MotionPro MERCURY (Oh, noooo!) carb sync gauge and TBS

[Bruce1300]

I got a 2004 in late May with only 5,000 miles. I've already put on another 7,000 and thought the bike ran great with the exception of a quiver at idle. It got a little worse and was a little difficult to start of in first gear, so I changed the plugs and tried to sync the carbs. The net result is that the bike idles well and and runs even better.

Here is my possible problem: When syncing the carbs I used an older mercury MotionPro gauge which I've always used with a couple old XS 650s. The gauge is marked in two digit increments (10, 12, 14 etc). I believe these increments are centimeters of vacumn pressure and I would need to multiply by 10 to get mm. The idle was set to 1,100 by the in-dash tach. My first reading from cyl 1 to 4 was 23, 23, 16 and 22. This being a Gen 1 I focused on syncronizing to cyl 3. The adjustment screw bottomed out at a reading of 22.5. I was hoping to set cyl 3 to 25, which I believe to be 250 mm, I then set the other three cylinders to 22.5 to keep the four cylinders balanced. The motor ran smoothly and a short test drive proved to be great.

Shoulld I be worried about the cyl 3 adjustment being bottomed out and only at 22.5 or should I go back and try to back off the adjustment for cyl 3, but increase the idle to make it run at a reading of 25 and then sync the other 3 cylinders to 25. I am assuming that backing off the vaumn adjustment to cyl 3 would allow me increase the idle adjustment without going over 1,100.

It seems like it would be a balancing act that may be unnecessary if the throttle bodies are now in sync and it is running better than ever?

I would also like confirmation that the MotionPro gauge two digit number are centimeters.

Thanks for any info that will help.

Bruce Leinaar

 

[jmgrif]

Not sure what to say? If it ain't broke don't fix it! You say it's running well, then ride it and enjoy. Fred W has a throttle body sync that may give you peace of mind but he may chime in here and say to leave things as they are?

 

[Fred W]

It doesn't work that way.

You just want all 4 to be the same, whatever vacuum they happen to come out to in the end. What the units of measure are is insignificant, and arguably false anyway.

You have no real control over what that will be. In other words, it will be whatever it will be in the end. Generally you want to adjust whichever one is the largest anomaly from the others, so in your case I would just have closed down screw #3 until you got the same vacuum as the others and you'd have been golden.

As long as they are balanced now and idling at the correct 1100 rpm, you are good to go.

 

[Bruce1300]

Based on the responses from jmgrif and Fred W, I'm feeling more comfortable about my TBS. This bike being my first "high tech" modern machine, I was afraid that not being at a particular throttle body vacumn rate might have an adverse effect on the air/fuel mixture or something else that might upset some kind of computerized sensor.

On older carburated bikes I never thought about vacumn pressure. It was just a mechanical adjustment between carbs to bring them together at an equal vacumn level which just meant adjusting the mechanical carb throttle levers to speed up or slow down the carbs until they were the same.

Now that I know cyl 3 is bottomed out and is as high as it will go, future TBS will be a piece of cake; just confirm that cyl 3 is bottomed out and adjust the other three to match.

Thanks for your help,

Bruce in Kingsport TN

 

[staintune007]

Need help guys Try, Try to perform a TBS with the motion pro sync with the blue DYE .Ok story did the calibration according to the instructions. Use the third cylinder as base .when I crank the engine al the dye was sucked inside the engine .Brain storm pls need the brains in this manner .Thanks Bill

 

[staintune007]

By the way idle goes up but not down!!