Dave I stated before, that all I did to the wife's savage was to take off the top of the carb, clean up the air piston/slide which ever you call it and replaced the white spacer with a couple of small washers, then adj. the screw under the brass cap (air/fuel mix?) till it sounded good.

She has never had a pop on shut-off yet and that's been about 5 months ago.

I did the white spacer mod and turned the air screw out to optimize idle speed but still had a pop after shut down.  Following the advice of members of this forum I opened the idle screw another quarter turn and the pop nearly disappeared.  It only happens now if I have been running it hard and shut it down very quickly.  So the final solution is to let it idle for about 30 seconds before I turn the ignition off and then it is OK.

There was a thread on this same topic not too long ago, last spring maybe.  If you can find that "after fire" thread there is lots of information.

That is probably what happened with me then.... I spent a good hour and a half playing around with the screw settings.

I'd run it down the road feeling throttle twist vers accel, then hit the house, let it idle for about one min., shut it down and listen. Then adjust more and rinse and repeat.

I have nothing to back it up but I think part of the pop problem is the large volume of fuel mix and the relatively small volume of the exhaust system.  It helps keep the mixture in the burning range where a smaller cylinder's mix would have proportionately more exhaust and be diluted, no pop.

I sort of like the pop after turning the key off.  With my particular jetting and exhaust, though, it sounds more like a paper bag being popped inside a small closet than a gunshot.

When I am around someone who might be annoyed with the sound of a gunshot, I shut it off this way:
-- move the raptor to off.
-- let it idle for ten seconds or so in gear with the clutch pulled in.
-- let the clutch out a tiny bit,... just enough to put a little drag on the clutch,... by just enough, I mean the rpm reduces by about 50 rpm.
-- then turn off the motor by using the kill switch.
-- make sure to put the transmission back in neutral.  (I removed the safety switches)
-- turn the key to off.
-- move the kill switch back to on.

With the drag of the partially engaged clutch, the motor stops spinning almost instantly, probably reducing the amount of unburned fuel pulled into the combustion chamber and exhaust pipe.


This cancels out the POP about 90% of the time.

Whenever you shut off the ignition......the engine pumps air and unburned fuel into the hot exhaust system.  A lean mixture will burn faster than a rich mixture......so jetting will have some affect on the loudness of the shutdown pop.  A lower engine speed will pump less fuel into the exhaust......so that is what a dragging clutch helps to do....slow the engine down and fewer piston pulses after the ignition is turned off results in less unburned fuel in the exhaust.

Some lawn mowers have a solenoid in the carb that shuts of the fuel flow when the ignition is turned off.....as lawn mowers are subject to this same backfire when the ignition is turned off.  This backfire also is avoided on fuel injected engines which stop fuel flow as soon as the ignition is turned off.

It may be that our double wall pipe also allows the inner pipe to stay hot longer than a single wall pipe would.....so there is more tendency for the unburned fuel to ignite after the shutdown.

   

DavidOfMA wrote on 11/18/13 at 05:59:30:


There are lots of things that could be different....including riding style.  If Mrs. Old-Rider does not go as fast, takes her time getting the bike parked and allows a bit of idlng time before she turns off the ignition - the exhaust might have cooled down enough that it does not ignite the fuel.  I know that my bike will occasionally pop if I shut it down soon after getting off the highway (gas station, etc.) - but it never pops after I have driven slowyly down my gravel driveway.