Author Topic: Carb sync "360 degrees" out of whack? (Read 2889 times)

Untold · « **on:** September 17, 2012, 10:42:20 AM »

Adjusted the valves on my 550 and then went to sync the carbs. Got them synced pretty close, and went to tighten the adjusters up. It was dark out, and I somehow knocked the carb linkage apart and it took some wiggling and forcing to get it back together. Then I tightened it all up and left it for the night.
Went for a ride this morning and it felt great. Knocks and ticks were gone, and it had great power. Rode for about 20 minutes, and it started to get a little sputtery, and then cylinder 1 was popping and backfiring. I figured maybe I'd better double check the carb sync, so I hooked it all back up. Trying to sync it, the idle was racing up to 4-5k. I manipulated the choke to get the idle down enough to work. The gauge needles were all in the ballpark, but I couldn't get a satisfactory sync.
Looking at the adjuster screws, I could see that at least 1 and 4 were backed out way further than they were originally, because of the line of grime on the screw. I screwed them back in a few turns, and checked the sync again. Was then able to get them all really close and called it a day.
So, this is basically just a long way of saying, could my carb adjustment have been so out of whack that the needle on the synch tool went all the way around the dial the wrong way, so that it looked like it was matching up but in fact it was way the #$%* off?
Haven't taken it for a ride again yet, had to run out. But it seemed to idle a lot better after I re-synched.

flybox1 · « **Reply #1 on:** September 17, 2012, 11:16:04 AM »

here's what i'd do...
remove the carbs.
first - set #1, #3, #4 vacuum set screws to their mid points.
second - bench sync carbs (again) to match slave carb(#2).
reinstall carbs and airbox and start her up
third - ensure all vacuum gauges are pulling the same # based on your slave carb. (if your gauge is off, you'll never be right)
lastly - re-vacuum sync.

phil71 · « **Reply #2 on:** September 17, 2012, 11:32:10 AM »

don't the 550s have adjusters on all 4 carbs? you prob sync'd solely by raising the slides, so now none of them can fall 'home' anymore. drop your slides, start over.

Untold · « **Reply #3 on:** September 17, 2012, 03:23:56 PM »

You are on to something. That's why I've got this hanging idle now I bet. Can you explain to me what you mean by synching only by raising the slides? I used the adjuster screws that are for each carb, kind of where it connects to the linkage. As seen on the youtube video showing how to sync carbs. Is there another way to do it? Pardon my ignorance. Air screws are at 1.5 turns out. Thanks

phil71 · « **Reply #4 on:** September 17, 2012, 03:37:43 PM »

Think of them all as being on threaded rods. Generally, if there's no 'master', meaning a carb that doesn't have adjusters on the slide, then I usually would pick the one that is sitting the lowest in the bore and sync to it. But if you chose one that was higher on the threaded rod and adjusted to that, then you'd be bringing them all up, and eventually they are riding so high on those adjusters that they no longer reach the 'parked' position when you allow the throttle to return.

Untold · « **Reply #5 on:** September 17, 2012, 03:38:54 PM »

Also, it seems the popping was actually from cylinder #2. Spark plug boot was arcing to the head. Replaced boot and no more backfiring. There's a new sound in the top end, a bit more of a rattle than a tap. Possibly cam chain? I did attempt to adjust earlier, may not have gotten it right? I've triple and qaudruple checked all valve clearances. Just that and the hanging idle. I can ride and everything feels great. Sometimes I'll come to a stop sign and it idles fine, sometimes it stays up around 3k. I can manually push the linkage down a few mm and it lowers the idle to a normal pace.

phil71 · « **Reply #6 on:** September 17, 2012, 04:17:28 PM »

the linkage is push-pull, so even at rest , you have a little bit of give in the other direction. Once you sync the carbs properly, all that should be fine again. As for the cam chain, you have to put engine in a position that places the cam slack at the rear, then you loosen the locknut, then loosen the bolt for a second. The spring will take up the slack (you'll hear it happen) and then you can snug the bolt, and the locknut. You'll be rotating the engine counter clockwise to place that slack where you need it. The shop manual gives you the method.

Untold · « **Reply #7 on:** September 17, 2012, 04:33:03 PM »

I didn't realize what the adjustment screw was doing. I looked at a spare carb set and realized that they screw raises and lowers the slide, like you said. So I screwed all the adjusts as far in as they could go, thinking that would lower the slides all the way. Then I synced it from there. Seems to idle a bit lower, but still hangs at 2500 rpm at stop signs. I'm trying to avoid removing the air box or carbs. Is that this has come to?

phil71 · « **Reply #8 on:** September 17, 2012, 04:57:00 PM »

what about the idle stop screw, and throttle cable routing?
Hanging rpm could mean an air leak. Spray some carb cleaner around the manifolds,

Untold · « **Reply #9 on:** September 17, 2012, 05:01:40 PM »

Yeah, it's acting like an air leak. It's just odd that I didn't mess with any of the connections. I figured it has to be something that I did. Valves, Cam chain, Carb Synch. Before I did any of those things, it was running ok. It's improved in some ways, which i attribute to the tappet adjustment. Gotten worse in other ways, such as this randomly racing idle. Cable is routed cleanly and operates smoothly. I'll spray for leaks tomorrow and see what that tells me. thanks

Untold · « **Reply #10 on:** September 17, 2012, 05:09:36 PM »

Throttle stop screw has been in every position imaginable. Even if it's completely backed off so that's it's not actually making contact with anything, the idle will race.

Untold · « **Reply #11 on:** September 17, 2012, 06:38:55 PM »

Seems like this thread addresses the same issues:

http://forums.sohc4.net/index.php?topic=112789.0

lucky · « **Reply #12 on:** September 17, 2012, 08:38:15 PM »

Start over. Get rid of the grime. Do not work in the dark.

360º out? makes no sense.

Untold · « **Reply #13 on:** September 18, 2012, 05:25:11 AM »

Thanks. Going to try to get the slides lowered and set a master, and start over again. I didn't have a "master" carb that I was trying to sync to, I just messed with all of them and got them to even out. But now I see where I went wrong. Oh well, only fought with it for about 4 hours yesterday. Time well spent.

lucky · « **Reply #14 on:** September 18, 2012, 06:45:16 AM »

Quote from: Untold on September 18, 2012, 05:25:11 AM

Thanks. Going to try to get the slides lowered and set a master, and start over again. I didn't have a "master" carb that I was trying to sync to, I just messed with all of them and got them to even out. But now I see where I went wrong. Oh well, only fought with it for about 4 hours yesterday. Time well spent.

If it was me I would buy a Clymer's workshop manual.

Untold · « **Reply #15 on:** September 18, 2012, 06:52:19 AM »

I've got the factory manual. May look for a Clymer as well if it's worth it.

flybox1 · « **Reply #16 on:** September 18, 2012, 07:31:23 AM »

see this thread...
http://forums.sohc4.net/index.php?topic=112789.0

phil71 · « **Reply #17 on:** September 18, 2012, 07:36:37 AM »

Clymers? I've found them to be vague and wrong about a lot of things . FSM is the way to go.

flybox1 · « **Reply #18 on:** September 18, 2012, 07:41:50 AM »

Quote from: phil71 on September 18, 2012, 07:36:37 AM

Clymers? I've found them to be vague and wrong about a lot of things . FSM is the way to go.

+1

Untold · « **Reply #19 on:** September 21, 2012, 07:29:06 AM »

Readjusted the valves. Synced carbs again by setting a master carb using twotired's method. Running great now, although I may have dropped the slides too far. The idle set screw is all the way in to get a 1200 rpm idle. I feel like I should readjust to have room to raise the idle with the screw. But good enough for now. Thanks for the help

crazypj · « **Reply #20 on:** September 21, 2012, 09:14:02 AM »

You have the link mechanism assembled wrong.
Hopefully you didn't break anything persuading it back together.
You'll probably have to remove carbs to fit it properly

Untold · « **Reply #21 on:** September 21, 2012, 09:49:54 AM »

How so? Everything seemed to go exactly according to plan, based on the input I received here. I confirmed that the slides were indeed set too high, and that was causing the racing idle. I hooked up the manometer, held the throttle to keep the engine running while I adjusted one carb to the highest vacuum reading, then locked that carb. Then adjusted the other 3 carbs to that one. All is great, idles just fine, rides strong. Just don't have the adjustability in the idle set screw. I have some, just not a full range. I feel like this will be easily fixed by raising the slide on the "master" carb just slightly, and then resynching the other carbs to that one again. Essentially just raising all 4 slides a hair, to allow me to back out the set screw a little bit. What am I missing?

Untold · « **Reply #22 on:** September 21, 2012, 09:50:32 AM »

Or were you responding to the original post?

phil71 · « **Reply #23 on:** September 21, 2012, 01:23:39 PM »

that doesn't make sense. Idle screw should only go UP from the 'parked' position.

Untold · « **Reply #24 on:** September 21, 2012, 01:41:10 PM »

Maybe we're talking about two different things. I mean the one large screw that presses against a plate, to adjust idle speed simultaneously on all 4 carbs. Right now, that it screwed in pretty far, to press against the plate that raised the idle to the appropriate level. If it screw it out, lowering the idle, it will be too low. I want the idle set around 1200k, but I want it to be at that rpm when the idle screw is basically at its midway point of adjustment, so that I could turn it in more to raise the idle, or out to lower it. As it stands, I have to turn it in farther than I would like I get the idle up. I believe this is because the slides are too low to start with. So I need to raise the slides a bit and resync. Makes perfect sense in my mind, but maybe I'm missing something?

Untold · « **Reply #25 on:** September 21, 2012, 01:49:43 PM »

Originally, I was at the other extreme. No matter how far OUT I turned it, it would still idle way too high. Then I readjusted, and now when it's screwed as far IN as it will go, it idles a little too low. I went to far in my slide adjusting. Somewhere in the middle is the sweet spot.
Right now, the highest I can raise the idle is about 14k with that screw. Prior to my adjustments, I could get it up to 2k if I wanted, or low enough to kill the engine.
Now I can get it LOWER than I ever could, but only as high as about 14k. I'm pretty confident that I know how to remedy it, just wanted to put it out there for future searches.

phil71 · « **Reply #26 on:** September 21, 2012, 03:45:57 PM »

yeah, you did go too far the other way.. however, if that bike wont idle at 1100, you have other problems on your hands

Untold · « **Reply #27 on:** September 21, 2012, 03:58:11 PM »

Oh, it will idle great at 1000k. But even so, I'm closer than I'd like to maxing out the adjuster at that setting. And sometimes when it's starting from cold, I like to turn up the idle until it warms up, rather than having to goose the throttle. Yeah, it'd be nice if I didn't have to do either of those things, but I expect it out of a 35 year old machine.

crazypj · « **Reply #28 on:** September 22, 2012, 11:30:19 PM »

You don't set highest possible vacuum on one carb and adjust the others to match, that just means you have slide closed down all the way.
Set vac around 15~20 cm/hg and get all the others matching.
Then the idle adjuster will work as it should
Swap the vac lines around after your done, check gauges are all giving same readings (or just connect one at a time to no1 or no4 cyl after fitting vac plugs to the other intakes)

phil71 · « **Reply #29 on:** September 22, 2012, 11:38:26 PM »

This shoulda been fixed by now. Step it up

Untold · « **Reply #30 on:** September 23, 2012, 04:51:46 AM »

Ha. It's all good now. Nice 1100k idle, full adjustability with the screw. And now I have intimate knowledge of carb linkages and adjustments, so it was a good learning experience.
I did calibrate the synchronizer tool by linking all the gauges up and running them in to one hose. Thanks for all the help.

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Author Topic: Carb sync "360 degrees" out of whack? (Read 2889 times)