GS450 idles at 3-4.5k

[Gambit]

Hey folks.
Been wrestling with this bike for a few months. Worked off a lot of PO issues to finally get it running enough to get it on the road legally. Legality does not equate to ride-able though. I took the carbs off and somewhat cleaned them. I say somewhat because I haven't replaced the O-rings YET. They're ordered and en route.

I received the bike with what looked like air filters from a weed wacker just kinda shoved onto the intake. They didn't even match. There's an aftermarket exhaust also. I picked up a set of UNI pod filters. Before you comment, there's also an exhaust on it, so I was going to have to deal with too much air anyhow. I'm not going for original spec, so don't bother trying to convince me of that route. Even if I did get everything back stock, it'd be the same procedures in an attempt to make it all run right again anyhow since the PO had no regard for factory anything. That sort of advice isn't helping. It's trying to turn my motorcycle into a revival for the factory specs. I don't want factory. I want working with what resources I have. If I wanted to spend another $800 to get all OEM stuff on this bike, I would have just bought a different bike. But I didn't. I bought this one.

Now that I've addressed the purists who claim that no cv carb can be tuned without an airbox and other such negativity, lets get to my issue. I turn the bike on, and it instantly shoots to around 4000 RPM. With the increased air both in and out, I believe the issue is now too much fuel. I can take the throttle cable completely off and it still does this, so no adjusting that will help. Pilot and other such adjustments are too small to really make a difference. There is suggestions that there's an air leak, which I may have considered if I didn't just have a ton of air already being supplied with little restriction already. An air leak may be the issue, but i'd like to work from the fuel side first. The main jets have "115" on them. My thoughts, based on what I've read, watched, and gleened from other forum posts on here is that I need a more restrictive main jet. If that is a wrong idea, please do correct me.

I have actually ridden this bike with the idle issue, which made it quite fun when it came time to shift. So, the engine and tranny work great. I just have to calm this hellcat down a bit. Thanks in advance for advice I can act upon.

If you want photos or video of something, let me know.

 

[Thumper88]

You need a less restrictive main jet...115 is stock...you've got more air flow, you need more fuel.

 

[jsandidge]

What he said.

 

[Gambit]

Thanks guys. Think just upping to 120 will be enough?

 

[Guest]

Thanks guys. Think just upping to 120 will be enough?

First, if the throttles are completely closing there is no way that the idle circuit will supply enough to get 4K rpm, and the main jet and slide circuit is incapable of getting enough fuel past the throttle butterflies to do it either, assuming the slides aren't stuck. So you've got a problem with the cable or some aspect of the throttle butterfly control mechanism that's hanging the thing up. Fiddling with the main jet will not do anything to address the problem.

Main jet size affects wide open throttle at high rpm only. Have you completely backed off the idle speed adjuster? Have you looked to see that the butterflies are closing fully? Do you have some slack in the throttle cable? Do you have a manual?

Hoe about the choke system? Is it shutting off completely? That, plus an air leak would give you about 400 rpm idle.

 

[tkent02]

You should learn how the carburetors work.

 

[Gambit]

Tkent, that's what I'm here for. Do you have any other insight other than "you don't know things." I know I don't know things. That's why I'm on this site. So if you don't want to take the time to type something out or at least provide a link, then I'm sure as hell not going to read anything. That's kind of how it works. So, move on. I don't need your negativity.

 

[tkent02]

That was not intended for you, it was intended for the guys suggesting a main jet swap to fix a high idle. Have you tried adjusting the idle speed screw? If that doesn't work you probably have an air leak. It will need different jetting to make it run well with those UNI filters, but that's not what the high idle is about. One thing to look at, the choke lever on the 450 is opposite of the other GSes, down is full choke and will make the engine race. Maybe that's what you have?

CVs can be tuned for anything you want.

 

[Gambit]

Ok, here's what I've got. I can completely disconnect the throttle cable entirely and it does this. The manual will point at things but not elaborate on what it does or carburetor theory. My slides are not sticking, and the floats, and float needles are clean and operating properly as far as i can test for (gravity feed some fuel and see if the needle stops it.) The choke is "closed" while it idles at 4k. If I "open" it, it reaches about 6k.

 

[tkent02]

OK, is the idle speed screw having any effect? It's the big knob between the carburetors. Screw it out and the idle should slow down.

 

[Gambit]

I'm going to research about these butterflies. Do I need a net?

 

[tkent02]

Just the internet.

 

[Gambit]

I've toyed with that and it hasn't done anything. No response. I didn't take it to the full extent in either direction, I just did a couple turns and figured whatever was wrong was bypassing that.

 

[Gambit]

If it helps any, while riding it, I can control engine speed with braking while in gear. I figure this is just the transmission slowing down the engine. But I'm providing all the information I can at this point. The PO was using the kill switch to throttle down to shift.

 

[tkent02]

Next choice, a big air leak? Around the boots to the head? Wiggle the carbs, does the idle fluctuate?

 

[Gambit]

To answer the other question about the butterflies, they seem fine and fully functional. No sticking.

 

[Gambit]

The air leak you are referring to is on the boot I'm assuming? From what I've seen, to test this I need to shoot some ether around the boot and see if that effects the idle speed. If it does, then I'll need to replace the boot. Cuz that sounds fun. I likely won't be able to hit this test until 6/23-25, work and leisure dependent.
I have not shaken it. I guess I'll try that too.
Edit: I won't be able to do this until at least Wednesday. I have to buy new jets regardless because I destroyed the old ones trying to get them out. I work during the same time that the bike shop is open.

 

[tkent02]

No just lift it up and down. That should make any leak get bigger or smaller which will change the idle speed. With pods, all of the carb's weight is supported by the boots, which are not really designed for that. Also they are thirty some years old, the weight makes them crack or tear. You can shoot anything on the boots to check for a leak. Carb cleaner, WD-40, most anything will change the idle a tiny bit. I like to use a propane torch (unlit) because it doesn't leave anything on the carb, doesn't attack the rubber.

It just seems that wiggling the carbs up and down will tell you the same thing a lot easier.

 

[Gambit]

I will try moving them around when I get it back together. The reason I'm thinking restrict the fuel is because something has to be burning in order to get that high of an idle. Since the fuel feed is vacuum based on the air side to motivate the slides up, I'm not sure how an air leak on the engine side would create more stuff to burn or higher velocity air from the air side. I would think an air leak would cause the mix to lean out and burn less, resulting in lower RPM. That is, unless the mix is being propelled out of the leak, but then I would think that any excess would be sucked out of the leak rather than going into the engine. I'm really just trying to understand the reasoning behind it. Not being argumentative. I just want to fully understand.

 

[Gambit]

Forgive me if I use my idle time to more fully understand the problem. I get that you have a theory that has proven correct many times with your experience. What I don't understand is why? Why does a leak in the boot cause a higher idle? Again, I'm not questioning your experience, I'm questioning the reasons it is true. The difference between an operator and an engineer is the understanding of why it does the thing it does. First, does the leak pull air into the flow? Or does the air/fuel mix escape? My thought is that the air might be escaping, causing a higher velocity of air through the carb, which in turn raises the slides, increases the fuel, and gives the engine more to feed on which results in the higher RPM.