Gas cap vent - where is it?

[Guest]

I've been getting some hesitation at highway speeds at about 4.5 - 5.5 while cruising. Could be too lean, but after searching the forums, sounds like I could have an obstructed vent, either carbs vents or gas cap vents.

So I just looked at my carbs vent lines, they look okay. However I tried inspecting my gas cap and I cannot see or find where the heck the vent would be.

it's an 82 1100EZ ....

any help on this one?

[salty_monk]

IT vents up through the keyhole. If you turn you cap over & remove the screws in the back you'll be able to clean it up inside.

Dan

[maro]

IT vents up through the keyhole. If you turn you cap over & remove the screws in the back you'll be able to clean it up inside.

Dan

AAAHHHHH.. thank you DAN! I'm praying to the gs carb gods that it is indeed clogged!!

[salty_monk]

I very much doubt it's your issue from the symptoms you describe but it might be.... You would think it would affect you all the time. I guess it might be partially blocked & the constant RPM never lets it catch up....

Could be a multitude of other things too (air leak, clogged jet, clogged filter etc)

Dan

[maro]

Could be a multitude of other things too (air leak, clogged jet, clogged filter etc)

Dan

uhhg, don't remind me. I'm gonna rule out the easy sh$t first.

[tone]

A quick way to test if the cap is venting is to run the bike (carefully) up the road with the cap off or undone, do it with a small amount of fuel in the tank to avoid spillage

[maro]

A quick way to test if the cap is venting is to run the bike (carefully) up the road with the cap off or undone, do it with a small amount of fuel in the tank to avoid spillage

what is this going to show me. My issue with the hesitation I am experiencing arrives when cruising highway speed between 4.5-5.5

[MacGyver]

I discovered my gas cap was venting nicely when I had the tank off the bike and drained the gas out of it. Even with the tank on the bike you can check your flow and hear the vent pulling air into the tank if you have a spare piece of tubing around. Disconnect the main line, connect spare. Get a bucket/container (about 1 gal/4 l. should do) and set the petcock to prime. In short order you should hear air being sucked in through the cap and there should be no slow down in flow.

Of course, if you do not have a petcock with a prime position, that sucks, and all bets are off.

Hope that helps eliminate the gas tank.

[maro]

Here's a dumb questions. Would have my tank bag that sits OVER the cap prevent air from venting. Since it looks like my cap keyhole is the vent?

[Sandy]

This is a quick easy test to do if you have a spare piece of gas line. Don't pull the one off the carbs, you might not get it back on.

OK, I did this test with my tank and got a flow of 1 quart in 40 seconds with the petcock on prime and the same results with the tap set to on and reserve while sucking on the vacuum line. The test was also the same with or without the gas cap installed to see if the cap vent was working. To simulate a plugged vent I sealed the fuel inlet with my hand and noticed substantial flow reduction by the 1 cup level. This was done with a tank about 1/3 full with the proper 7mm fuel line attached but not connected to the carbs. If you don't get these numbers about the only things that could be wrong are the petcock screen plugged or dirty (clean it), plugged fuel cap vent (disassemble and clean it), bad vacuum line (replace it) or the petcock itself needs servicing or replacement. If the vacuum diaphram in the petcock is shot you'll see fuel in the vacuum line or taste it if you do the vacuum test above before looking and you'll need to replace the petcock. I've heard most people have had problems with aftermarket rebuild kits so you may just want to get a replacement from Suzuki or a Pingel. Before replacing though I'd try disassembling your petcock first to see if it just needs to cleaned or if something is making it stick shut, nothing to lose there but about ten minutes of your time.

[tone]

what is this going to show me. My issue with the hesitation I am experiencing arrives when cruising highway speed between 4.5-5.5

Its going to show you if the vent is blocked air must pass into the tank for fuel to pass out so opening the cap will eliminate the vent as air will pass freely into the tank through the open cap Eg the problem goes away = the tank is not venting & you need to sort it

simple enough for you ?

[Sandy]

Here's a dumb questions. Would have my tank bag that sits OVER the cap prevent air from venting. Since it looks like my cap keyhole is the vent?

If it has a foam backing and fits tight against the tank it definitely will.

[hikermikem]

I discovered my gas cap was venting nicely when I had the tank off the bike and drained the gas out of it. Even with the tank on the bike you can check your flow and hear the vent pulling air into the tank if you have a spare piece of tubing around. Disconnect the main line, connect spare. Get a bucket/container (about 1 gal/4 l. should do) and set the petcock to prime. In short order you should hear air being sucked in through the cap and there should be no slow down in flow.

This works very well, I just drained my tank this way to repair my fuel gage & you can easily hear the air being sucked through the fuel cap...

I guess it's venting ok

Mike

[maro]

Its going to show you if the vent is blocked air must pass into the tank for fuel to pass out so opening the cap will eliminate the vent as air will pass freely into the tank through the open cap Eg the problem goes away = the tank is not venting & you need to sort it

simple enough for you ?

Tone, I'm still not getting it, any chance you can draw me up a diagram? ... just kidding bro. I get it, I was more concerned on why this effected me at high speed as opposed to low speed

If it has a foam backing and fits tight against the tank it definitely will.

SOOOooooo, last night on my way home I took my tank bag off, and low and behold, I had no hesitation. I'm not yet convinced this is the cure, so I will try a few more rides like this to see. I'm hoping it is the reason though

thanks ya'll

[hikermikem]

I was more concerned on why this effecedt me at high speed as opposed to low speed

When the engine revs higher, it needs more fuel. As the larger volume of fuel leaves the tank quicker, it must be replaced (vented) with more air faster.

Your tank bag apparently restricted this venting process.

Good find!!