Question on using the vacume gauge

[XS1100 Newbie]

As some of you know, i have been fighting a carb problem for a year. Or what appeared to be a carb problem. With having set the float level correct, it improved 100%, but not good enough. After synching, and adjusting, i made it worse. It will still turn up to 8000, but that is all. It is also very, very cold blooded, and it never has been that way. Yesterday i broke down and bought a vacume gauge. I have been adjusting carbs for years by ear, and with a vacume gauge. I hooked it up, and the thing just goes wilt fluctuating. In an automobile this would indicate to me that either i have some bad valves, and or guides, or i have a vacume leak. I would assume that a bike would be no different. Has anyone ever checked for vacume leaks using propane? I have used acetelene before, but not propane, or should i just stick to carb cleaner? I have sprayed everything with carb cleaner before, but found no leaks. Any ideas?

[clcorbin]

That is actually normal. Bike rev a LOT higher than most cars, so the cams have a lot more overlap, which can cause vacuum issues. Plus, on the bike, you are looking at the vacuum level of ONE cylinder through it's entire range, where as on a V-8, it is basically the average of all eight cylinders that you are seeing.

You need a good restrictor in the vacuum line to dampen out the pulses so you can see the "average" vacuum. The hole in the restrictors that came with my carb sync kit are so small I almost didn't see it at first. It make a pilot jet look huge.

[Yahman]

It helps to put a plenum in between the carb and the vacuum gauge along with a restriction in the line. There are some photos on here somewhere of the setup you need.

Yes, you can use propane just like you would use acetylene to find a leak.

Larry

[yamtom]

experience with vaccuum synch

Hi,

Ive used vacuum gauges and tubing manometers, but found that both of these made for more problems than a simple bench synch in my late model carbs.

I used the tiny bare wire from the bread wrapper, and set the number three to approx three turns on the master idle screw to get the proper opening for number three, then set the 1,2 n 4 throttle plate adjusters to match. Bike fired and runs well. I had to back off the master idle screw about two turns once the bike warmed up.

Wont mess with gauges or manometers again until I figure out what was going wrong before. In order to get the gauge or manometer to match cylinders, had to open number two throttle plate way too far. Tried propane, apparently no vacuum leaks so will stick by my bench synch until I know more.

[Mroadrunner3]

Hay Newbie, I also am new kinda, I just rebuilt my carbs and want to sync them as soon as poss, had a friend recomend a manometer, looked up on the u-tube and how to make one, so i did and all it would do was suck the liquid right down the intake, so again back to Utube on how to, that showed a lot of diff ways to sync the carbs including vacuum gauges, said the way to get the flexing out was to rev the engine up a little so the gauges would level out, and that sence the bike would be running at a higher rev it would put you in a better setting cus the bike is running at that range, may run a little rough at idle would be the traid off, hope that helps some, i will be doing mine this weekend with gauges. good luck

[dbeardslee]

I vacuum sync mine regularly with good results. If your gauge(s) is/are bouncing around all over the place, a small cable clamp over the line works well as a dampener. Just put one around each line, and tighten the bolts by hand till the needle(s) settle down. Don't shut it down all the way - you want a little bounce in the needle so you can tell that air is still moving through the line. JAT

[DGXSER]

Here is a link to a thread on carb synching, particularly a good video I found on how to do it.

http://www.xs11.com/forum/showthread.php?t=21280

[psycoreefer]

I use an aquarium airline valve in-line with the vacuum gauge. Just turn the knob on the valve in until the bounce goes away - easy and adjustable.

[petejw]

also if your using multiple vac guages,
they need to be calibrated to each other.

[WMarshy]

also if your using multiple vac guages,
they need to be calibrated to each other.

I'd hope they come calibrated!

[petejw]

.......they dont.

[WMarshy]

Could you please be so kind and tell us how to calibrate them? Seems to me that a manufacture of gauges would calibrate them to some standard before they leave their door. Doesnt make sence not to, if they truly dont calibrate them they would at least inform you that you need to do it prior to use...or am I expecting too much from a ~$80 pair of $20 gauges!

[petejw]

to calibrate, remove the rubber plug from one
of the intake manifolds and connect 1 vac guage,
start the engine and note where the needle is sitting,
then connect the nxt guage to the same intake rubber
and note the reading, if its different adjust by removing
the clear lens cover and adj the small screw situated on the face plate.
do the same for the other guages.
hope this makes sense.

[dbeardslee]

I used to calibrate mine with a brake power bleeder. I would just connect the mity vac to each valve, and pump until the vacuum registering on the mity vac gauge was 10" hg exactly. Then I'd get a reading from the guage it was connected to and record it. When you've done all four, compare the numbers, pick one gauge as your baseline and mark the rest relative to it (+1 cm, -1 cm, etc.). You can also do it the way Pete mentioned, but I found the vacuum gauge easier and more accurate as you don't have to deal with vacuum pulses from the engine while you're trying to maintain a constant rpm. The biggest variation I saw between my four Harbor Freight combination guages was 1.5 cm hg. To properly sync your carbs they need to be within 2 cm hg of each other, so 1.5 cm makes a difference.