Manometer design

[NonComp]

Would putting a coil of oil-filled tubing at the bottom of the home-made manometer that I am planning, reduce the sensitivity of the instrument, instead of adding pinhole or similar filters?

[T__]

Glen, I doubt it.. You don’t want to add a lot of extra fluid to the system in case the balance is way off or a line comes loose as that could allow enough fluid ingestion to possibly harm your engine..

 

Try a simple U tube with a light fluid in it.. Light oil (like ATF) is fairly well self dampening as it has a lot or surface cling to the tube walls..

 

Personally I use a water filled U tube with about a 50% water & 50% antifreeze as that is very active,, very accurate,, doesn’t freeze,, & is just thick enough to be self dampening & not need any restrictors or cigarette filters added..

 

Twisty

 

[NonComp]

I've got some two stroke oil kicking around. Would that do?

[EddyQ]

Thin tubing and a viscous fluid will do some dampening. The coil would likely do the same. But, with a nasty pressure difference, you will still have issues with fluid traveling to the engine.

 

Try putting a bypass tube with a valve.

Simply buy two T's and a valve from your local pet shop and install

them somewhere far away from the liquid. With the valve open, the manometer looses sensitivity. With the valve closed, it is very sensitive. I've heard that simply pinching a bypass tube also works well.

[Boffin]

I've got some two stroke oil kicking around. Would that do?

 

I use 2-stroke oil in my manometer. I damped it by a central constriction at the base of the loop. I have a lot of tubing between the loop and the bike, to allow time to shut down in the event of a large miss-match in TB vaccum. I have also seen a manometer where two equal-sized sections of wider tube are put in at the top of the loop - one in each leg - these act as dampers and a catch-tank for miss-matches.

 

Andy

[NonComp]

So if I put a wide spot inline on both sides, similar in size to a fuel filter, that would also work as a safety reservoir?

[Boffin]

That is essentially what was on the manometer I saw.

 

Andy

[ShovelStrokeEd]

I have built a couple of manometers in my time. Almost always use water with a little food coloring to make it easy to read.

 

In re restriction, I have a collection of jets laying around from various carb modifications. A little pilot jet in the small diameter tubing solves two issues. It damps the signal and will not permit much, if any water, to transfer into the engine.

 

Another very simple thing to do is to use an 8 foot high board to mount the manometer. You can slant it back a bit if ceiling height is an issue. You then only fill to the 4 foot level so it is easy to see the columns. Only costs a few pennies more for the extra tubing. The extra height helps in those odd situations where vacuum difference between the cylinders is large.

[T__]

So if I put a wide spot inline on both sides, similar in size to a fuel filter, that would also work as a safety reservoir?

 

Glen, not necessarily.. There also needs to be some sort of break in the continuity of the lines through the wide spot.. If just a wide spot in the lines with no direction change or dam to force the fluid to fall out of the air stream it will just suck the fluid out of the wide spot & onto the engine..

 

Little plastic 4oz bottles work good.. Put two holes in the cap then a sealed fitting in each hole..

Have one fitting extend about ½ way down into the bottle & the other end right at the bottom of the cap.. Hook the side going to the liquid to the bottle inlet with the extension then hook the side going to the engine to the side that ends just under the cap..

 

With the above,, any liquid that gets sucked into the bottle falls out of suspension & to the bottom of the bottle as the high side exit fitting pulls air through the bottle above the liquid.. (works very good)

 

Or just use smaller lines with not a lot of liquid in them & just let it go through the engine if a mishap happens.. It usually aerates the liquid as it pulls it thorough so unless a lot of liquid it really doesn’t hurt anything..

 

Twisty

 

[NonComp]

What you describe sounds like the catch cup for a brake bleeding system. I think I have a couple of these kicking around.

 

Another alternative is that I have some hose pinchers somewhere from my wine making days. The hose runs through and you squeeze it with your thumb to pinch off the line. It is self-locking.

[Boffin]

If the volume of the wide section is greater than the volume of liquid, and the wide part is wide enough, then once the liquid is in 'pot' the air in the lower section will just bubble through. In any case, any wide pipe will slow the flow enough to let you shut down the motor.

 

Andy

[NonComp]

If the volume of the wide section is greater than the volume of liquid, and the wide part is wide enough, then once the liquid is in 'pot' the air in the lower section will just bubble through. In any case, any wide pipe will slow the flow enough to let you shut down the motor.

That's what I thought. Maybe I'll experiment a bit before I choose a method.

[T__]

Andy, not necessarily.. If the wide spot doesn’t have something to cause the fluid to fall to the bottom a lot of it will just keep on going with the air stream right out the other end.. If the wide spot had most of it’s volume below the outlet & the inlet & outlet were offset or at opposed angles then most fluid would probably drop out to the bottom.. If the inlet & outlet were in line & the wide spot volume was above the outlet then it would be virtually worthless as a water trap..

 

 

Twisty

 

[Jeepster]

Hi all,

I stumbled accross this little gem Link to two bottle manometer and thought that it was a great idea.

Has anyone seen or heard of this design? And what are the thoughts of more experienced minds than mine?

[Ken H.]

I stumbled accross this little gem Link to two bottle manometer

Complex solution to a simple problem IMHO.

 

Take a tube, loop it, put some low viscosity liquid in it and balance your bike. That’s all there needs to be to it!

 

[Jeepster]

Complex solution to a simple problem IMHO.

Your right about the complexity. I was basically wondering about minimizing the threat of drawing fluid into the motor.

Plus the Rube Goldberg-ness of the design does have a draw to that part of me also.

Just think instead of bottles I could use graduated beakers, glass coils somewhere along the tubing,

and try to figure out a way of working a Tesla coil in there just for effects.

Ok, forget the coils. Both Tesla and glass. But, the air gap between the fluid and vacuum source seems like a good idea to me.

[RBertalotto]

 

 

BTW...Carbtune seems to be the last word in this tune stuff.....

http://www.carbtune.com/

 

 

 

[ianboydsnr]

I think your worrying to much about a problem that does not exist, you will find that once set initially, by running the motor, checking then stopping and adjusting, before the fluid reaches the engine, at each subsiquence service, you will find that its not off by much and you can adjust it easly when its running, I have the origonal mercury carbtune, the carbtune 2 and my home made manometer, and I allways use the home made one when tuning my Gs and Rt, as its easier and more sensitive.

[NonComp]

My final 'design' was the simple 20 ft of 1/8" ID continuous tube with 2-stroke oil, nailed to a board approx 40 inches tall. It works a treat. I kept a fuel line pinch plier handy in case it got out of hand, but I didn't need it. The oil viscosity dampens the response nicely, but you can see when it settles in.

 

I compared the results to a borrowed twin-max. Given the simplicity of the rig, I would say that it is much more accurate than the twin-max -- although, I did discover that there is a band of imbalance that seems to shift with RPM. But I think I need to to a more thorough balance/setup of all the cables to get it right (thanks Ken H.)