Ragh! Adjust Pilot Fuel Screw when on the bike (VM22SS / '79 550)

[roeme]

As the title says; after I put the carb bank back on for the umpteenth time, just as I got them synchronized into the ballpark, the engine began to wind up considerably (> 4K when fully synced).

The throttle cable almost loose, idle adjustment screw not even close to touching, and choke off. So, I suspect the pilot circuit to be way too rich, or to far open on both air and fuel – did turn out the pilot air screw quite a bit to check if leaning out would make a difference. Not really.

So, any trick to adjust the pilot fuel screws without taking off the carbs?

P.S. The screws were too far out to begin with – 2 turns for some -, and beginner me didn't feel confident enough to turn them out less than 1.5 turns after cleaning the carbs, so as not to detract too far from the presumably known good PO setting. Today I know better.

 

[chuck hahn]

Do you have a service manual to follow the sync process?? If not, heres a website you must save and a link to the service manual. Carb stuff starts on page 63. Do they have the pilot screws on the bottom along with the side mixture screws?? If they have the bottom pilot screws set those at 1 and leave them alone after that. Do all youre tuning with the side screws and carb syncs.

And in the STICKY at the top of the carb section the very first bike mentioned is the 550s.

http://www.thegsresources.com/_forum/showthread.php?73723-Carb-OEM-specs-as-per-factory-manuals

http://zeus.mtsac.edu/~cliff/storage/gs/GS550_77-82_all.pdf

http://members.dslextreme.com/users/bikecliff/

 

[chuck hahn]

Thinking about the symptom, I am thinking that your sync is all jacked up. Look at the adjuster screws on top of the linkages with the jam nut. If the screws is sticking way above the nuts then youre slides are way too high and they wont drop to idle because they are held up by the adjuster screw...follow me here?? By "way above" I mean like 3/16 or close to that. The slot shouldnt be very much above the surface of the jam nut usually....... A little above but not a huge amount.

What I would do is take them back off and bench synch them real close again. When you bench sync, turn the big idle knob in just till it hits the throttle cable linkage. Then go in 1 1/2 turns and then set the slides. Use a small paper clip wire as a feeler gauge to check the gaps on all 4 slides is the same. Reinstall the carbs and restart your sync with the vacuum gauges.

EDIT...once you bench sync them back off the idle knob and look to see all the slides have dropped down and the gap is almost gone. Reset the idle knob about 1 1/2 in after touch off and youll be ready for the restart.

 

[chuck hahn]

Do the vacuum sync with the RPMs set bat around 2,000 and youll need to adjust the idle as youre tweeking the adjusters.

 

[roeme]

Thanks a bunch chuck for your responses.

Do you have a service manual to follow the sync process??

I have both a physical manual with some dealer notes scavenged and the manual downloaded from Cliff's website. Also, I read the application notes of my carbtune.

Do they have the pilot screws on the bottom along with the side mixture screws?? (?) If they have the bottom pilot screws set those at 1 and leave them alone after that.

They do, and it's the bottom pilot (fuel) screws I have trouble accessing without taking off the carb bank. The starter motor leaves very little clearance at #2. In any case,
adjusting these is what I'll be doing next, since as I wrote in the first post, they're definitely too far out.

Thinking about the symptom, I am thinking that your sync is all jacked up. (?) If the screws is sticking way above the nuts then youre slides are way too high and they wont drop to idle because they are held up by the adjuster screw...follow me here??

At this point it surely is. Following you exactly. At some point ? frustrated and tired ? , I even have turned all screws in as much as possible, and then began syncing from there. Still began winding up as soon as I got close.

Though I re-reading the process, I realise that I have made a mistake, I began syncing with #3 as a reference, as opposed to #4, like the manual says.

 

[Nessism]

The pilot fuel screws should be open no more than 1 turn. You gotta be careful to not jamb the screw tip in too hard when seating the screw or the tip will break off in the carb body.

 

[chuck hahn]

Yes, the manual calls for the bottom pilots at 1 out. Like i said, remove the carbs and reset the pilot screws and rebench sync them and start from zero again.

 

[roeme]

Took the carbs off, adjusted pilot fuel screw to 1 turn, pilot air screw to 2 turns, each.

Then bench synced visually; I forgot about the procedure you described, chuck. But I took the VM rebuild guide from Cliff's page as a guide.
Referenced to #3, as this one was the first to bottom out.

Put the carbs back, #4 overflowed when on PRIme, and when the engine was running. Really frustrated, I took off the bowl and the needle valve out in situ to avoid pulling the whole bank. It was surprisingly easy.

Found the bowl gasket (rubbery type) shrunk too much, and scraping the floats. I guess cycling them through air and gasoline repeatedly does not only harden them, but changes their dimensions as well.

Took a fresh paper type bowl gasket (luckily I ordered more than one set) and remounted the bowl, fixed.

While another carb overflows on PRIme, she holds her water, er, gasoline while the engine is running and the petcock set to ON.

Now going for a short night spin to confirm:

a) No longer a high idle/sync'd enough to take the ride to the place I have the vacuum sync tools
b) Really not leaking

 

[chuck hahn]

The bench sync gets them real close..close enough to ride as you say. Youll probably find they will be very little adjusting to do once you get the gauges at them

 

[roeme]

F$!k that was cold - 1?C (32?F).

You're right chuck, even a beginner like me, I was able to get them back in the vicinity of a proper sync. Since she pulled well and ran smooth, I did had to try out more, and brought her up to 150km/h (93mph). This is the area where the power output of the engine normally begins to plateau (180km/h - 111mph marking the current top speed).

I didn't dare to go higher, as a) I didn't want to have a serious run-in with the law, and b) the road conditions are worsening by the minute, and the bike told me so. The streets began to glaze over. No thanks.

However, I now have the problem that the RPM's stay high sometimes – blipping the throttle however will bring them back down to idle. Hm. Not sure if I have pinched the throttle cable somewhere :-k Have to investigate this as soon as I get around the vaccuum sync

 

[Nessism]

A hanging idle is typically a result of a vacuum leak and/or a lean condition.

 

[roeme]

A hanging idle is typically a result of a vacuum leak and/or a lean condition.

That crossed my mind, thanks for confirming. I'm wondering where exactly the leak would be however. The intake boots are still fine, and I have replaced the intake O-Rings.
Though the issue would become apparent with a hot engine...which would point at the boots. Ugh.

When I got back, I did notice the throttle shaft seal (the outer plug, not on the shaft itself) on #4 pinched however.

Oh well, another chase.

 

[chuck hahn]

Get some starting fluid and start the bike. Give each intake manifold a shot right where the carbs go into them. If theres a leak there the RPMs will change as it sucks in the staring fluid. That doesnt necessarily mean the rubber is seperating on an intake either..it could well be stretched out clamps and they arent tightening enough. The starting fluid will for sure indicate an area thats sucking air..then all you need to do is find out why.

You can gently pry those aluminum end caps off and ding them back out. If they dent in that may be a source of dragging. Little smear of JB Weld to glue them back on is all it takes. basically they are caps to keep crud out of the shafts.

 

[roeme]

Little intermission before answering properly:

(...)it could well be stretched out clamps and they arent tightening enough.

That's a hot tip; since I was unable to tighten the clamps any further: Turning the screw closed them fully soon, leaving nothing for the screw to tighten.
Some resistance from tightening was there, but I guess it should be the tightening forces that stop, not the clamp closing.

I also don't like the fact that self-tapping screws are used, but from a quick google search, it looks like that was stock for some time.

 

[chuck hahn]

The intakes rubber may be pliable enough to get the carbs on and off and still be a bit "hard" for the clamps to squeeze it down good. Get new clamps and set the carbs in place. Then use a heat gun to heat the rubber up really good and then tighten the clamps. The rubber will squeeze down onto the carbs much easier being warmed up good.

 

[roeme]

Alright, time for an update.

I have since taken off/put back on the carbs one more time, replacing the clamps with some nice stainless worm-gear type ones from the local craftsman (? not sure if translated correctly) store.
Reason the carbs came off one more was as mentioned earlier, #3 carb's bowl gasket shrunk and scraped the floats like #4 earlier, resulting in intermittent overflow.

Still, I seem to have a vacuum leak somewhere: When hot, the RPM's like to stay high. I was able to reproduce the issue reliably by SLOWLY turning the throttle a bit from idle - bike went up to 3K on its own.

Giving the throttle a quick blip, i.e. twitching once (and I mean really twitch, like supercharged parkinson), the RPM's fall down to idle with a reasonable speed (not slow as one would expect under vacuum leak condition).

Inlet boots seem ok, I couldn't see a tear from a cursory glance, and I had replaced the O-Rings earlier.

But given the gasket scraping floats, I'm not sure how much I can trust my earlier float measurement. Could a level too low cause the mixture to go lean? (Remember, VM22SS)

Next I will try the starter fluid spraying, still trying to figure out how to do that without setting my bike on fire. Can't really get the can close to the inlet boots, might need attach a hose or something.
Also have to jury-rig some auxiliary tank thingy.

The hunt is still on...

 

[chuck hahn]

Maybe a cable is dry or the grip itself is hanging up inside the switch housing. The grip also should get a little swipe of LIGHT grease as well.

 

[roeme]

Intermediate question: Could an airleak on the airbox side of the carbs cause a lean condition as well? I haven't yet bothered to check there as thoroughly as the inlet boots, reasoning that a leak there surely couldn't cause a much havoc as on the inlet boot side of the carbs.

Finally have the time to do the leak tests tomorrow.

 

[Nessism]

Air leaks on the back side of the carbs will mess up the mixture. My old 1000 wouldn't run for crap with the back side of the air box disconnected.

 

[roeme]

Update:
I have just checked there, and sure enough, #2 and #4 are leaky on the air box side. Could confirm with spray fluid. Reseated and tightened them up as much as I could - the clamps have definitively stretched.

Intake boots are fine and have hefty new clamps.

Going to put new clamps on the air box side as well.