popping on deceleration


13 replies to this topic
  • honda0071

Posted January 15, 2008 - 04:13 PM

#1

i start my bike and first it doesn't like to idle no matter what the idle screw is set at... and then i go to start it and it doesn't like to start warm no matter if hot start is on or choke. then it likes to start under like a 1/16th of a throttle when i go to kick like it doesn't either have enough gas or air not sure... but back to the problem i will ride the bike around and throttle response up to about 1/8th throttle is a little slow. it also pops on deceleration.. please help with ne of these problems thank you any help greatly appreciated.

  • grayracer513

Posted January 15, 2008 - 04:22 PM

#2

http://www.thumperta...599#post3710599

  • Family Man

Posted January 15, 2008 - 07:13 PM

#3

try turning the fuel screw out a 1/2 turn.

  • honda0071

Posted January 15, 2008 - 09:29 PM

#4

i have tryed every turn on the fuel screw and it idles with choke great but it wants to die when i get on the throttle quick like i flick the throttle from closed to about 1/8th throttle maybe. and i dunno it seems like it needs a re-jet on carb so ill prob send to Zip Ty racing and have them do the racing carb rebuild on it... do u think it will solve the problems?

  • Wes Woodin

Posted January 16, 2008 - 12:40 PM

#5

i have tryed every turn on the fuel screw and it idles with choke great but it wants to die when i get on the throttle quick like i flick the throttle from closed to about 1/8th throttle maybe. and i dunno it seems like it needs a re-jet on carb so ill prob send to Zip Ty racing and have them do the racing carb rebuild on it... do u think it will solve the problems?

I would get a powerbowl first!

  • Wes Woodin

Posted January 16, 2008 - 12:41 PM

#6

Oh yeah. What bike, what elevation, current jetting? Temp. Need to know

  • M3A1Scout

Posted January 16, 2008 - 12:58 PM

#7

Unless you've changed the stock jetting or you're riding in some really extreme conditions, it sounds like there's a clog in your carburetor.
Could also be an airleak between the carb and intake. What's your plug look like? Is your compression ok? Low compression will have a lousy draw on the carb at low RPMs.

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  • grayracer513

Posted January 16, 2008 - 01:05 PM

#8

I would get a powerbowl first!

Until the bike can be made to run as it should, there's nothing to be gained by dumping expensive aftermarket parts on it.

  • msk20

Posted January 16, 2008 - 03:02 PM

#9

I have a 2008 YZ450F. I put a Dr D titanium exaust system on it, but left all jetting stock. According to the folks at Dr D, you can either run stock jetting, OR go up one on the main (to a 162) and to drop the clip one. If I go up one on the main and drop the clip, will this help with the popping I get on decel?

  • William1

Posted January 16, 2008 - 04:15 PM

#10

First, do the pilot jet test. Bike MUST be fully heated up. That should resolve the poor idle when warm. Cold, off choke, these bikes are not happy till at full operating temp.
Once that is resolved, you need to look at the AP. What leak jet is in your bike? Did you do the O-Ring mod yet?

Do not do this stuff all at once. Work on first things first.

Sending the carb off to have hundreds of dollars of 'secret mods' when it may only need 20 bucks worth of brass bits and rubber.

Do the pilot test and correct fuel screw adjustment:
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method.
Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,500 rpm, but go by the spec in your manual.

You will then want to visit the needle and set it right. I assume the main is already fine. Once you have the pilot and fuel screw correct, you can open the fuel screw no more than 1/2 turn to help reduce popping. Popping can come from a too lean idle circuit and it can come from a too rich needle or main. You will never eliminate it.

  • honda0071

Posted January 16, 2008 - 06:40 PM

#11

my bike is a 1998 yz400f it has a fmf titanium 4 pipe im pretty sure is a whole pipe system not a slip on.... but ne wayz i dont know of any other mods since i am second owner and he did not do anything except the pipe. i am running my bike at about 2500ft-5000ft at the max of 5000ft. it is about 40-65 degrees here but will be warming up with the seasons change.... it gets very hot here in the summer about 90-100+ degrees here... other than that i do not know what the jetting is since i haven't taken the carb apart yet but i am assuming stock since the guy did not do anything else since he got it... so please any help greatly appreciated... should i just buy a full jett kit from JD jet kits? or jsut single jets... also the throttle response from closed to about 1/16th throttle maybe 1/8th throttle is slow... it doesnt like to grab until about 1/8th throttle then it grabs fairly hard. so yet again any help greatly appreciated

  • grayracer513

Posted January 16, 2008 - 07:38 PM

#12

I have a 2008 YZ450F. I put a Dr D titanium exaust system on it, but left all jetting stock. According to the folks at Dr D, you can either run stock jetting, OR go up one on the main (to a 162) and to drop the clip one. If I go up one on the main and drop the clip, will this help with the popping I get on decel?

No, because neither the main jet nor the needle have anything to do with anything when the throttle is closed. That is the idle (pilot) circuit. Set the idle up as above, and don't worry about popping on decel. A correctly jetted YZF will pop a little. If it seems excessive, and you're sure the idle is about right, examine the exhaust to see if it has an air leak at the joint between the pipe and header, or at the exhaust port.

  • ktmdestroyer

Posted January 17, 2008 - 09:45 PM

#13

Yeah thats all good info.

But that fact is you ain't got enough fuel. back out the fuel air screw and bump your needle up. that doesn't work larger pilot.

Good luck. Hope the popping goes bye bye along with the roasts.:cool:

  • BBrown626

Posted January 18, 2008 - 09:03 AM

#14

i start my bike and first it doesn't like to idle no matter what the idle screw is set at... and then i go to start it and it doesn't like to start warm no matter if hot start is on or choke. then it likes to start under like a 1/16th of a throttle when i go to kick like it doesn't either have enough gas or air not sure... but back to the problem i will ride the bike around and throttle response up to about 1/8th throttle is a little slow. it also pops on deceleration.. please help with ne of these problems thank you any help greatly appreciated.


Too rich, not lean as others suggest. I had the same problem with my new '07. It starts with the throttle cracked because that lets more air in. Follow William1's guidance and you will be fine. :cool:





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