fresh carbs (again), now "idles" at 6000 rpm

[82 GS550L Basket Case]

it's official ... we're frustrated.

after finishing the senior project, getting a good grade and graduating, Tanner rode the bike for a bit, but it never ran right. We went through the carbs again, got the valve clearances right ... and still it ran rough and smoked from the right pipe. he gave up and parked it for a while.

took the carbs to the shop, and he went through them again and fixed one of the jets we'd managed to munge up. he bench synced the carbs and we put them on last night.

got everything hooked up, and when the engine started it ramped right up to 6000 rpm. it would rev even higher when we goosed the throttle.

we would try something, start it and see how it ran, then shut it down after 10seconds or less

we checked the idle screw on the back side of the carbs, screwing it all the way in and all the way out. no change.
disconnected the choke cable. no change
disconnected the throttle cable. no change
we could rev it up manually with the cable disconnected
tapped the carbs with a rubber mallet. no change

taking it back to the shop on Monday. any suggestions before then?

 

[82 GS550L Basket Case]

oh, and we checked the vacuum line to make sure it and the fuel line are connected correctly.

 

[tkent02]

Here's a suggestion, Quit taking it to the shop.

 

[82 GS550L Basket Case]

Here's a suggestion, Quit taking it to the shop.

ok, that's helpful.

since, as Tanner would say, (and has said) "every time we touch the carbs it runs worse" would you be willing to come over and show us how to get it right?

We've looked at, printed out, and used the various resources on basscliffs site. we got through a lot of it, but the carbs are beyond our collective ability.

so if we can't fix it, and you say we shouldn't take it to the shop ... kill it with fire?

 

[tkent02]

Your problem is simple, the hard part is that you haven't found it yet. Sorry I'm being a smartass, I can't resist when someone thinks a shop whose first job is to sell new motorcycles will fix their old motorcycle better than they can. I don't do Georgia in August, but if you bring it to Colorado I'll help you fix it.
Seriously, there is only one way for an angine to idle too fast, somehow it's getting too much air, and enough fuel for it to run. The throttle is not closing all the way, or there is an air leak, there is no other way. Does the throttle make that nice "CLACK" sound as you close it quickly? If not it's probably not closing. Maybe the air leak is from the choke not closing correctly, maybe its from bad boots or a missing hose, but somehow too much air is getting in. Idling at 6,000 requires a large amount of air getting in, it should be easy to find the source.

Put the synch gauges on, are all four reading about the same or are one or two cylinders doing all of the work? This could help you figure out where it's leaking.

The fact that it didn't do this high idling the first time you had it running tells you something you did the second time is causing the problem, what did you do?

The fact that the big idle speed screw isn't doing anything should tell you where to look too.

 

[GateKeeper]

something in the reassembly is off......

maybe your bench sync is off, butterfly's are open way too much, your idle screw is not on correctly, since you say it don't make a change no matter which way you turn it, throttle cable is holding the system open and not allowing it to close, and as Tkent02 says there is a air leak somewhere, is your gas tank being used or a IV bottle, make sure the vacum ports are closed off if using an IV bottle

make sure all the unioins for the carbs are seated correctly and they open and close uniformly pay attention on how they are joined together....

Best of luck...

.

 

[Tamara]

Take a close look at the boots. Are they cracked? Are the carbs seated firmly in the boots with no pinching? Are you using the stock air box or pods?

 

[chuck hahn]

By idle screw, you do mean the nbigb knob in between 2 and 3..right?

Also look to see that there is some slack in the cables when you hook them up and have them on the linkage brackets. Doesn't take much of an over tight cable to make her rev like mad.

You have two places to adjust slack in the cables..the turn buckles at the grip and at the carbs themselves where tha cables bolt to them. I suggest you turn the turn buckles at the grips all the way IN..as in toward the end of the bars.

Then put the cables on at the carbs, but leave the jam nuts loose. The bracket should be about 1/3 the way down the cable end from the top. That way, once you have adjusted most of the slack out with the turnbuckles at the grips, you can adjust even more at the carbs if needed.

Set up the cables right before you worry about any air leaks..because to me it sounds more of a hanging cable issue. Fiddle with the adjustments so you see what they do and then set out getting them just right.

Base spot to start with the big adjustment knob is about 2 to 2 1/2 full turns in once it touches on the throttle linkage itself. This may still be bit too high, but it sure wont be at 6G!!!!!


And I agree with Gatekeeper..recheck the bench sync..should just be a sliver of an opening at the butterflys. I try to set them with a piece of 020 MIG welder wire as my feeler gauge. Adjust till the wire just starts to grip right at the very bottom of them.

 

[chuck hahn]

Post script...a regular size paper clip wire is a good feeler gauge for benching them too.

 

[Triam]

I hope I'm not sending you on a wild goose chase with this comment, but my GS850 was doing the same thing until I realized that two of the cylinders had no compression because the valves weren't closing completely. Only 1 & 4 would fire and it'd always be at above 3,000 RPM. Even if it is a wild goose chase, double-checking the clearances is always a good idea.

 

[jsandidge]

I had the same problem. 6000 rpm. Throttle cable was just a hair too tight.

 

[82 GS550L Basket Case]

Your problem is simple, the hard part is that you haven't found it yet. Sorry I'm being a smartass, I can't resist when someone thinks a shop whose first job is to sell new motorcycles will fix their old motorcycle better than they can.

ah, assumptions. the shop is actually a small, independent "performance" shop, and Frank the owner helped Tanner out a LOT with his senior project. Frank not only knows his stuff, he's a Very Nice Guy who has helped a lot. and since he's been working on Japanese bikes since this '82 Suzuki was new, it's a certainty that he knows more about bikes than either Tanner or I do.

I don't do Georgia in August, but if you bring it to Colorado I'll help you fix it.

if only the bike would make it that far. or if I had enough PTO banked for a trailer trip. or if ANYONE on GSResources lived close, and had time to help.

Seriously, there is only one way for an angine to idle too fast, somehow it's getting too much air, and enough fuel for it to run. The throttle is not closing all the way, or there is an air leak, there is no other way. Does the throttle make that nice "CLACK" sound as you close it quickly? If not it's probably not closing. Maybe the air leak is from the choke not closing correctly, maybe its from bad boots or a missing hose, but somehow too much air is getting in. Idling at 6,000 requires a large amount of air getting in, it should be easy to find the source.

now, this is very helpful. thank you. the throttle seems to open and close right, and it definitely clicks when it snaps shut. we are going to pull the carbs off AGAIN and make sure we didn't tear or fold a boot when we put them on last night.

care to educate me how that Big Idle Screw actually works?

Put the synch gauges on, are all four reading about the same or are one or two cylinders doing all of the work? This could help you figure out where it's leaking.

The fact that it didn't do this high idling the first time you had it running tells you something you did the second time is causing the problem, what did you do?

The fact that the big idle speed screw isn't doing anything should tell you where to look too.

we don't have a carb sync tool, mostly because I have No Idea how one works. it's probably the next tool to get.

the only thing we did intentionally is put the carbs back on. I don't know what magic Frank did when he worked on them Friday. I'm going to trust that he put them back together right, and we somehow installed them wrong.

I'll doublecheck the air intake path and see if there's something wrong there.

 

[82 GS550L Basket Case]

thanks for all the other replies, too. I'll try to answer the questions ...

compression is good. 125-135 on all four. we just adjusted the valve clearances, even though the bike was running rough (I had thought the rough running before might be a rings/valves problem, but the clearances and compression are in spec)

we were running it off the gas tank, and we double checked the vacuum line. at both ends. didn't matter if the petcock was on prime or run.

we disconnected the choke cable, and the throttle cable, and the revs were still at 6000.

we *thought* we got the carbs seated in the boots correctly, but we will doublecheck that today. the boots are new, as part of the rebuild last winter.

stock air box with a new k&n filter, properly oiled. Frank said we needed to rejet for the increased air flow. the filter box is sealed with new gasket.

 

[terrylee]

Maybe take some pics. of carbs., where cables hook up, all the springs between carbs. and idle screw area. Maybe something is not hooked up right or stuck? Maybe something will stand out to someone on here. terrylee

 

[tkent02]

The idle screw just opens all of the the throttles more and more to raise the idle. Screw it in, idle gets faster. It usually doesn't take much to effect a change, like 1/4 turn in or out and the idle will go up or down several hundred RPM. If it has zero effect there is something wrong, perhaps the throttles are open so far the screw isn't even touching it? Not sure but you should be able to find it.

 

[82 GS550L Basket Case]

update ...

we *think* we solved it. the boot from the air box to carb #3 was pushed in/folded slightly, like a grommet that's about to pop out. it wasn't obvious but when we got good light in between the carbs and the engine we could see a gap. well, not a gap, but it didn't look exactly like carb #2.

pulled them, double checked that the butterfly valves are sealing and everything else looks right, and put it back together. much better, but still rough and hesitating. sprayed some starting fluid up around each boot in turn, and still some increased rpm when the ether got in around the edge of boot 3.

pulled them apart again, pulled the boot out, and no apparent tears or problems. put the boot back in rotated so what was the bottom is now the top (even though its symmetrical, unlike the boots for 1 and 4) and tried a slightly different approach to putting the carbs back in.

short version: lightly secure the air box to the frame, fully seat the carbs on the air box boots, tighten clamps, carefully seat carbs into intake boots, tighten clamps, and THEN tighten the air box to the frame.

in any case ... it runs better, no variance in RPMs when sprayed with ether, and the idle adjust screw actually adjusts the idle.

it's been raining for three days, so no test ride ... but it looks promising at this point.

tl;dr too much air into carb thanks to poor installation

 

[tkent02]

Excellent. I don't have to go to Georgia after all.

 

[82 GS550L Basket Case]

woo hoo! test ride, and while Tanners not convinced, I am. I put a couple dozen miles on it on a variety of streets and speeds, and I'm convinced its running like its supposed to. it will definitely get up and gallop.

looks like there might be a bit of a leak between the heads and jugs, but it doesn't drip or run, just a minor seep. sounds good, just a tiny bit of smoke (still) from the right pipe on unloaded revs.

definitely a fun ride.