help with specifications for a home made synchro

[deQuincey]

hi

i would like to fine tune my carbs, so i would like to ask you about the size of a hole that must be made in the tupperware cap

i would prepare a mix between this system:

and the vacuum meter one, this is i will prepare two caps and install vacuum meters in them,

the vacuum meters will be prepared for a 0 to -1 bar meassurement

but i have an important question:

which is the size of the hole that i have to do in the cap in order to let enough air for the normal engine function while doing the synchro ?
(the hole arrowed in red)

thanks

 

[Stevehose]

If I understand correctly you have vacuum gauges there, both those gauges and the homemade manometer hook up to the manifold vacuum ports on the carbs (below the throttle plates), not over the tops of the carbs like synchrometers/Uni-syns so you wouldn't need the plastic covers. Careful on the manometer, if your carbs are out of balance too much it will suck the oil out of the tube quickly and into the carb, I use vacuum gauges and synchrometers and gave up on the manometer for this reason.

 

[deQuincey]

If I understand correctly you have vacuum gauges there, both those gauges and the homemade manometer hook up to the manifold vacuum ports on the carbs (below the throttle plates), not over the tops of the carbs like synchrometers/Uni-syns so you wouldn't need the plastic covers. Careful on the manometer, if your carbs are out of balance too much it will suck the oil out of the tube quickly and into the carb, I use vacuum gauges and synchrometers and gave up on the manometer for this reason.

you are right

just by the case i decide to use the plastic covers and the oil and everything, i would like to know which size (diameter) should be the open hole in the plastic covers

regards

 

[61porsche]

The center hole for air is approximately 3/4"- NO more. This is good for about 3000rpm. Don't blip the throttle or the plastic bowl will be deformed. ( Weber or Redline, etc. had the size written on the caps they sell.)

Seal the bowl to the carb. I use clear packing tape. You're on your own here.

Make sure the plastic cap on the carb linkage is in place or tape that off if missing as air will enter from the side and under.

I used two cycle oil- the type for mixing with gas for chainsaws, etc. Comes in very small sizes if you don't have some already. It is heavy( less chance of sucking up into the engine), takes a while to settle as you adjust (watch the liquid that clings to the side of the tubing) but you can get pretty precise.

Use the guage but USE your ears and eyes too. Mechanical differences in cylinders, valves, cam, etc. cause small differences so your looking for balance, smooth running, good exhaust note ( sound).

Press down on the bowls one at a time, to see if your seal job was perfect or not so. The guage will pick it up.( Double check for vacum leaks at this stage.)


I know I keep saying this- make sure everything else, points, plugs, timing, etc. are all perfect as you can so you're not fooling yourself that the carbs are the issue. Make sure. If you have a cylinder off compression or two a bit, nothing you do to that carb is going to fix it. But you can help, so do your best.

You'll get it. Keep the faith and may the force be with you!

 

[deQuincey]

thanks mr.porsche

some steps beyond:

and now it comes the question, do you think i can use the caps with the vacuum meters like this picture ? or i will need the oil tubes for this type of assembly

finally, taking into account your advise, i will do a 3/4" diameter hole in the center of each cap

the problem is that 3/4" is 19,05mm, and i can do 18mm or 20mm, so what do you think ?, probably 18mm is better ?

regards

 

[61porsche]

18mm is fine. ( If you cut the hole in the center you don't have to take off the air cleaner stud.)

On the guages- as long as you can seal the bowl, should be fine. ( weight of the guage vs the the stability of the plastic bowl)

Looks good.

I also use vacumn guages to see how the engine responds to the carb tune. Highest vacumn; then slightly less. Kinda the best of both worlds.

 

[Tony_V]

Hi,

What is the difference when use:

1. Vacuum gauges to the manifold vacuum ports on the carbs (below the throttle plates)
2. Vacuum gauges at the top of the carbs like synchrometers/Uni-syns with plastic covers.
3. Oil level

Point 1 seems to be the easiest to do if there is no difference in the result.

What do you think?

Rgds/Tony

(I have followed all about the carb problems,,,thanks for all help in this forum.)

 

[61porsche]

carbs- vacumn, volume, weight

Vacumn- guages below the throttle/ manifold takes into consideration timing and A/F ( air/ fuel) A good running engine should be between 18 and 22, no fluctuations, etc. A slight ticking of the needle means you usually have an igniton issue to resolve.

Volume- balance; the amount of air should be as equal as possible. The Zeniths are fixed jets meaning there's an optimal amount of air for a given amount of fuel at a set rpm that once set at idle, continues that ratio higher into the rpms/ hp until aprroximately 2500, then the main jet comes in to the equation, then the secondary. Typical Zenith issues tend to be idle, transition or stumble, or the secondaries don't open.

Manometer- professional manometers for purchase have restrictors or use mercury to dampen the level. Ones made up by enterprizing owners, usually don't have that luxury, so a heavy weight oil is best as the oil tends to stay in the tube if hooked up to only one carb rather than to two or more carbs.

Plug color- you can tell a bunch by observing the spark plugs although you have to have an understanding of how you drive. For example, a car that is just infreqently used might have more evidence of the the choke being used. Of course, there are many variables in between. Something to pay attention to.

For the ultimate set up, there are air /fuel meters now that are reasonable for most of us. They do require an O2 sensor with wideband being the better preference. Two carbs or more- one for each bank fitted into the exhaust. This would give you the best reading of what's happening with the engine and a faster tune. Exhaust temps are another way, but less accurate. An infrared gun on your manifolds/ headers might give you some indication which way to go when tuning.

Keep the shiney side up!

 

[deQuincey]

hi

after preparing the bolws i must say that they are not working, if i use the bolws with a 18mm hole, the vacuum meters will say nothing but zero,

so i throwed the bowls away and used the vacuum ports under the throttle plates

at iddle i found -0,6 bar in both vacuum meters, and rough fluctuations, so i reduced the diameter of the pipe (stretch the hose with a clamp) that connects to the mentioned ports, and the fluctuation was reduced significantly

what does this mean ?

any ideas

 

[61porsche]

It's likely the guages are dampened. ( Internal device which limits needle movement; they may not be sensitive enough.)

Show me a picture of how you have them hooked up now as I don't understand if they are T'd together or seperate? And the valve cover adapter.

You can always go with the tube and fluid method.

A regular vacumn guage below the throttle plate will show vacumn. What were the readings after you altered the tubing?


You have to measure air from the top of the carb.You have to measure with something that covers the whole carb as the secondary plate is open slightly.

 

[Stevehose]

Use the bowls with the air meters (Synchrometer/Uni Syn). Here are some links for intake manifold vacuum gauge readings:

http://www.centuryperformance.com/tuning-with-a-vacuum-gauge-spg-148.html

http://autospeed.com/cms/title_Using-a-Vacuum-Gauge-for-Engine-Diagnostics/A_2393/article.html

http://www.tuningmadeeasy.com/tuning/vacuum-gauge-the-wonder-tool/

http://automotivemileposts.com/garage/vacuumgaugereadings.html

hi

after preparing the bolws i must say that they are not working, if i use the bolws with a 18mm hole, the vacuum meters will say nothing but zero,

so i throwed the bowls away and used the vacuum ports under the throttle plates

at iddle i found -0,6 bar in both vacuum meters, and rough fluctuations, so i reduced the diameter of the pipe (stretch the hose with a clamp) that connects to the mentioned ports, and the fluctuation was reduced significantly

what does this mean ?

any ideas

 

[deQuincey]

It's likely the guages are dampened. ( Internal device which limits needle movement; they may not be sensitive enough.)
they are supposed to be of a +/- 1,6% precission type

Show me a picture of how you have them hooked up now as I don't understand if they are T'd together or seperate? And the valve cover adapter.
i will post a pic, but i can tell that the carbs are completely separated for doing the synchro process

You can always go with the tube and fluid method.

A regular vacumn guage below the throttle plate will show vacumn. What were the readings after you altered the tubing?

they meassure aprox. -0,6 bar each

i am using the 4 mm tube that comes off the carbs, the one that is normally capped in each carb.

You have to measure air from the top of the carb.You have to measure with something that covers the whole carb as the secondary plate is open slightly.

,

 

[deQuincey]

i have made a units conversion,
you usually see that a round good figure for vacuum is 20 "Hg, that is exactly 0,68 bar, and my gauges tell me 0,6bar at iddle, so sounds good ?

another documents say between 17 to 22 "Hg (0.58 to 0.75 bar)

regards

 

[61porsche]

Vacuum is measured by negative in.mercury. There would be a negative number. Here in the US on guages that would be -28 as the limit. A good running stock engine should read 18- 22. Most of this is the idle screw or timing.

Bar to me means positive pressure as in compression readings. The guage type must read negative inches of mercury or whatever the Euro/ Metric standard is. I don't know enough about the guages you have to be certain the do measure vacuum on an engine. Here we usually just buy from the local auto parts supplier- something around or less than $10.

By pinching off the hose, it simply lessens the negative vacuum until the guage reads something.

The opposite should be happening.

The percentage of error is a calibration where there is a small adjustment screw on the back or face somewhere. Most guages as shown work off a diaprahm, tube, etc.

Since you have the bowls and tubing- humor yourself. Make up the tube in my picture with your favorite fluid. Try it. Just put both on before you start.

 

[61porsche]

If your reading is 0,6 bar, yes that's good. I apologize for the misunderstanding of terms before. We must have both been posting at the same time.

Is one more than the other? if so, pick the lower and try to adjust to match the higher which is not always possible but get as close as you can.

Check your timing, then rotate the distributer to the highest reading, then rotate the other way so the reading is slightly less. Make note of your timing mark as this should be the optimum timing.

You may have to adjust your idle speed.

You'll need to still measure carb air flow and adjust slightly for best balance.( butterfly screw)

You may have to adjust the idle mixture screws as all gets close to optimum, smaller and smaller adjustments need to be made.

If you don't have any stumbling; your done.

p.s. It gets much faster and easier the next time.

 

[deQuincey]

hi have you seen the pics i posted about the reading point ?

hi have you seen the pics i posted about the reading point ? are those reading points ok ?

more questions inside your text

thank you very much

If your reading is 0,6 bar, yes that's good.
yes is -0,6 bar, so more or less 20"Hg,
the problem is the vibrations of the needles, they vibrate a lot
i am using a silicone hose of internal diameter = 4mm

Is one more than the other? if so, pick the lower and try to adjust to match the higher which is not always possible but get as close as you can.
i assume that when you say "the higher" you mean the higher vacuum possible, right ?
to adjust this, i will use the air butterfly screw, right ?

Check your timing, then rotate the distributer to the highest reading, then rotate the other way so the reading is slightly less. Make note of your timing mark as this should be the optimum timing.

You may have to adjust your idle speed.

You'll need to still measure carb air flow and adjust slightly for best balance.( butterfly screw)

You may have to adjust the idle mixture screws as all gets close to optimum, smaller and smaller adjustments need to be made.

If you don't have any stumbling; your done.
i still have some stumbling, but i have done the synchro from the point i had the settings, so now i will repeat all the carb settings from the start (i.e. doing the iddle screws and undoing them 1 and 1/2 turn,...


p.s. It gets much faster and easier the next time.

 

[deQuincey]

Bar to me means positive pressure as in compression readings. The guage type must read negative inches of mercury or whatever the Euro/ Metric standard is. I don't know enough about the guages you have to be certain the do measure vacuum on an engine. Here we usually just buy from the local auto parts supplier- something around or less than $10.

please read the next post too, i have some questions,...

this is my gauge or vacuum meter (around 8 €uro), it reads negative bar units: (you can see the black numbers from right to left (anticlockwise) from 0 to -1 bar

 

[61porsche]

Fluctuations in the guages- try to describe the fluctuations: Both guages?

1. Small, but rythmic.( fast). Usually means points, spark plug wires, etc or said another way- ignition. Could be small leaks too but you just rebuilt the carbs. Check the nuts for torque. use a hose to slowly go around the carb/ manifold/ vacuum connections/ hoses listening for small leaks. it's very easy to overlook for even the best of us. Before analyzers and computers, a vacumn guage was the mechanic's best friend. The principle of the motor as an air pump still hold true.


Higher vacuum- yes the throttle plate screw; slowly. The idle mixture screw at some point will have some effect too. Again, with today's gas formulation I find the mixture screws to be out more than the factory manual.

Stumbling- try to describe at what rpm. Think of the carb as seperate at idle, part throttle, accelerating, up to about 2500 to 3000 rpm.

Up to about 1100 rpm the carb is just using a small orfice ( idle mixture screw) mixed with a small amount of air ( throttle plate position.)

Then a transition starts to the primary jet. So, if the stumble is at 1200 or so it can be:

Slightly lean as it transitions to primary jet.

Slightly rich same as above. ( tailpipe spitting may be a clue)

Accelerator piston ( squirter) needs attention. More squirt. ( Less squirt causes harder starting as well, since you should be pressing down on the halfway or more on the accelerator pedal before turning the key to set the choke, but gives that extra squirt before the carbs come into play and yes it's important since it gives the motor a squirt to help the transition when accelerating just past idle, between the main jet rpm and secondary jet rpm, and the transitions.

 

[deQuincey]

sorry for late answer, i,m out of the office !!

,

Fluctuations in the guages- try to describe the fluctuations: Both guages?
the fluctuation happens in both gauges

1. Small, but rythmic.( fast). Usually means points, spark plug wires, etc or said another way- ignition. Could be small leaks too but you just rebuilt the carbs. Check the nuts for torque. use a hose to slowly go around the carb/ manifold/ vacuum connections/ hoses listening for small leaks. it's very easy to overlook for even the best of us. Before analyzers and computers, a vacumn guage was the mechanic's best friend. The principle of the motor as an air pump still hold true.
the fluctuation of the needles is fast and changes while adjusting/synchronising the carbs, so i would like to study this a little bit more

i have carried over a fresh new starting-from-the beginning adjust process, ,but i had only the time for the first part of it (just set the iddle at 900rpm), so i will need at least another session to recheck and do the 1700rpm adjust

i found that when i change the air butterfly screw the needle fluctuations vary, and they decrease when reaching a synchro status

still there remains some vibration in the needles and some stumbling too ! ???

Higher vacuum- yes the throttle plate screw; slowly. The idle mixture screw at some point will have some effect too. Again, with today's gas formulation I find the mixture screws to be out more than the factory manual.

Stumbling- try to describe at what rpm. Think of the carb as seperate at idle, part throttle, accelerating, up to about 2500 to 3000 rpm.

Up to about 1100 rpm the carb is just using a small orfice ( idle mixture screw) mixed with a small amount of air ( throttle plate position.)

Then a transition starts to the primary jet. So, if the stumble is at 1200 or so it can be:

Slightly lean as it transitions to primary jet.

Slightly rich same as above. ( tailpipe spitting may be a clue)

Accelerator piston ( squirter) needs attention. More squirt. ( Less squirt causes harder starting as well, since you should be pressing down on the halfway or more on the accelerator pedal before turning the key to set the choke, but gives that extra squirt before the carbs come into play and yes it's important since it gives the motor a squirt to help the transition when accelerating just past idle, between the main jet rpm and secondary jet rpm, and the transitions.

 

[deQuincey]

additional info about ostumbling issue

difficulties to edit previous post, so here additional info about stumbling

after adjusting and synchronising the carbs, reached 900rpm's, but little stumbling remains at iddle

no problem in transition is detected, also good performance at high revs

i will come back with more info after another session, i will check for leaks too

thanks