Chasing a Hanging Idle ('79 550 VM22SS) (questioning an air-leak though)

[roeme]

It is time to choose a more methodical approach. The observant reader may recall my various threads in which I have chased a merry mix of problems with my bike, some related to this problem, some not.

For reference, this is a video how the idle manifests (Apologies if you have seen this in other threads, embedding it here once again to keep the thread consistent):

What I have done so far:

• Rebuilt the carbs:
  1. Replaced o-rings
  2. Inspected needle valves
  3. Checked float height and set to 24mm where necessary
  4. Ensured that floats can move freely
  5. Checked fuel level (see pic below)
  6. Set fuel pilot screws to 1 turn out, air screw to 1.5 turns initially, currently at 1 turn as well.
  7. Visually synced carbs
• Cleaned Petcock, practically rebuilt
• Replaced intake boot O-Rings
• Replaced vacuum port screws and their washers (cut new ones from gasket paper), even added teflon tape to screws
• Replaced clamps on both inlet and airbox side of carbs
• Had Valve clearance checked 8000 km (~4970mi) ago (required a correction on a single exhaust valve, otherwise good)
• Added filter element to airbox, soaked in engine oil as directed by manual (the original filter decomposed a long time ago)
• Extracted boots between airbox and carbs, soaked them in vaseline, put them back on (more on that below)
• Checked throttle cables move properly

Here are pictures of the fuel level, off-bike, carbs upright:



The reason why I took the boots from the airbox was the last time I sprayed starter fluid around the area of #2/#3, the RPM changed - slightly, but it did. After a lengthy vaseline bath, I had quite some trouble to put them back in, and they didn't swell much, if at all (I have yet to acquire xylene/wintergreen). I beginning to doubt that they're leaking, pending further investigation.

Things I investigate/fix/do next:

1. Re-check (again) for air leaks with starting fluid: carbs themselves, seal between filter housing and intake manifold, boots again to be absolutely sure
2. Repair RH Exhaust significat rust hole (at the beginning of muffler, IIRC approx. 8cm²). I have no idea if this can even cause a hanging idle, but I gotta fix that anyway.
3. Try to turn pilot fuel screws further out. When I got the bike, #1, #2 were 2 turns out, #3 1.5 turns, and #4 1 turn. Currently they're all at 1 turn.
4. Fabricate some screws to monitor fuel level when the engine is running, to make sure the jets are not starved
5. Swap airbox from other bike (again awful work on the 550, but whatcha gonna do)

I don't think vacuum-syncing the carbs makes sense at this point.

Your thoughts? What else could be there? Is a lean condition the sole cause for a hanging idle?

[steve murdoch]

Wish i had something concrete to offer but i wanted to commend you on the posting.
Pics, video, previous info all being provided should give the carb guys enough to solve your problem.

I was a little surprised at the amount of cranking you had to do to get the revs to rise at all.
Do you have a ton of excess play in the throttle cable?

[roeme]

Wish i had something concrete to offer but i wanted to commend you on the posting.
Pics, video, previous info all being provided should give the carb guys enough to solve your problem.

I was a little surprised at the amount of cranking you had to do to get the revs to rise at all.
Do you have a ton of excess play in the throttle cable?

Thank you - I admit the post took quite a bit longer to write than to read Let's hope somebody can offer additional insight.

The video was recorded some time ago when I was working on the carbs, throttle cables not mounted permanently then and hand motion exaggerated to show more clearly what's going on.

Right now, the cables are moving as they should, no binding, and little play, no excess.

[850 Combat]

I have had mechanical ignition advance stick, but not on a Suzuki. I've never even heard of it on a Suzuki. I think that until 1982, all even with an electronic ignition used a mechanical advance. Sometimes the flyweights wear notches into the backing plate and hang up. Usually, you can hit the kill switch momentarily and it will allow the idle to go back down.

[thebrandonbeezy]

How did you post the video like that ?

[Lorenzo]

Roeme, since you mentioned vaseline...
I had the same issue, when I did smear the intake boots, with vaseline to ease them in.
After a couple hundred km's the problem sorted by itself, with the odd throttle stop and pilot air adjustment, trown in, for good measure.

[1948man]

Aren't the washers for the vacuum port screws usually copper? I would wonder if gasket paper would hold up. I'm not sure if that would allow enough of an air leak to get lean especially if the threads are sealed.

[roeme]

Just a quick update; I've solved the hanging idle, and am now back to a high idle. This is progress; even though it might not sound like it to some ears.

Real-Life comedy...

I will write a proper post including answers later on.

[TiggerKZN]

Not sure if this has been mentioned before...
Is there a possibility your accelerator cable is sticking?
Possibly not allowing the slides to close fully?

[76_Mike_82]

Sorry, this isn't helpful but I had a sticking Idle after a run. Best example is highway and theboff ramp. It would stay high for most if not all of the stop light at the end of the off ramp. If I really pushed it I could make it do it aon city streets but much harder. I chased everything finally I bought a second bike and finished rebuilding the carbs so I tried swapping them. One the new carbs were sync'd the problem was gone. Those carbs were dipped twice and rebuilt 3 times prior. When I get the other bike ready I'll havr to figure it out but for now this boke runs well.

Best of luck to you.

[roeme]

Alright, so I went to the nearby bike mechanic which already worked once before on my bike and asked for some advice, i.e. second opinion (well, far higher than second ). He confirmed that a high idle is caused by a lean condition (I didn't doubt this), most likely caused by one carb far not in sync with the others. The hanging idle however can only be caused by one or more slides not correctly returning to their idle position.

While this echoed what I've been told in here, it left me a bit confused: I did sync the carbs visually already, so how could they be that much out of sync? And I confirmed the throttle cables to move correctly, and with the correct amount of play. And the slide assemblies couldn't just bind up, lest it would block everything from moving...hmmm.

Well, nothing else to do than inspecting the top of the slide assemblies, throttle shaft and everything...

..no sooner than when I lifted up #3's hat, that's when I found the root cause of the hanging idle:

In case you missed it: the screw fixing the throttle cable carrier (not sure what it's called) to the throttle shaft was loose - this allowed for comparatively huge play. And it's also the reason why blipping the
throttle brought the engine back to idle, but going back slowly did not: The throttle return spring is mounted to the cable carrier, so with this screw loose, it's only gravity which pulls the slides back to idle for the last mm or so - and they're comparatively light. That's why slamming them back by blipping did "help".

So the case of my hanging idle is closed, thanks y'all for your help.

I went on to synchronize the carbs, but as I earlier, I found the RPM to go high like mad as soon as I got them close. I will debug the high idle in one my other threads, this one here; clicky.

How did you post the video like that ?

If you haven't already figured out by now, you can do so through "Go Advanced", then using the VIDEO tag with a youtube link. Those get embedded automatically.

Aren't the washers for the vacuum port screws usually copper? I would wonder if gasket paper would hold up. I'm not sure if that would allow enough of an air leak to get lean especially if the threads are sealed.

They are, gasket paper held up, and I confirmed them to be properly sealing by spraying starter fluid directly on them. Nonetheless, I'll use copper washer as soon as I can source them (need to that online).

I have had mechanical ignition advance stick, but not on a Suzuki. I've never even heard of it on a Suzuki. I think that until 1982, all even with an electronic ignition used a mechanical advance. Sometimes the flyweights wear notches into the backing plate and hang up. Usually, you can hit the kill switch momentarily and it will allow the idle to go back down.

I have confirmed the advance to not bind some time earlier, while inspection the ignition unrelated to this issue. You're right, mine is mechanical as well.

This one bike really doesn't like having the ignition interrupted when driving. I did it twice I believe so far, once on purpose («..well I'm just coasting down this hill, no need for my cylinders to fire..»), once inadvertently (gosh, these winter gloves are bulky...hey is that joe? *winks*). Both times («...wait, this is a carbureted engine...» / hey where's my power gone?!) I got a massive bang out the exhausts, nearly jumped off the bike.

Sorry, this isn't helpful but I had a sticking Idle after a run. Best example is highway and theboff ramp.(...) chased everything finally I bought a second bike and finished and finished rebuilding the carbs so I tried swapping them. One the new carbs were sync'd the problem was gone. Those carbs were dipped twice and rebuilt 3 times prior. When I get the other bike ready I'll havr to figure it out but for now this boke runs well.

Well, make sure to take into account what I have discovered here, and then I'd recommend looking at the boots.

[niepoort]

mine stick using the wrong fuel , i think there just a bit to mutch throttle cable play and a bit of play in the bolt containing the throtle pivoting axle