Idles great, but won't rev...

[oldbikefixer]

I've looked for a similar problem to mine on this forum so I wouldn't have to bother anyone with a repeat question, but this seems to be the first time for this particular problem.

My '80 GS550E will start up very easily and idle all day, although the idle is a bit high (almost 2000 RPM), and won't slow down any more by adjusting the idle screw - it's all the way out... but that's not what's ticking me off.

After starting the engine and letting it run for a bit to warm it up, it WILL NOT rev up. If the throttle is opened more than 1/16 of the way, the engine just bogs down & will die if the throttle is not released.

I cleaned the carbs (I've cleaned at least a few dozen carbs over the past 20 or so years, so I'm fairly sure that I know what I'm doing) and I'm reasonably sure the petcock is working properly, although there's really no way to tell now, is there?

I detest CV carbs and vacuum petcocks, as they've always been nothing but trouble for me. Unfortunately, I don't have an adapter handy that will let me mount a Rochester Quadra-Jet to a GS550.

Although I've owned nearly 100 motorcycles over the years, this is my first Suzuki GS. After reading about all the problems (carbs, electrical, etc.), associated with these bikes, I'm about ready to take this bike to the scrapyard. If I can't find a solution to make this nice looking, 6500 mile bike run correctly, that's where it going to end up.

[gs850cafe]

you've got a vac leak somewhere..or unsealed airbox..if you can disasemble an clean carbs like u say you should know what to do...

if it go the the scrap yard let me know..i need a few minor parts

[Nessism]

Did you install the airbox?

Just for giggles you might want to read though the carb rebuild tutorial and Top Newbie Mistakes threads and see if anything there strikes close to heart.

[BassCliff]

Hi,

Yes, it sounds like an incomplete carb cleaning or massive air leak. Go through the maintenance lists in your "mega-welcome" again to see if you've missed anything. Skipping steps or taking shortcuts will lead to much frustration and/or catastrophic failures.


Thank you for your indulgence,

BassCliff

[JimmyR]

Sounds like a stuck choke maybe?

[oldbikefixer]

Thanks for the helpful suggestions folks, but I'm thinking that maybe I didn't describe the problem in my last post clearly enough...

The airbox is on the bike, although the lid & element are missing until I can find replacement parts. The rubber cylinders that connect the carbs to the airbox are attached, and in good shape.

The missing airbox lid & element could have an adverse affect on the way the bike runs at higher RPM, such as causing it to run lean or even "break up" within a certain RPM range, but not enough of an effect to completely shut the engine down when the throttle is opened the slightest bit.

If there was a vacuum leak, the idling characteristics would be affected much more than the higher speed running. The fact that the bike starts easily & idles suggests that a vacuum leak is not causing the problem.

While it is possible that I might have missed something in cleaning one or two of the carbs, the engine is not running poorly on just a few cylinders, the problem affects all 4 cylinders at the same time.

Here's a step-by-step description of what is happening:

1) Pull the choke out, hit the starter button, and the engine fires up like a brand new bike. The idle is high (about 3500 RPM) while the choke control is pulled out.
2) Gradually push the choke control back in, and the engine slows to a faster than normal idle (about 2000 RPM).
3) Let the engine idle for a few seconds, then open the throttle a bit to rev the engine, and it falls on it's face and will die if the throttle isn't released quickly.

Opening the throttle has pretty much the same effect as hitting the kill switch.

And yes, I've tried opening the throttle with the choke pulled out, but the same thing happens either way.

[JimmyR]

That does sound weird because you would expect it to run a bit lean rather than rich as it sounds. Ok, here's a suggestion, and I only make it because it's something I might do so don't take offence! Did you put the pilot jets back? What about the little rubber covers inside the float bowl?

[airbornespud]

Sounds like a stuck choke maybe?

i'm kinda with jimmy on this one. the first thing i would do (if it were me) is find the choke slide on the rack of carbs and make sure that when the choke cable is pushed in all the way, the slide goes in to where it should. if it's not, push it in and reset your idle. then see what happens with the throttle. if it's still no-go, then maybe kill it a with the throttle and pull a plug or two to see what that looks like. maybe it will give you a direction to head. i would also, just for S & G, put the airbox back to where it should be. something has changed, and right now variables are bad. eliminating them will only help you, even if, in theory, they shouldn't change anything, too many of them stacked together might. does that make any sense?

[Nessism]

If we were in Vegas I'd throw down a C-note that the problem is the missing airbox lid and filter. Also, GS bikes require some warm up before they will accept throttle. Of course this assumes the carbs are properly clean. Many people think their carbs are clean when they aren't. The carb rebuild tutorial is linked in my signature. In particular it's important to make sure the pilot jets are clear.

[JimmyR]

Hey Nessism - is that right about GS bikes needing some warm-up before taking throttle? That answers a question I had. I am delighted with how my '82 GS1100 is running now but it almost feels like it's running rich when I first start it, even after I lose the choke. After about a minute it's fine. What you say makes a lot of sense for my experience but it puzzled me.

Sorry for the dereail!

[Nessism]

Hey Nessism - is that right about GS bikes needing some warm-up before taking throttle?

Sorry man, I just made that up. You caught me.

Seriously now, GS bikes were famous for being lean from the factory. Particularly the early CV carb bikes. Opening up the pilot mixture screws helps this situation though. One other fix is to shim the needle higher, which requires changing the spacer on TOP of the needle (contrary to what some people think). At any rate, yes, GS bikes typically require some warm up time. And of course, any modifications to the intake system have a very drastic negative effect.

[tom203]

The fact that you have idle stop screw backed off with no drop in idle speed would seem to mean that the "choke" circuit (even when fully off) is supplying all the mixture needed to keep this high idle (2000 rpm)- openning the throttle even a wee bit overwhelms this mixture with excess air. I think your pilot circuits are plugged and not delivering fuel into this burst of air. The normal position of idle stop screw allows a tiny bit of air to slip under throttle plates and scoop enough fuel to maintain a stable idle once warmed up.

[cowboyup3371]

Oldbike, see my post in the for sale section. I have a complete airbox set up for you if you want ($45 shipped priority mail).

[oldbikefixer]

Thanks guys! If you're still curious, the choke slide mechanism that runs through the carb bodies, as well as the individual plungers and their pivoting arms, all seem to be working as they should.

I had previously (a few days ago) thought that the choke parts might have been "goobered", so I WD-40'd the snot out of all of the choke parts. I then tried gently tapping each individual plunger in to see if any of them were not seating properly. However, everything seemed to be fine as far as the choke parts, and the problem didn't change a bit.

I'm going to pull the carbs off again and re-do everythng... again. I wouldn't mind doing it so much, but the Phillips screws under the airbox that hold the airbox to the frame are permanently rusted in place, so I have to perform a series of upside-down gymnastics to remove the carbs, and then again to put them back on with the airbox still in place.

Also, I'll take that complete airbox set-up that you have for sale, Cowboyup. Lemme know how one goes about buying stuff from this website.

What some of you might not be aware of is that I just got this bike. It was left abandoned, out in the weather, for 9 years before I dragged it home.

The carbs are not the originals, as the originals were ruined beyond hope from sitting all those years. I got a GS550L parts bike (no title) that had useable carbs & other parts.

I'm just trying to get this old machine to run again...

[cowboyup3371]

I sent you a pm