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Author Topic: Carb question  (Read 1088 times)

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Online jacksoni

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Carb question
« on: March 15, 2020, 10:53:25 AM »
My question is generated from Mikuni carbs but may apply to others. Two stroke application. There are a couple of vent lines to the float bowl or somewhere that if the carb is other than upright will leak fuel. Besides not being plastic, how are these handled? Seems to me could be a safety issue for fire if fuel spills. I don't see this addressed in the SCTA rule book. BMST may be different I suppose. Suggestions? Advice?
Thanks.
Jack Iliff
 G/BGS-250.235 1987
 G/GC- 176.245  2018
 G/GMS-182.144 2019

Offline Doc B.

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Re: Carb question
« Reply #1 on: March 15, 2020, 12:10:20 PM »
As far as I have experienced with my bike at BMST the past couple of years, vent lines are not considered part of the plumbing that needs to be firesleeved. All the hose between fuel tank and carbs does need firesleeve secured with hose clamps (not safety wire), or can be plumbed with stainless braided fuel hose.

You may wish to run your vent lines into a catch can (though this is not a requirement as far as I know). Gen-Xers made the empty Red Bull can the stylish choice years ago. Considering the average age of us land speed racers, perhaps an empty Ensure can would be more appropriate.

Online jacksoni

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Re: Carb question
« Reply #2 on: March 15, 2020, 12:46:59 PM »
Thanks. My application happens to be in a car and though I don't plan to be upside down, things that easily might leak fuel do not appeal to me. Had a fire at 260 or so once and don't wish to repeat the experience (not going that fast these days but you get my drift....  :oops:
Jack Iliff
 G/BGS-250.235 1987
 G/GC- 176.245  2018
 G/GMS-182.144 2019

Offline Doc B.

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Re: Carb question
« Reply #3 on: March 15, 2020, 04:48:17 PM »
You might want to move this inquiry to a board for one of the events that runs cars. BMST is a motorcycle only event and the AMA/FIM rules wouldn't really apply to your application.

Online jacksoni

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Re: Carb question
« Reply #4 on: March 15, 2020, 05:37:20 PM »
Thanks, I appreciate and understand the thought. My thinking was the bike guys likely would have more experience with the type of carb and these issues and could offer some advice or insight. My concern is arriving at inspection and have some one say, "no way jose", with those carbs that might leak. Just trying to figure the options before that happens....Anyway, thanks Doc.
Jack Iliff
 G/BGS-250.235 1987
 G/GC- 176.245  2018
 G/GMS-182.144 2019

Offline mc2032

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Re: Carb question
« Reply #5 on: March 15, 2020, 08:09:31 PM »
Jacksoni, page 45, 3.I and 3.I.1 lists the fuel system and fuel shut off req's.  As I read the rules, car fuel lines have to be separate from the driver's compartment so do not require fire sleeve or other fire protection (bike rules say any un-valved line has to be fire protected as they are usually really really close the rider where leaks are a bad thing).  As for vents and/or vent lines off the carb, I would route them to a small catch can equal to the volume of the bowl(s) and fuel line from the shut off even thought not specifically called out in the rules.

Here is an older picture of the right side of the bike.  remote petcock at the tank, fuel line down to a lower pressure facet/purolator fuel pump feeding a puck style regulator.  From there it dead heads at the carb.  My best friend is sponsored by Gates so I have access to fire sleeve.  The carb vents to the atmosphere in two places, only one has a hose and it's not sleeved.
« Last Edit: March 15, 2020, 08:27:25 PM by mc2032 »
#1032 1350 A-PBG & F, Bunches of passes down the salt and quit counting.

Offline panic

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Re: Carb question
« Reply #6 on: March 16, 2020, 08:14:16 AM »
a small catch can equal to the volume of the bowl(s)

Since the needle & seat will open when the carb is inverted, "equal to the volume of the fuel tank"

Offline Lemming Motors

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Re: Carb question
« Reply #7 on: March 16, 2020, 08:31:31 AM »
Gen-Xers made the empty Red Bull can the stylish choice years ago. Considering the average age of us land speed racers, perhaps an empty Ensure can would be more appropriate.

I can so relate to that but not for the reason implied.  :laugh:
There is a canoe marathon event (125 miles) in the UK at Easter - starts on a canal, joins the Thames and finishes in London (cancelled this year) and after a lot of research several of us have competed doing the entire thing on Ensure as the only source of nutrition - easier to digest, quick to take on at portages, reduces the general fluid intake requirements. The reference brought bake memories - luckily fatigue dulls pain.
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Online jacksoni

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Re: Carb question
« Reply #8 on: March 16, 2020, 08:50:53 AM »
a small catch can equal to the volume of the bowl(s)

Since the needle & seat will open when the carb is inverted, "equal to the volume of the fuel tank"
well if my systems work with inertial switch to shut off the pump and actually I have a solenoid valve in the line also on that switch hopefully just the volume of the lines and carbs. Still a bunch of fuel. I appreciate the thought Mr Panic. Always enjoy your insight.
A catch can would require its own vent designed not to spill if inverted. There are carbs available that don't have this vent feature which might work but I have the current ones and others are very pricey. Then again, my neck or skin as the case may be.  muutt
Jack Iliff
 G/BGS-250.235 1987
 G/GC- 176.245  2018
 G/GMS-182.144 2019

Offline Doc B.

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Re: Carb question
« Reply #9 on: March 16, 2020, 11:31:33 AM »
It seems like you might be headed toward plumbing the vents into a fuel tank return line with a check valve or something along those lines (pun intended). Not knowing the relationship of the fuel tank to the carbs - perhaps the tank is below the carbs on your car? Not going to work on a bike with the tank above the carbs.

Online jacksoni

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Re: Carb question
« Reply #10 on: March 16, 2020, 11:46:23 AM »
It seems like you might be headed toward plumbing the vents into a fuel tank return line with a check valve or something along those lines (pun intended). Not knowing the relationship of the fuel tank to the carbs - perhaps the tank is below the carbs on your car? Not going to work on a bike with the tank above the carbs.
That could work. Tank in the  back of the car but originally was set up for EFI so there is a bung and I have the old line.  Only question is would the carbs object to having the vent so far away and possibly restricted. Will think on that one but anyway, good idea. Thanks.
Jack Iliff
 G/BGS-250.235 1987
 G/GC- 176.245  2018
 G/GMS-182.144 2019