For those of you who shut down your bikes by turning off the gas, how long do you have to let the bike run before it dies? I think that this is a good method in theory, but I've tried it and it seems to take forever (definitely longer than 5 minutes, after which I get impatient) for the bike to run out of gas. I've also tried shutting the fuel off about a mile from my house, to see if I could time it to shut down at a convenient time, but it just kept running. Just curious about how long it takes the rest of you, because I'm not going to be hanging around for half an hour every time I want to shut down my bike. I know that my petcock is functioning, because I can close it and leave the fuel line disconnected overnight without a drip. What gives?

I just wait for a minute or two while I'm opening the garage door and backing it in to the garage. I do the same for my Ironhead. I also get impatient. Plus I don't think the neighbors would appreciate either one of those loud bikes running for any longer.

All of my bikes take less than 20 seconds to shut down this way. This is also the way the manual says you should shut down. You have an issue somewhere, probably float valve. The petcock won't give you drips you can see. It will allow the extra gas to enter the crankcase via the intake valve and will ruin your oil and could cause bigger problems. If it takes 5 minutes, there is an issue. My guess is the float valve is bad and you are using all the gas in the fuel line between the carb and the tank. It also may be that the petcock leaks internally which is still giving some fuel after you turn it off.



My 68 XLCH and my 72 sprint will take a bit longer, being due to the carb float design. On the 68 and before sprint carbs, the float fills nearly the whole bowl, leaving little room for gas. This is why the float valve setting is so critical.

Basically, if it runs for 30 minutes after it is shut off, you are somehow getting a MPG rating of about 400 miles per gallon or something is faulty. I wish.

This post was last modified: 04-23-2010 12:53 PM by sprintdoc.

Ok this may be a dumb question, but with the petcock closed, if there is fuel in the line between the carb and the petcock, that should burn prior to the bike shutting off, shouldn't it? I mean, the idle circuit would continue to drain the float bowl, right up until there wasn't enough volumn to feed it (and it would sputter/die), at which point the float would be at its low point, consequently the float valve would be pretty much as open as it could be as it tries to refill the bowl. So any fuel upstream of the float valve (in the line up to the petcock) would pass through by design, yes?
I shut down my old two-stroke oil-injected dirtbikes this way (shutting the petcock) and it usually takes two or three minutes, depending on the bike. I know it drains the fuel line because the in-line filter is empty.

There are no dumb questions. You are exactly right. The fuel in the line does get burned. I guess a better explanation is that the petcock is letting some gas thru while the valve is open. Granted, it doesn't require much gas at idle. Just because it doesn't leak sometimes with the line off doesn't mean it doesn't at other times. A small difference in handle position changes things alot sometimes depending on the case, gaskets and spring washer conditions. Like you, I know it drains the line because I ran a clear hose for a while. Time to empty the carb, if the petcock works, is dependent on float bowl design (how much it actually holds - amount of space float takes up) and fuel hose length and diameter. Don't forget that if the float itself leaks, probably slowly, this will keep it idling quite a while as it does so.


Also your point is well taken. When I said "float valve" I was thinking of the whole float system, not just the valve.

This post was last modified: 04-23-2010 01:16 PM by sprintdoc.

pull you're float and needle valve-inspect rubber tip on valve,if it looks a little deformed,shoot some wd40 and massage it a little,does wonders,then with the float,bend it down just a little[very carefully],that way when the float goes up, it will put more pressure on needle valve,shuting the fuel before it flows over the bowl, that cured my problem anyhooo,extra 2 cents

where in the manual does it say to shut down this way?

Excellent question. The answer is that I really don't know. I do, however, know the following:

If I shut mine down that way, It'll (they) start with a single kick 90+ % of the time. If I shut the petcock off after the motor has died, I'll have to kick 10-15 times.

Also, have you ever opened up the float bowl on one of these? All that white powder that coats everything is caused by the reaction of aluminum to something, I am not sure what, but gas is the only thing in there. Water would, and sometimes is, readily apparent.

I have also removed the hose and left gas in the bowl and the results are the same.

I have cleaned aluminum parts with gas (cylinders and heads) and they have a different "dusty" look to them.

My personal belief is that the gas somehow reacts with the aluminum to reduce the octane level. In these carbs you have a small amount of gas in contact with a large surface contact area of aluminum.

In any case, it works. If I had to rub a rabbit's foot to get one kick starts, I'd do it if I got results. And I do get mostly one kick starts by using the "shut it off before" trick. It is the thing that makes the biggest difference.

Others have had the same results, but I don't know who told me about it first or who told them or where they read it.

If yours start great without doing it, awesome. Mine don't.

Thanks for all the replies and comments so far. One thing I don't understand... Other than the possibility of the floats leaking and holding fuel, how could the float/needle valve system have anything to do with the issue? My question was about running for a long time after the petcock was shut off. Of course the float is going to go down and the needle valve open as the fuel in the bowl is consumed. For what it's worth, the bike in question is a '73 SS350. I was doing some diagnostic work yesterday, and I disconnected the fuel line from the tank to let the bike run out of gas and shut down. It still took about 2 minutes, even though I held the RPMs around 2500 just to burn fuel faster.

On another note, I also found that the tach cable was in contact with the reserve lever for the petcock. It was not causing fuel to leak at the time, but I saw how it could potentially be an issue.

I don't think it does. The manuals always say that you should turn the fuel off when you shut down (as with all motorcycles), but I've never seen reference to letting the fuel burn up to shut down.