Another hanging idle (gs450l)

[Vantreeseba]

So, starting with what I've done.
1. Cleaned gas tank, red kote, rebuilt petcock (actually worked ).
2. Cleaned the carbs, throughly, twice, dipped for 12 hr, then 24. Blew air through all the passages and circuits, replaced o-rings with kit from guy on here.
3. Replaced Air Filter(K&N in airbox, with light oil), Air Box Boots, Intake Boots, intake boot o-rings, and boot clamps, all new.
4. Replaced clutch cable, and adjusted according to manual.
5. Replaced throttle cable and adjusted according to manual.
6. Relay mod for coils, this actually made the biggest difference in my bike actually running almost all the time .

I have NOT done a valve adjustment, but I am planning on doing that fairly soon (i.e. next week or two when I have some time).

The only 2 weird things are, my main jets are 120's instead of 115 stock (the stock ones were "glued" because po broke them) and the choke plungers are plungers from a set of gs450ga carbs.

The reason I mention the plungers is that there is a slight gap between the plunger and the hole in the top part of the carb where the diaphrams are, I'm assuming that when the choke circuit is opened, this allows air to get pulled in through the hole at the near the airbox top part of the carb throat, and into the enrichment circuit.

look at the end of the choke plunger pictures here, and I think you can see the "shrink" of the GA compared to the LF plunger.

GA Plunger:

LF Plunger:

So, my question is, I cannot get the bike to idle at 1100 without running the choke, or turning the idle knob up quite high. Now this would be fine, but if the idle knob is turned up enough to keep the bike from dying without choke, I get a hanging idle once I pass 4.5k rpm.

Does anyone thing that the slight gap in the GA plungers could somehow be allowing enough air to get into the enrichment circuit that I'm running lean, hence the need for choking / opening the throat so much?

As I've said, I changed out everything that I would think would be causing an air leak, so if anyone could point me in a direction that makes sense, I would be a very happy camper.

 

[AJ]

Clogged pilot jets.

Hanging idle is when you blip the throttle and the revs take a while to return to normal. By your description, you need to either keep the "choke" (enrichener) on or turn the idle screw up to keep the throttle plates open. (CV carbs, right?).

 

[Nessism]

Where are the pilot screws set? Try 3 turns and see if that helps, if they are less than this that is. Also, vacuum sync the carbs after you adjust the valves. 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.

 

[AJ]

Your enrichener plungers look fine.

Verify that the slides mover freely and drop down all by themselves. Use a drop of Marvel Mystery Oil or othe light machine oil on the slides if they hang when you push them up. (Do NOT use WD40 !)

Read this site, especially the section 4 on the low speed circuit.
http://www.factorypro.com/tech/carbtune,CV,high_rpm_engines.html

 

[Vantreeseba]

@AJ, I cleaned all the pilot circuits, made sure carb cleaner came out the right places. Also, it starts hanging once warmed up and hits above 3.5 - 4.5 k rpm, so if I set the idle to where it will run, and blip it, it will just stay at 4.5 - 5k idling, and I have to kill it with the kill switch. Yes, these are CV carbs (bs34's).

@Nessism, I have them at 3 turns, should I keep going out and out if it needs it to idle?

 

[AJ]

Ditto on Nessism's comments. But I still bet clogged pilots.

 

[Vantreeseba]

@AJ, those are not MY plungers, my LF plungers are torn to shreds cause I jacked em up when I was trying to get them out after breaking the plastic nut. If you look at the GA plungers, which are the ones I'm using in my carbs atm, there is a slight "cut" to the bottom part of them, and I was wondering if this is leaning out my pilot system perhaps?

 

[Vantreeseba]

Ok, sounds like I have a few things to try, I'll double check that the slides are returning properly, and try cranking up those mixture screws. Thanks guys.

 

[AJ]

Thanks for the explanation about the plungers. I believe it is the pin on the plunger that controls the enrichener, and the body is just a seal. It the seal is leaking, it would allow excess air in and the enrichener would not work to start the bike. I'd have to double check the diagrams to be sure of that, but think you are ok.

While I am sure you cleaned all your pilot jets, they are tiny and can clog again really easily. That's why I recommend drilling them with pin drills, but a lot of people here strongly disagree. Just soaking them and poking a wire through doesn't always open them up to proper size, plus you are likely to have crud in your gas lines. I've had to re-clean those buggers multiple times before everything was clean enough.

 

[AJ]

If you re-read my first post, I believe you are not getting fuel from your pilot jets. The idle knob holds the throttle plate open, allowing you to get fuel from the main jet.

Also, double check your throttle cable to verify that there is a little slack in it so you need a little turn on the throttle before anything happens at the carbs.

Hope this helps. Good luck!

 

[Nessism]

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.

 

[AJ]

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.

That's a good thought too, although I'm not sure this really is "hanging idle" (in the classic sense).

To test Nessism's idea, you could spray some carb cleaner onto the seal where those plungers exit the seals while the bike is running.

 

[MisterCinders]

Tell us more about the hanging idle above 4,500 RPM. If you blip from your 1,100 idle to >4,500 RPM, does it come back down normally? If the hanging idle triggers only at bigger throttle movements, then maybe you are picking up a lean patch in the mid-range (needle setting).

If you have to turn the idle screw in a lot to get a normal 1100 RPM idle, then your slides may just be at the low end of their individual adjustment range. Or you have a deficiency in air or fuel (probably) fuel at the pilot circuit, such that you have to open the slides beyond that circuit to get a running mixture. The problem with the second theory (to me) is that if you are opening the slides to >1/4 throttle (if that's even possible) your RPMs should be much higher than 1100.

You can check the slide adjustment range with a bench synch.

 

[Vantreeseba]

@MisterCinders, These are BS34 CV carbs, so the idle screw isn't moving the actual slides (I think this is how the VM carbs work?).

I was looking at how the enrichment circuit works, and theres no way that the GA plunger would effect the circuit compared to the LF plunger, since the opening to the air mixture pipe is closed by the larger part of the plunger anyway.

Ok, so if I have the choke fully open, the bike idles just fine "cold" (~1100), and starts great.

If I warm the bike up (drive it up and down the street for 5 mins or so), it idles at a much higher rpm with the choke open (like we would expect) so ~1500.

If I then turn off the choke, the bike might idle at ~800 or just die. So, what I did was warm it up, go through highest idle method with air mixture screws, and adjusting the idle screw so that it idles at 1000. It seems to have helped, and is working mostly.

This works fine, but when the bike is warmed up, "sometimes" it will hang at 3500 - 4500 rpm after a good twist on the throttle. By hanging, I mean, stay at 3500 - 4500 rpm without me touching the throttle at all. This goes away if I put any load on the engine to drop the rpms below this point.

Could this be caused because of an intake valve hanging open or something?

 

[old_skool]

Watching this thread, even if there are plenty like it, have the same problem with the 650 parallel twin, choke circuit operates normally, after warm up, idle ok until run a little, then idle hangs at 3k until a load is put on it. Tomorrow will be double checking sync and increasing mixture 1/2 turn, currently at 2-1/2. Also, PO removed a portion of the baffles, might be my problem. Back to your regular Bat channel.

 

[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.