Reving on it's own

[Kabonkie]

Okay, my buddy called me and this 80 GS 450 E is still reving on it's own.

Here's the scoop.
It sat for a couple of years so I pulled the carbs and cleaned them and put them back on. It runs fine when the engine is cold to warm, but if it gets pretty warm, the engine starts running badly. Stumbles and so on, but it also will, without any one touching it and it sitting and idleing, take the rpms from 1K to 3K. It doesn't back down, it'll stay there until you shut it off. But if you refire it, it'll idle fine for a little bit and start this all over again.

Now we did find the petcock was not sealing properly and fixed that, but when we changed the oil it was full of gas as well. So the oil and filter were swapped out. I didn't have the bike warm when we drained it and have been thinking that there might be some residual gas still in there. Thinking when it gets warmed up it's getting funneled back thru the crankcase breather to the air box. We've already talked about changing the oil and filter again.

We've got the throttle cable loose, so I don't think that is causing us the problem either. The carb boots, although I didn't change them, looked soft and supple yet and didn't have and visable cracks. I can check those if you think that could be the problem.

I'm just out of ideas. Help?

[Steve]

Sounds like a classic case of bad o-rings to me. :shock:

That would be the o-rings where the intake boots meet the cylinder head. 8-[


.

[chef1366]

Yep, intake leak.

[deves3000gt]

i've got to agree with the first two guys. It has to be an air leak. As far as the oil i would change it once agian. As someone here once oil makes a horrible lubricant. good luck with the boots.

[Kabonkie]

Thanks for the ideas. I see I can get the o-rings from mama suzi for only $1.82 each.
I'll get them on order tomorrow and as soon as they come in I'll get it back over here and change 'em out.

Was already planning the second oil change, but wanted it warm this time. Filter is only $5, and the oil shouldn't be that bad. So still isn't much and if this finishes this up with another sync, my buddy will have under $50 in it and only gave $500 for it and it has under 4,500 original miles. It's a definite good deal. And maybe I'll take him along and get the tires on order as well, so with this, it'll be all done and ready to go...


Thanks guys.

[bwringer]

Hey, has anyone mentioned an intake air leak? :-D

Also, make sure air does not have a path to get into the airbox or carbs other than where it's supposed to enter. Any covers or seams need to be sealed with foam weatherstripping or whatever works.

The only proven way to fix a petcock is to deposit it into a trash can and order a new one from Suzuki. Unless this is what you did, chances are excellent that the petcock is still dumping gas into the engine when it's running. Don't screw around with rebuild kits or home brewed fixes.

[49er]

Hey, has anyone mentioned an intake air leak? :-D

Also, make sure air does not have a path to get into the airbox or carbs other than where it's supposed to enter. Any covers or seams need to be sealed with foam weatherstripping or whatever works.

The only proven way to fix a petcock is to deposit it into a trash can and order a new one from Suzuki. Unless this is what you did, chances are excellent that the petcock is still dumping gas into the engine when it's running. Don't screw around with rebuild kits or home brewed fixes.

Home brew?
Do people try and run that through their petcocks?
No wonder they have leaks!!

[Kabonkie]

The petcock is fine and working perfectly and can't be part of this problem as it's doing it while the bike is running.

I replaced the o-rings as suggested, and found a intake boot that had a pinched area on it so that was also replaced.

I re-synched the carbs and while waiting for the engine to full warm up, it still does it. It'll rev from idle to 3000 RPM all by itself. But I think I found the problem. Looks like the throttle return springs were weak. As I could use a long screwdriver and push down on the area where the two carbs connect and the idle speed goes back down to where it should.

So I again pulled the carbs and removed the springs and tightened them up to provide more tension when in the idle position. I didn't get them put back on the bike last night, but later this afternoon I should get that done. I'll let you know if that fixes it. But something else to look at when this happens and you're dealing with a 27 year old bike.

[kurifu]

I am having the same problem, but I don't think it is intake related. I checked my plugs and the engine temp seems to be fine, and intake leak should cause it to run lean and bring up the temperature.

I have a missing spring in on my my carbs, the long spring that goes over top of the CV slide, I was cleaning them out the get my bike back on the road and noticed that the third carb didn't have one, at all...

So I just replaced it, I will find out tomorrow if this worked or not.

[phaedrus]

Re: bike revving on its own

Do not overlook the 'chokes'. I hate to call them chokes, 'cause that's what they ain't, but calling them something more accurate, like 'enrichers' would sound goofy.

I hadn't ever dinked with CV carbs until recently. My son bought an '85 GS550EF. It would rev on it's own ... other times, when it seemed to be behaving, we'd blip the throttle and ... it would ever so slowly come back down, or maybe not at all.

I got to thinking that maybe the choke plungers weren't seating completely when the choke was off. It looks like they work by routing a bit of manifold vacuum up over the diaphragm. This would have the effect of opening the needle valves a bit without opening the throttle plates. Enrich? Choke? Whatever.

We pulled the choke plungers and stretched the springs to give them (probably temporarily) more closing power. The springs are what actually force the plungers closed. The cable works against the spring to pull the plungers open, but the spring has to be stout enough to close the buggers.

And ... it worked. No kidding. Absolutely and completely. \\/

We ordered new plungers, o-rings, springs, caps, and guides from flatoutmotorcycles.com. They arrived this past week. We'll put 'em in when it's raining.

[Kabonkie]

I just re-read my message and I didn't tell you which springs...

The throttle return springs weren't tight enough. Looks like at idle it the vacuum from the pistons would actually pull the throttle plates open slightly.

Bike was running pretty well and was no longer reving on it's own. The owner took it home and was riding it to work when it went to running rough. He said just on one cylinder. It's again back in my garage, it's running on both cylinders but not too well.

As soon as I'm a little more healed, I'll get back to it and try to figure out what's going on. (Pulled a muscle in my left shoulder, and I've got no idea what I did or how I did it.).

[Kabonkie]

Here we are again. I had it running on each cylinder and so it was running on both. I checked and looks like good spark on both plugs. I thought maybe the carb slides were sticking or not closing properly or maybe had a leak in the diaphram. So I again pulled the carbs and the slides move easily and when I put my finger over the upper hole on the intake side, they stop moving down until I allow air back in. So looks like the slides are fine as well.
The intake o-rings were replaced when trying to diagnosis the reving problem.
I couldn't get it to fire prior to pulling the carbs, but I really didn't try too hard to do so. Maybe a sync? I'm at a loss, don't know where to go next.

To refresh the issue.

It was running pretty good, was finally idleing. It wouldn't come down real fast, but it would come down. So my friend was riding it to church, about 5 miles, when a block from his destination, it lost power and wouldn't idle. Acted like it was only running on one cylinder. And at that time only one exhaust was warm. Even after I verified it was running on both, it wouldn't idle and would struggle to reach 3K rpm, but at that point it sounded like it was running like it should.

[Mark whiz]

If your crankcase was full of gas - you have more than a petcock problem most likely. That happened to me once and the petcock was fine - the problem was the float needles & seats in the carbs. If you didn't replace them when you had the carbs off, I HIGHLY recommend doing so.
Over the years, I've found that float needles are a wear/maintenance item just like chains, brakes, etc - they need to be swapped out every 3 to 5 years, depending on how the bike is (or isn't ridden) and since you was getting that much gas in the crankcase, the seats should be swapped now as well.