Vacuum Gauge Connection

"I have decided to run a thoro

"I have decided to run a thorough vacuum study on each engine. There is no clearly defined access port on my 1992 engines other than a 3/8 pipe plug on top of the intake manifold 3" or so behind the carb. My plan is to remove the plug and adapt a tight seal to the gauge to obtain vacuum readings.

This port is not centered but I might think the vacuum should be distributed somewhat equally? Any suggestions about whether this would be acceptable?
vac

"If that port is on top of one

"If that port is on top of one of the runners, that's what it is there for. The best connection is with a "pipe plug to hose barb" adapter. If you expect to experiment, buy two and get the rubber caps to cover the barb connections when not connected to the gauge.

Don't your 1409's have PCV fittings on the baseplates? they should provide that same vac signal as that port.

Also, would suggest you do the whole RPM range and measure where your "step-up" spring operates at the same time. You can always change that operating point if you desire to tweak your fuel economy."

"Thanks for the tips Mark, I

"Thanks for the tips Mark, I was planning that exact configuration and figured testing thru about 3000 just to see what happens at invervals. I have no port on these carbs so it may have been an ordered option 17 yrs ago? There is no PCV on these engines either so, hows that?

I found it confusing when I read discussions about the pcv valve but I don't have em.

I am not happy NOT knowing what the previous owners DID NOT do or did improperly. Frankly, I spent two days going over that engine we pulled out, looking, checking, detailing, tightening, etc.etc."

"17 years ago.....???? I thoug

"17 years ago.....???? I thought you just converted to the 1409's.

Not knowing what transpired before always sucks but, that's included in the 'discount' that comes with a used vessel. Best thing is to fix the obvious and take care of what comes along... very much like you have been doing.

The PCV systems were not standard issue on many marine engines of our vintage and flavor. The breather tubes going to the flame arrestors provide a similar function. There's nothing to keep you from adding a PCV loop if you want to...after over 3000 hours on each engine, I haven't seen anything that warrants the mod.

FWIW, when I did the carb tune process, it started with the vacuum vs RPM measurement. We then lowered the float setting, changed the equivalent "step-up spring", and a couple cheap (< $10) parts and reduced fuel consumption at cruise almost 25%....no jets or rods changed."

""figured testing thru abo

""figured testing thru about 3000"

If you dare, do a WOT vacuum test as well. It will validate (or question) the logic of using the 600cfm carb."

"with the current overpropped

"with the current overpropped situation, I'd expect "plenty" of vacuum at the current WOT."

"Another case for a permanent

"Another case for a permanent vacuum gage. My engine runs at 18" mercury at 800 RPM. If a plug fouls it will drop to about 15". Also the vacuum will drop below normal with rich mixture, i.e., a stuck choke. Somewhere I have seen a trouble shooting chart based on how the vacuum gage is responding.

Chuck"

"This might help:
[url=""]htt

"This might help:
http://www.secondchancegarage.com/public/186.cfm"

I have referred to that site m

I have referred to that site many times in the last 2 years. It has a nice demo on gauges

CHUCK has hit the nail on the head "as they say" ...My brother and I were discussing this exact thing. I am re-doing the dash this winter and we are talking about installing 2 vac gauges for each engine but the upper distance requires about 20 foot of hose...IS that a problem with vacuum being so far away? Would I need to use a hard POLY type hose on the way to the fly bridge?

Chuck's already better off

Chuck's already better off - he's tailored the cartoons to his application and has numeric values for the trigger points....

You may want the 'hard' tube as it should make installation much easier. It isn't necessary because of the vacuum; good old rubber is adequate (but is easily crushed). A 50ft roll from the 'ice maker' installation kits would probably be just enough.

"If I had the space for 4 more

"If I had the space for 4 more guages, I'd add just 2 for vacuum, and 2 more for fuel pressure. Using an electrical sender for the fuel, of course."

"Dave,

SAME PROBLEM....that

"Dave,

SAME PROBLEM....that is why I am re-doing the helm up top. When they made these boats they placed every switch and accessory control you need to start up the day in the lower helm and nothing up top. To flip on a blower, its down below.

There is ZERO room to add anything. I even STILL after 1 year, have my 3" swing needle sync gauge in its original clear plastic sales package with a hole in the bottom for the wires. I used a zip tie thru the hole where it hangs on the store peg board and crimped it into the face of the dash for extra hold and support. IF I took the wires off, you could hang it back in the store!

My plan is to add about 9 - 10 inches of height across the face, add the chartplotter display to the center and run switches across the bottom while the gauges are on each side. Of course now I am definately adding the vacuum gauges. IF nothing else, they will add a bit more animation to the instrument panel

Anyone like the 4 in 1 style gauges? I know they are in small scale an not as easily read but they take up even less room.

BTW: Do you believe the 600 cfm is too small?"

"funny, my winter/springtime p

"funny, my winter/springtime project is going to be to re-do my dash as well. Ocean has all of teh gauges clustered in the center which is great. BUT, the previous owner decided to add a dizzy-ing array of now old useless electronics. Some mahog and re-flush mounting all of my electroncs, should look pretty slick, especially with teh radio flushmounted now. Speaking of 600 CFM, i was thinking I may replace the starboard carb...with an edelbrock..?."

"Al, you need to minimize the

"Al, you need to minimize the volume in the lines. You will notice on the referenced site that some of the troubles are manifested as fluctuations in the vacuum reading. Excessive volume in the line between the engine and the dash will act as a damper and as a result you may loose sensitivity to change. On the other hand average readings will be accurate and this may be sufficient for your purposes.

I wonder what happens to vacuum when the four barrels open. If there is a response on the vacuum, it may be a good instrument to have on the panel just so you will know when these suckers open. As for me, they never do because I just don't run that hard.

Chuck Hanson"

"Ted: I FULLY understand that

"Ted: I FULLY understand that problem. I had to rip out a recording LORAN receiver and a radar box big enough to carry lunch for 4....I used to walk into that thing hangin from the ceiling almost every time I went towards the bow

YOU WILL LOVE the Edelbrock carb. It looks like the cost has risen a bit on them. Tuning it in is a snap and the performance is smooth, consistant and reliable. My carbs are probably 5-7 yrs old. I rebuilt each 2 years ago after the first season we owned it. ZERO problems with the carbs

Chuck: I was afraid of that.. I understand what you are telling me about the damper effect. Are you thinking that the super skinny thin line would be better? I have the ICE MAKER poly line that Mark had mentioned and I thought it may work also but I can see your point. I wonder if that make electronic senders ? "

"the e-sensors are MAP sensors

"the e-sensors are MAP sensors. basically two choices - 1 atm and 2 atm versions. All you have to do is provide a +5V reference and the pressure reads out as a voltage, usually between 0.5 and 4.5 V.

I think you'll find the vacuum gauge does some averaging anyhow; the intake surely does.

The vacuum falls as the throttle restriction is minimized. Where it stops is driven by the air flowing thru the remaining restrictions Throttle bores. Can't say how edelbrock/carter rated their carbs but the old RPD guys provided a given CFM with a stated vac reading. If you can get it to go to zero at WOT, you have too much carb."

"Al, in retrospect I believe I

"Al, in retrospect I believe I have raised a non-issue. Fifty feet of 1/4 inch tubing has only about 7 cubic inchs of volume. Because of the much greater volume of the intake manifold, the dampining effect will not likely be much. You could test by hooking up about 50 feet of tubing and chech the responsiveness before stringing the tubing.

Chuck Hanson"

"Chuck,

that is good news b

"Chuck,

that is good news because if that is what you calculate with 50 feet...I am only using about 25 each gauge...so that makes it even better.

How do you figure that stuff out?"

"I work on the older Volvo Pen

"I work on the older Volvo Penta engines/drives..... and I am just an on-looker on this thread, but I am curious about something.
It sounds like every one here understands manifold pressure. We know that a marine engine has no coast time (no off throttle time, so to speak) once we throttle up and get under way.... therefore, no great manifold pressure.
IOW's, very little manifold pressure once the engine starts it's work load and the fuel delivery system air flow opens up.

My question is..... what are we trying to achieve with manifold pressure readings, other than to set low speed idle circuits and to maybe determine if a given carburetor could be sized up to the next larger CFM?
I am particulary curious as to a helm instrument (vacuum guages at the helm)!

Again, just curious and am not criticizing the thread here. You guys all sound like you know very well what you are doing!

BTW, I can see no issues with using the poly tubing that won't collapse under negative pressure. I'd think that the distance would be a non-issue. "

Ricardo...
I would believe th

Ricardo...
I would believe that we are looking simply at diagnostics...Operationally... I agree with your statement: the engines are opened up and moving the boat at a relative constant.

I picked poly tube as it is something I had lying about and it has enough rigidity against collapse yet easy to snake thru the tight spots

""My question is..... what

""My question is..... what are we trying to achieve with manifold pressure readings, other than to set low speed idle circuits and to maybe determine if a given carburetor could be sized up to the next larger CFM?
I am particulary curious as to a helm instrument (vacuum guages at the helm)! "

great question. Here is my take, others my vary:

Compared to my other motor hobbies (flying, driving) it seems ocean boating is more prone to component failure. I think about my past engine defects offshore and there have been many, some over 300 miles from home. Clearly, the casual boater won't know what to do with a vacuum reading staring at them at the helm. BUT, a mechanic/boater, especially with twins, can detect and maybe even analyze failures sooner with more instrumentation. I know i've spotted a bad ignition wire using just a fuel flow meter as the only indicator of a problem. BBC are pretty smooth on 7 cyclinders even at cruise power. That 12.5% drop in efficiency wasn't going to go unnoticed at $5 per mile, either. We were eastbound off of the south coast of Grand Bahama island at the time.
I'd also like fuel pressure guages measured at the carb to detect plugged filters, bad pump, clogged anti-siphon, air leak in a valve stuffing, or similar.
Now, I know that tons of instrumentation will degrade reliability and in itself have issues as well. So, I suppose there is that happy medium, one that will keep us entertained and not make us crazy.
p.s.; not having a transmission pressure guage cost me a rebuild this year, when the fluid starting leaking out. On the other hand, a month later,HAVING a voltmeter saved $300 in house batteries as the regulator turned on full, this time, 80 miles from home on a 240 mile trip."

"There are a couple though rel

"There are a couple though related benefits to having the VAC gauge in the dash. For the example Chuck provided earlier, I'd put it in the Early Warning catagory. Like most instruments, its not the number shown, its the deviation from normal. Add to that Al's "Diagnostics" capability and you can assess the engine's tune as well as gauge any 'improvements' without having to keep the tool box open. It would also aid in the carb's idle adjustment as you indicated. Another twist on the theme is its use if you are tuning your carb to the engine. We all know the engine OEM picks the carb but can't control the hull it is bolted into. Having the VAC gauge can aid you tremendously in tuning certain areas. The overall goal is to get enough RPMs to make the desired cruise speed with MAX VAC to deliver all the "economy" possible....at $3+/gal, ounces add up with substantial run time."

"A vacuum gauge is certainly u

"A vacuum gauge is certainly useful for the early detection any mis-fire whether it be fuel, spark or mechanically related. In the mid sixties several GM cars (Pontiac Gran Prix, Olds Starfire and others)came with console mounted vacuum gauges. Other than it's benefits as a diagnostic tool, the vacuum gauge was also one of the most "exciting" gauges because unlike the oil pressure, temperature and amps gauge, it actually moved alot as the car was driven. It was labeled "power" on one side and "Economy" on the other. I would doubt the average owner enjoyed it's diagnostic powers but it sure was fun to watch it move and it gave you another good reason to stomp on the accelerator."

"Bob...I remember as a kid in

"Bob...I remember as a kid in my grandfathers 1965 SS 396 Chevy...Right there on the dash that red /green economy/power vacuum gauge.

That's the one I'll put on the dash ! I could use the "economy" part.... "