Idling at 4k after tuning

[Guest]

Hi all,
soaked and cleaned carbs, benched synced, valve shims in spec, and plugs changed on my 79 gs425- running better than ever- but with idle throttle screw way out I'm idling at 4k rpms. Just went for a quick cruise and ran well except when I pull the clutch engine won't settle down below 4k, seems to come down once gear is engaged.

Should i I try to mess with idle screw more? I put mixture screws at 1.3/4 turns from lightly seated - should I play with these? Where should I start?

thanks!

[tkent02]

Throttle cables too tight? Throttles should close with a loud "Clack!" when you let it go.

Big air leak? Did you replace the O rings on the intake boots?

Is the choke on? The 425 may be different but the lever up is choke off on the 450s.

[Gs425FridayHarbor]

Thanks for the thoughts! Not the choke, I did replace orings on intake boots. I guess it could be the throttle cables too tight- how do I check or adjust this? I don't hear a sound when I release the throttle.

Thanks for for the help.

[tkent02]

I don't hear a sound when I release the throttle.

This means the cable is too tight. You have one cable or two? Either way it should be loose enough that the throttle isn't pulling the throttle open at all when its not being held open, even when you turn the handlebars from side to side. There is an adjuster on the cable down net to the carb, another up by the throttle grip. Two 10mm wrenches, you are basically shortening the outer cable which makes the inner one longer. Too loose is fine for now, once its clacking you can fine tune it. It should close with that "Clack!" sound, then adjust it so there should always be a tiny bit of slack.

[Gs425FridayHarbor]

Awesome. Did some tinkering, and got the cable to clank shut. Still idling high so I turned out the idle screw two turns and its sitting pretty at 1200 rpm. thanks!

but I took it for a spin and for the first time ever heard some popping or knocking sounds every 45 secs more or less. Pulled in and did a compression test to see 120 on the right and 80 on the left. I also noticed right plug was pretty white when pulled (brand new this morning).

Thoughts?

[tkent02]

Brand new plugs are white.


Adjust the valves.

[Gs425FridayHarbor]

Hey Kent,

new plugs were shiny bright metal. After a couple of quick runs one of them (the side with 120psi) was pretty white (too hot?), the other plug (80psi side) was darkish but still with shiny metal showing.

When you say adjust the valves are you talking about seals and rings or shims? Just got shims in spec so thinking I might have to go further (leak down test?). How will I know if I need to tear down the head and replace valve seals/rings?

think it's okay to ride in the meantime with 120/80 psi?

thanks.

[tkent02]

Hey Kent,

new plugs were shiny bright metal. After a couple of quick runs one of them (the side with 120psi) was pretty white (too hot?), the other plug (80psi side) was darkish but still with shiny metal showing.

When you say adjust the valves are you talking about seals and rings or shims? Just got shims in spec so thinking I might have to go further (leak down test?). How will I know if I need to tear down the head and replace valve seals/rings?

think it's okay to ride in the meantime with 120/80 psi?

thanks.

I meant the valve clearances, didn't know you just did it, but riding it a little and checking them again wouldn't hurt. A chunk of carbon could have gotten in there and messed up your measurements. Then ride it a few thousand miles and see what the compression does. That won't hurt anything except maybe a little bit lumpy idle. If the metal part of the plug is getting black that's too rich or too cold or maybe not sparking very well.
I have ridden several of these bikes with zero compression on one or more cylinders, most of them come back up at least some. A few of them got to be every bit as good as the other cylinders.


If it's got low compression after riding it a while a leak down test is great. You have an air compressor?

[Gs425FridayHarbor]

Hey Kent, this is awesome and thanks for the reply. I'm going to try riding this week to listen and feel the ride now that I've had the bike in pieces for two months. I will try and lean the mixture on the darkening plug, and deal with the bumpy idle for now.

I do have an air compressor (nice bday present from my kids so I could really get my carbs cleaned up) - did you ask because I will use one for a leak down test after riding around for a bit?

thanks again for the help, I really appreciate it.

[habsdoc]

if the plug is turning white, then it is running to lean on that cylinder. Richen up that carb.