Topic: How exact does a vacuum sync need to be? '76 CB550

[Paul Lowe]

I used the vaccuum gauges pictured above on my 350F worked a treat.  gotta spend it to make it!

[WarwickE36]

Anyone who lives in Maine or nearby southern Maine is welcome to use my vacuum gauge setup. 

[Deltarider]

WarwickE36,
What I've always wanted to know: is there a Crab Apple Cove in Maine?

[WarwickE36]

Its as real as the loch ness monster, yeti's, and UFOs.  It's all a state of mind.  MASH is a bit before my time, but I do know the reference.  If it's crab apples you seek my back yard has plenty of those two, and Im about a half mile from the water, so maybe my back yard is crab apple cove?

[DustyRags]

There's a Crab Cove not five miles from my house, but narry a mention of apples. Also, I live in California.

[Deltarider]

There's an Ottumwa, Iowa, however.

[mono]

Jamie Farr is still an icon here in Toledo, OH ... lol.

[DustyRags]

Because folks asked- here's my manometer. It's a four-foot piece of wood that happened to be painted white, and some 3/16th vinyl tubing, and those quarter-inch barbed T's they sell in the garden section. I connected it all up, drilled a bunch of holes, pulled off the #1 tube, wired it all to the board, dangled the end of the tube into a jug of motor oil, sucked it full, connected it, wired that last tube down, stood it up to even out and went for a ride.

At the top, I used some cheap connectors from Amazon to screw into the carb bodies, and the tubes slip right over. They're a bit large, so not very tight and I'm not sure if they're giving me a proper seal, so I'll wrap them with some electrical tape next time.

[750resurrection]

 Nice Dusty and whole lot better than $100. Yeah man. They work.

[DustyRags]

This stupid thing is seriously stretching my patience. I haven't worked on it in about a week because of a nasty cold (and I'm still dragging a bit), but put new caps on it this evening, fired it up and... nothing. Dead battery.

So much for setting the timing or syncing. I had a feeling it might do this, but I was really hoping not. I at least got the front brake light switch replaced and the brake line bled, but I'm getting really close to selling it off. Just finish it, get it running and put it on Craigslist to get something more modern where I don't need to replace every little thing that's failed after 36 years with some obscure part I have to track down. Argh.

[lucky]

I manned up and bought a 100 dollar unit.  Its both good and bad.  They unit wasnt calibrated perfectly, so I had to dial it in a bit to 0 all 4 gauges out.  The good part was the orifice is adjustable do you can stabilize the needle pulses down to a very very minimal amount.  I got mine set perfectly, but still thought to motor was noisy.  I finally realized these bikes aren't silent, there will be some chatter.  The biggest improvement I made was by rebuilding the motor , My primary chain was loose and it lets the poor sync take on a mind of its own.  If you search you can find videos I took of the slack before and after the rebuild, its a huge difference.   Hope this helps.

Trim those ears!!! Lol..lol

[72_350_FOUR]

Dusty... here is what worked for me. I synched mine 3 times without this knowledge... After i followed this sequence (i found here on  the forum somewhere) my bike sounds and runs like a whole new bike. Some of this may not apply it was in response to a guy trying to start from scratch... hope this helps.. I use the Motion Pro gauges BTW, and they work great for me.....

So you need to constantly adjust your idle screw (the large screw with spring on linkage) when you are doing the sync.. When you adjust them the idle will be directly affected. You MUST keep the idle between appr. 800-1300. Letting the idle get too high will negate the adjustments because your carbs will be operating outside of the idle circuit. Adjust one, wait a few seconds for the idle to differ, then adjust idle back up/down to range previously mentioned, then continue with syncing adjustments constantly bringing the idle speed into the appropriate range when necessary.
1. To continue from where you are now, I would go ahead and lean out your mixture screws first at 1/8 turns just until smoking stops.
2. set all nuts on the carbs where you were adjusting during the sync so that 2-3 threads of the screw are showing above the nut.
3. Adjust number #1 carb to #2. Make sure to adjust idle speed after back down/up
4. Adjust #4 carb to the same vacuum as #3 carb. Adjust idle.
5. Adjust #3 to #2. Adjust idle.
Repeat sequence until they are all reading the same vacuum. Adjusting in this sequence will keep you from going in circles since adjusting one will affect the others.
Once you have them synced you can fine tune your idle mixture (rich/lean)

Remember, you must have valves in adjustment, cam chain tensioned and a clean air filter before you sync the carbs. It will do you no good to sync them if this hasn’t been done FIRST.

[DustyRags]

Thanks, that sounds about what I've been doing. I just did a top-end rebuild, so the chain and valves are freshly adjusted, the air filter looks clean, and it's had a fairly recent (40 miles ago) timing adjustment. Then I synced it, only to find at the end of the sync that one of the spark plug caps was arcing. Replaced those on Tuesday, and then found that my battery was dead from the last carb sync and then sitting for a week.

My approach was to re-check the timing to make sure the new caps didn't throw it, and then check the sync. I'm mostly frustrated because every time I fix something, I find something else I need to fix first, which means a trip to the shop, and since I don't have a garage, I don't have access to the bike more than 2 or 3 days a week right now. I've had it since the beginning of August, and been on two rides. Put less than 60 miles on it. I'm just getting frustrated with the whole damn thing.

Wanna buy a bike?

[72_350_FOUR]

That's how it goes with these bikes, took me a while to get mine on the road.  Just take it slow and dont give up and you'll get there, i felt the same way more than once.. but now i'm riding more than wrenching, and i know my bike from front to back....

[LesterPiglet]

Once you have these 30+ year problems solved you will have one of the most reliable bikes on the planet, stick with it. I dunno about where you live but I get kids waving when I pass, makes me feel good.   

[DustyRags]

Thanks for the encouragement! I'll probably tackle it again tomorrow evening and/or Sunday morning. This is my first bike, and I thought I was buying an old but solid bike. I never expected to put this much work into it. I'll get over it

[DustyRags]

It lives! Oh, holy hell, it lives!

New caps... Dead battery. Bitter, bitter disappointment! So I replaced the front brake light switch. Tonight, I came in and it fired right up. Still a bit rough, so I timed it better... Better, but not there yet. Cleaned and set the points... That screwed it right up, it only fired in the middle cylinders. More frustration, but eventually did enough voltmeter testing to figure out two of the points weren't connecting. Eventually I just set the gap to the thickness of a matchbook, visually, and that was spot on. Fired every time. Re-set the timing, and took it out. Once it fully warmed up, it was smooth, quiet, faster and more powerful than I ever experienced. I still might do another vacuum sync later this weekend, but for now I'm satisfied that it's finally running and running well!