Erratic Idle

[DMB]

So I went to work on my bike tonight to test the spark to each plug, compression, and timing. I checked the spark and I am getting good blue spark at each plug. I start the bike up, and it starts up OK and idles pretty well for about 3 minutes with the choke off, but then all of a sudden it jumps up to 4-5k. So I back the idle screw out to get the RPM down and that works but as soon as i get it back to a little over 1K it starts to die and I have to put the idle screw back to where I had it. It is idling find for about another 2 minutes when the exact same thing happens. I have to back the idle screw out to get the RPMs down but then I just have to screw it back in after I get them down so the bike doesn't die. The whole time the choke was off. Never the less, I didn't get to checking the compression and the timing.

Any thoughts on my erratic idle?

Thanks.

[Guest]

Classic example of an air leak at the intake. Change the o-rings behind the intake boots and make sure the carbs are sealed at the airbox also.

[DMB]

Classic example of an air leak at the intake. Change the o-rings behind the intake boots and make sure the carbs are sealed at the airbox also.

I replaced the o rings on the intake boots during my carb cleaning, but I will have to look closer at the air box assembly. I put new foam on the airbox lid as per the guide on BassCliff's site. Thanks.

[BassCliff]

Hi Mr. DMB,

Eratic Idle? Isn't he the guy from Monty Python?

That "airbox fixup" is from Mr. roostabunny. I sealed my airbox a little differently. My airbox was in a little better shape than Mr. roostabunny's (but still leaked) so I actually put weatherstripping around the edges of the airbox side covers themselves. I had to change it recently. I also put weatherstripping around the top of the air filter cage so as to hold the air filter firmly against the top of the airbox when I slide it in.

Other leak sources could be the airbox-to-carb boots. Have you replaced those? Or ensured you have a good seal there? Is the air filter lightly oiled? Keep us informed.


Thank you for your indulgence,

BassCliff

[DMB]

My air box is a little different too. Mine is a large sheet metal box with a lid and a hole in the side that goes to the air box to carb boots. The box is sealed up pretty well (new weather striping on the lid) so I am going to have to investigate the connection between the air box and the carb boot box assembly.