balancing carbs

[olderthandirt]

If carbs are balanced by adjusting throttle position why can't a person use a Vernier caliper to measure throttle position instead of using vacuum gauges and standing between propeller and wing with running engine...may try it anyway..thoughts...

[rvbuilder2002]

Originally Posted by olderthandirt

If carbs are balanced by adjusting throttle position why can't a person use a Vernier caliper to measure throttle position instead of using vacuum gauges and standing between propeller and wing with running engine...may try it anyway..thoughts...

That makes the assumption that if the position of the throttle arms are exactly the same, that each carb. will flow exactly the same amount of air and fuel.
That assumption would be false.

This type of procedure has been commonplace for decades with engines that have multiple carburetors (cars, motorcycles, etc.). If there was a better/easier way, someone would have figured it out by now.

BTW, most gauge sets / tools used for sinking the carbs have long enough hoses to bring the tool into the cockpit (you can pass the hoses through one of the fresh air vents or just leave the canopy in the propped open / vent position.

[Bob Martin]

I don't have a RV12 or a 4 cylinder rotax.
But I did work on motorcycles as a youngster.
the Honda 4's....aka 750-4's started the need for balancing carbs as they had one carb per cylinder and they would not run smoothly without balancing them. Balancing was hooking up a vacuum gauge (think manifold pressure) to each carb and adjusting the throttle linkage to achieve equal vacuum pressure. The gauge takes out or adjusts for small variances in the linkage.

You might also think of the procedure as a poor man's fuel injection balancing system.

If you use to tune up cars with points?? Remember the Dwell meter verses the feeler gauge? Same concept.

[DHeal]

There is no need to stand behind the spinning prop when performing a carb balance. Here is the way I balance my carbs:

Not wanting to subject myself or any of my friends to standing near a rapidly turning propeller while looking at two carb balancing gauges and wanting to do both the engine operating monitoring and looking at the carb balancing gauges at the same time myself, I devised the following plan:

I positioned the carb balancing gauges inside of the cockpit by adding extensions to the two rubber hoses -- the extensions' were cut so that there is equal length between each gauge and the respective connection elbow on the intake manifold (not that having the lengths the same makes any difference at all). I ran the two extended rubber hoses through the open air vent on the copilot side and positioned the gauges on the copilot seat where they fall "readily to hand" as the British say.

Next, I tied a length of 50# monofilament fishing line to the top of each throttle arm and ran each line aft under the canopy fairing and into the cockpit where I terminated each line with a little "finger pull" loop.

Now I can start up the engine in the safety of the closed (and warm!) cockpit and gently pull on each loop to see what carb needs to be tweaked to balance the gauges. Then I shut down the engine, make the adjustment on the carb linkage, restart the engine and double-check my settings. Repeat, as necessary to achieve vacuum perfection.

[pyolet]

Originally Posted by olderthandirt

If carbs are balanced by adjusting throttle position why can't a person use a Vernier caliper to measure throttle position instead of using vacuum gauges and standing between propeller and wing with running engine...may try it anyway..thoughts...

I had a Rotax 912 in a Kitfox and it made a HUGE difference in power and smoothness once I bit the bullet and bought a CarbMate (http://www.lockwood.aero/p-3301-carb...stic-tool.aspx) and finally got them vacuum synchronized correctly. I checked the sync at each conditional and it did change slightly with use.

Woody.

[Rayh]

Woody I sent you PM.

[epaslick]

Originally Posted by pyolet

I had a Rotax 912 in a Kitfox and it made a HUGE difference in power and smoothness once I bit the bullet and bought a CarbMate (http://www.lockwood.aero/p-3301-carb...stic-tool.aspx) and finally got them vacuum synchronized correctly. I checked the sync at each conditional and it did change slightly with use.

That link only goes to the front page of the website. It doesn't look like they carry it anymore.

[Mike H]

Try here.
http://www.aircraftspruce.com/catalo...lickkey=170960

[Piper J3]

Try this - much less expensive. eBay $32.85 including shipping...

[DHeal]

I can't tell from the picture but the low-cost Honda vacuum guage set appears to lack the two hose needle valves that are necessary to dampen the guage pulses. These valves could be readily added, but that means a bit of additional cost. Otherwise, that looks like a reasonable price for two vacuum guages.