Trouble Syncing Using Manometer

[smg65]

1976 XS650C. Starts/runs great. Burns no oil. Under 8,000 miles, if odometer and PO are correct. Cam chain tension good. Valves adjusted good (003 and 006). Compression with warm engine and wide open throttle is 145 right cylinder and 140 left.

I built a manometer last week and used it yesterday for the first time. I had the proper barbs installed and everything fit tightly. I tried it at different idle speeds and no matter what I tried (idle speed, center syncing, or left side idle screw), the right tube would not rise much above the bottom of the manometer. It was always a couple of feet below the left tube. Any idea what I'm doing wrong??? I have 150 main jets in the tubes to steady the fluid. One thing that I've noticed, is when the tubes are capped for storage, one side is always lower than the other. Remove the caps and tubes are immediately level. Please see pics.

I ended up using the "feel" and dead cylinder methods, and they seemed to work fine. Actually, it was almost spot on from when I used the "feel" method a few weeks ago. Ideas and suggestions are, as usual, appreciated!

Thanks!!

 

[5twins]

Did you try swapping the tube connections side to side to see if the low reading shifts? Maybe you have a vacuum port blockage?

 

[angus67]

maybe the jets you shoved in the tubes are dirty?

 

[smg65]

Good suggestion! I'll do that this afternoon. I also thought that the connections where the jets are located might not be exactly equal in length. But I know I got them extremely close, and the fittings seem very tight, although the jets move a bit.

If it is a vacuum port blockage, is there a way to clear it without removing the carbs? Would rather not do that as the bike does run well.

Thanks!

 

[5twins]

Yes, it's got to be something effecting the vacuum signal because these things are pretty much stone ax simple. Are you sure the jets are the same? Maybe remove them completely and test it, or swap them side to side and see if the low side reading shifts.

 

[smg65]

maybe the jets you shoved in the tubes are dirty?

I didn't have any old jets laying around, so I bought new ones. I'll pull them to see if one is blocked though. Thanks!

 

[5twins]

If you have the vacuum nipples on the manifolds, maybe you could just poke a wire through them to ensure they're clear. Or a pipe cleaner, that would probably work good.

 

[smg65]

Yes, it's got to be something effecting the vacuum signal because these things are pretty much stone ax simple. Are you sure the jets are the same? Maybe remove them completely and test it, or swap them side to side and see if the low side reading shifts.

The jets are the same. But I'll test both ways... I'll swap sides, and also remove the jets after (if there is no blockage indicated). Thanks guys!

 

[jd750ace]

Check for leaks at your intake boots between the carbs and the head. If you connect a vacuum gauge to each side individually, keeping the jet for the damping, you may find a weaker vacuum on the lazy side. If it's more than 2 inches Hg difference it'll make a huge difference in your tubes due to the lower density of your test fluid. If one side oscillates radically more than the other you have a big ol air leak.

 

[smg65]

Well, this is embarrasing! The problem was probably a combination of sloppy workmanship putting the jet portion together, and not ensuring a good connection at the port. When I removed the jets, the manometer worked fine. It was a little jumpy, but not bad at all. The jets I used were hexagonal Kehins, making for a sloppy fit. I kinda feel like Chicken Little crying "the sky is falling", when there really wasn't much of a problem at all! And I do plan on replacing the boots and other items when I tear it down this winter.

On a good note, today was the first time I was able to take it on a decent ride. It does run great, and I was surprised at how smooth it was between 60 and 70 mph.

Thanks much for all your advice. It is not wasted.... I'll file it away for future reference!

 

[jd750ace]

Good synch makes a huge difference in smoothness. Worth the effort!