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Message started by Mark_R. on 03/29/06 at 04:35:32

Title: Still not right!
Post by Mark_R. on 03/29/06 at 04:35:32

Ok, I think I know the answer to my question, but I thought I would pose it to y'all before I go and possibly do something stupid! Here's the recipe: '05 S40, white spacer 1/2-2/3rd ish, brass plug removed & screw 2.5 turns out, MAC 'muffler', K&N filter.

It seems to have more mid-range power and torque, but I have a terrible backfire or popping when I let off the throttle which sounds like a .357 thanks to the MAC (I really should have listened to a few of you out there who said that it is more than LOUD, it is obnoxiuosly LLLoouUUUDDDD!). It doesn't run well when you are putting along with just a little bit of throttle; it likes it much better when you twist it more than a quarter way. The final thing that I'm surprised and not happy about is that all of this hasn't increased the top speed at all...in fact it has actually decreased it from a pathetic 86 down to 84mph.

Now having vented some of my negativity, here is what I think...I either have a massive air leak somewhere and/or I need to up the pilot jet. What do you think and where would you suggest I start? Thanks in advance and I look forward to talking with you.

Mark

P.S. Most of my test driving has occured in 20-30 degree weather (not sure if it would make a difference at all).

Title: Re: Still not right!
Post by necropsy on 03/29/06 at 04:53:15

You didn't mention the Main jet.
That's where I would start.
Up at least 2 or 3 sizes.
145 ---> 152.5

Title: Re: Still not right!
Post by SeeAPierce on 03/29/06 at 06:14:13

you're on the right path - check for leaks, up your main jet to at least 152.5 and turn out your pilot screw another .5 turn. If that doesn't do it, you'll need to go up on your pilot jet as well.

Title: Re: Still not right!
Post by Mark_R. on 03/29/06 at 11:01:12

Ah yes, I did forget to say that the main jet is now 152.5.

Title: Re: Still not right!
Post by Savage_Rob on 03/29/06 at 12:44:02

Definitely ensure there are no exhaust leaks. New exhaust gaskets/seals are cheap and can make a huge difference in eliminating backfiring. Also, don't just use a generic rule of thumb (like 2 turns or 2.5 turns) in adjusting your pilot screw. Below is a quote from Lancer that I think makes the process pretty simple:

Quote:

-start with the pilot adjusting screw at 1.5 turns out as a reference point, and count as you turn in and out so you always know where you are during the process. Everything is done and referenced in the "# of turns out".
-turn idle up a little so you have a smooth fast idle
-turn pilot adjusting screw "in" until engine begins to slow downand note the # of turns out
-turn pilot adjusting screw "out" until engine begins to slow (it will speed up initially then go down) and note the # of turns out
-then set the pilot adjusting screw in the "Happy middle" of those two positions
-after the pilot circuit is happy, turn the idle adjusting screw back down for the idle you desire.

*for ex...if the turn in setting was at 1 turn out, and the turn out settig was 3 turns out, then the happy middle is 2 turns out.
**Turn slowly as you do this, no more than 1/8 or 1/4 turn at a time...then pause and wait 5 seconds or so in order to give the engine time to adjust, then turn again if necessary. If you have a tach, then you can set the pilot adjusting screw by just tuning for max rpm, then set idle speed.
***If after you have finished this process, the pilot adjusting screw is 2.5 -3 turns out, then you definitely need the next larger pilot jet. For myself, if I go over 2 turns out then I go up to the next size pilot jet.

When the pilot is properly adjusted, and assuming there are no exhaust leaks in the system, you will not have any backfiring. It is normal to have some mild crackling and popping on brisk-hard deceleration, but there will not be any backfiring.

Title: Re: Still not right!
Post by Dynobob on 03/29/06 at 12:53:10

Air leak, exhaust leak, or something's not right inside your carb - the float got bumped or you didn't reassemble in the correct order. There's some good pics in the Technical Reference area.

Title: Re: Still not right!
Post by riptide_fl on 03/30/06 at 09:19:15

Have to agree with Mark ..Did the spacer mod and main jet upped to 152.5..Stock muffler and air cleaner..Doesn't matter where the mixture screw is ,it still backfires..No exhaust leaks...So, going to put everything back to stock and let it backfire..Might as well get better mileage while it backfires !!.. Kinda gettin used to it !! ;D

Title: Re: Still not right!
Post by Savage_Rob on 03/30/06 at 10:33:00

riptide_fl wrote:

Doesn't matter where the mixture screw is ,it still backfires..No exhaust leaks...

I'm assuming your statement of no exhaust leaks is correct though I'll say that can be hard to determine sometimes. Don't count on soot to reveal it, especially where the header meets the cylinder head. That particular gasket caused a lot of backfiring on mine and replacing it mnade a world of difference. However, if we assume you have no exhaust leaks, the pilot screw should have an effect. If it doesn't, the pilot jet may need to be cleaned or upsized. I had to upsize mine to a 55 to be able to see any difference. With a stock exhaust I would think the stock pilot jet should be sufficient but you never know. $3 to $5 for a new one and maybe 10-15 minutes could be worth it. If you like the backfiring, that's fine. Remember that a lean engine runs hotter though.

Title: Re: Still not right!
Post by riptide_fl on 03/30/06 at 10:52:27

Ty Rob, ..I'll order a new exhaust gasket and bigger pilot jet and give it a try..Will let ya know how it Turns out...John

Title: Re: Still not right!
Post by magicfairy on 04/05/06 at 13:29:44

See my post "Bike Shop Instructions" I had all the mods done and Jardine exhaust, and it was way too loud and poppy. Very similar to what you were experiencing.
So I had stock exhaust put back on but left 152.5 jet, K&N filter and the guys in the bike shop adjusted needle height and pilot and idle screws again. (Spacer was filed to half way as well)
Now she is running sweet, virtually no backfiring, extra power is there and quiet.
I was tempted to get them to put it all back to stock including jets but I am glad I didn't.
Don't know if this helps but you may be able to sort out probs and keep the new jets etc.

Title: Re: Still not right!
Post by vroom1776 on 04/05/06 at 13:36:09

Easy way to detect exhaust leaks. Light a cigarette. Hold it near the suspiscious flange. See if the smoke gets blown around by exhaust gas. Easy to notice.

Title: Re: Still not right!
Post by vroom1776 on 04/07/06 at 08:38:02

Or a better idea, spray soem carb cleaner or starter fluid where you think you might have an intake leak. If the engine speeds up, you have a leak.