BUBBLES in mercury column - Motion Pro

[Peder_y2k]

Question for you science types..... air bubbles appear in the mercury columns while using my 20 year old Motion Pro mercury manometer. These bubbles interfere with the accuracy of balancing the carbs. What causes the bubbles, and how to eliminate them? When new, bubbles were not present. Unit was always stored upright and indoors, and there is no evidence of mercury loss.

Inquiring minds want to know...........

-Pete, in Tacoma WA USA

'83,88

[djh3]

Hmm that is odd. Maybe its not really air but moisture instead. I mean it is a tad humid there right?

[Snaggletooth]

I'm curious for a better answer myself. I have two merc sticks myself that I keep in the unheated garage year round. I noticed the spring before last I had the bubbles. I could tap them down a bit not get rid of them. Looking at the bubbles they appeared cloudy so figured it was condensation build up.

 

I drained both sticks into a glass test tube while filtering them through medical gause. Stuffed a cotton ball in the top of the test tube and set it out in the sun for a couple hours. I knew heat would help but heating mercury with a heat gun didn't strike me as being all that great of an idea. I settled for solar.

 

But it seemed to help. The bubbles went away. Until this spring. So I do think moisture causes the problem.

 

And I have the Morgan. But I still like my sticks.

 

NOTE: I do not belive my method is EPA approved. Just sayin'

[Peder_y2k]

I'd never thought about moisture in the mercury, but is very possible because the unit was stored in an unheated garage, and yes, this area is definately humid most of the year, just not warm and humid like the south.

Maybe I'll set the carb sticks unit out in the sun today for several hours and test it tomorrow.

-Pete, in Tacoma WA USA

'83,88

[DragonRider]

Trash that mercury balancer and get a Morgan Carb Tune, no mercury and uses alum. rods instead, works every time, and easy to use. I wouldnt use anything else. Check it out here.

 

http://www.carbtune.com/delivery.html

[Peder_y2k]

Well it's not a moisture problem as mercury does not absorb water. Must be dirt of some sort in the fluid. Setting it out in the hot sun for 7hrs. did nothing. Read that one can filter mercury through a chamois, so will give that a try.

Gonna stick with mercury sticks as mercury is still used for most accuracy in science instrumentation. If it's good enough for them (science types) then it's good enough for me........

-Pete, in Tacoma WA USA

'83,88

[Brake Pad]

home.comcast.net/~loudgpz/GPZweb/ManometerNotes/ManometerNotes.html

[BlueVenture87]

Still could be moisture. If the condensation were to be absorbed you wouldn't see it as a discreet bubble.

 

Best

 

-JK

[Peder_y2k]

I took a look at the manometer notes refferred to by brakepad, and found them to be very helpful. Here's the link for those who want to know:

 

http://home.comcast.net/~loudgpz/GPZweb/ManometerNotes/ManometerNotes.html

 

-Pete, in Tacoma WA USA

'83,88

[mbrood]

I simply blew softly into the affected hose and SLOWLY let up once the bubble exited the tube... don't know how it got there but I know where it went.

[Snaggletooth]

That's what I keep ending up with. With the cloudy looking "bubbles" I think it was the moisture condensation in the tubes creating a drag on the walls and maybe making air bubbles in the mercury. Once everything dried out, no more problem.

[kevin-vic-b.c.]

I got air into my carb manometer first use, I believe I got the carbs too far out instead of in. The instructions that came with my non mercury manometer said to shake the tool as you would a a liquid filled thermometer. That cleared most of it but I ended up shaking it upside down and pulling the air into the storage vials.... assuming the mercury manometers are constructed the same as the non mercury units.

[Heartbeat]

I had a similar thing earlier this week with my manometer that I got from Sabercycle 4 years ago. I haven't used it in 2 years and when I was using it the other day, it had liquid above the mercury of unequal heights so I was concerned about its accuracy. My guess is that since I left it hanging with the hoses uncapped all this time that condensation entered the manometer due to seasonal, humidity, and temperature changes in my garage. I actually drained the mercury last night and separated the mercury from the contaminates. I then tested the manometer with trans fluid but as I suspected, it is too light to use in this small manometer. I then flushed out the tubes and reservoir but ended up breaking one of the tubes in the process. So today I ordered the Carbtune. I was going to order the Carbtune when I bought the other one 4 years ago but opted to "save" some money. But in the end, I should have paid the extra then. The Carbtune is also easy to transport which the other I had was not.

[Peder_y2k]

Well I realize now that it was operator error (my fault...dummy) in that I did not open the vent adequately, resulting in the air being drawn into the manometer tubes. I looked at this concept from reading the manometer notes mentioned in earlier posts. With the vent properly open the columns of mercury were bubble free..... for a while, then small bubbles slowly began to appear, so reconnecting the vacuum tubes from the carb connection one at a time would refill the tubes with solid mercury allowing my adjustent to proceed. I am now satisfied with the results, all 4 manometer tubes same 31cm level, and the engine purrs at the 1000RPM idle I set. I then proceeded to adjust the pilot screws by 'ear' for a best setting for very stable and smooth idle and crisp throttle response. Now I can button the 52,000 mile bike back up for its next adventure. A satisfied customer........

-Pete, in Tacoma WA USA

'83,88

[RSTDdog]

Looks like you got it fixed. Mercury does evaporate, particularly if you forget to close the vent on the back of the manometer. Mine (motion pro also) are quite old (bought them in 1991) and closing the vent consists of moving a tube on the back between a fluted post (open) and a solid post (closed). Mine had bubbles and upon examination it was low on Mercury in the reservoir. I was without a bike for 10 years so it just hung in the garage, shop or wherever was convenient.

[Prairiehammer]

Mercury does evaporate, particularly if you forget to close the vent on the back of the manometer. Mine (motion pro also) are quite old (bought them in 1991) and closing the vent consists of moving a tube on the back between a fluted post (open) and a solid post (closed).

 

My Motion Pro mercury manometer (2002 vintage) does not have any vent to close. I stuck golf tees into the ends of the vinyl tubes.

[RSTDdog]

My Motion Pro mercury manometer (2002 vintage) does not have any vent to close. I stuck golf tees into the ends of the vinyl tubes.

 

Interesting?? It doesn't have 4 solid plastic pins molded on the back to secure the loose ends of the tubes that connect to the bike when not in use?? Thats what mine has (Mine looks the same as the one in the link above)

 

The vent is for the mercury reservoir snd you should have one of those. Mine has a short hose that fits in the hole in the back you initially fill it with mercury with. The other end of that short hose connects to a solid pin for closed or you swap it to fluted pin for open. Those two pins are located Below the 4 plastic pins on the back for the tubes on the engine. When I get a chance I'll post a pic.

[Prairiehammer]

Interesting?? It doesn't have 4 solid plastic pins molded on the back to secure the loose ends of the tubes that connect to the bike when not in use?? Thats what mine has (Mine looks the same as the one in the link above)

 

The vent is for the mercury reservoir snd you should have one of those. Mine has a short hose that fits in the hole in the back you initially fill it with mercury with. The other end of that short hose connects to a solid pin for closed or you swap it to fluted pin for open. Those two pins are located Below the 4 plastic pins on the back for the tubes on the engine. When I get a chance I'll post a pic.

 

Apparently Motion Pro cheapened their manometer in the intervening years between yours and mine. Mine has no retaining pins for the hose ends and a simple hole in front with a rubber plug to fill the reservoir.

[kevin-vic-b.c.]

I then proceeded to adjust the pilot screws by 'ear' for a best setting for very stable and smooth idle and crisp throttle response......

-Pete, in Tacoma WA USA

'83,88

 

Can someone please explain this to me

[Peder_y2k]

Hard to describe, but by 'ear' means listening closely, and feeling the resonance of the running engine for changes as one makes adjustments. The ideal is smoothness in steady running and crisp throttle response. Roughness is to be eliminated, and is felt and heard in the human senses. It is very easy to recognize the difference between rough and smooth running when one has a base to compare to, such as experience, or example.

When I tune my bikes, I first synch the carbs, then start playing with the pilot screws, adjusting each of them in and out until I arrive at what I 'feel' and 'hear' is satisfactory. Blipping the throttle in Neutral also gives me a 'feel' about quickness of response for any further pilot screw adjustment. 'Sensing' the exhaust temps with the back of my hand at the muffler outlet also give me input. Both my bikes have exhaust so cool I can leave the back of my hand 1" from the tip indefenately...... or until my body objects from getting down to the exhaust. I have yet to incorporate an non-contact temperature indicator (infrared thermometer) that I have, but that could be helpul. I can smell the back of my hand for exhaust, and have learned the difference between rich and lean smells. Riding the tuned bike at varying load conditions provides more feedback, and I'm listening and feeling for misfire, exhaust popping, crackling sounds, and detonation, and any hesitation or stumbling. My final proof of tuning is fuel economy, and when my '88 gets 48+mpg US two-up riding, I know it's right. I'd say that tuning by 'ear' is an art form, with some science thrown in there somewhere.

Hope this helps.............

-Pete, in Tacoma WA USA

'83,88

[RSTDdog]

Can someone please explain this to me

 

What Pete describes above is the way most veteran mechanics adjust the pilot (mixture) screws if there is no EGA (exhaust gas analyzer) available (and sometimes even if there is). There is one pilot screw in each carb body. They adjust the air fuel fixture at idle for each cylinder and also affect off idle throttle response before the main jet comes into play.

 

The pilot screws are different than the screws you adjust the carb sync with. With carb sync you are adjusting the throttle plates relative to the base carburetor.

 

Without looking it up, I don't remember if the Pilot screws on these carbs meter air or fuel in the circuit, but I believe its fuel IIRC. The pilot screws are tapered metering screws. If you slowly start turning one pilot screw in (cw) you will reduce the fuel at idle to that cylinder, leaning it out and eventually leaning it out to the point you will get a lean missfire and also a drop in rpm as that cylinder does less work. Hearing and sensing big changes is obvious, subtle changes takes some experience. Turn it back out CCW you will start to add fuel in and rpm will increase to a point until you start getting too rich.

 

Two methods for those that don't have an ear for it are EGA and Lean drop. All Yamaha multi cylinder bikes have threaded ports in the head pipes of the exhaust. 4 cylinder, 4 thread ports, one in each head pipe upstream of the collector. The dealer I worked at inthe ealry 90's used to have a 4 sensor EGA and you could adjust the pilot screw so the CO in each cylinder was exactly the same. For emmissions they were really lean fromthe factory, around 1.5-1.75% CO. Ideal was typically 2.5-3% IIRC, its been a long time ago. Carbureted bikes properly sync'd and tuned with an EGA ran like a watch.

 

The second method, absent an EGA was lean Drop. lean drop used to be the method for carbureted cars as well. With an accurate and stable tachometer you would set the base idle speed and then adjust the pilot mixture screw on each carbureter to obtain maximum rpm at idle. then reset the idle speed screw to spec, typically 1000 and recheck the mixture screws if there is anything left to be gained. Then you would turn one mixture screw in (lean) to drop the rpm by 50. reset to spec and repeat for the other cylinders.

 

The above is the general idea and its been a while so some of it may not be 100% correct. I don't recall specifics anymore on multi cylinder lean drop if there was an order you started with or not. Lean Drop was primarily for making it close to emissions compliant. You can simply tune for max smoothness and throttle response. A good tach helps you see the changes if you can't hear/sense them.

 

Typically you set idle rpm, adjust sync, adjust mixture and idle rpm,recheck sync

 

If your carbs aren't clean and your pilot circuits are plugged, none of the above will help. If turning the pilot screw makes no change in the running at idle, the pilot circuit is blocked. Odds are it will also be idling poorly or need the choke to idle.

 

RSTDdog