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General Category >> Rubber Side Down! >> New Muff and Rejet
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Message started by ohms on 07/24/06 at 05:49:41

Title: New Muff and Rejet
Post by ohms on 07/24/06 at 05:49:41

Hey guys,

Just finshed installing the Jardine pipe and some new jets a few days ago. Holy nuts is it loud. I really wasnt expecting that at all.

Anyway, I started off with a 145 stock main jet which with the new pipe and K+N, I immediately upped to 152.5. The bike was backfiring on decelleration like hell I adjusted the idle mix screw and seemed to reduce the backfiring, but still prevalant and loud at times.

After riding it over the course of a day, the bike seemed a bit rich on the top end, so I swapped out the 152.5 with a 150. Midrange to top end performance is great. Its like a totally new bike, but i still have the darn backfiring on decelleration or throttle roll off. I checked the header bolts to see if they were loose and tightened them up, thought maybe that was the prob.

The bike was still backfiring, so I thought ok its too lean I'll try to up a pilot jet to 55. I rode to work this morning and the bike is still doing the same thing backfiring and popping on decelleration. I've kinda gotten the hang of holding the throttle in such a way to avoid the backfiring but I shouldnt have to do that. Does anyone have any ideas of what i can try now to eliminate the backfiring?

Thanks for the help.

Title: Re: New Muff and Rejet
Post by lancer on 07/24/06 at 06:00:28

Larger pilot jet ... like you were thinking.

Title: Re: New Muff and Rejet
Post by Reelthing on 07/24/06 at 06:31:19

what did you do for the mid range (spacer/needle) ?

Title: Re: New Muff and Rejet
Post by ohms on 07/24/06 at 07:12:22

I currently have a shaved 1/2 spacer. The pilot jet i have in now is 55.

Maybe I dont have the idle mix screw adjusted properly. How I went about adjusting it was to warm up the bike first, take it out for a little ride. Let it idle in the driveway and then seat the idle mix screw all the way in counting the turns I originally had. The engine sounds like its going to die at this point. Now i slowly unscrew counting turns until the idle speed is at its highest.

Is this the correct method for adjusting the idle screw or should I be doing something else?

Title: Re: New Muff and Rejet
Post by lancer on 07/24/06 at 15:18:16

You are doing that correctly.

Title: Re: New Muff and Rejet
Post by Jim_R on 07/24/06 at 15:48:56

I think u got a leak in ur exhaust. I know u check ur nut (haha couldnt resist ;D ) but check the connection from the muffler to the header. Let ur bike idle and see if u can feel the exhaust escaping. Any carbon streaks coming from the connection? Did u use any kind of gaskets for the exhaust? I would check it over again and make sure before swapping the pilot.

Title: Re: New Muff and Rejet
Post by Brewbrother on 07/24/06 at 15:57:21

you should also check to make sure you have not crimped either side of the intake boot. An air leak at the intake causes a backfire like an exhaust leak.

Title: Re: New Muff and Rejet
Post by DianeS. on 07/24/06 at 19:10:40

I had the shop re=jet my savage and it still backfires a bit too. (I have a jardine muffler on my bike - it came that way when I bought it used). The mechanic said that due to a lack of back pressure from the jardine muffler, that they couldn't jet as much as they might have. I gave them the jetting specs. from this website and they said they'd do what I asked.

Anyway, the backfire is tolerable becuase the jetting did improve the performance and it isn't lean like it was. I get a bit of backfiring sometimes on decel - but no loud pop when I shut her down like I used to. Plus, if I don't decel rapidly I can avoid the backfire pretty well.

I'm no expert on mechanical stuff though - but I just wanted to give my views based on my bike and the jardine muffler.
DianeS

Title: Re: New Muff and Rejet
Post by wild one on 07/24/06 at 19:47:47

I'm with Jim on this one. Check the fit from the header to the muffler for leaks. Mine was leaking like a sive but I wasn't aware of it. An easy check is to put some soapy water where the muffler and header attach to each other then, with the engine idling, cover the muffler outlet with something. I used a potatoe but you can use anything. I was shocked when I saw all the bubbles coming from under the muffler clamp.

Helmut

Title: Re: New Muff and Rejet
Post by Brewbrother on 07/24/06 at 19:54:25

DianeS. wrote:

Thumpers get mild backfires on decel. Do you get any backfires when shifting up in gears?

Title: Re: New Muff and Rejet
Post by ohms on 07/25/06 at 09:59:09

Thanks for the help guys, I think the exhaust might have been leaking. I did the whole cover up the end of the pipe and soapy water bit but I didnt see anything. So just to make sure I put some silicone sealer around the connection and tightened the hell out of the clamp.

This morning I drove to work and voila I wasnt getting any backfires on decel or at least nothing major, occasional put puts. Now what seems to happen is backfiring on upshift from 1st to 2nd, all other gears seem ok. Am I running too rich now?

Title: Re: New Muff and Rejet
Post by Brewbrother on 07/25/06 at 16:06:38

ohms wrote:

I had a similar backfire. It was in the intake boot. It was overtightened and had pinched thus creating a leak. Check them carefully.

Title: Re: New Muff and Rejet
Post by ohms on 08/03/06 at 07:12:32

Well i finally fixed the bike.

I ended up pulling the intake boot off and reseating it properly so i was sure there were no leaks there. Then I pulled the header bolts out and put some locktite on them and put them back in. No leaks at the header. Bike was still backfiring at this point but not as badly. I pulled the top of the carb and shaved my 1/2 spacer prob down to about 1/4 maybe a little less. Then I adjusted the mix screw which is at about 2 1/2 turns now.

Been riding the nuts out of the bike now for 3 days and the backfiring is gone, the bike is also a lot more responsive now. I'm thinking the additional spacer shave must have helped. It still backfires but very rarely and it doesnt sound like a gun shot.

Thanks to everyone for their assistance. Much appreciated.

Title: Re: New Muff and Rejet
Post by Savage_Rob on 08/03/06 at 07:39:35

Hmmm, loctite on header bolts may be something you regret. I hope not.

Title: Re: New Muff and Rejet
Post by vroom1776 on 08/03/06 at 09:57:01

If you go w/ the loctite, replace the bolts w/ something stronger than the factory garbage. like grade 8s. If you can find them in metric.

On the other hand, how do grade 8s do w/ thermal expansion? Anyone know? Same as regular steel? or pot metal?

Title: Re: New Muff and Rejet
Post by thumperclone on 08/03/06 at 13:30:13

ohms wrote:

in the morning odds are the ambient air temp is cooler than other times of the day
this changes motor operation as does humidity

Title: Re: New Muff and Rejet
Post by Brewbrother on 08/03/06 at 17:44:01

ohms wrote:

Glad you got what you wanted. I'd be concerned about the locktite on the header bolts. I run no spacer and get no backfires on upshift but decel you can detect low "sputs" but I think they are just part of the thumper mechanical mystic.

Title: Re: New Muff and Rejet
Post by klx650sm2002 on 08/04/06 at 02:08:40

S/S allen bolts for header/head interface. They don't rot like plain steel.

Clive W :D

Title: Re: New Muff and Rejet
Post by thumperclone on 08/04/06 at 08:02:04

there is a "milder" type of lok tite. I forget which is which red or blue or permatex? id think a ss lok washer would be better if stud length allows..jmo

Title: Re: New Muff and Rejet
Post by vroom1776 on 08/04/06 at 08:59:06

blue is the milder loctite. Red can be bad news.