Dan-Marc Fuel Shutoff 1/8" in and out...kinda small?

[valknomad]

Wanting to order the Dan-Marc Fuel Shut-off (as described in Mark-T),  
part# 79-AFC11112, noted that the specs say 1/8" in & out female threads.
That seems very small "restriction".   The fuel line ID (inside dia. is approx 1/4" - 5/16").    Any thoughts on the subject.
I know 1/8" barbed x male fittings are significantly smaller.  ( Think "friction loss" and "gravity feed" x 6 thirsty carbs).

[Louis Durocher]

This the one i have on my I/S and works fine. No starving

[BonS]

The most restrictive part of the Dan Marc is the internal orifice. This little hole is where the solenoid plunger seals off fuel flow when deenergized and where fuel flows through when energized. The Model 111 has a 0.156" diameter orifice so the fuel line is 60% larger than a 1/4" ID hose and 100% larger than a 5/16" ID. In short: no problem.

[Jetflyer]

I have this unit. She gets all the gas she ever demands in all situations!

[pago cruiser]

I have seen some other threads on this topic with folks using it with no problems; that said, I believe the reduced sizing disparity is real.  I have a Model 111 in my hands, and per the AFC website it has the same dimensions. From the AFC website: "Orifice size .156" for adequate flow of all fuels".  That ...appears to be the case by testimonials, but ... here's my $0.02.

0.156" diameter orifice = an area of 0.019 in sq.
0.25" diameter line = an area of 0.049 in. sq.

BonS - I don't understand your response "...the fuel line is 60% larger than a 1/4" ID hose and 100% larger than a 5/16" ID."

My guess is that the about 2.5X smaller orifice, with a length of about an inch, while appearing significant, just isn't.  The resulting pressure drop across that short length is (based upon others comments) not enough to affect flow noticeably with the members who have reported on it.  

I'd love to hear if a heavily loaded Valk (say with a sidecar, rider, wife, canine, tools, and a weeks worth of gear), doing 70 over the Grapevine in CA in July getting 20MPG would have any fuel starvation issues.  Maybe, maybe not - I'll let you know in July.

But I am pretty sure than if you made the entire fuel line 0.156" you may have issues at higher rpm's draining fuel from the float bowls faster that it could gravity fill.  

[BonS]

0.156" diameter orifice = an area of 0.019 in sq.
0.25" diameter line = an area of 0.049 in. sq.

You're certainly right that a 0.25" orifice is way larger than the 0.156". There is certainly no harm in using a fuel valve with this larger orifice (as some have done).

BonS - I don't understand your response "...the fuel line is 60% larger than a 1/4" ID hose and 100% larger than a 5/16" ID."

Yeah, that's not a very clear, or perhaps well thought out comment. I was trying to say to the OP that the fuel line is considerably bigger than the orifice in any case. I used the same OEM inlet and outlet fuel line diameter with my model 111 install.

I'd love to hear if a heavily loaded Valk (say with a sidecar, rider, wife, canine, tools, and a weeks worth of gear), doing 70 over the Grapevine in CA in July getting 20MPG would have any fuel starvation issues.  Maybe, maybe not - I'll let you know in July.

I've been running the Model 111 for many years. I've never had any issue whatsoever unless I had a fuel filter or kinked fuel line. Last Summer, I ran my Interstate two-up with a trailer, into a very strong Kansas headwind and crosswind, on a very hot day, at around 80 mph. I got around 22-24 mpg, as I recall, and never had any fuel flow issues.

But I am pretty sure than if you made the entire fuel line 0.156" you may have issues at higher rpm's draining fuel from the float bowls faster that it could gravity fill.  

You certainly may. There is even a difference between a thin and thick orifice plates with the same diameter hole let alone a long length of fuel line of that diameter. It has to do with the drag of the fuel along the side walls of the hose. Technically, the flow velocity at the wall is zero due to frictional drag.

[pago cruiser]

BonS
Thanks for the very detailed reply.
Yours is the first post I have seen on this indicating no problem under a pretty good load.
Good to hear.

[valknomad]

Thanks for the replies.   I went ahead and ordered the Dan-Marc Shut-off.
(I'm in the middle of Winter / Carb Maint., Slow Jets..., so a good time to do the Fuel Shut-off.