MAC Troubleshooting

[brandonclan]

I would be interested in a used ab 67 pipe for my greenhead. Let me know!!

Dan

 

[Douglas P Shepherd]

I would be interested in a used ab 67 pipe for my greenhead. Let me know!!

Dan

Allan, Been there and done that also. Tried the .510 bore tried the OS 9B. As Brian said and I have said alot of time and money was spent here. I said enough here, enjoy!

 

[Don Ferrette]

I don't know which is more amusing, some of the "answers" or all the people trying to get Russell's AB pipe.

Russ, we've talked, you know what to do.

 

[Brian Schymik]

I had first dibs on it, Don......

Brian

 

[Don Ferrette]

I had first dibs on it, Don......

Brian

And I'm sure you still do. I have 2 on the parts wall. And no they are not currently for sale.

 

[Dan_Cousin]

That black AB pipe Russell is running is a special double stamp version. Very Rare!!!!!

Gotta be worth at least $300 right Russell?

 

[Wasted wages]

Maybe I'm missing something here,,,,why would larger fuel lines be needed,,,

is the needle or spray bar 5/32nds or larger ?

I would think that the smallest restriction ( the needle ) in the fuel system would dictate line flow carrying capacity---In other words, at WOT the needle becomes the most restrictive part of the fuel system,,

as long as the rest of the sytem is bigger or can carry at least the amount required by the restriction

larger lines do nothing,,,

I just ain't buyin' it,,,,

 

[P THOMAS]

Maybe I'm missing something here,,,,why would larger fuel lines be needed,,,

is the needle or spray bar 5/32nds or larger ?

I would think that the smallest restriction ( the needle ) in the fuel system would dictate line flow carrying capacity---In other words, at WOT the needle becomes the most restrictive part of the fuel system,,

as long as the rest of the sytem is bigger or can carry at least the amount required by the restriction

larger lines do nothing,,,

I just ain't buyin' it,,,,

When I switched from a picco 67 to a Mac 67 in a mono, it was starving for fuel. I removed the needle from the line and started it up with no needle it sounded real rich but when running at open throttle on the lake it would still go lean and die. Changed the brass tube pickups to 5/32 tube and larger lines and then the needle valve had control of the fuel flow agian.

Belive it or not Ripley

 

[Russell Bear]

I don't know which is more amusing, some of the "answers" or all the people trying to get Russell's AB pipe.

Russ, we've talked, you know what to do.

Yep, got it setup to go test.

That black AB pipe Russell is running is a special double stamp version. Very Rare!!!!!

Gotta be worth at least $300 right Russell?

That's what I was thinking. It's one of a kind for sure.

I had first dibs on it, Don......

Brian

Brian, I happen to have a greenhead in a Roadrunner extreme. If I need to go to the parabolic (Got one reserved at CMD today), I will take it out of the scale and give it a try on the RR. I'll let ya know though.

Thanks........

 

[Wasted wages]

Maybe I'm missing something here,,,,why would larger fuel lines be needed,,,

is the needle or spray bar 5/32nds or larger ?

I would think that the smallest restriction ( the needle ) in the fuel system would dictate line flow carrying capacity---In other words, at WOT the needle becomes the most restrictive part of the fuel system,,

as long as the rest of the sytem is bigger or can carry at least the amount required by the restriction

larger lines do nothing,,,

I just ain't buyin' it,,,,

When I switched from a picco 67 to a Mac 67 in a mono, it was starving for fuel. I removed the needle from the line and started it up with no needle it sounded real rich but when running at open throttle on the lake it would still go lean and die. Changed the brass pickups to 5/32 id and larger lines and then the needle valve had control of the fuel flow agian.

Belive it or not Ripley

This would have to assume several things,,that the spray bar,needle valve were all larger than the fuel pick ups or fuel lines and that the engine can consume the maximum amount of fuel suppled by the tank pick up and hoses prior to you changing them out.

what size were the lines prior to changing them ?

let's assume 1/8 inch,,your telling me that a .67 motor can consume a stream of fuel out of an 1/8 line under pipe pressure with no needle and still go lean ??

still ain't buyin' it.

 

[Don Ferrette]

This would have to assume several things,,that the spray bar,needle valve were all larger than the fuel pick ups or fuel lines

Nope, that's not it at all.

and that the engine can consume the maximum amount of fuel suppled by the tank pick up and hoses prior to you changing them out.

Yup, they sure can. Think along the lines of on demand volume not needle setting. For example, take 2 identical needles set at exactly the same rate of flow. Now one will have 1/8" lines and one has 5/32" lines. Which one will deliver more volume at the same needle setting & be capable of maintaining that volume? :blink:

And BTW wasted wages- do you have a regular name you can share with us?

 

[SayMikey]

This would have to assume several things,,that the spray bar,needle valve were all larger than the fuel pick ups or fuel lines

Nope, that's not it at all.

and that the engine can consume the maximum amount of fuel suppled by the tank pick up and hoses prior to you changing them out.

Yup, they sure can. Think along the lines of on demand volume not needle setting. For example, take 2 identical needles set at exactly the same rate of flow. Now one will have 1/8" lines and one has 5/32" lines. Which one will deliver more volume at the same needle setting & be capable of maintaining that volume? :blink:

KEY WORD VOLUME a cars fuel pump can deliver the proper pressure but fail a volume test EG starve for fuel same here......Mike

 

[AndyBrown]

There are three problems here.

#1. The prop is too big and #2. the pipe too short for the 15.5 pound boat and 45/18% fuel combo.

I would recommend the X455/3 with stock cup or with reduced cup. One of the very fastest Scales in Southern Calif. has a MAC pulling that prop. That's with 60% nitro, so yes the MAC likes to rev. The AB 67 is a high rev pipe too. I would say that most who found better results with other pipes were just determined to turn big props. The Brown 67 parabolic pipe does make more torque solving this issue for some racers.

Pull the pipe out to the 12" to 12.5" mark.

#3. For this time of year a .430" stinger bushing is needed in the AB 67 pipe.

The stock .470" bore stinger will never deliver enough pressure to the tank, and therefor fuel to the carb, to match all of the high density air going through the .550" carb on the top end. And yes the 1/8" brass tube and med. fuel lines make the situation worse. That is why your idle on the beach is so rich and the engine is detonating on the top end.

Wasted wages,

Some things do not follow the rules of simple logic.

 

[Russell Bear]

There are three problems here.

#1. The prop is too big and #2. the pipe too short for the 15.5 pound boat and 45/18% fuel combo.

I would recommend the X455/3 with stock cup or with reduced cup. One of the very fastest Scales in Southern Calif. has a MAC pulling that prop. That's with 60% nitro, so yes the MAC likes to rev. The AB 67 is a high rev pipe too. I would say that most who found better results with other pipes were just determined to turn big props. The Brown 67 parabolic pipe does make more torque solving this issue for some racers.

Pull the pipe out to the 12" to 12.5" mark.

#3. For this time of year a .430" stinger bushing is needed in the AB 67 pipe.

The stock .470" bore stinger will never deliver enough pressure to the tank, and therefor fuel to the carb, to match all of the high density air going through the .550" carb on the top end. And yes the 1/8" brass tube and med. fuel lines make the situation worse. That is why your idle on the beach is so rich and the engine is detonating on the top end.

Wasted wages,

Some things do not follow the rules of simple logic.

Thanks Andy. Now I'm really lost, getting conflicting fixes. Sounds like I still have some trial and error testing to do. I'll play with the pipe length and stinger bushings.

BTW, the fuel tanks were both built with 5/32 brass and the large fuel tubing from the beginning.

 

[AndyBrown]

The tank part sounds good Russell, so now just do the pipe and prop thing and you'll be going good.

No real magic, just a matter of getting all the ducks lined up.

Oh yea ....and pull the glow plug wire out. That will help your idle and bottom end throttle response too. B)

 

[Russell Bear]

The tank part sounds good Russell, so now just do the pipe and prop thing and you'll be going good.

No real magic, just a matter of getting all the ducks lined up.

Oh yea ....and pull the glow plug wire out. That will help your idle and bottom end throttle response too. B)

Cool. Thanks, be calling tomorrow for the bushings......

 

[Wasted wages]

This would have to assume several things,,that the spray bar,needle valve were all larger than the fuel pick ups or fuel lines

Nope, that's not it at all.

and that the engine can consume the maximum amount of fuel suppled by the tank pick up and hoses prior to you changing them out.

Yup, they sure can. Think along the lines of on demand volume not needle setting. For example, take 2 identical needles set at exactly the same rate of flow. Now one will have 1/8" lines and one has 5/32" lines. Which one will deliver more volume at the same needle setting & be capable of maintaining that volume? :blink:

KEY WORD VOLUME a cars fuel pump can deliver the proper pressure but fail a volume test EG starve for fuel same here......Mike

Still ain't buyin it,,,

here's a hypothetical,,,

take your 2 identical needle valves at identical settings ,,both can flow (for the sake of arguement) 1.0 gallon per min of 50 % @ 14.7 psi (atmospheric ) 70 deg F and that the 1/8" fuel line is capable of delivering 1.5 GPM. It would be safe to say that the needle is the "restrictive " part of the system. All things remaining equal anything "upstream" of the valve makes absolutly no difference as long as the line that supplies the needle stays the same size or larger.

You could hook it up to a 6" line and a water tower,,, it's only going to flow the amount the needle will let pass. 1 GPM. period.

now if you change the pressure across the needle ,or lower the temperature of the fuel the flow rate will change and thus the volume will increase.( this is not simple logic Andy,, this is the law of physics )

now,, at idle there is not a whole lot of negative ( suction) being drawn across the venturi or needle.

and the needle does not play in to the picture,but as the throttle is opened to WOT the pressure difference

across the needle increases and a higher flow volume occurs. the point is,,as long as the line can carry the amount of fuel up to the maximun flow rate of the needle then anything bigger is not needed. Period.

In reality what is happening is the entire system is not capable of sustaianing the volume of fuel at WOT due to pressure drop and the fuel is " flashing " or creating bubbles in the fuel mixture and the engine goes lean.

this was proven when the needle valve was removed from the line and the line was connected straight to the carb and the engine still went lean.

at this point it is safe to say that the needle valve was NOT the most restrictive point in the fuel system,,

so something else must be,,,increasing the line sizes allows the fuel to flow below it's flash point and a solid stream of fuel is delivered to the needle. Another method to correct this problem would be to add additional pipe pressure to the tank thus increasing the flow across the needle but this has it's practical limits.

I will agree to this explanation,,, but I still have a hard time believing that a .67 uses more fuel than a 1/8 ' line can supply,

 

[Don Ferrette]

Guess you're the expert then. Still want to know who you are.......

 

[SayMikey]

Guess you're the expert then. Still want to know who you are.......

Hey Don got your BEER GOGGLES ON thats the POPE......ha ha ha Mike

 

[Don Ferrette]

Guess you're the expert then. Still want to know who you are.......

Hey Don got your BEER GOGGLES ON thats the POPE......ha ha ha Mike

Guess since he's so good on this fuel flow subject we need him to bless all our needle settings.