Another hanging idle (gs450l)

[d_sal]

A while back my bike was sometimes idling a little high while at stoplights (right around 2500 - 3000). After some inspection, I noticed that my clutch cable was catching one of the springed mechanisms that opens up one of the butterflies. It would move in and out of the way as I turned corners while riding, so it did not happen all of the time.

-Daniel

[AJ]

Let's clear up some concepts so we speak the same language.

1. The "choke" is an enrichener circuit. It is like a mini carburetor that operates when the throttle is closed. It has it's own fuel pickup jet (the brass tube). The plunger regulates how much fuel is mixed with air coming through an air passageway separate from the main body of the carb.

2. The choke should make the bike start with an initial idle of maybe 1500 rpm (not 1100), then the engine rapidly races sometimes over 3500 rpm unless you reduce the choke to maintain rpm at some low level for the engine to warm up.

3. Once the engine warms up, you should be able to remove all choke and get the engine to run on just the pilot (low speed) circuit. If the pilot circuit is blocked, you won't get it to idle without either choke or throttle.

4. The idle position screw adjusts the butterfly valve. The slide adjusts itself as required to maintain a constant velocity (CV).

Ok, wife says we're going to dinner. Will come back later.....

[old_skool]

Plugged pilot jets will not cause a hanging idle. Most likely there is an air leak somewhere. I'm not sure about those choke plungers, but if they allow bleed air into the carbs it could cause the issue.

I trust this guy, as he's pointed me in the right direction more than once, doesn't usually mince words trying to convince anyone, usually points directly to the correct info the first time, thanks ED, I know I'm not the OP here, but will be looking into this tomorrow, also found this multiple times on the web...



Although the butterfly seals can cause this, usually not the culprit unless you have an older than dirt carb, or one that has been dipped in something a little too caustic.

[Nessism]

Unfortunately, WD-40 is a poor indicator of vacuum leaks....but worth a try.

Make sure the throttle butterflys are snapping shut all the way to the mechanical stop - they should close with a thud. Make sure the choke is closing all the way. Make sure the carbs are vacuum synced. Make sure the pilot circuit is clean and the screws are opened to approx. 3 turns. Make sure the airbox is fully seated and sealed.

If these items don't solve the problem, I'm sorry but I give up.

[Vantreeseba]

@Nessism the only thing on that list is the carb sync I'm not sure of, I bench-synched them, but I don't have a manometer atm.

@AJ to satisfy you, I will double check that the pilots are clean.

Thanks for the help guys, I'm still not sure what the root cause is, but if I figure it out, I will let everyone know.

[AJ]

Vantreeseba, you don't need to do anything to satisfy me. I'm just trying to help. If you do indeed have a hanging idle, you most likely have a vacuum leak as suggested by Nessism and well described in the FactoryPro site I gave you earlier. Read that last section again. A lean condition gets better as the bike warms up. But a vacuum leaks is easier to test than pulling your carbs so you should check that first. Start with the factory settings for the idle mixture screws, maybe plus 1/2 turn. Otherwise you may be masking the problem. Good luck.

[Nessism]

A getto sync job can be performed by setting the idle up to 2500 rpm or so, and then pull one spark plug cap off and seeing where the idle settles. Repeat for second cylinder. Adjust the sync so the idle speed drop is the same for both cylinders.

@Nessism the only thing on that list is the carb sync I'm not sure of, I bench-synched them, but I don't have a manometer atm.

Thanks for the help guys, I'm still not sure what the root cause is, but if I figure it out, I will let everyone know.

You can not diagnose running problems unless all the basic maintenance is complete. You might want to check the Newbie Mistakes thread linked in my signature to see if anything clicks.

[Vantreeseba]

@AJ, sorry I didn't mean to sound snooty or anything, "satisfy" is just a term we use in the software world to say that "our product does what it should", so I meant that as "I will test it and make sure its working". I really do appreciate the help.

@Nessism. You're totally correct, I've just been messing with this thing forever and kind of want to just get out and ride, but I need to stop being lazy and cover ALL the bases before I try to make any kind of assumption about the whole system. So before I go any further on trying to figure this out, I will do a valve adjustment and then do a vacuum sync, and see where we are from there. That, and the previous work I've done, should cover all the things in the "newbie mistakes" guide, and the basic maintenance guide from bikecliff.

Thanks again.

[Vantreeseba]

I did do something that was silly, and now thats its mostly fixed, the bike seems to run better.

The choke return spring (not the ones inside the carbs, but the one on the "bar") was not on correctly, so the choke was not returning all the way, strange thing is, that it only moves like 1/8 an inch, but when pushed all the way closed, my bike idles and runs fine, but if I just slightly tug it out, at most 1/8 an inch, the bike bogs and drops like 2-300 rpm. Its really strange.

Anyhow, I will keep working on it and checking the things mentioned in this thread, and update as I discover strange things :P.

[Vantreeseba]

Yea, so I tore my bike down to double check all the electrical connections, since one of the ground wires was ugly and crinkled (the connection from starter relay to ignition coil gnd). I still haven't done the valve adjustment or carb sync, but those are coming.

I seem to have fixed the issue with the hanging idle though.
The choke cable was "bent" at the end, I figured it was "no big deal" since it was a cable and a bend shouldn't effect it too much. Well, I was wrong.

The bend was keeping the choke from closing completely, which of course caused issues. I've ridden up and down the street again after adjusting the idle and resetting the mixture screws, and it seems to be running good.

Once again, double check silly mechanical things before trying to diagnose more complicated problems .

[sammy123]

Cool. Thanks for the update. Glad you figured it out.

[Vantreeseba]

Sorry to dig up an old thread, but I finally got it running much better, turns out, you can't always trust what a jet says on the size of it.

I had gotten a spare set of carbs from a gs450ga, and the carbs are, as much as I can tell, identical, except for the pilot circuit. So the original pilot jet from the gs450lf carbs is a smooth bodied jet (no holes except for the end), stamped with 45. The gs450ga is a "aerated" jet, stamped with a 45. If you look at the actual output aperature, the gs450lf is obviously visibly much larger, like twice the size compared to the gs450ga pilot jet.

So, I of course, swapped back in the original torn up jets, and she is purring right along.

In short, make sure you are using the right parts :P
Now to stop being lazy and finish the rest of the checklist.

So AJ it turns out your thoughts that the pilot circuit was clogged was correct, except it wasn't gunk or anything that was clogging it, it was the smaller jet :F