HPRE

Menu

Members Rides

Bullet 500


in
Members Rides

56 Guests, 3 Users (1 Hidden)
Sailorjohn, DanKearney
Welcome, Guest. Please login or register.
Did you miss your activation email?
October 21, 2014, 12:39:16 AM

Login with username, password and session length

 

Author Topic: fuel line vs. petcock size  (Read 374 times)

flyboy

  • Bulleteer
  • ***
  • Posts: 116
  • Karma: 0
  • Keepin the shiney side up
fuel line vs. petcock size
« on: April 24, 2014, 05:11:47 PM »
Gentlemen,
I've recently fitted a new TM32 flatslide, with Ace Air Canister and Alloy Manifold. (Thanks Tom, beautiful work!). It's jetted properly and running great. ('99 500ks)

Although, here's my issue. I've replaced the fuel line to the carb with 1/4" clear tube. Also placed in-line filter. The petcock nipple is smaller, probably 3/16". So, from the petcock to the filter, I placed smaller fuel line and worked it onto the 1/4" filter "in" side....then the 1/4 from filter to carb. (Proper size for the TM32).

I have not had any issues with fuel starvation, but have noticed (since fuel line is clear) that the 1/4" line does NOT stay full of fuel. In fact, it has gotten to the point where there is NO visible fuel in the line, but keeps running...obviously the bowl stayed full. Once parked, the line will partially fill back up again. I'm assuming that is due to the smaller sized petcock. I've read the issues of different sized petcock threads throughout the years of RE models and difficult to find the proper one to thread into the tank. Yes, it's threaded not the 2-bolt flange type. Also has what appears to be a step-down threaded adapter.

Question is....Is this most likely the problem, with the smaller petcock? OR, could it be due to the fact the fuel line has to run up/over the head steady, resulting in not having a direct gravity flow to the carb fuel inlet? I'm guessing it may be a combo of both??

As always, your advise is well appreciated.

Tim

flyboy

  • Bulleteer
  • ***
  • Posts: 116
  • Karma: 0
  • Keepin the shiney side up
Re: fuel line vs. petcock size
« Reply #1 on: April 27, 2014, 01:04:35 PM »
Does anyone use the clear fuel line? Have you ever noticed air in the line after the filter?...or, should it always stay completely full? See my issue below....

Thanks!

DanB

  • Grand Gearhead
  • *****
  • Posts: 500
  • Karma: 0
Re: fuel line vs. petcock size
« Reply #2 on: April 27, 2014, 02:50:01 PM »
Yes, I use a clear line and there is air in it after the filter.  I also have a Mikuni tm32 with Ace's inlet and have to run the line up and over. At the hump it's air, but I can watch the 'fill' into the carb. Haven't noticed a problem at all. May run it under then back up, but didn't like the angle of the line at the carb.
Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
2006 AVL Electra

tooseevee

  • Grand Gearhead
  • *****
  • Posts: 1214
  • Karma: 0
  • There Are No Truths Outside The Gates of Eden
Re: fuel line vs. petcock size
« Reply #3 on: April 27, 2014, 04:37:22 PM »
    I'll be facing the same thing when it comes time (?) to mount the new TM-32 on my '08 AVL. I've thought about it over the past few months, but it hasn't been top of the list.

     There are two choices:;

       (1) Put a short nipple of the small hose at the petcock & run large hose from there to the carb or;

        (2) Put a short nipple of large hose at the carb & run small hose from there all the way to the petcock.

        Comments on what might be better? Why?

         The other way would be a different petcock, but I ain't agoin' thataway.     
2008 ACE Head AVL Classic
1977 Shovelhead Hardtail Bobber

DanB

  • Grand Gearhead
  • *****
  • Posts: 500
  • Karma: 0
Re: fuel line vs. petcock size
« Reply #4 on: April 27, 2014, 05:59:13 PM »
Hi 2CV,

I did your option 1.  I'll upload a photo when I get the chance.  Also used a fuel filter with a 90 degree turn on it.

~Dan

Pic:
« Last Edit: April 28, 2014, 02:47:59 AM by DanB »
Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
2006 AVL Electra

flyboy

  • Bulleteer
  • ***
  • Posts: 116
  • Karma: 0
  • Keepin the shiney side up
Re: fuel line vs. petcock size
« Reply #5 on: April 28, 2014, 01:47:52 AM »
@ DanB - this is exactly what mine is like most of the time, air at the hump,  but never fuel starvation. I didn't know if this air was from a slower feed from the petcock due to the 3/16 size. As long as it keeps running, I guess.

I looked at running the line under, but would end up with a 180 at the top of the carb to come down to the inlet. Much less direct route.

Thanks!

tooseevee

  • Grand Gearhead
  • *****
  • Posts: 1214
  • Karma: 0
  • There Are No Truths Outside The Gates of Eden
Re: fuel line vs. petcock size
« Reply #6 on: April 28, 2014, 05:09:11 PM »
Hi 2CV,

I did your option 1.  I'll upload a photo when I get the chance.  Also used a fuel filter with a 90 degree turn on it.

~Dan

           I like running it the way you have it (both the way it's run & using the large hose all the way to the petcock). Looks good. I wouldn't choose to go down under the carb & then up again & into the inlet either.

            I was wondering this morning about possible fuel starvation at the float bowl due to the "small" petcock size compared to the "large" TM-32 size, but I don't believe it will ever be a problem. If you look down into the interior of the brass inlet fitting on the TM-32 you will see that a very short distance inside this fitting the I.D. decreases dramatically. I would say that it's no larger than the BS-29 inlet. So no matter what the size of your hose you're not going to get any more fuel into the bowl than this fitting (which only "appears" to be larger) allows.

           Ace, am I making any sense at all here? Have you looked at this? Have you built engines that outsuck the stock petcock? 

           I'm going to find a small glass fuel filter with the petcock size as an inlet & the large carb inlet size as the outlet. It will make the transition look like it's 'sposta be that way.
« Last Edit: April 28, 2014, 05:15:52 PM by tooseevee »
2008 ACE Head AVL Classic
1977 Shovelhead Hardtail Bobber

Arizoni

  • Grand Gearhead
  • *****
  • Posts: 4433
  • Karma: 0
  • "But it's a dry heat here in Arizona
Re: fuel line vs. petcock size
« Reply #7 on: April 28, 2014, 09:11:44 PM »
IMO, it would be almost impossible for the engine to use more fuel than a 3/16" (4.75mm) fitting would allow to flow thru it.
These fittings have a hole thru them that's about 3/32" (2.4mm) in diameter or larger.

Just imagine a 1 gallon (3.4 ltr) bucket of gasoline with a 3/32" (2.4mm) hole in the bottom.  (That's just a bit smaller than 1/8 of an inch (3.17mm) for those of you who don't work with 32th's.)

The amount of fuel pouring out of that hole is about the same amount that will flow thru a 3/16 inch fitting and there is just no way a 500cc engine can burn that much fuel.
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary

flyboy

  • Bulleteer
  • ***
  • Posts: 116
  • Karma: 0
  • Keepin the shiney side up
Re: fuel line vs. petcock size
« Reply #8 on: April 29, 2014, 04:28:53 AM »
Understood and agreed...no way can the fuel burn be beyond what a gravity feed stock petcock could deliver.

But, why the airlock? Albeit, not a true airlock, as fuel seems to pass at a sufficient rate, this is still an area of constant concern for me. I find myself looking at the fuel line at every traffic light...and continuing to see AIR at the hump.

Would a 1/4" petcock keep the fuel line "full"? Does this airlock not concern others, as it concerns me?

OR, perhaps I should simply go back to solid color fuel line.

tooseevee

  • Grand Gearhead
  • *****
  • Posts: 1214
  • Karma: 0
  • There Are No Truths Outside The Gates of Eden
Re: fuel line vs. petcock size
« Reply #9 on: April 29, 2014, 11:50:47 AM »
IMO, it would be almost impossible for the engine to use more fuel than a 3/16" (4.75mm) fitting would allow to flow thru it.
These fittings have a hole thru them that's about 3/32" (2.4mm) in diameter or larger.

Just imagine a 1 gallon (3.4 ltr) bucket of gasoline with a 3/32" (2.4mm) hole in the bottom.  (That's just a bit smaller than 1/8 of an inch (3.17mm) for those of you who don't work with 32th's.)

The amount of fuel pouring out of that hole is about the same amount that will flow thru a 3/16 inch fitting and there is just no way a 500cc engine can burn that much fuel.

          This has been my thought from the beginning & I think I said early on that I thought delivery from the petcock should never be a problem. But it was a good area of discussion, wasn't it?  :) It was during this discussion that I thought of finding a filter with both sizes on it to make the hose transition. Good idea, no?  ;)

         I also decided to go with clear hose after I saw DanB's picture. I probably would have stuck with black hose otherwise. So it's all good  ;D
« Last Edit: April 29, 2014, 11:55:09 AM by tooseevee »
2008 ACE Head AVL Classic
1977 Shovelhead Hardtail Bobber

tooseevee

  • Grand Gearhead
  • *****
  • Posts: 1214
  • Karma: 0
  • There Are No Truths Outside The Gates of Eden
Re: fuel line vs. petcock size
« Reply #10 on: April 29, 2014, 12:07:01 PM »
Understood and agreed...no way can the fuel burn be beyond what a gravity feed stock petcock could deliver.

But, why the airlock? Albeit, not a true airlock, as fuel seems to pass at a sufficient rate, this is still an area of constant concern for me. I find myself looking at the fuel line at every traffic light...and continuing to see AIR at the hump.

Would a 1/4" petcock keep the fuel line "full"? Does this airlock not concern others, as it concerns me?

OR, perhaps I should simply go back to solid color fuel line.

            I can't explain the physics, but it's more or less an illusion (not really, but you know what I mean). I've seen it on many bikes over the years & they never run out of fuel.

             There are "some" engines that will outsuck "some" stock petcocks. That's how Pingels became famous, I believe. And, boy, do you PAY for them. But not our little RE engines.
2008 ACE Head AVL Classic
1977 Shovelhead Hardtail Bobber

ace.cafe

  • Grand Gearhead
  • *****
  • Posts: 8515
  • Karma: 0
  • World leaders in racing or performance Bullets
Re: fuel line vs. petcock size
« Reply #11 on: April 29, 2014, 01:09:30 PM »
As long as the fuel delivery system passages are bigger than the main jet orifice, it should never have feed problems.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

Please visit my new website:
http://groups.yahoo.com/neo/groups/AcePerformanceBullets/info

Arizoni

  • Grand Gearhead
  • *****
  • Posts: 4433
  • Karma: 0
  • "But it's a dry heat here in Arizona
Re: fuel line vs. petcock size
« Reply #12 on: April 29, 2014, 06:58:38 PM »
If the hose from the fuel cock first goes down and then has to go upward over something like the head steady and then down to the carb, any air bubble in the high area of the line will continue to rest at the high point of the tube.

The only thing that could move it downward would be a massive flow of fuel with enough velocity to force the air downward and out of the line.  Of course the small amount of fuel that is actually flowing thru the line isn't enough to do this.

I'm sure the fuel level on the fuel cock side of the "hump" in the line where the line goes up over the head steady is at the same level as the  lowest height of the inside of the tube where it just starts to go back downhill towards the carb.
There is probably another area just below the fuel cock that looks like it has air in it with the top of the fuel appearing at the same level.

The reason the carb is getting fuel in spite of these air bubbles is because the small amount of fuel being consumed is trickling down from the fuel cock to the first low area in the tube.
It then flows thru to the low level of the tube at the high point and then trickles down to the carb where it flows thru the float chamber valve into the carb.

Confusing, but that's the best explanation I can give.

If some of the transparent tubing is available use it to make a downward loop which climbs up to a upward loop which again turns downward.
Pour some water into the tube and notice how the low area fills with water but the high area of the tube and the exit seem to be empty.
Pour some more water into the tube and notice that although the water does flow thru the tube, the air "bubble" at the top of the loop remains "empty".
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary

tooseevee

  • Grand Gearhead
  • *****
  • Posts: 1214
  • Karma: 0
  • There Are No Truths Outside The Gates of Eden
Re: fuel line vs. petcock size
« Reply #13 on: April 29, 2014, 11:37:49 PM »
If the hose from the fuel cock first goes down and then has to go upward over something like the head steady and then down to the carb, any air bubble in the high area of the line will continue to rest at the high point of the tube.

The only thing that could move it downward would be a massive flow of fuel with enough velocity to force the air downward and out of the line.  Of course the small amount of fuel that is actually flowing thru the line isn't enough to do this.

I'm sure the fuel level on the fuel cock side of the "hump" in the line where the line goes up over the head steady is at the same level as the  lowest height of the inside of the tube where it just starts to go back downhill towards the carb.
There is probably another area just below the fuel cock that looks like it has air in it with the top of the fuel appearing at the same level.

The reason the carb is getting fuel in spite of these air bubbles is because the small amount of fuel being consumed is trickling down from the fuel cock to the first low area in the tube.
It then flows thru to the low level of the tube at the high point and then trickles down to the carb where it flows thru the float chamber valve into the carb.

Confusing, but that's the best explanation I can give.

If some of the transparent tubing is available use it to make a downward loop which climbs up to a upward loop which again turns downward.
Pour some water into the tube and notice how the low area fills with water but the high area of the tube and the exit seem to be empty.
Pour some more water into the tube and notice that although the water does flow thru the tube, the air "bubble" at the top of the loop remains "empty".

              Eureka!!   ;D
2008 ACE Head AVL Classic
1977 Shovelhead Hardtail Bobber