Do I have to bench sync?

I just recently checked my vavles to get them in spec. The parts /should/ be arriving today to replace out of spec shims.

Now the fun begins. After cleaning my carbs last I never bench synced my carbs. The idle has always been fine. A little lacking on cold days (1100rpms) but after a few minutes warmed up she comes right in range. The rev's always seemed to rise and fall good at idle. Is this good enough or should I tear the carbs off and do a proper sync.

Also I never wet set the carbs, but they've never leaked even with prime on.

Here's where fitz comes on and scolds me.

 

I would bench sync the carbs while they're off.
It's a right PITA when you get them back on only to find that they leak.

 

I wouldn't pull the rack if the motor is running nice, won't hurt to fine tune the sync', if you have the equipment.

 

Everyone will say you should. If the bike runs great, why mess with it? I see you are in PA like me!

 

Will be syncing for sure.. If I can't fine tune that I'll pull the rack and start from scratch. but the bike was running great (in my mind) even with valve clearance WAAAAAY out of spec..

jayo84 -- yes i'm from PA the far corner from you though! You're sw I'm ne. =oP

 

if it ain't broke, dont fix it!

And I'm just south of Harrisburg, PA

 

If you have the carbs on the bike & it runs good enough to idle then there is no needs to pull them off for a bench synch. The bench synch is really just intended to get it close enough to run so if you're already idling then there's no need to go back and do it. Have you performed a running vacuum synch? That's where the real magic happens! The truth is though, there's nothing magical about it. Even if you don't have the YICS tool or a fancy vacuum synch gauge set I would definitely recommend it. Check my original build thread or do a couple searches for "homemade manometer". You can build one for around 10 bucks and will be amazed by the difference. I almost didn't do it because I bench-synched my carbs and it ran pretty smooth but after the true vacuum synch (even without blocking the YICS passage) it was like a whole new machine.

I would definitely recommend doing the vacuum synch after you get your new shims in.

The float levels are a whole different story. If you're not having problems then I'd say 90% of us would agree to leave them alone but if you ever pull that rack of carbs off again I would HIGHLY recommend setting them as well. It's a pain in the ass but once you've got them right & you know they're right it elimnates a large piece of the guessing game when you start running into problems. Plus if you have any that are WAY off you'll never get it to run quite right.

 

That much is true, especially with the Mikunis. However, you CAN at least CHECK the float levels with the carbs on the bike (although the process is a bit more complicated.)

If the float levels aren't right, you'll have a heck of a time getting it running "consistently."

But no, you don't necessarily need to bench sync. The reason for the bench sync is to get you close enough so the bike runs and can then be vacuum sync'ed. (The running vac sync is what truly matters.)

 

Great -- One further question. vac sync uses pilot screws behind the carb hats, correct?

If i run into issues with my plugs being to dark or light ( being too rich or lean) than that's a different screw -- the mixture screw. Correct?

In other words, I can adjust these independently ? Or does one rely on the other? I've read so much and haven't done any work in awhile so everythings running together, some clarifncation would be nice. Thanks!

 

NO. Vacuum sync uses the THREE screws on the throttle linkage, on carbs, 1, 2 and 4. Carb #3 is "home base" its only adjuster is the big knob.

Pilot screws=mixture screws. Their full name is pilot mixture screw.

The mixtures can throw off a sync; synchronizing generally won't mess up mixture settings.

Set the pilot (mixture) screws at 2.5 ~ 3 turns out and leave them until after the vac sync is done. THEN you can tweak the mixtures. Doing that may throw the sync off a tad so that you'll have to back and "touch it up."

 

Pictures for clarification..


So the one in the middle is what I want to adjust for the vac sync? The ones in the "holes" are the pilot screws, set pilots to 2.5 ~3 turns out and then adjust the CENTER screw to vac sync?

 

You got to do a lot more reading before you start turning those screws,
Small amounts will put you way off.

 

With all do respect, I've done a lot of reading. I've been reading this forum for years. Theory and practice are two different things. I often second guess myself and ask the obvious questions for reassurance. I'd rather ask a stupid question than make a stupid mistake. I'm aware of the effects of small turnings such as dimes widths and so forth.

 

It does seem as though you don't pay attention sometimes.

Do you have a service manual yet? If yes, which one?

Yes, THAT screw, plus the other two that are just like it. The ones "in the holes" are indeed the pilot mixture screws.

There is one of those sync screws on the throttle linkage of carbs 1, 2 and 4. Number 3 is adjusted only by the main knob.

The linkage on carb #2 "carries" carb #1 with it.

So; You sync #1 to #2 using the adjuster on #1. Then you sync #2 to #3, using the adjuster on #2, which will bring #1 with it. Then you sync #4 to #3. If using a two-bottle system it pays to check the 1-3 sync, even though it can ONLY be adjusted via #2.

Overall idle is adjusted via #3, if you need to increase or decrease it slightly during the process (generally required) plus to set the final idle speed (1200rpm on the 550s.)

Bike needs to be fully warmed up (10-mile ride) and YICS blocked. Use a common house fan to blow air across the motor to prevent overheating.

If, during the process, the motor begins "racing" and won't behave any more, it's getting too hot. Shut it off, let it cool and repeat.

 

Yes I have a clymer. ISBN 0-89287-372-8.

I apologize for all the dumb questions. Most times I already know the answer, Don't have anyone else to bounce idea's thoughts off of in the real world. I'll have to take my word for it and cut back on the repetitive questions. Take off the training wheels to speak!

I made a two bottle manometer and the yics tool out of a threaded rod with some copper and plastics with a wing nut.

Thanks for the help.

 

Cool. Knowing which manual you're using helps immensely in answering your questions.

Be prepared for your homemade YICS tool to melt in the passages. Mine did; I ended up just buying a proper one from Len.

 

Yeah ive been worrying about that, might just go with an oily rag instead. I'll wing it when I get there. Any sync is better than no sync.. the proper tool is on the list.

 

Well the vac sync went well. I finally got around to doing it. The bike ran slightly better. Seems alot smoother. My only problem is after taking it out for a 10 mile ride to test it I seem to have a fouled plug on number 4. It idles fine right around 1200, drives fine. I notice a slight hiccup around 3k-3.5k. Other than that she runs great. Anyone able to help me trouble shoot this? Got a decent ride tomorrow and would like to see this problem go away. I have the pilot screw out about 2 turns. Spark seems good. going to pull the hat and test the enrichment circuit. Always something! Here's a pic.