

Title: Re: Pilot jet size?
Post by 911radioman on 06/20/06 at 20:50:55

Good luck. I upped mine to a 55 pilot and still get backfires when upshifting from 1-2 and 2-3. I've checked every joint on that thing that could leak as well as gone thru the carb and verified no plugged jets/passages.

Title: Re: Pilot jet size?
Post by Jim_R on 06/22/06 at 07:53:00

sure its not a leak in ur exhaust??

when in doubt . weld it. haha

it will work.

Title: Re: Pilot jet size?
Post by 911radioman on 06/22/06 at 11:55:51

Jim_R wrote:

sure its not a leak in ur exhaust??

when in doubt . weld it. haha

it will work.

Jim, as far as I can tell there are no exhaust leaks. I used new gaskets at the muffler and at the header, and the bolts are torqued very well at both locations. I'm going to go back to the carburetor at the advice of Brewbrother and check the boots on the intake/exhaust sides of the carb to make sure they're not overtightened.

Other than that, I don't know which way to go next but I know it is about to pi$$ me off! :(

Title: Re: Pilot jet size?
Post by Brewbrother on 06/22/06 at 14:47:23

911radioman wrote:

over or under tightened. either way you will have a leak and a potential backfire.

Title: Re: Pilot jet size?
Post by azjay on 06/22/06 at 15:32:15

debby's backfires just about the same as yours, you can see by our signature, we've done all the mods, i dont truthfully think the pilot jet had much effect on the shift-bang, but it did change the idle mix sweet spot and added a little poof in the tailpipe a couple seconds after the engine is shut off. i can nearly eliminate the backfire/shift-boom, by not returning the throttle to the totally closed position between shifts, and rapping the throttle during downshifts. i attribute the current state of pop/bang to a rather short (17") and open muffler, i may futz with it later to see if i can eliminate it for real, but for now, i make her ride on the right side of me ;D

Title: Re: Pilot jet size?
Post by steelwolf on 06/22/06 at 16:25:05

The only way I got my bike to stop the backfire compleatly after the new #55 pilot was to turn out the mix screw. I reworked all the joints in the intake and the exhaust, turn my mix back and forth 8 thousand times and it still poped at the shift. Finally I got mad turned it out to 3 and no more pop. Since then I have been working it back in. It now sets comfortably at 2.75 turns out. But keep in mind I am running an open 1.75"OD pipe and the stock air filter in the stock air box with my 152.5 main, #55 pilot, and 1/2 spacer.

Title: Re: Pilot jet size?
Post by lancer on 06/22/06 at 16:44:31

Carbs are fun, aren't they? ;D

Title: Re: Pilot jet size?
Post by 911radioman on 06/22/06 at 17:05:49

lancer wrote:

Carbs are fun, aren't they? ;D

NO!
;D

Title: Re: Pilot jet size?
Post by klx650sm2002 on 06/23/06 at 05:37:20

Definitely yes carbs are fun.

Clive W :D

Title: Re: Pilot jet size?
Post by JerryAssburger on 06/23/06 at 06:34:23

Okay- don't laugh, but here's a quick and dirty check for exhaust leaks. (Mine leaks)......
Start it up cold- within the 1st minute of running plug the end of the exhaust pipe with your hand as it's idling. (The pipe shouldn't get too hot yet.) You will hear hissing/leaking noises from wherever the leak is; or, you'll hear nothing and your engine will slow down and die. That's how I found several pinhole rust leaks in the the stock muffler. Hope this helps.

Title: Re: Pilot jet size?
Post by azjay on 06/24/06 at 07:59:54

neat hint, thanks we'll give that a try. sometimes the simplest ideas can be the ones that elude us.

Title: Re: Pilot jet size?
Post by serowbot on 06/24/06 at 09:43:09

To rich can also cause a throttle off backfire. I often ride from 2600ft where I live, to 9000ft. The thinner air up there causes a richer mix and a very noticable corresponding increase in backfires. I noticed the same thing with my yamaha 225 serow and cured it by decreasing jet size in it from 130# main to 127.5#.
Your needing no choke when cold is a tell that your on the rich side.
I know this is against common logic, but it did work for me. A lot of people don't have the advantage of a 7000ft elevation change to try this, but if you do it can be a useful tuning tool.

Title: Re: Pilot jet size?
Post by wild one on 06/25/06 at 19:34:21

JerryAssburger wrote:

Thanks for the tip. Istead of using my hand I used a potato to plug the end of the muffler (saw it in a movie) ;D and sure enoughthere were leaks at both ends of the 10 degree adapter. I put some soapy water by the clamps to get a visual on any leaks and the bubbles were very easy to see. I'm off tomorrow to the local muffler place to get a new adapter and their recommendations for sealing the system. Maybr I need better clamps or possibly weld the pipes together.

Title: Re: Pilot jet size?
Post by lancer on 06/27/06 at 04:38:47

A properly done weld WILL seal that puppy right up ... permanently. Whenever possible, I weld.

Title: Re: Pilot jet size?
Post by wild one on 06/27/06 at 21:17:11

lancer wrote:

A properly done weld WILL seal that puppy right up ... permanently. Whenever possible, I weld.

Got a poor welding job done today. Had to go back to have it redone and even then it's not 100% sealed but it is much better than it was. When doing the soap & potato test there are at least two pin hole size leaks that I can see where the weld does not seal completely. The backfiring is reduced but not eliminated. It seems there is less poping during upshifting and just as much if not more during deceleration and engine braking.

I'm getting a #55 primary jet any day now. Hope that helps some, we'll see.

:-/

Title: Re: Pilot jet size?
Post by lancer on 06/28/06 at 06:09:37

There you go, it's mostly in the pilot circuit. You're the right track.

Title: Re: Pilot jet size?
Post by rokrover on 06/28/06 at 10:28:48

There's so much been posted about the backfire problem others may have already noted the following. Backfiring is inherent to single cylinders exhausting through one pipe. Especially when that pipe has a restrictive muffler to accumulate unburned mixture. Fiddling with the mixture and exhaust too much overcompensates in other areas of tune even if it eliminates the "backfire prone" zones. Multiple-cylinder engines don't suffer as much when they have a header that uses the exhaust from one cylinder to help extract the flow from the others. This "tuned extraction" effect makes gas flow more efficient for better running. All my old 4-stroke singles (Matchless, Velocette, Yamaha, Ducati) backfired to some extent under certain conditions of throttle / load. Certainly the SooZook 650 is the worst thanks to EPA jetting and restrictive muffler, but don't overcompensate by going too rich on one jet.

Title: Re: Pilot jet size?
Post by Savage_Rob on 06/28/06 at 10:42:01

Fixing the exhaust leaks, opening up the airflow (both supply and exhaust) and tuning the fuel circuits methodically (including rejetting) eliminated nearly all of the backfiring for me without making it too rich. I occasionally get a little decel rumble/pop if I use the engine and drive train to slow down. Some folks call it engine braking; I always just called it gearing down. That's basically the only time and I actually like it then. I never have it occur on throttle snapback at all

Title: Re: Pilot jet size?
Post by 911radioman on 06/28/06 at 11:35:40

Believe it or not, I have finally reached Nirvana (I hope)!!! Just as you, Rob, I only have pops on engine braking/gearing down now. I can snap the throttle closed with no backfiring at all.

I found my situation similar to Brewbrother, where my problem seemed to be in the rubber boots at the carburetor. Those things don't have to be torqued down to get a good seal, and I believe I was overtightening them and getting a slight air leak there.

I'll say this. It is darn near an art form to get these thumpers dialed in correctly. At least it is for me! ;D But, it is nice to finally get there.

Title: Re: Pilot jet size?
Post by lancer on 06/28/06 at 12:51:03

Outstanding!

One more success for the home team.

We can change the thumper world one man/machine at a time.

Title: Re: Pilot jet size?
Post by Island_Biker on 06/28/06 at 13:23:28

I guess I'm one of the lucky ones. I have no idea what kind of carb mods might have been made before I got my '86 this year, but I just get the popping on gearing down and the backfire on shutdown - which has been virtually eliminated by allowing some transmission tension during shutdown.

Title: Re: Pilot jet size?
Post by 911radioman on 06/28/06 at 13:31:07

Oh yeah, I get a fart on shutdown. ;D 8)

Title: Re: Pilot jet size?
Post by steelwolf on 06/28/06 at 20:10:24

Congrats to all that remove the backfire. Keep pluggin' away and it will end all together.

;) I love carb tuning! ;)

Title: Re: Pilot jet size?
Post by wild one on 07/02/06 at 21:34:09

This begs the question, does the backfiring hurt the engine? I've seen it written here by some that they fear engine damage if the backfire is not eliminated. Could Suzuki sell a product with this condition knowing it is damaging to the engine?

Title: Re: Pilot jet size?
Post by lancer on 07/03/06 at 08:04:43

Damage from backfiring is one of those "over time " things, not an instantaneous event. The Suzuki warranty is 12/12000, and they are probably figuring on the fact that if there is damage from this, it will be out of warranty by then. Besides, if the backfiring gets really bad, the customer will bring the bike to the dealership and want it fixed ($$), so they will do something to reduce the backfiring. My dealership pulled the plug off the pilot adj screw and turned it out a bit at the 600 mile checkup ... because I had been complaining about it everytime I went in prior to that, and at the 600 checkup I demanded something be done. I do have a better than average dealership, they actually listen (the shop supvr is a really good guy) and the mechanic knows what he is doing (he is about 40 and has been around the block a few times).
Anyway, it is a cost/return thing. Suzuki will make a lot more money on the bikes than they will have to spend on the remote possibility that there is engine damage during the warranty period.
I don't know of anyone who has left the bike bone stock with the backfiring and not done something about it. There are a few stock bikes that do not seem to backfire much... OF COURSE THAT MAY BE BECAUSE THE PEOPLE ON THE ASSEMBLY LINE MAY HAVE ACTUALLY ADJUSTED THE PILOT SCREW CORRECTLY IN THE FIRST PLACE. I know, but it COULD happen.