83 Seca 550 Carb Sync

Well, all I can say is, I'm amazed at the difference!! I've sync'd 4 or 5 carb banks over the years, but I don't think I've ever done a set of 4 CV carbs. As it happens, most all have either been CV or non-CV twins or non-CV 4's. My ego said I had it pretty darn good on the bench, but....

I'd rebuilt the carbs earlier, and bench sync'd 'em using a piece of 3x5 card. I felt they were pretty dern good judging by the 'drag'. My ego (having last done a set of Honda CB750K8 non-CV) said they'd be within the 2cm Hg I've heard is a rule-of-thumb.

So, I cleaned out the YICS passage first. Opened one side and hooked up a catch-funnel and container. Used a spray can of carburetor cleaner and tightly-rolled paper towels:

 

Next, inserted my home-made YICS block-off tool, made from directions found on this site. Then, set up the temporary fuel supply IV tank. Set up the Morgan Carb-Tune and two big floor fans. Ready to go.

(This was the first time for the Morgan. I've used mercury tubes for years, but my Dad and I share it back and forth, and I finally just bought the Morgan).

 

So, just as an experiment, I started the bike WITHOUT the YICS tool in first. As Found, they were within 2 cm Hg. Hah, just like I thought they'd be!! 8)




So, in went the tool, and.... oops! Boy, that's not too good. 6 cm Hg off! That's all new to me. I'd have NEVER guessed the YICS ports made that much difference!






So, I sync'd 'em up nice. They responded nice and sweet. In the end, I got 'em to within 0.5 cm Hg. Sweet!

 

Took the tool out and there was no change! Woo Hoo! 0.5 cm Hg difference.

So, I hooked up a test tachometer and tweaked all the mixture screws. I had started with them at 2.5 turns out but ended up around 1.5 turns out on all 4. No real change to the readings on the Morgan.

I'm thrilled! Idles rock steady right down low, blips instantly and settles right back down. Takeoffs are nice and smooth now.

Actually, I had put about 250 miles on the bike since putting the carbs back in but before today's adventure and was getting a disappointing 41~42 mpg. I had been pleased with the way it was running, but this bike is new to me, so I didn't really know what I was missing! The only problem was that if I sat at a redlight for a minute or so, the motor would 'load up' and give just the briefest stumble as I tried to accelerate away. If you blipped the throttle a couple times during that same light, the problem didn't occur, or if you blipped it just before you took off from the green. I suspect it was too rich with the mixture screws 2.5 out, because now, after sync and screws at 1.5 out, it doesn't do that at all! I'm kinda looking forward to seeing if I get any better mileage.

So, when the experts here say that 'bench-syncing only gets you close', I'm a believer now!!

Kirk

 

Nice progress, iam in the same boat now, i do not have a morgan thingy or yics tool as of yet, iam still waiting on my carb parts, I cannot wait ! ! !

 

Kirkn, you should really go back in and re-synch the engine.........fiddling with the mixture screws throws the synch off. The proper procedure would be to do the inital synch (which you did), and then:

adjust mixture screw #1 >> re-synch engine >>adjust mixture screw #2 >> re-synch engine >> adjust mixture screw #3 >> re-synch engine >> adjust mixture screw #4 >> re-synch engine


You can repeat the above steps as often as you like (although, you'll need to allow for cool-down time or you might melt the YICS tube seals in the chamber!)

The use of a colortne plug will make your mixture screw tweaking much quicker and more accurate.


Also, it appears (picture is hard to tell by) that the YICS tool that you made is lacking the sealing washer at the very end of the tool.......this introduces a vac leak by the last cylinder. The "internet" diagrams showing how to make a home-made tool omit this sealing washer for some reason......

 

Hi, Chacal,

Well, actually, that's mostly what I did. I did the initial sync with tool in, tweaked all mixture screws with tool out, then checked sync again after all mixture screws with tool back in again. The mixture adjusting only threw the sync off a tiny bit. But, I brought it back to within 0.5 cm Hg again.

But, only the one time. Not in between each carb mixture. I didn't think about it, actually, or I probably would have.

And good observation on the gasket. That picture was taken out of step with my narration. *busted* That picture was taken when I was first fooling around with building the tool. After that, I had the same thought and I made a sealing washer before I did the syncing.

BTW, sorry for the low-res pix. Normally, I use the 'good' digital camera, but my wife has it with her on an outing today, so I was stuck using the camera in my cell phone.

Kirk

 

Kirk, don't sweat the picture quality. The results are nothing short of amazing are they not? It idles like a sewing machine now, doesn't it?

One concern: 1.5 turns is a bit lean on the mixtures; keep an eye on the plugs. You may need to richen it up a bit. Might want to invest in a ColorTune, too.

The Morgan makes it so easy to get it dead on, and it shows you how the YICS "masks" an imbalance.

Good work.

 

Thanks! Yep, really amazing.

On the other hand, I like the old-fashioned mercury-filled syncronizers better. They're taller, so in that case, 2 centimeters is actually 2 centimeters. On the Morgan, it's, like, less than 1 centimeter = 2cm Hg. So, it makes it just a bit cramped for fine adjustments. But, that's really just picking nits.

Yeah, I really considered the ColorTune but just didn't quite justify the $$ right now. Normally, I rarely hesitate over a tool that's applicable to so many different bikes, but, well, y'know, things are tight, etc.

But, maybe Santa's coming...