Exhaust pop-pop-pop on decel (afterfire)

[KatScratchFever]

But I think I'm running rich. A friend riding behind me claimed to be able to "really smell fuel" when I accelerated. So I'm a bit lost here. Afterfire on decel normally indicates lean and obviously fuel smells indicate rich. So which is it?

My bike is stock intake, Ivan's jet kit (with air-fuel mixtures adjusted per their recommendations), Factory Pro ignition advancer, D&D slip-on. Thoughts?

[Tmod]

Ahhh what bike is it?

Tmod

[KatScratchFever]

Shoulda' put that. Sorry - '99 Kat 750. Stock except for the aforementioned bits.

EDIT - another thing worth (possibly) mentioning is that I do get some sooty black buildup on the inside of the D&D outlet over time, possibly more evidence of richness... Possibly.

[mjangus89]

my '05 750 kat does the exact same thing!!!

let off the gas and pop pop pop. Black sooty residue near the end of the exhaust. The ONLY thing i've done is Yoshumura RS-3 Slip on.

Any thoughts?

[dsmith367]

Well, if we could get some direction that would be great, I am having the same thing with a '91 1100 Kat, stock exhaust..

[JHONNY_ICE_420]

A lot of those afterfires were there before the slip-on, you just couldn't hear them. Also, factories tune exhausts to help quiet ANYTHING that a typical soccer mom wouldn't like.
Afterfires are almost always caused by a lean condition or from slow ignition timing wich leads to unburned fuel vapors in the pipes wich are hot as hades. The fuel will ignite with a "pop" ANY time there is enough oxygen.
Long story short, the lean condition is caused by chopping the throttle at 10k and you should live with it, or get a +5 timing advancer to help because if you set the idle mixture rich enough not to pop on decel, then it won't idle

[KatScratchFever]

I do have an ignition advancer (see above) and I have reasons to believe I'm RICH, not lean. Hence my original question.

It sounds like the IDLE mixture might be lean and the RUNNING (normal operation, open throttle) mixture might be rich. Possible?

[Kaster120]

i have same thing on 96 600 it pops in higher rpms on the way down

[scottynoface]

Going an extra 1/4 turn out on the A/F mix screws is the usual fix, but if you're already running rich...all that said my bike is totally stock and pops like nothing I've ever heard. I kinda like it

[JHONNY_ICE_420]

Ditry carbs can cause this, but what you suggested could also be happening.
You very well could be rich in the midrange due to different amounts of airflow caused by the slip-on. Popular opinion around here says you don't need to do anything accept re-set the fuel screws when adding a slip-on, though.
dirty carbs could also cause a rich spot at one place and lean at idle.
The easiest way to explain it is "if it aint broke, don't fix it" So is it broke? does it run bad? does it stumble or sound rythmic at any throttle positions? a stumble along with a backfire (NOT an afterfire) says lean. A rythmic or "cammed" sound means you're rich.
The easist way to tell is riding the bike when the motor is cold. If it runs bad when cold but gets better as it warms up, it's lean
if it runs good cold but bogs and trys to flood out when warm its rich.
Throttle position when the bad spot happens tells you what part to change in the carb. wot=main;
1/4-3/4=needle shape and clip position;
1/8-1/4 is throttle valve cutaway, and
under 1/8 is pilot jets and fuel screws on the bottom of the carbs.
If it idles good and has good throttle response, then leave it alone and let it pop.
If there is a specific problem besides the pop, find out what throttle position it happens and if its better with a cold or hot motor

DON'T FORGET A COLD MOTOR SHOULD BE JUST A LITTLE LEAN, OR ELSE IT'LL BE TOO RICH WHEN WARM.

[scottynoface]

The easist way to tell is riding the bike when the motor is cold. If it runs bad when cold but gets better as it warms up, it's lean if it runs good cold but bogs and trys to flood out when warm its rich.

Definitely good info.

[KatScratchFever]

Nah, bike runs pretty well cold and warm, just wondering about the pop-pop-pop on the decel and if it's really worth turning the earth over trying to remedy it. It sounds like it's best to let sleeping dogs (or Kats) lie...

Now I need to figure out why my clutch is slipping under WOT around 6,000 RPM (and I think I know the answer, and I have a feeling I won't like it...)

[Psycho1]

lol that obvious huh? If you have at least 1/4" of free play at the clutch lever and still have slippage, it's probably clutch time. Mine slipped when I was in So Cal back in Mar twice, as soon as I got on the freeway and hit 9k in 4th gear. I loosened the cable a little bit to give it more free play and it's been working fine since.

[jetmerritt]

exhaust fresh air system

I have a post 600, and I read somewhere, probably on here, that the exhaust air injection system needs to be capped off and disabled to remedy the decel popping condition with a slip-on muffler. The purpose of the system is to allow fresh air to be sucked into the exhaust after the valves to help burn any remaining hydrocarbons and reduce emissions. I am not sure if pre's are equipped with this system.

Anyone??

[Psycho1]

If I'm not mistaken, In the US, that was only used on bikes that had the California emmisions package on both pres and posts.