Carb sync? Never again.

[mr bill]

What if you used a piece of 1 inch water or fuel rubber hose, with no metal tube?

[Wheels]

I don't actually know why the tube is metal except for the nipple that is on some of the metal tubes used for MAP. My old tube is metal and has no Manifold Pressure attach point. So I think If I had a rubber tube, it wouldn't matter. But I have a question.
If a person used a large diameter crossover tube and simply adapted the size for the existing manifold fittings without making them larger, As Rodney did, why wouldn't that do the same as enlarging the fittings? I understand that the air in the crossover tube is largely static, so the benefit is not in "bernoulli, or venturi, principle but rather from the larger mass of air in the tube giving a "buffer" area to the molecules in transit from acceleration to static. Have I been watching to many re-runs of Star Trek, or am I actually ... close?

P.S. My mom used to say "better to be judged a fool than to open your mouth and remove all doubt." ... I never listened to her. Maybe I should have.

[Av8r3400]

What if you used a piece of 1 inch water or fuel rubber hose, with no metal tube?

The Aluminum tube is lighter, that's why I used it.

[Rodney]

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Here are some pictures of my balance tube.

The main tube is made from Schedule 40 1.5" PVC.

Bent the tube to match the proper angle (approx 60 degrees) so the 1/2 rubber hose's would fit the existing 3/8" fittings in the intake manifold.

Then I found two 1.25 x 3/4 schedule 20 inserts. Turns out the 3/4 threaded fitting fits the 1/2" fuel tube I used.

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Next, I turned the inserts down to fit inside the Schedule 40 pipe. I couldn't find Sch 40 fittings at my local store so had to use the Sch 20 size and make it fit.

The main pipe is 11" long - then took the pipe and fittings and hose out to the airplane for a final fitting before gluing it all up. Used regular PVC cement for the inserts and screwed the hose into the fittings with clear GE Silicone seal to secure the hose to the inserts.

I think that this could all be built out of Schedule 20 material and instead of bending it, there are 60 degree elbows available. So, maybe two short pieces of 1.5 OR even 1.25 inch PVC with a 60 degree coupling and two inserts with a threaded 3/4" female threads might work. Haven't built one, so am being a little conservative here.

After a 1 hour flight yesterday, I landed, took off the cowling and I could hold the balance tube with my hand. That tells me it isn't getting too hot.

So far, I'm really pleased with the setup. If anyone sees a serious problem, please let me know. I don't know the long term affects of heat on the plastic, but I know it took about 300 degrees of heat to bend the main tube, and it's not getting anywhere near that hot under the cowling. I didn't have to modify the manifolds, just used the existing ports.

I did go back this afternoon and used Kitfox 2009's procedure for balancing the carbs. I hooked a 1/2" fuel tube from one carb to the other, and using the idle adjustment on one carb, got the engine as smooth as I could. Then hooked up the carbmate and balanced at 3500 rpm.

I have about a six hour flight tomorrow, so will report back on how things went. Also, and I haven't really figured this out yet, I can now use my Hacman system to lean the engine. Before the balance tube mod, running anywhere from 5300 to 5600 rpm, as soon as I cracked open the leaning knob, the engine got rough. Could not get any temp rise in the EGT's or decrease fuel flow. A quarter turn was too much. Then, on my first flight after installing the balance tube, I can now lean the engine. I've been trying to get my EGT's up in the 1400 degree range to seat some new oil rings, and I can finally do that.

So far, this has been a really good improvement to the way my engine operates. Nice slow idle (1400 rpm) and I can lean the engine at cruise

Rodney

[Paul Z]

Here is another picture of Rodney's install. It shows the cross over tube really well.

[kitfox2009]

Hi Rodney
Think I might experiment a bit with this as well. Did you just glue in the nipple for your manifold pressure gauge?
Don

[Rodney]

Don. I found a plastic nipple that had a 1/4 pipe thread on it. Drilled a hole in the balance tube, screwed in the nipple and sealed it with silicon seal.

Think I got it at a local farm supply store, but I'm sure there must be other sources too

Thanks Paul for posting a better picture. Appreciate it

Rodney

[kitfox2009]

Update.
Well today just for fun I made up a larger balance tube for my 912Ul.
Material required is a 14 inch length of 1 inch heater hose plus two 1inch pieces of 3/4 inch and 2 approx 3 inch pieces of 1/2 inch. 4 hose clamps and 1 Mini hose nipple if you have a manifold pressure gauge.
Assemble as shown. I used the adhesive in the photo.
Have not flown yet but runs smoothly through all RPM ranges on the ground test. I realize this only increases the balance tube to 1inch diameter but might be interesting results. Ran smoothly before but maybe even better now!

Cheers
Don