MAC Troubleshooting

[Scott Norris]

I've been thinking about this in a different way. If what some say on here is true, I got ripped off on the sprinkler system in my yard. They put 1/2" ID pipe in to supply the .0125" nozzle openings in the sprinkler heads. WTH is up with that!!! A 1/8" flexi tube should have worked fine huh?

 

[LH7018]

Got me thinking too. Belay that. It's giving me nightmares of air and water balancing classes as an apprentice. Hmmm, somethings nagging me (besides the wife) concerning pressure differential across the device. Or, as Journeyman Graves would say "Delta Pee".

Regardless, the large fuel lines work. Or, more simply, when reality differs from theory, change your theory.

 

[Scott Norris]

May the Force be with you Luke. And good Luck with the Wife.

 

[Terry Flynn]

WOW, 2,115 views in 3 day's I think this might set some kind on new record :lol:

 

[Charles Perdue]

Do all you MAC runners go through that much trouble to start your MAC 67s?

Nope. B)

Nope, mine starts so easy sometimes I dont even need the starter just turn on the radio apply glow starter and she fires up. No not every time but its happened several times lately.

Ron

Thats what I Like!!!! My CMBs are like that once they are properly fogged. Start on the first bump almost every time.

Russell,

If you're ready I can meet you out there. As you know there is another project X on my setup bench.

Andy,

I believe the on the water accounts of needing larger fuel line for the MACs but I don't under stand why.

Would you care to go into the theory choosing the correct size fuel line so we can all understand

(go as techical as you want, I'll catch up. )?
thanks.

"Would you care to go into the theory choosing the correct size fuel line so we can all understand"

Yes,,,we WOULD like to hear YOUR theory of flow and fluid dynamics,,,,,

You don't need a degree to know that as the flow in any diameter of tube increases, the friction of the fluid againt the inside of the tube increases. The smaller the diameter of the tube for the same volume means more friction, less total flow with everything else being the same. Increasing the diameter of the tube will slow the speed of the flow causing less friction for the same volume thus increasing the amount of fluid that will pass through the tube. A tube too large will be affected more by the acceleration, deacceleration and the G forces in the turns as it has more fuel weight inside of the tube at any given time. Just my $1.02 worth. (Inflation don't you know)

 

[AndyBrown]

You don't need a degree to know that as the flow in any diameter of tube increases, the friction of the fluid againt the inside of the tube increases. The smaller the diameter of the tube for the same volume means more friction, less total flow with everything else being the same. Increasing the diameter of the tube will slow the speed of the flow causing less friction for the same volume thus increasing the amount of fluid that will pass through the tube. A tube too large will be affected more by the acceleration, deacceleration and the G forces in the turns as it has more fuel weight inside of the tube at any given time. Just my $1.02 worth. (Inflation don't you know)

Charles is honing in on the answer! ..........he's actually got one side of the equation.

 

[Krusty 181]

wouldnt pipe pressure come into play at some point??, sure the carb is sucking fuel ,but different pressures to the tank from different pipes/lengths/revs surely has to affect flow at the other end.. doesnt it???? :blink:

Andrew

 

[Russell Bear]

wouldnt pipe pressure come into play at some point, sure the carb is sucking fuel ,but different pressures from different pipes/lengths surely has to affect flow at the other end.. doesnt it???? :blink:

Andrew

Andy can elaborate further but yes. The temperature of the air and the size of the fuel lines (and that giant carb) will need more pressure. I am adding the stinger bushings to help with this.

 

[ALLAN YUEN]

wouldnt pipe pressure come into play at some point, sure the carb is sucking fuel ,but different pressures from different pipes/lengths surely has to affect flow at the other end.. doesnt it???? :blink:

Andrew

Andy can elaborate further but yes. The temperature of the air and the size of the fuel lines (and that giant carb) will need more pressure. I am adding the stinger bushings to help with this.

Did you check inside dirt piece plastic (very tricky)into the tanks also should be put fuel filter onto line also maybe flush out into the CMDI 3 remote value (inside small piece dirt) Hope to find where choke

 

[Russell Bear]

wouldnt pipe pressure come into play at some point, sure the carb is sucking fuel ,but different pressures from different pipes/lengths surely has to affect flow at the other end.. doesnt it???? :blink:

Andrew

Andy can elaborate further but yes. The temperature of the air and the size of the fuel lines (and that giant carb) will need more pressure. I am adding the stinger bushings to help with this.

Did you check inside dirt piece plastic (very tricky)into the tanks also should be put fuel filter onto line also maybe flush out into the CMDI 3 remote value (inside small piece dirt) Hope to find where choke

Allan, I have flushed the system a time or two, seems to be clean.

HOLY COW ALLAN

Just checked out your avatar when I clicked on your name!!!!! Nice err, twin engine boat there.LOL

WHOA NELLY@!!!!!

 

[ALLAN YUEN]

How many of turn out for 3ch remote valve? Don't turn lean better open more bit of rich if you see more blue smoke. will you try to run.

 

[Russell Bear]

How many of turn out for 3ch remote valve? Don't turn lean better open more bit of rich if you see more blue smoke. will you try to run.

It is two full turns off the seat. When it is running it is very rich, lot of smoke and oil out of the pipe.

 

[ALLAN YUEN]

Should be turn down touch close then turn up 3 1/2 open. Will run test.

 

[Krusty 181]

HOLY COW ALLAN

Just checked out your avatar when I clicked on your name!!!!! Nice err, twin engine boat there.LOL

WHOA NELLY@!!!!!

Geez it seems Allan has the answer .. just click on his name and all your troubles disappear..... :lol: :lol:

 

[Wasted wages]

You don't need a degree to know that as the flow in any diameter of tube increases, the friction of the fluid againt the inside of the tube increases. The smaller the diameter of the tube for the same volume means more friction, less total flow with everything else being the same. Increasing the diameter of the tube will slow the speed of the flow causing less friction for the same volume thus increasing the amount of fluid that will pass through the tube. A tube too large will be affected more by the acceleration, deacceleration and the G forces in the turns as it has more fuel weight inside of the tube at any given time. Just my $1.02 worth. (Inflation don't you know)

100% true,,,,BUT--If the friction of the fuel moving thru the line is high enough to cause a problem then the line it self has become the restriction not the needle.

All of this means nothing to the needle valve,,,

THE WHOLE POINT I HAVE SAID FROM THE START IS:

IF the line size from the tank to the valve is big enough to handle the MAXIMUM flow of the needle setting

then a LARGER line size will do nothing to improve flow at static pressue.lets leave all pipe pressure out of the mix for now,,and compare apples to apples,,

Lets look at it another way,,,,if you took a piece of brass round stock and drilled a .015 hole thru it and connected it to a 1/8 inch fuel line and a gallon of fuel,,,it would drain out at the rate of the .015 hole,,,,if you connected it to a 1/2 garden hose and repeated the process it is still going to drain out at the rate of the .015 hole.

The size of the hose supplying the fuel does not matter as long as all other test elements remain equal.

it would be the same as if you poked a .015 hole in the jug,,

Andy ,I did agree that the test of attaching the fuel line straight to the carb proves that the pickup and lines were to small. because the motor still went lean ,,with no restrictions in the line. I just don't buy that once you have established that the line supplying fuel to the valve is OK then a LARGER line will do anything,,down stream of the valve,,yeah it can make a big difference due to volume change.

To all on the board,,I have worked in the refrigeration field for over 30 years,,and I'm not talkin' domestic refrigerators,,I'm talkin large commercial refrigeration racks and large industrial stuff with 600 hp Frick screws. I have seen my share of BAD piping and problems caused by poor design. I have been involed with solving flow isssues due to undersized lines , lift (head ), oversized lines, lines with to long of a run for the size of the pipe and on and on and on.

I've solved flow issues on refrigerant and water alike,,,and one thing has alway's remained a constant,,,

You can only flow the maximum flow as the smallest fitting in the system will allow. Period. I don't care what size line is connected to it. I'm still waiting for someone here to disprove this,,,,

Flame away,,,

 

[AndyBrown]

WW,

I supplied one hint and Charles has provided one half of the equation and Greg just added another little tidbit.

Maybe you need a little more help.

Here it is:

When the engine is running at low speed (rpm) the velocity of the fuel through the lines is low, therefore as Charles stated the resistance due to velocity is low.

When the engine speed is high the fuel velocity becomes high and therefore finds more resistance as the engine speed increases. Basicaly the fuel line is acting like a varible needle vavle that is directly proportional to the velocity of the fuel through the lines.

Our engines are constantly changing in rpm as the boat goes around the lake even though the carb opening may remain at full bore.

This means fuel delivery rate is constantly changing and it is NOT necessarily changing at the same proportion to the engine's needs.

This is just another hint to help you understand the first half of the equation.

WW wrote:

"You can only flow the maximum flow as the smallest fitting in the system will allow. Period. I don't care what size line is connected to it. I'm still waiting for someone here to disprove this,,,,"

WW, You are going on the assumption that the med. fuel line is in fact less restrictive than the needle valve. If the lines are short this is true. However, if the lines are long and a multiple plastic tank system is used as is found in many Scale hulls the resistance of several cross section changes adds up. ( mutiple brass tubes with sharp corners and so on.)

In this situation it is a high probability that the needle is NOT the most restrictive part of the system. Meaning your .015" hole and 1/2" pipe illustration , even though it is in fact true, is irrelavent.

Sweet dreams! B)

 

[John Knight]

I am not the wizard of knowledge that you all are debating with but it seems to be rather simple to me. Two sides of the equation:

Fuel delivery process

Fuel pressure process

Both equally important but seperate. I have a 60 rigger with a MAC 67 and a CMDi parabolic pipe (stinger drilled). Starts and runs like a dream every time.

Fuel delivery process - Simple to understand the principle. Large fuel lines, large capacity needle, large fuel lines in tank. Standard size lines will NOT deliver enough fuel above idle or coasting speed. Fuel starvation every time.

Fuel delivery process - The pipe pressure acts as the fuel pump for the engine. Found that I could use standard sized tubing for the pressure line. Was thinking that large fuel line means large pressure line but it did not come out that way. Not smart enough to understand the physics of why but it is.

That is what runs for me. May not be the same for all either. BOTH of these processes MUST be in synch with each other and properly balanced to work.

Andy - questions for you. Would going to extra large sized fuel tubing be of benefit or increase performance? What size do you and John use? What about the pressure line size?

 

[AndyBrown]

I am not the wizard of knowledge that you all are debating with but it seems to be rather simple to me. Two sides of the equation:

Fuel delivery process

Fuel pressure process

Both equally important but seperate. I have a 60 rigger with a MAC 67 and a CMDi parabolic pipe (stinger drilled). Starts and runs like a dream every time.

Fuel delivery process - Simple to understand the principle. Large fuel lines, large capacity needle, large fuel lines in tank. Standard size lines will NOT deliver enough fuel above idle or coasting speed. Fuel starvation every time.

Fuel delivery process - The pipe pressure acts as the fuel pump for the engine. Found that I could use standard sized tubing for the pressure line. Was thinking that large fuel line means large pressure line but it did not come out that way. Not smart enough to understand the physics of why but it is.

That is what runs for me. May not be the same for all either. BOTH of these processes MUST be in synch with each other and properly balanced to work.

Andy - questions for you. Would going to extra large sized fuel tubing be of benefit or increase performance? What size do you and John use? What about the pressure line size?

John,

The pressure is part of the equation too, but there is one more piece that goes with the pressure.

We use large for the fuel pick up and med. for pressure.

As I mentioned before John, there is a correct size. Bigger isn't always better. The correct SIZE MATTERS!

WW, You stated in two different posts that you did not Buy the fact that 1/8" lines don't supply enough for a .67.

I think now that several have posted their experience on here that the 1/8" is not big enough you are wanting to change your focus a little more toward "as long as the lines are big enough the needle is all that matters".

The needle will NEVER be all that matters.....even if we are dealing with a no pressure, 'draw' only system.

It does not matter where the needle is...in the carb or up stream in the line somewhere.

 

[Wasted wages]

WW,

I supplied one hint and Charles has provided one half of the equation and Greg just added another little tidbit.

Maybe you need a little more help.

Here it is:

When the engine is running at low speed (rpm) the velocity of the fuel through the lines is low, therefore as Charles stated the resistance due to velocity is low.

When the engine speed is high the fuel velocity becomes high and therefore finds more resistance as the engine speed increases. Basicaly the fuel line is acting like a varible needle vavle that is directly proportional to the velocity of the fuel through the lines.

Our engines are constantly changing in rpm as the boat goes around the lake even though the carb opening may remain at full bore.

This means fuel delivery rate is constantly changing and it is NOT necessarily changing at the same proportion to the engine's needs.

This is just another hint to help you understand the first half of the equation.

WW wrote:

"You can only flow the maximum flow as the smallest fitting in the system will allow. Period. I don't care what size line is connected to it. I'm still waiting for someone here to disprove this,,,,"

WW, You are going on the assumption that the med. fuel line is in fact less restrictive than the needle valve. If the lines are short this is true. However, if the lines are long and a multiple plastic tank system is used as is found in many Scale hulls the resistance of several cross section changes adds up. ( mutiple brass tubes with sharp corners and so on.)

In this situation it is a high probability that the needle is NOT the most restrictive part of the system. Meaning your .015" hole and 1/2" pipe illustration , even though it is in fact true, is irrelavent.

Sweet dreams! B)

Andy wrote,,

Meaning your .015" hole and 1/2" pipe illustration , even though it is in fact true, is irrelavent.

Thank you Andy,,,

I know my illustration is totally irrelivent to this conversation,,it just kinda took that turn somewhere in this post.

I never said that the theory applied to boats,,,only to the principals of fluid flow,you can only fit so much thru a fixed restriction,,regardless of the size of the pipe supplying it,,as long as it can support the max flow of the restriction.

And I know that length, bends, elbows, lift ,velocity, etc all factor into the mix,,,

Believe me,,I totally understand the entire scope of "the fuel line needs to be bigger to support the flow

thing,",I have even been down that road myself,, my purpose here was to wake up a few people to the possibility that bigger is not ALLWAY's better,,or needed.

besides,,being a newbie on the boards is allway's taken with a raised eyebrow or two,, :unsure:

and I just love the friendly wit and banter that everyone interjects into the conversation,,

sorry for waking everybody up :lol: :lol: :lol: :lol:

 

[AndyBrown]

WW,

I supplied one hint and Charles has provided one half of the equation and Greg just added another little tidbit.

Maybe you need a little more help.

Here it is:

When the engine is running at low speed (rpm) the velocity of the fuel through the lines is low, therefore as Charles stated the resistance due to velocity is low.

When the engine speed is high the fuel velocity becomes high and therefore finds more resistance as the engine speed increases. Basicaly the fuel line is acting like a varible needle vavle that is directly proportional to the velocity of the fuel through the lines.

Our engines are constantly changing in rpm as the boat goes around the lake even though the carb opening may remain at full bore.

This means fuel delivery rate is constantly changing and it is NOT necessarily changing at the same proportion to the engine's needs.

This is just another hint to help you understand the first half of the equation.

WW wrote:

"You can only flow the maximum flow as the smallest fitting in the system will allow. Period. I don't care what size line is connected to it. I'm still waiting for someone here to disprove this,,,,"

WW, You are going on the assumption that the med. fuel line is in fact less restrictive than the needle valve. If the lines are short this is true. However, if the lines are long and a multiple plastic tank system is used as is found in many Scale hulls the resistance of several cross section changes adds up. ( mutiple brass tubes with sharp corners and so on.)

In this situation it is a high probability that the needle is NOT the most restrictive part of the system. Meaning your .015" hole and 1/2" pipe illustration , even though it is in fact true, is irrelavent.

Sweet dreams! B)

Andy wrote,,

Meaning your .015" hole and 1/2" pipe illustration , even though it is in fact true, is irrelavent.

Thank you Andy,,,

I know my illustration is totally irrelivent to this conversation,,it just kinda took that turn somewhere in this post.

I never said that the theory applied to boats,,,only to the principals of fluid flow,you can only fit so much thru a fixed restriction,,regardless of the size of the pipe supplying it,,as long as it can support the max flow of the restriction.

And I know that length, bends, elbows, lift ,velocity, etc all factor into the mix,,,

Believe me,,I totally understand the entire scope of "the fuel line needs to be bigger to support the flow

thing,",I have even been down that road myself,, my purpose here was to wake up a few people to the possibility that bigger is not ALLWAY's better,,or needed.

besides,,being a newbie on the boards is allway's taken with a raised eyebrow or two,, :unsure:

and I just love the friendly wit and banter that everyone interjects into the conversation,,

sorry for waking everybody up :lol: :lol: :lol: :lol:

:lol: :lol: :lol: There you go WW! Just as I predicted earlier......there you go saying I Knew that!

Since you KNOW, go ahead and explain to us the other half of the equation.