Curvy idle mixture tuning? - SV650.org

08-08-13, 10:34 AM

I ride an '01 S. On the subject of pilot, idle air mixture or whatever this screw is called. Other topics I've read seem to only suggest baseline settings that would get one started on their bike. Since every bike is different, even stock bikes require fine tuning, and we cannot depend on guessing or run with baselines.

After trying out some suggested base settings for pilot screws, including stock settings, Dynojet's recommended settings, and my own; unsuccessfully; with each adjustment the same for both carbs, I decided to do a test, since my issues weren't getting resolved.

Standard procedure for this adjustment seems to be to set your screw to show the highest idle, then back it out a half of a turn. Since normal carb tools don't allow easy access to both carburetors when the engine's running, i need to do my adjustment with the carb separated from the engine.

My bike seemed to present symptoms of both a lean pilot circuit and a rich one, so I tried a different method of gauging idle mixture. When I bought my new digital multi meter and noticed it came with a temperature probe.

To assess the condition each cylinder was in, after the bike has been run and was warmed up and had been idling, I supply ran the probe to each cylinder's head pipe to measure the temperature of combustion.

My gauge read 370° F on the rear cylinder and 430° on the front
My mixture screws are set both at 2 1/4 turns out. I will start by turning the front out 1/4 turn to richen it and cool it down.
My symptoms are: a worsening condition as the engine heats up AND popping on deceleration. It gets rougher at low throttle cruising as it gets warmer.

Thanks for anyone's thoughts.

Sent from my Nexus 7 using Tapatalk 2

yorkie_chris · 08-08-13, 11:41 AM

Normally they run fine with stock carb settings, generally attempts to tune out problems lead to chasing around the underlying problem.

Have you done any modifications and/or carb adjustments?

08-08-13, 11:47 AM

According to the MM, some models came with #17.5 pilot jets, and the base mixture screw setting for those is 2 1/2 turns out. Others came with #15 pilot jets, and the base mixture screw setting for those is 3 turns out.
The easiest way to set them right is to check plug color.

08-08-13, 11:41 AM	#2
yorkie_chris Noisy Git Mega Poster Join Date: Apr 2007 Location: Halifax/Leeds Posts: 26,645	Re: Idle mixture screw tuning Normally they run fine with stock carb settings, generally attempts to tune out problems lead to chasing around the underlying problem. Have you done any modifications and/or carb adjustments? __________________ Currently Ex Biker Now rebuilding a 63' fishing trawler as a dive boat

08-08-13, 11:47 AM	#3
wideguy Guest Posts: n/a	Re: Idle mixture screw tuning According to the MM, some models came with #17.5 pilot jets, and the base mixture screw setting for those is 2 1/2 turns out. Others came with #15 pilot jets, and the base mixture screw setting for those is 3 turns out. The easiest way to set them right is to check plug color.

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08-08-13, 10:34 AM	#1
Logon Bump Guest Posts: n/a	Curvy idle mixture tuning? I ride an '01 S. On the subject of pilot, idle air mixture or whatever this screw is called. Other topics I've read seem to only suggest baseline settings that would get one started on their bike. Since every bike is different, even stock bikes require fine tuning, and we cannot depend on guessing or run with baselines. After trying out some suggested base settings for pilot screws, including stock settings, Dynojet's recommended settings, and my own; unsuccessfully; with each adjustment the same for both carbs, I decided to do a test, since my issues weren't getting resolved. Standard procedure for this adjustment seems to be to set your screw to show the highest idle, then back it out a half of a turn. Since normal carb tools don't allow easy access to both carburetors when the engine's running, i need to do my adjustment with the carb separated from the engine. My bike seemed to present symptoms of both a lean pilot circuit and a rich one, so I tried a different method of gauging idle mixture. When I bought my new digital multi meter and noticed it came with a temperature probe. To assess the condition each cylinder was in, after the bike has been run and was warmed up and had been idling, I supply ran the probe to each cylinder's head pipe to measure the temperature of combustion. My gauge read 370° F on the rear cylinder and 430° on the front My mixture screws are set both at 2 1/4 turns out. I will start by turning the front out 1/4 turn to richen it and cool it down. My symptoms are: a worsening condition as the engine heats up AND popping on deceleration. It gets rougher at low throttle cruising as it gets warmer. Thanks for anyone's thoughts. Sent from my Nexus 7 using Tapatalk 2 Last edited by Logon Bump; 08-08-13 at 10:36 AM.