Engine RPMs racing once it warms up

[ERJpilot]

did you check you carb diaphraghms for pinholes?
I had one that was ever so tiny and it made my life hell till i found it and replaced it.

I inspected them for holes when I had the carbs out and apart but that doesn't mean I didn't miss one. Doing a carb rebuild is a new experience for me so I couldn't say what looked right and what didn't when I had the carbs apart, but I know I checked for holes in those rubber diaphragms.

 

[centeno711]

Little trick I use....guys stop him if its bad for motorcycles

If its leaking air a little soapy water will tell you where

If its drawing air a little ether spray will also tell you where....spray it in likely places just in quick bursts...when the motor revs up suddenly you know where its drawing at.....obviously at the air filter it will rev.....

Gl

 

[BassCliff]

Hi,

There have been many members here who have had to dip their carb bodies two or three times before they are really clean. Just a thought.


Thank you for your indulgence,

BassCliff

 

[1_v8_merc]

Airleaks will easily cause RPM's to rise, or "hang".

Even extremely small airleaks, I had an airleak that was causing my RPMs to slightly hang, I sprayed WD-40 and carb spray all over the carb boots and never got RPM's to jump....then 5 minutes later found 2 of my carb boots weren't quite tightened down enough.....they were tight, but not TIGHT TIGHT.
I torqued em down with my trusty screwdriver.
Bike instantly ran better RPM's dropped right away like they should after revving......

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Choke operates okay right?(look at it on the carbs visually as you play with the choke knob, make sure it's not hanging)
-----

What about your throttle cable?

Believe it or not, even moving or touching the cable can cause your RPM's to rise sporadically and hang there or slightly move as you turn the wheel or even not turn the wheel!
(this is common when changing handlebar styles, i've dealt with it myself)


Sometimes you may need to adjust the locknuts on the throttle cable too!
There are usually two, one at the handlebars, and one at the bottom near the carbs.

So if you just did the carbs and now your RPM's are hanging or revving, it's POSSIBLE you didn't install the cable locknut back on correctly or it got over-tightened!?
(i mean it could simply be holding your throttle wide open damn near.....so check it out!)


Just back-trace your footsteps of everything you did, check everything, then check it again and again....

There's no mysteries here....RPM problems are usually very simple and straight forward, usually just something stupid that was over-looked....we ALL do it sometimes!
------

don't be hard on yourself, i got my first bike ever last year, i've learned TONS about it......and I kind of got thrown to the wolves.....like usual.
My bike ran like complete **** when I first got it, I put so many hours into replacing and tweaking stuff, it's been quite a journey already!

But it's been totally worth it.....if you can work on an old GS, you can probably work on mostly anything.....(so i've heard)
Because I'm used to working on modern fuel injected stuff, so classic bikes are a first for me!

Learning is part of the fun.....it always sucks when you're doing it at the time, but when you complete it and look back, you're like "wow im glad that part broke, i learned a lot from that experience"

And it helps confidence with future mechanical problems and makes them a lot easier to tackle.....(like working on your buddies bikes or cars, or lawnmowers or whatever.....)

 

[drukin]

I have the same exact bike.
If your running lean it will cause the throttle to hunt at idle. i know mine was too lean from the factory. The only problem with that is to change the air/fuel mix you have to jet up or down accordingly. If no one has messed with it ever, i doubt its a problem.
also the single throttle cable setup doesnt help any, i know mine likes to stick now and again at very low RPM's.
If theres an air leak, it could only be coming from a few places. (intake manifolds or the carbs themselves seeing as theres no vacuum lines except for the one back to the petcock.)
My bike did the same thing when i got it. I used a ton of white lightning in the throttle cable housing to free it up but that single throttle cable is notorious for that kind of thing. Check to see if the airbox has a leak also.
(just to give an idea, if you remove the airbox like i did, you will have to go up 5 sizes on each jet and these 450 twins are very particular on how they want to run.)
My carbs were overflowing also when i got mine. I found a hair line crack in one of the floats after submerging it for 30 minutes, which was about the time i had to ride it for it to over flow. soldered it up and sanded it and works fine ever since.

All i can say is clean and inspect them, but do so very carefully. Make sure all the seals are tight when you reassemble (intake and boots to airbox), and most importantly dont over tighten any of the screws on the float bowls or diaphragm tops. Those threads in the carb will strip before the screws do. i found out the hard way. suzuki still makes all the rebuild kits, floats, and jets. And they are actually affordable.

hope that helps a little.

 

[Nessism]

Where are the pilot screws set? How many turns open?

 

[Nessism]

So what happened with this one? Lots of people trying to help but the thread has died? The idle will hang if the pilot screws are misadjusted so how about posting up where you set them? Since you said the seals were replaced we trust you removed the piliot screws and replaced the O-rings before reinstalling them. A wildly misadjusted carb sync will also cause the idle to hang so that's another thing that needs tending to.

 

[Guest]

EJR,
Where do you live? Maybe you are close to a member that will swing by... I am not a carb guy, but my bike is running a little rough before the mains kick in. So if you are close I can experiment on your bike instead of mine I am in northern Illinois and Trippivot is close. If I break it, we can show upon his doorstep and suprise him.

 

[drukin]

unfortunately all the screws are sealed in on the 82 450.
only adjustment is jetting and idle screw.

 

[Nessism]

unfortunately all the screws are sealed in on the 82 450.
only adjustment is jetting and idle screw.

What do you mean sealed? There may be a cap over the pilot screw but it's easy to remove.

 

[ERJpilot]

It is still a work in progress for me, unfortunately I have been flying a lot and getting reassigned over and over so I haven't had time to work on the bike lately. Hopefully I will get a chance to work on it some more tomorrow.

To answer some questions:

I did replace the throttle cable and adjusted and tightened the screws. When the bike is first started it idles fine and the throttle cable itself isn't sticking, so I don't think that is it unless it is sticking only after the bike warms up. From initially starting the bike the RPMs are slow to come down but it just gets worse and worse as it gets warmer.

The pilot screws are set at 1 1/4 turns open. I forget where I read it and I don't have the books in front of me but I will double check that again. And yes I replaced the O-rings when I reinstalled them.

I will give everyone and update tomorrow if I get the opportunity to work on it some more. Thanks everyone for the advice and help, it is definitely appreciated.

 

[Nessism]

Try 3 turns out and see how that goes. I just tore down a set of virgin GS850 carbs and the pilot screws were set at 2.5 turns from the factory.

 

[davidduarte]

what kind of shape is your gas tank in? No rust in it I hope? I had my tank lined, had a buddy clean out my carbs with his parts cleaner, and replaced the airbox and intake boots on my 450. I also put in a new petcock, something you might want to invest in. It runs much better, and will hold an idle, which it never did before. It still won't hold an idle if it's cold. I have a new throttle cable but just haven't had the chance to put it in. Good luck!

 

[ERJpilot]

So I decided to bring the bike to my apartment and just work on it here since we have covered parking and driving the 45 minutes to my friend's was just too far to be able to have the convenience of a garage.

I will try adjusting the pilot screws to 3 turns out and I'm going to double check the o rings on the intake boots in case I somehow messed one up when installing the new ones, if that doesn't change anything I suppose I'm going to take the carbs off again and dip them again, and I'll update more as I can.

As far as the gas tank goes, I don't see that there is any rust in it, but it is dented from a drop at one point in its history, is that something that I should be worried about?

 

[ERJpilot]

Well I've finally had a day free to work on the bike and I have been at it for a while.

I pulled off the carbs again and rechecked the float height with a new set of calipers I bought. The float heights were both off a bit so I adjusted that. Next I checked the O rings in the carb and all seemed fine since I had already replaced them.

However, one of the O rings in the boot between the carb and the engine was a little messed up so I replaced it with another (thankfully I bought several extra). Maybe I messed it up when I was putting the boot on before but I was hoping that would fix my problem.

I did also discover that my fuel petcock FOR SURE isn't working. The fuel would flow freely in the PRI and the RES positions (I didn't have enough fuel in the tank for it to flow in the ON position).

Unfortunately one of the carbs started pouring out fuel after I let it prime for a minute so I'm assuming I screwed up something with the float height on that one.

I have a petcock rebuild kit on order to fix that problem, and now I just need to resolve the fuel pouring out of the carb and maybe soon I will be on my way to having a running bike...

 

[BassCliff]

Hi,

I would suggest new float valves and seats, and a new petcock.


Thank you for your indulgence,

BassCliff

 

[Flaming Chainsaws]

I have a petcock rebuild kit on order to fix that problem, and now I just need to resolve the fuel pouring out of the carb and maybe soon I will be on my way to having a running bike...

About the petcock rebuild kit... Based on what I've read, a lot have people have been very unsuccessful with petcock rebuild kits. I think it was like a 5% success rate. With those numbers, I would personally just buy a brand new petcock. Suzuki still sells them at around $70. Or you can go with a Pingel petcock which a lot of people seem to like.

 

[davidduarte]

About the petcock rebuild kit... Based on what I've read, a lot have people have been very unsuccessful with petcock rebuild kits. I think it was like a 5% success rate. With those numbers, I would personally just buy a brand new petcock. Suzuki still sells them at around $70. Or you can go with a Pingel petcock which a lot of people seem to like.

if you go with the Pingel you have to make sure you turn it off every time you turn the engine off, otherwise the fuel will keep flowing. You'll also have to plug up the vacuum port on the left carb otherwise it will run lean.

 

[ERJpilot]

Is it better to go with a new Suzuki petcock or the Pingel?

 

[Flaming Chainsaws]

Is it better to go with a new Suzuki petcock or the Pingel?

I guess it depends on what you want. The Pingel is a bit more pricey than the stock petcock. And if you go with the pingel, do what david said, "Turn the petcock off every time you turn the engine off. Or else fuel will keep flowing. And plug up the vacuum port on the left carb."

Personally, I would go with the stock petcock. Simple swap with no mods necessary