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General Category >> Rubber Side Down! >> Engine studder after throttle closed
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Message started by Airizzy on 02/02/10 at 20:32:53

Title: Engine studder after throttle closed
Post by Airizzy on 02/02/10 at 20:32:53

When the throttle is closed the RPM drops below the set idle speed and then stabilizes. If the idle is set where it sounds right the engine will die so it needs to set a bit higher. I opened up the carb and cleaned it out. While I was in there I reduced the thickness of the needle washer. The transient enrichment valve was a bit crudded up and wouldn't move freely so I cleaned that up. It looked like there was fuel on the spring side of the enrichment diaphragm. As I understand, it should be dry, or am I wrong. I could not find a hole in the diaphragm.

Anyway, the engine is running very strong. Almost all the backfiring is gone. The washer mod made a big difference. If I can solve the studder when the throttle is closed quickly I will be very happy. Any ideas?

Title: Re: Engine studder after throttle closed
Post by dasch on 02/03/10 at 08:34:55

I had a similar problem, and I also blamed the enrichment valve. And then somebody here advised me to try with petcock on "Prime". And it was all gone. My petcock diaphragm leaked a bit, so the engine would suck raw fuel through the vacuum line when throttle was closed. Try that first.

Title: Re: Engine studder after throttle closed
Post by Charon on 02/03/10 at 08:42:34

Idle speed is supposed to be 1100 - 1200 rpm. It is better to set it a little high than low. That will help reduce the afterfire (backfire) on throttle shutdown. It will help avoid engine stalling, and it will help keep adequate oil delivery up into the cam journals in the head.

Title: Re: Engine studder after throttle closed
Post by PhilM on 02/04/10 at 01:06:42

For reference - in this sound file the bike is idling at about 1080 rpm, ie slightly too slow.

http://suzukisavage.com/images/uploaded/Savage_ScreaminEagle.mp3

Title: Re: Engine studder after throttle closed
Post by Airizzy on 02/04/10 at 13:21:28

Thanks for the sound file. I have to idle a little faster but not much. You helped put my mind at ease.