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Message started by mau2wu on 04/11/07 at 18:15:26

Title: is sputtering/popping normal?
Post by mau2wu on 04/11/07 at 18:15:26

I just put a Sportster muffler on my bike and rejetted the carb. I am using a 144 main jet, the stock pilot, and have used the dynojet needle with about a 2/3rds spacer. The bike runs great and I have no more backfires, but when I am "coasting" down a hill (meaning in gear but giving the throttle no gas) I hear sputters and little pops coming out of the pipe. Now I am wondering if this is normal or something I have to work on fixing? Its not obnoxious but I never noticed it with the stock pipe.

Title: Re: is sputtering/popping normal?
Post by georgekathe on 04/11/07 at 20:50:34

it might help others give you advice if they knew what altitude you are running @. welcome to site! :)

Title: Re: is sputtering/popping normal?
Post by Reelthing on 04/11/07 at 20:52:00

mine both sing pretty good on decl - no bangs or anything

By the way the dynojet needle has several groves right? - shouldn't need to sand the spacer down

Title: Re: is sputtering/popping normal?
Post by Dr_Jim on 04/11/07 at 21:07:16

Title: Re: is sputtering/popping normal?
Post by Greg_650 on 04/11/07 at 21:37:34

Welcome to Thumper country.

All thumpers tend to rack off and pop to some extent on a decel. Just the nature of a big single. As Jim said, it is a serenade song to thumper lovers. Mine makes all kinds of ruckus when I'm coastin'. I love it ;D

If it is running good and isn't backfiring or belching out black smoke you are probably just fine.

Just remember, "Suck, Squeeze, Bang, Blow". That's as good as it gets :P

Title: Re: is sputtering/popping normal?
Post by justin_o_guy on 04/12/07 at 07:31:58

I've spent a good bit of time & $$$ getting that poor asthmatic Suzuki 650 to where it is. I think I may have a slight leak at the Trapp/header joint. I don't get the big shotgun backfires but I get some racket. I can't help but smile. Now that I have the Trapp on it, I sometimes use the clutch to shift, just so I can hear that engine rumble as it unwinds. It's a fun machine & the sound is a part of it. I know WHY I blip the throttle. Those guys riding the bikes that have the strangled exhaust that is barely audible? I know why they blip the throttle too. They are wondering if theirs is still running. I want to HEar mine,,,

Title: Re: is sputtering/popping normal?
Post by mau2wu on 04/12/07 at 08:06:05

I live in Florida so probably I am at 0 feet above sea level. I've read that with the dynojet needle you don't need to shave the spacer, but since mine was only shaved down only about 1/3 of the way, it fell in between two "grooves," making it only slightly deeper than what would be a half-spacer with the stock needle. Since it was running great I didn't change it but kept the original needle just in case I need to go back. I might be running a bit rich b.c. the muff has deposited a bit of black soot on my rear brake arm over the past three weeks, but the smoke itself comes out looking clear.

I am getting a shipment of jets in soon and thinking of going up to 150 for the main and maybe a 52.5 for the pilot (the one with the holes). What do you all think? Should I go back to the original needle and not use the dynojet?

It sounds like it is running fine and so maybe I shouldn't tinker with it. I will enjoy the sweet music of the exhaust now rather than worry! Here are the jets I ordered that I may experiment with:

MIKUNI PILOT JET BS30/96 #52.5
MIKUNI PILOT JET BS30/96 #55
MIKUNI PILOT JET N151.067 #52.5
MIKUNI MAIN JET N100.604 #150 AFTERMARKET
MIKUNI MAIN JET N100.604 #152.5 AFTERMARKET
MIKUNI MAIN JET N100.604 #155 AFTERMARKET

Title: Re: is sputtering/popping normal?
Post by Greg_650 on 04/12/07 at 08:08:24

..."sometimes use the clutch to shift"....? Hmmm.

That's almost a new topic all by itself. I believe in clutches and use them :P

Title: Re: is sputtering/popping normal?
Post by Greg_650 on 04/12/07 at 08:18:15

mau2wu wrote:

With the Dynojet kit, the needle is completely different than stock...It isn't just the clip positions (which do what the spacer change does), but the taper of the needle is different too.

You might notice that the main jet doesn't have the same numbering sequence as stock. As well, the main jet and the needle work together. Changing one does affect the other.

Since you invested in the Dynojet kit, I don't know if (or why) you want to bother with the other jets. You should be able to just ride it now....

Here is a nice little web site for carb theory....

Carbs (http://www.dansmc.com/carbs2.htm)

Title: Re: is sputtering/popping normal?
Post by Reelthing on 04/12/07 at 08:19:05

mau2wu wrote:

I might be running a bit rich b.c. the muff has deposited a bit of black soot on my rear brake arm over the past three weeks, but the smoke itself comes out looking clear.

It sounds like it is running fine and so maybe I shouldn't tinker with it. I will enjoy the sweet music of the exhaust now rather than worry!

I'll say the black soot is normal if you do not have a turn out - me I'd likely ride a lot and fiddle with the mixture just a bit like 1/8 turns either way looking for mr sweet spot - you may already be there - get several of the cheapo champion plugs and fiddle around with a plug read throttle chop exercise - fun stuff to do as long as a cop isn't around!

Title: Re: is sputtering/popping normal?
Post by mau2wu on 04/13/07 at 16:10:08

I just checked the plug and it was sooty. So I replaced the dynojet needle with my old needle and the shaved spacer. Put in a new plug. Then I did the carb tuning thing again, around 1 and 3/4 turns out or so. Then I ran around the neighborhood a few times in mostly the mid throttle range in 2nd and 3rd. Kind of loud but oh well. Popped the seat and tank off again, looked at the plug. This time it came back with a thin film of light grey. Is that the color I am looking for? Lesson learned from this--don't use the dynojet needle with a shaved spacer. I think I have to fine tune it a little more.

Title: Re: is sputtering/popping normal?
Post by Savage_Rob on 04/13/07 at 16:41:31

I love the decel grumble of my thumper. It's like she's annoyed at slowing down. On the issue of the DJ needle, I found no difference in the needle at all except for the multiple clip positions. I did not mic it but I held both up together and inspected them with my reading glasses on. The taper appeared to be identical.

Title: Re: is sputtering/popping normal?
Post by geo on 04/13/07 at 23:37:19

Mine Kapops after shifting and upon deceleration sometimes. I think it give the machine character.
Don't worry about it.

Title: Re: is sputtering/popping normal?
Post by Greg_650 on 04/14/07 at 08:33:10

mau2wu wrote:

In my opinion there is another lesson learned.

Skip the "easy fix" of the Dynajet Kit and use the really easy fixes discussed in this forum. Cheaper and more proven.

IMHO ::)

Title: Re: is sputtering/popping normal?
Post by mau2wu on 05/10/07 at 00:21:36

Hey all, here is some good information on the sputtering/popping issue. http://www.mikuni.com/fs-tuning_guide.html

Basically it says it is normal to have moderate popping on closing the throttle hard. This only happens when the exhaust is opened up with a free flowing muffler. This would explain why I didn't notice the popping/sputtering until I put the Sportster muffler on the bike.

My bike is now running real good--some weeks ago I took it on its first road trip of over 600 miles. I really enjoyed passing all those Harleys and found that the bike will do 75+ quite easily. It actually shakes less than my other vehicle at that speed--a Geo Prism.

I found that checking the plug is a pain but necessary to really find out what is going on in the engine until it is tuned right. I now am running a 150 main and half spacer with the stock needle. In the end, the dynojet kit was a waste of money.

Title: Re: is sputtering/popping normal?
Post by LANCER on 05/10/07 at 06:49:23

Quote:

Good motorcycles are supposed to have a snarl, a rasp, and an edge when pushed hard - they should talk back to you in no uncertain terms - it's what takes them from inanimate lumps of poo to full fledged fire-breathers when you twist the throttle....

Cheers

Jim

Ahh, a man of true understanding.

The sounds are indeed normal for a properly running engine.

Title: Re: is sputtering/popping normal?
Post by justin_o_guy on 05/10/07 at 18:11:50

Well, the 155 main & the stock pilot with a Supertrapp wearing 14 baffles results in a WAY too quiet machine for me. Only rarely does it make a sound. No more decel snarl & I miss that. I( guess I should pull the plug & just have a look, I did clean it so I should be able to get a clue.