Yoshimura deceleration noise

[cheeterpasteen]

So I feel like a bit of bragging, just bought a 2007 gs with 10,000 miles for $800.  The thing came with a yoshimura slip on and a k&n drop in filter. She sat for a year before I got her so I cleaned the carbs and checked all of the hoses. Still need to do a tune up (plugs, clean air filter, oil and filter change). The yoshimura sounds sooo much better than the stock exhaust on my other GS500.

One thing puzzles me though, when I cleaned the carbs, I had to drill out the brass plugs on the air mixture screw circuit. This probably means that the carbs were never cleaned or at least not fully cleaned. Im pretty sure that the carb jets are stock as well. So with the new yoshi, and the higher flow of the k&n, the bike should be running leaner. To compensate I went out 2.5 turns on the air mixture screws. (they came as 2 turns before I cleaned the carbs).

I think i may have somehow gone to rich though. Anytime that i down shift or decelerate into a turn by letting off the throttle, the exhaust sounds like its interrupted by small backfires. It sounds a lot like a coffee percolator. So is this a sign of being too rich? The restrictor ring in the k&n is still in so I can try removing that tomorrow to give it a bit more airflow.

And should I rejet? What are the pros and cons, if any, of not rejetting?

[RossLH]

Classic case of "Don't fix it if it ain't broke!"

The idle mixture screws adjust the mixture for very low throttle positions only, and yes it sounds like its a bit rich now. The drop-in filter with the restrictor should flow similarly to a stock intake--that's why it's there. If you pull the restrictor out and enrich the idle mixture, the bike will run well at idle and low throttle positions, but lean in every other situation. For simplicity's sake, put the restrictor back in and turn the idle screws back to the original 2 turns.

[cheeterpasteen]

alright. So if its too rich right now, if i remove the restrictor ring, wont the extra airflow counteract the richness? And the percolator sound occurs when the rpms are dropping from any level down between shifts or when i just simply let off the throttle. I don't know if thats the air/fuel mixture or what. What other things could cause the sound upon deceleration? Im going to try setting it to 2 turns. I can do that easily without having to take apart anything.

'preciate it. 

[Funderb]

correct me if I'm wrong, but if the bike afterfires when engine braking, it is almost always every time a lean condition..

[jestercinti]

Bone stock, the bike is a bit lean.  Thank the EPA for that.  Add a different air cleaner and a custom exhaust, you have more air with the same amount of fuel.

Save yourself a lot of grief, and rejet.  +1 on pilot and +2 on the main.  Put 2 washers under the needle or go +1 on the mid-main.  Set the mixture screws to 3 turns out.  Note that these suggestions are a starting point, and should not indicate an exact setting.  Jetting is a black art, and will vary by temperature, altitude, and humidity.

Also, if you eliminate the Pulsed Secondary Air (PAIR) system, your backfires may mellow a bit.  If you are in a state that checks motorcycle emissions, don't eliminate the PAIR or rejet since you will not pass.  All the PAIR does is send pulses of air into the exhaust ports to further burn unburnt hydrocarbons.  Again, emissions related.

[crzydood17]

I have heard that a properly tuned carb engine should pop during decel.

[jestercinti]

All I know is that my bike does not 'pop'.  That said, I have a K&N lunchbox with stock exhaust.  My jet settings are in my signature if that helps.

Some popping may persist, but bad popping typically indicate an overly lean condition.

[The Buddha]

The main idea of rejetting is that it runs cooler. The better running and better warm up times etc etc are just a side effect. Popping may be ok ... or not, it actually has very little to do with the way the bike is tuned.
Cool.
Buddha.

[cheeterpasteen]

Alright, cool. The popping isnt bad at all. Its very quiet, I didn't even notice it for the first 50 miles of my ride yesterday. I was just cruising highways until then. So Buddah, what jets would you recommend? And where can I get them? (poor)
my bike:
yoshi slip on
k&n drop in
300 feet above sealevel, most of the year its hot as balls and humid (east texas)

thanks.

[RossLH]

alright. So if its too rich right now, if i remove the restrictor ring, wont the extra airflow counteract the richness?

Read my previous post, I explained why that wont work. By adjusting the idle mixture, you've added more fuel at low throttle position only. Removing the restrictor ring brings in more air across the board. The result would be an adequate air fuel mixture at low throttle and a lean condition at anything more than ~25% throttle. If you keep the restrictor ring in and take the mixture screws  to 2 turns, it should be a good mix at any throttle position.

[mustangGT90210]

Sounds like I have a little mixture screw tuning to do. 60% of my riding is at <20% throttle in 5th or 6th gear. Am I reading correctly that the mixture screws will help this range?

[cheeterpasteen]

Alright, now that makes more sense. Cool, before my next ride ill reach in the bike and do one less half turn on the mixtures screws. Ill see if that makes a difference.

[Watevaman]

 I'm pretty sure popping on decel isn't that bad. Buddha fooled with my carbs and my V&H still pops, and sounds damn awesome, when I'm coming down from high revs.

[Suzuki Stevo]

CLICK>>>http://gstwins.com/gsboard/index.php?topic=62555.msg731552#msg731552

[jestercinti]

Read steveo's post. Delete the pair system and see if the popping went away.

[Suzuki Stevo]

Read steveo's post. Delete the pair system and see if the popping went away.

The consensus on decel popping at the GSX650F forum I belong to is....the popping was always there, you just hear it after you add an aftermarket slip on. From my own personal experience with my GSX650F, EFI & PAIR, I would have to agree. I am only assuming the story would be the same with a carbureted bike with a PAIR system like the GS500 

[cheeterpasteen]

Alright, cool stevo. That makes a ton of sense. The bike is actually very peppy. I feel a good deal of power in the midrange. This makes me think its tuned pretty well, and I wasn't bothered by the popping, I just didn't know if it was a bad thing or not. Im going to go with Ross's logic "if it and broke, don't fix it" and not do anything with the mixture. That plug on the PAIR system looks like an easy thing to try, and if nothing improves, I can just hook it back up. I do like me some fresh air. 

Thanks for all the help guys. Here's my baby before new paint and gauges.

[Calpantera]

Popping on engine breaking is not a bad thing unless its very exccesive, the less restrictive the exhaust the more you will hear it. Have you ever watched road racing, they pop on decel all the time.