Why is is bad to leave Fuel supply to carb in On position when not using the bike?

Dustin Schings /

Normally I wouldn't question this at all, as I wouldn't care. But I just got an FA50 and it has a vacuum activated petcock with RUN, RES, and PRIME. The only position that works is Prime (which is just a constant flow to carb, much like "ON" position on normal petcocks).

I am just wondering if there is a reason I cannot leave it on prime? The float needle in the carb seems to be doing a good enough job of stopping fuel flow once bowl is full.

I have also forgotten to shut off the petcock on normal, non-vacuum activated petcocks and I dont recall it really being a problem then I went to start the bike the next day.

Is there a reason to rebuild this FA50 petcock with new Orings and diaphram or just leave it in PRIME permanently?

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

i always turn the fuel off and let the bike run its course then put it away

i like to watch the fuel flow when i get back on it, although i think if left for a good while the jet will get gummed up

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

A lot of carbs leak so if you leave the petcock on it will leak all of your gas onto your floor. If your carb doesn't leak you shouldn't have a problem.

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

Probably Fred /

I like to run the bike a little bit with the petcock on off, no need drain the carb bowl all the way but just run it down a little bit to relieve the pressure on the rubber tip of the float needle, this works especially good with Bing carburetors to keep them it leaking. Having the float soaking all the time in the gas the float can get gas-logged, again Bing carb float, other brand carbs other floats and needles not so much.

So If for more then a few days a week or so then ya I run the bowl dry or remove the bowl. On a Bing I can unscrew it while on the bike.

Daily driver bike I do like what I said like above I turn the petcock to off as I'm coming down my street to drain it some.

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

Dustin Schings /

Thanks for all the input so quickly! No leaks right now. I will rebuild the petcock or replace (somehow) with a standard one sometime soon.

May replace the whole carb soon though as well. The pilot jet is stripped in there and cannot be unscrewed anymore. Same goes for the drain screw on the bowl.. It presents no problems now, but I would rather replace it before it causes any issues.

Is there a cheap and easy carb I can throw on there with minimal to no other modifications needed? The only thing that I see different from my other carbs on my Hondas (aside from lack of vacuum line since this isn't auto choke) is that it has two fuel feeds. What is the second one for? Will I need a carb with two fuel inputs as well or what?

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

yeah. your petcock is bust OR you have a vacuum leak on the signal to the petcock. if that's the case you have an airleak and that should be taken care of ASAP.

the prime just bypasses it yeah. it's so if you leave the bike awhile and the gas evaporates outta the carb you don't need the motor turning over to actuate the vacuum petcock until it fills. it really does prime it.

but yea as long as the float is OK in the carb its OK to stay on "prime"

if the lines or the float leak any you can wind up with puddles or worse, a good flooded cylinder.

once I hydrolocked my bike cuz the gas was left on and it slow leak filled the cylinder. it wouldn't turn over so I took the plug out and turned it over to push the excess gas out. unfortunately the bike was still set to run so when I turned it over it sparked, as a huge gush of gas shot outta the cylinder, and the whole bike burst into flames.

I saved it, but wow. OOPS!

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

2 fuel feeds? do you mean 2 fuel lines to the petcock? if so then one just draws from the bottom and one higher up in the tank for normal vs reserve.

if there appear to be 2 fuel lines to the carb itself, one probably isn't fuel, either oil injection or the vacuum to drive the petcock, or overflow etc.

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

Dustin Schings /

hmm, here are the fuel lines as they appear in the service guide, as well as the oil lines. It appears to match the setup on my carb so I think they are ran correctly.

fuellines.JPG
oilline.JPG

As you can see, the petcock appears to have two fuel lines going to it (I cannot see on my bike, it is hidden) and then two lines from different spots on the petcock down to two different spots in the carb. (You can see the two fuel lines in the second pic (for the oil) but they are cropped off after an inch or so in the pic.

The oil resevour feeds oil to pump, them pump sends it into the engine, so I don't think it ever hits the carb on this bike.

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

Try taking the vacuum line off the carb and lightly suck on the end while turning the petcock to on and reserve. That'll tell you if the diaphragm is shot or something is clogged up. If it's good you'll hear the lightest of thunks as it moves and fuel will flow. If it doesn't flow then take the petcock apart and give everything a good cleaning. Change the hose as well and make sure there isn't an air leak at the nipples.

If the diaphragm is shot your screwed. Suzuki never sold a rebuild kit as they expected you to just replace the entire unit. You can rig up an aftermarket petcock with on, off, and reserve settings but it honestly it'll look like cobbled together crap.

If you really need an on/off switch then get one for a lawn mower and put it downstream of the original petcock.

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

Dustin Schings /

> If you really need an on/off switch then get one for a lawn mower and put it downstream of the original petcock.

This is what I think I will do. Leave it in prime and just put a small valve below it. Thanks for the suggestion as the replacement is like $80!

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

does fuel flow out of both of those "fuel lines"? My guess is that the line closest to the intake is just a vacuum line that gives the signal vacuum pulse that runs the petal valve diaphragm in the petcock. and only the back one is actual fuel flow.

the 2 going into the petcock from the tank are reserve and normal.

I often use in-line petcocks if the tank ones are funky. theyre super cheap on ebay amazon or for like an extra few bucks you can go pick one up today in the small engine section of any hardware or autoparts store.

Re: Why is is bad to leave Fuel supply to carb in On position when not using the bike?

Dustin Schings /

> for like an extra few bucks you can go pick one up today in the small engine section of any hardware or autoparts store.

me, after work. thanks!

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account