How to diagnose climbing idle RPMs?

[Guest]

Hi guys.

I sorted out my earlier charging issues with your help and now we're on to the next part that needs some troubleshooting.

Now before I start I need to clarify I have never taken any engine, airbox or carb apart. I'm trying to figure out all the basic steps I need to take before and during the repair process without making a mess of things. I also need to say that I have not done anything yet besides (newbie)detective work on the bike, and a little online.

Ok, the bike and the issues. After the bike gets warm (after 10-15 mins) the idle goes up, and up. Up until around 3.2k RPM. Maybe more if I keep riding. I also noticed that the drain tube that comes out of the air box is leaking fuel. Quite a bit of it, about a drop every few seconds.


What do I think meeds to be done:

Well I don't really know, right? From the materials on the forum and on BikeCliffs site there's probably 3 parts that I really should focus on.

Airbox: filter, connection to the carbs etc.
Carbs: Clean it (oh crap..)
Valves: check clearance

I'll also change the oil and oil filter.

For the carbs I'll follow the carb cleaning series from the frontpage.

I think I'll have to remove the fuel tank from the bike to go through all these steps. How do I get the fuel out(or at least keep it from spilling? Can I muck anything up taking the tank off?


What have I done so far:

I have not taken anything apart yet, mainly because I have no idea what I'm doing and I need a clear picture of what to do, in what order, before (hopefully not) screwing it up.

I checked the airbox for leaks using WD40, but there are no apparent problems.
No idea how the inside is, and what type of filter is being used in a '82 GS450. I believe it's a piece of foam with oil? Can anyone confirm this?


Am I going in the right direction with my train of thought? What am I missing? Please enlighten me with your arcane knowledge of the steel horse.

Anyone from EU, especially Benelux or Germany, that knows a site where I can get quality o-rings for all the connections from airbox to carbs to engine? Also the rings inside the carbs. I have no idea what I need... A reading resource on what to look out for is also greatly appreciated.

 

[Grimly]

https://www.cmsnl.com/suzuki_model13052/
They're not the cheapest, but relatively local to you.

 

[Redman]

Can take off fuel tank with fuel in it. It is just heavier.
Need to disconnect the fuel line and the vacuum line (maybe tip up back end of tank a bit to give some more finger room). Other think is will need to disconnect the fuel level gage wire connectors.

Climbing idle rpm is often intake air leaks, like the orings in carb boots up against the head. And/or the boots themselves.
If you adjust the idle when engine is hot and then idles okay when hot, but is too low when engine cold. And if adjust odle when engine is cold, but then is too high when engine is hot . . . . yah, that is the air intake leaks.

 

[Gorminrider]

....I also noticed that the drain tube that comes out of the air box is leaking fuel. Quite a bit of it, about a drop every few seconds.

You'd better fix this!

Possibly the carb float needles are not sealing. As the bike warms up, the carbs are overflowing because the vacuum petcock allows fuel as long as the engine runs. When you stop the engine, if the drip is stopping (eventually), that should mean your petcock is working ok. Extra gas overflowing might explain the revs .... I'd expect some smoky exhaust too unless the overflow is slow

I believe it's a piece of foam with oil? Can anyone confirm this?

Yes. URETHANE foam will work. It's usually grey-black permeable. Pretty common as soft packing too. Some other foams will degrade quickly when oiled. But you could make a paper one from a car's airfilter too, i think.

 

[Guest]

Grimly: Thanks. Looks like that site has a ton of parts. Time to figure out what I need exactly.

Redman: I already lifted the tank to get a clearer view under it. That let me check the fuel sender unit thing, since the fuel gauge isn't working. Turns out the gauge works but the sender doesn't. Might have to do with a float that has gone rogue and is swimming in my tank instead of being attached to the arm like a good boy. I might just empty it once I get the tank loose so I can see if I can fix this as well.

With the "carb boots up against the head", do you mean the connection to the the engine, am I correct?

Gorminrider: Yeah that's an issue that I don't like and need to fix. It stops eventually after what I think is called the storage tank is empty, the one that comes from the air box. This extra fuel, it comes from the engine and gets spit back out again, through a pipe to the air box, is that correct?

Could that also be a cause of climbing idle RPMs because it's running richer? I thought that with a more lean mixture it would get idle higher if warm due to not wasting energy burning excess fuel?


Is there anything I can do that will destroy the air intake? I understand carbs are relatively delicate, how delicate is an airbox? For what it's work, I don't consider myself to be fat fingered.

 

[Nessism]

Please check the Newbie Mistakes thread and carb rebuild tutorials linked in my signature. There is also a 450 specific carb rebuild tutorial on Basscliff's website.

Raising idle is vacuum leaks, most of the time from the carb boots and/or their O-rings.

 

[Redman]

.....

With the "carb boots up against the head", do you mean the connection to the the engine, am I correct?.

.

Yes, the carb boots between the carbs and the engine head. THe o-ring in the carb boot up against the engine head.

For replacement, find Cycle ORing website. (a fine GSR member doing us all a great service.)
.