Question about emptying carb during periods of non use

I have a 5.7L Chevy 350 engine in boat with 1991 OMC Sterndrive King Cobra. I have fought cab for a couple years. I've had recurring issues with fouling of the spark plugs . I've recently experienced engine sputtering and back fires and very rough idle at low RPM, so I suspect my power valve may have blown. I recently cleaned the plugs and it has resolved for the moment, but I expect the issue will return. I believe my timing is good because I timed it with light last season.

I've put two partial carb kits in in two years but the carb always ends up running rich. I recently watched a you tube which alerted me that I require a special clutch screw bit to get into the secondary metering block which I have never removed. I've ordered another kit and all the supplies to tear it down further and insure I clean it more thoroughly, including carb cleaner dip and brushes. Talking to a local mechanic, he tells me that even with ethanol free fuel, I should still use stabilizer and not leave fuel in the carb (I have not been using stabilizer and not drained the carb during off season. I thought with Ethanol free fuel, I did not have to worry about varnish and gumming up my carb. I was apparently wrong.


I could install a shut off valve to the fuel inlet on the carb and burn all the fuel in the primary bowl but the mechanic tells me the secondaries only open at 2/3 throttle so even if I could isolate the fuel supply there is no way to empty the secondary bowl and metering block of full of fuel which sits in the carb. I run it several times a month in warm weather (April-October). My concern is when I put it away for the short Texas winter.

Does any one know of a way to evacuate the fuel in secondary bowl, besides taking carb off and pulling the fuel bowl off?

Carb is Holley 650 Model 4175 with vacuum secondaries, electric choke and a transfer tube which transfers fuel from primary bowl to secondary bowl. I tried to load pics but can't seem to successfully execute.

Only the method you listed is the one I'd use for draining the secondary bowl....

Using stabilizer over the winter is common practice; your fuel supplier should be able to give you the details on what they supply. Most of today's gasolines will start to deteriorate after sitting 30 days.....

Maybe it would be worth the effort to get the carb tuned so the engine is happy with it.

Thanks Mark,
I think when I replace the full kit this time I'll have better luck. I have the instructions for tuning the carb and will give it another shot. If I don't have better sustained performance, then I'll seek professional service. Its hard to find a good mechanic that I trust.

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swc65 said:

I have a 5.7L Chevy 350 engine in boat with 1991 OMC Sterndrive King Cobra. I have fought cab for a couple years. I've had recurring issues with fouling of the spark plugs . I've recently experienced engine sputtering and back fires and very rough idle at low RPM, so I suspect my power valve may have blown. I recently cleaned the plugs and it has resolved for the moment, but I expect the issue will return. I believe my timing is good because I timed it with light last season.
Your Marine 5.7L SBC should be seeing a progressive advance and an approx 28* TA @ 3,200 RPM.


I could install a shut off valve to the fuel inlet on the carb and burn all the fuel in the primary bowl but the mechanic tells me the secondaries only open at 2/3 throttle so even if I could isolate the fuel supply there is no way to empty the secondary bowl and metering block of full of fuel which sits in the carb. I run it several times a month in warm weather (April-October). My concern is when I put it away for the short Texas winter.
You are far better off using Non-Ethanol gasoline as you are doing.
The fuel should withstand a short Texan lay up.

Does any one know of a way to evacuate the fuel in secondary bowl, besides taking carb off and pulling the fuel bowl off?

Carb is Holley 650 Model 4175 with vacuum secondaries, electric choke and a transfer tube which transfers fuel from primary bowl to secondary bowl. I tried to load pics but can't seem to successfully execute.


Your Holley has one fuel bowl vent at each end.
Removing the carburetor and gently turning it upside down over a container will ensure that both bowls are empty.
You will want to activate the accelerator pump to clear it's chamber.

A PITA, but it will do what you're after.

Click to expand...

RicardoMarine said:

Your Marine 5.7L SBC should be seeing a progressive advance and an approx 28* TA @ 3,200 RPM.

Click to expand...

What is SBC? short Block Chevy? I assume the 28* is 28* timing advance. I have used a timing light to set timing at idle. What is best way to check the TA at 3200 RPM? I know its a dumb question.

Another thing occurred to me and would like your opinion. I removed a dial type fuel regulator a few years ago because my mechanic told me it might be related to a burned # 8 piston I sustained which appeared to be from running lean. Replaced piston and removed fuel reg. I have read in internet research that its important for Holley carb to have regulated fuel pressure. I am not wondering if the chronic rich running condition I have is due to excessive pressure. I have a small inline electric pump. Can I simply disconnect the fuel feed and dead head into a gauge to check pressure by just turning on the key or does the gauge need to be inline with fuel flowing to carb? If not then what is correct way to check fuel pressure?

SBC= Small block chevy------In most garage talk.

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swc65 said:

What is SBC? short Block Chevy?
SBC = Small Block Chevy

I assume the 28* is 28* timing advance.
That would represent the TA or total advance of which occurs at/near 3,200 RPM.
TA occurs at the Full In RPM.
Your engine's ignition system should be at the Full In advance at around 3,200 rpm or so.


I have used a timing light to set timing at idle.
Yes, that is referred to as BASE advance.
We start up on BASE, and we idle on BASE..... and that's it.
Any advance beyond that is the progressive and total.


What is best way to check the TA at 3200 RPM?
You can use one of two methods:
.... a digitally advancing timing light as you increase RPM.
.... a degree marked off harmonic balancer and a standard strobe style timing light as you increase RPM.

For me, I want to see Real Degrees in Real Time by using a standard style strobe light (or a digital in standard mode) aimed at the harmonic balancer's degree markings.

Another thing occurred to me and would like your opinion. I removed a dial type fuel regulator a few years ago because my mechanic told me it might be related to a burned # 8 piston I sustained which appeared to be from running lean. Replaced piston and removed fuel reg. I have read in internet research that its important for Holley carb to have regulated fuel pressure.
The Holley should be capable of accepting 4 to 7 psi fuel pressure.

I am not wondering if the chronic rich running condition I have is due to excessive pressure.
Excessive fuel pump pressure may over-come the carburetor's needle/seat, in which case excessive fuel would enter the float bowl.

I have a small inline electric pump.
An electric fuel pump must be Marine approved.

Can I simply disconnect the fuel feed and dead head into a gauge to check pressure by just turning on the key or does the gauge need to be inline with fuel flowing to carb?
A correctly installed and wired Marine electric fuel pump first needs to see power from the "start by-pass" circuit.
In other words, turning the key to the ON position (w/ no starter motor activity) should NOT operate the pump.
If it does, it is not installed correctly.

If not then what is correct way to check fuel pressure?
If you can circumvent the start-by-pass system circuit, and operate the pump, you will be able to check the pressure.

Click to expand...

RicardoMarine said:

A correctly installed and wired Marine electric fuel pump first needs to see power from the "start by-pass" circuit.
In other words, turning the key to the ON position (w/ no starter motor activity) should NOT operate the pump.
If it does, it is not installed correctly.

Click to expand...

Hmmm. I'll be researching that. I never felt good with having the pump running with key on. Not sure if that is in my manual, I don't have possession at present, its at the lake. I do not know if the pump is marine grade, all the markings are smudged but I doubt that it is marine based on other things I have found with the boat since I have owned it. Thank you for pointing this out, I assume this is a safety concern.

Regarding your last comment, my current wiring does bypass the start by-pass circuit so I interpret that I may successfully check pressure by dead heading.

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swc65 said:

............ I never felt good with having the pump running with key on. Not sure if that is in my manual, I don't have possession at present, its at the lake.

USCG regulations state that a gasoline engine's electric fuel pump must not continue operating in the event of a stalled engine. This is achieved with the use of a N/O LOP switch (normally open low oil pressure switch).
Reason: if the stall was due to a severed or leaking fuel line, the continued fuel supply could cause a severe issue. The N/O LOP switch prevents continued operation.

I do not know if the pump is marine grade, all the markings are smudged but I doubt that it is marine based on other things I have found with the boat since I have owned it. Thank you for pointing this out, I assume this is a safety concern.
Yes. The Marine grade pump will be "ignition source protected"!
Post a few photos of the electric fuel pump.

Regarding your last comment, my current wiring does bypass the start by-pass circuit so I interpret that I may successfully check pressure by dead heading.
If key ON operates the fuel pump, yes..... you could do that to check the fuel pump pressure.

Please note that this would NOT be USCG approved!

Nut shelling a correctly powered carburetor style electric fuel pump for you:

..... fuel pump's electrical power must pass through the N/O LOP switch that is installed within the engine's oil pressure system.
..... the N/O LOP switch will not close it's contacts until a certain amount of oil pressure is present.
..... during cranking, there is not enough engine oil pressure to close the contacts.
..... in order to operate the electric fuel pump during cranking, a "start-by-pass" circuit is implemented.
..... the start-by-pass system uses the starter motor S circuit. (S = solenoid)
..... during cranking, the power from the S circuit triggers the relay and momentarily operates the fuel pump.
..... once the engine is running, the N/O LOP switch now closes, and continues to supply power to the fuel pump's relay.

Basically, the starter motor must be engaged in order for the fuel pump to operate while cranking.

You can also power the fuel pump's relay via a momentary helm switch.
You would install a momentary helm switch and run that new circuit to the fuel pump's relay on the triggering side!
This will allow you to circumvent the need for a standard or normal "start-by-pass" system.
NOTE: the helm switch must be a "momentary" switch.

You would push and hold the helm switch for several seconds, while priming the carburetor prior to start up.

Some prefer this as it actually extends battery and starter motor life over the course of years.

Click to expand...

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Excellent Rick, I found some of your previous posts on the forum on this issue, starting to clear the fog. I have basic understanding of circuitry but transferring to execution always takes me a bit. Took me a while to research how to post pics (I hope this works) and I have uploaded the pic of the pump and pics of my block showing what appears to be Oil Pressure Light switch and Oil Pressure Sender. These are old pics and I am not near the boat at present. I have no idea what the Light switch is wired to because I do not have a light( that I know of and I do have an oil pressure gauge which IO assume is wired to the Oil Pressure Sender.

I like the momentary switch to start the motor especially if I have an empty slot in my rocker switches but I cant remember if I have any unused rockers that I could replace. Momentary would be like my horn.

I researched alot about the relay method and it look to be the most comprehensive way but more complicated. I'd need more coaching on that solution. Are you aware of any diagrams that would lead me all the way through? I hope to have access to my OMC manual this week and can study the wiring harness digrams. The more I dig into this the more i realie there were some short cuts taken on my boat, by previous owner and my self.

Any suggestions on best practices/tip for boat electrical wiring? I've treid to solder the marine wire beore and had a very difficult time. Maybe my iron not hot enough. Thats is another matter for another post I suppose. Only good think about Covid is that its giveing me some study time...

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swc65 said:

................. Took me a while to research how to post pics (I hope this works) and I have uploaded the pic of the pump and pics of my block showing what appears to be Oil Pressure Light switch and Oil Pressure Sender.
Yes.... it looks like someone installed what we used to call an "idiot light" system.

I have no idea what the Light switch is wired to because I do not have a light( that I know of and I do have an oil pressure gauge which I assume is wired to the Oil Pressure Sender.
Correct...... the oil pressure sending unit is for the oil pressure gauge.


I like the momentary switch ..... Momentary would be like my horn.
Yes.... momentary means that the switch cannot remain closed.
In other words, it will open the circuit that moment that your finger is released.
You could actually use a horn switch.

I researched alot about the relay method and it look to be the most comprehensive way......

Look up five pin relays in either 30 or 40 amp.

I prefer Bueller!

They work well, and are easy to understand schematically.




Any suggestions on best practices/tip for boat electrical wiring? I've treid to solder the marine wire beore and had a very difficult time. Maybe my iron not hot enough.

Use the correct wire fittings and the correct crimp tool.

Click to expand...

continued:


Regarding the picture of your starter motor:
The yellow w/ red stripe wire is your S (solenoid) circuit. This is the circuit that may be used to create a "start-by-pass" circuit that will momentarily trigger the fuel pump's relay.

By the way, your old school Delco non-gear reduction starter motor needs the front bracket attached.
The nut for securing that bracket appears to be loose.
If not too late, I would return that starter motor in exchange for a Marine SBC HTGR/PMGR starter motor.

Regarding the picture of the oil pressure switch and oil pressure sending unit:
Yes, the unit that you are calling a light switch is a simple N/C pressure switch. It takes the idiot light circuit to Negative.
I seldom see an idiot light and switch being used on a Marine engine. Furthermore, it is not the type that can be used for the fuel pump circuit.



The electric fuel pump shown is not correct for a main engine fuel supply.
That style is used for small engines like a Marine generator.

You need an electric fuel pump similar to this Carter 4594 .....

RicardoMarine said:

continued:


Regarding the picture of your starter motor:
The yellow w/ red stripe wire is your S (solenoid) circuit. This is the circuit that may be used to create a "start-by-pass" circuit that will momentarily trigger the fuel pump's relay.

By the way, your old school Delco non-gear reduction starter motor needs the front bracket attached.
The nut for securing that bracket appears to be loose.

I'll put a nut on it.
If not too late, I would return that starter motor in exchange for a Marine SBC HTGR/PMGR starter motor.
Unfortunately, I installed starter moter a couple years ago. I guess I'm lucky nothing has happened. Is the main concern ignition of fuel vapors. How is a marine starter motor different.

Regarding the picture of the oil pressure switch and oil pressure sending unit:
Yes, the unit that you are calling a light switch is a simple N/C pressure switch. It takes the idiot light circuit to Negative.
I seldom see an idiot light and switch being used on a Marine engine. Furthermore, it is not the type that can be used for the fuel pump circuit
I ohmed out the wires and the oil pressure switch wire rund to the helm but is not connected. Perhaps I could use it for a momentary switch?

Further reseach lead me to this switch https://www.amazon.com/Carter-A68301-Engine-Pressure-Switch/dp/B000CSWR10

Do you agree with the comments from the Amazon Q&A section on this Carter NO LOP switch I pasted as an image.

The electric fuel pump shown is not correct for a main engine fuel supply.
That style is used for small engines like a Marine generator.

You need an electric fuel pump similar to this Carter 4594 .....

Click to expand...

Does this diagram look correct?

swc65 said:

Does this diagram look correct?

Click to expand...

You are looking at an automotive schematic. The text quoted is also for automotive.
And no..... it does not look correct for marine use!







Here is my suggestion:

Example ONLY

Correction:

If a momentary helm switch is used to trigger the relay, you will need to install a diode in the yellow/red stripe circuit to pin #85.
This will prevent the momentary switch from activating the S circuit.

Rick, you are showing a two position switch where the Carter switch and this Sierra switch are three position. IT would seem the three position switch is designed to power pump in Start position as well as run position. Can you help me understand why you show two position?

Serra switch https://www.westmarine.com/buy/sierra--oil-pressure-safety-shut-off-switch--10527075

I have a secondary issue. Should I start a new thread in the Forum? It is regarding difficulty shifting. Lat year I had an anchor break on the shifter cable in the control box. I replaced but ever since then the movement of the shifter is not correct. It biased toward reverse, meaning from Neutral it takes very little movement backwards to engage reverse and opposite for forward, I have to move the shift farther forward to engage forward. Also, I don't feel a clean detent when approaching neutral. I removed the control box and viusually inspected the anchor and cable, I don't see anything visually. When I measure the distances between forward and neutral they do not meet spec. I can tell how to adjust. The manual says if measurements are not within specs, check remote control installation which I have done. I'll double check.

RicardoMarine said:

What is best way to check the TA at 3200 RPM?
You can use one of two methods:
.... a digitally advancing timing light as you increase RPM.
.... a degree marked off harmonic balancer and a standard strobe style timing light as you increase RPM.

For me, I want to see Real Degrees in Real Time by using a standard style strobe light (or a digital in standard mode) aimed at the harmonic balancer's degree markings.

Click to expand...

Is it safe to run max RPM in Neutral, in the boat slip, or should I be under way with load on engine? You indicated, " Your engine's ignition system should be at the Full In advance at around 3,200 rpm or so"

I am experiencing continued sputtering and popping during some acceleration unless I ease into it. I was able to slowly throttle up on the water and reached wide open throttle and seemed to run well. Bring boat back in, when I run throttle at idle, engine runs very rough and eventually dies at idle.

I'd like determine fur sure if its fuel or fire. I have to replace fuel pump die to misapplication. I measured the pressure and it only registers 2 psi. I can understand problems due to lack of fuel delivery during acceleration but don't understand how insufficient pressure would would cause poor engine idle.

I know I'm throwing multiple issues out for discussion and I apologize if it is unorganized thinking and trouble shooting. Thanks for continued support.

I am wondering if perhaps the ESA is causing some of the performance issues I see. The fact that the shift cable engages ESA made me think engine performance might be related.

swc65 said:

I am wondering if perhaps the ESA is causing some of the performance issues I see. The fact that the shift cable engages ESA made me think engine performance might be related.

Click to expand...

The ESA functions (or should function) only when shifting from gear into neutral.... not while making a shift into gear!
When returning to neutral, the dog clutch engagement teeth do not want to separate while under idle speed prop thrust load.
The resistance felt by the outer cable jacket is what moves/operates the cam lever arm, which in turn momentarily operates the micro switch.
Again, only while returning from gear into neutral!

Look to see if the micro switch is being activated while the drive is in FWD.
If so, your system is either out of adjustment and/or you have a bad cable, etc.



.

Thanks Rick. I confirmed the ESA is working as it supposed to. I also resolved my shifting issue by uninstalling and re-installing the shift cable.

I’m still wrestling with the switch comments you offered. Could you respond to the post from yesterday at 9:42 am regarding the NO LOP switch having three terminals vs the two which you showed. I’ve got a call into Carter to ask them about the switch but they have not responded.

I Appreciate your time and comments.

RicardoMarine said:

Correction:

If a momentary helm switch is used to trigger the relay, you will need to install a diode in the yellow/red stripe circuit to pin #85.
This will prevent the momentary switch from activating the S circuit.


View attachment 23192

Click to expand...

What are you thoughts on this diagram from Sierra? I emailed their tech support and they sent me the instructions. I tried to upload the PDF to this site but was unsuccessful. I can email or you or put it on a file exchange where you could download if interested. You can PM if you need to see it.

I do not see a momentary switch nor a relay. Diagram shows the switch accommodates the Start Circuit. My assumption is the P and S terminals are normally closed and P and I are normally open.

When pressure is applied to diaphragm, the P and S terminals open, and P and I terminals close.

Am I interpreting this correctly. I want to be safe, and I also do not want to do more that is necessary with with electrical components. More points of failure, and electrical not good with fuel.

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swc65 said:

What are you thoughts on this diagram from Sierra?
I looks to be automotive!
Note how in figure C that they label the switch on the right as an OE "pressure switch".
In a marine application, this would be an oil pressure "sending unit".

I do not see a momentary switch nor a relay.
Correct. A momentary switch is optional, and a relay likely won't be shown.

Diagram shows the switch accommodates the Start Circuit. My assumption is the P and S terminals are normally closed
Probably so. That allows the S circuit to operate the fuel pump until oil pressure is achieved.

and P and I are normally open.
Probably so again.

When pressure is applied to diaphragm, the P and S terminals open, and P and I terminals close.
Yes, that would allow the fuel pump to operate while oil pressure is up, and would open the circuit in the event of no oil pressure.... i.e., engine stalled.

Am I interpreting this correctly. I want to be safe, and I also do not want to do more that is necessary with with electrical components. More points of failure, and electrical not good with fuel.


My preference would be to use a relay to power the fuel pump, allowing the S circuit and the oil pressure switch to trigger the relay only.
Your call on that!

Click to expand...

Got it, thanks for indulging me.

On previous post you offered a corrected wiring diagram (attached) and you indicate to use diode for momentary switch use case on pin 85 of relay. Do you have an example of one? I google marine diode and found several. Not clear on how to specify rating but I assume amperage ratings vary. Am I looking for something like this?
https://www.crowleymarine.com/d/tech_article/diode-kit. Am I looking for what appears to be a large resistor?

Any coaching?

swc65 said:

Got it, thanks for indulging me.

On previous post you offered a corrected wiring diagram (attached) and you indicate to use diode for momentary switch use case on pin 85 of relay. Do you have an example of one? I google marine diode and found several. Not clear on how to specify rating but I assume amperage ratings vary. Am I looking for something like this?
https://www.crowleymarine.com/d/tech_article/diode-kit. Am I looking for what appears to be a large resistor?

Any coaching?

Click to expand...

No.... a resistor limits DC current, whereas a diode allows DC current flow in one direction only.

Imagine a momentary helm switch powering pin #85 (for fuel pump operation and priming the fuel system prior to cranking), and simultaneously powering the starter motor solenoid!
The diode (between the helm switch lead and the S circuit) will prevent reverse current flow to the solenoid.

If the starter solenoid still has the R (small) terminal, neither the relay or diode is required....and the wiring will vary depending upon the switch configuration used....i wouldn't add all the wires and connectors if not needed - just introducing potential problems later on...

makomark said:

If the starter solenoid still has the R (small) terminal, neither the relay or diode is required....and the wiring will vary depending upon the switch configuration used.............

Click to expand...

Mark is correct if your starter motor solenoid offers the R terminal.
Some of the Marine starter motors do not and may also incorporate a slave solenoid.
I'm not sure about the 1991 OMC Sterndrive King Cobra system.

The early automotive starter motor solenoids offered the R terminal as to send full voltage to the ignition coil while cranking (in lieu of resisted coil voltage).
The same R terminal could be used for the electric fuel pump's start-by-pass system.

makomark said:

If the starter solenoid still has the R (small) terminal, neither the relay or diode is required....and the wiring will vary depending upon the switch configuration used....i wouldn't add all the wires and connectors if not needed - just introducing potential problems later on...

Click to expand...

I think we are getting somewhere! See my posted pics of solenoid and wiring diagram from the manual. Looks like they match to me.

So based on this confirmed information, is my diagram correct? I it seems matches what Sierra sent me. I like the Makomark is thinking but again, I want to do what is right and safe.

No R terminal on that solenoid.....so you have to use the SPDT pressure switch.

Based on the part numbers provided, your diagram looks fine.

I'd suggest adding the wires' color codes and adding it to your maintenance log....and getting a spare switch to have on hand....they always fail on Sat afternoon when the weather forecast calls for a beautiful boating Sunday....