Gas spewing out the vent

Alright, so I'm having carb problems yet again and it's really getting on my nerves. I recently stripped them down and cleaned them thoroughly, but before that I thought I had a busted fuel filter that was leaking gas. The bike was sitting and idling while I messed with the idle screw on the #4 cylinder, and I noticed a bunch of gas spewing out of the same spot. I installed new fuel filters on it, so I knew that wasn't the problem. It turns out that fuel was spewing out the vent in between the #1 and #2 carbs and spraying on the fuel filter and all over my new carb boots. Here is a pic of what I'm talking about, except this is in between the #3 and #4 carbs.



I shut the gas off and let the carbs dry, just to make sure something wasn't caught in between the needle and seat. Afterwards, it still spewed gas. I did the same thing again, and removed the bowl drain screws from both carbs and started it up again, with gas spewing out after 30-45 seconds of running. I rode the bike home from our farm and after I got home, I let it idle for about 30 seconds again, with the same results. Here is a pic of the thing spewing gas.


The only thing I think it could be at this point is a bad diaphragm in the accelerator pump. I noticed some fine cracks in the diaphragm that controls the fuel flow, so it could possibly be leaking. I installed all new accelerator pumps about a year and a half ago, so I'm guessing these diaphragm kits are junk and I'll probably be changing them every year.

I don't know what to do at this point. I am so sick of working on carbs and never having this bike run how it should. How much trouble is it to disable the accelerator pump? Seems like it does nothing but cause me trouble and cost me money. I'm running VM26's on a 79 KZ1000 with #20 pilot jets and #110 main jets and an older style MAC header. I've read that someone had to increase their jet size after installing a MAC header, so maybe that is causing me problems as well.

Also, on my ride home, the bike would just pop a lot after I reached 6k rpms. I don't think it has ever really ran great over 6k rpms since I've owned it, so I don't know what to think anymore.

first things first it sounds to me like you are having needle and seat problems gas spewing out of the vent tubes are a good indication of that. next thing if it wont pull past 6000 then you are probably lean on your jetting try going up to a 117.5 main or a 120 depending on your elevation you may have to raise the needle up one clip as well.check you float valve needles for grooving and look at the seats for pitting also try brasso or somesort of mettel polish and a q-tip and try polishing up the seats. when you cleaned the carbs was there anything in them like dirt or rust. if the accelerator pumps where leaking it would not do that what your dicribing it would only make it tough to transition from idle to part throttle.

I installed new needles and seats last summer, so I would hope something isn't wrong with them. I guess I will have to take them apart though and double check for any junk in the bowls or caught in the seat. I didn't notice anything last time I cleaned them, and I made double sure they didn't get anything in them while they were apart. It's good to know the accelerator pump isn't the problem, because I really don't want to buy another kit already.

Something I think I forgot to mention was my #4 cylinder running cool. I was checking the temp of the header pipes and #1-3 would be running around 220*F, and the #4 cylinder would only be 100*F. I synchronized the carbs using the drill bit method, because I don't have 4 vacuum gauges to do it the right way, but it shouldn't be far off if it is.

Floatbowl overflow circuit(s) likely also obstructed.

Would sniff-test and physically examine condition of crankcase oil to determine whether fuel has invaded the crankcase. If so, would change oil and filter and not start engine or allow fuel to carbs (disconnect fuel line from petcock) until carb issues have been resolved.

Are carb floats incorrectly installed or misadjusted or binding or bent or stuck or leaking or sunk or otherwise defective or malfunctioning so as to allow continuous flow of fuel into floatbowl?

Good Luck!

I've got the carbs off again and haven't noticed anything wrong. I removed the seats from each carb and there was no junk in any of the carbs. I shot compressed air through the overflow circuit on all carbs with no problems, along with the gas inlet hoses. The floats are all fine and intact, nothing out of the ordinary. Needles look fine as well. I ordered #120 mains that I'm hoping get here tomorrow, but I still am clueless on this overflow issue.

A friend had the same problem with her Zephyr 750, it turned out to be crap got in behind the diaphragm in the Petcock (After a Tank repair)which in turn got caught in the needle and seat of one carby, fuel spewed everywhere. She had actually got a hydraulic lock in one cylinder because fuel was spewing everywhere.

After blocking the fuel line with a bolt we pulled off the carb bowls and got the crap out, we emptied the tank and pulled the petcock apart to see why fuel was coming out. We found some thread sealer had gotten in there, maybe the is some rust flakes or something.

Another thing we found is the tube that distinguishes the normal fuel level to the reserve level tube was missing in the tank so it would always pickup the crap from the bottom of the tank with no filter.

Hope this helps.
Noel

I had the same problem with one my carbs, one of the floats would stick and it wouldnt take much and didnt do it all the time.:S

toadson wrote:

I've got the carbs off again and haven't noticed anything wrong. I removed the seats from each carb and there was no junk in any of the carbs. I shot compressed air through the overflow circuit on all carbs with no problems, along with the gas inlet hoses. The floats are all fine and intact, nothing out of the ordinary. Needles look fine as well. I ordered #120 mains that I'm hoping get here tomorrow, but I still am clueless on this overflow issue.

If not already done, would assure no kink or blockage in overflow drain tube attached to floatbowl overflow outlet nipple. Such kink or blockage will prevent fuel from escaping out through the nipple.

The better practice is of course to turn the petcock off while the bike is parked to avoid relying solely on the float valves (and related float assembly) to stop the incoming fuel flow at the desired service level inside the bowl.

But even where the float valve for whatever reason fails to stop the incoming fuel at the desired level, the overflow circuit is supposed to kick in to avoid excess fuel from rising further upward into the carb.

This is important, because the issue (excess fuel flow into floatbowl for whatever reason) may occur while riding the bike, when the petcock must be flowing fuel.

Where the overflow circuit actually is clear from orifice at top of intake tube to end of drain tube routed underneath the bike, it's difficult to understand why gas won't flow through it.

WEAR EYE PROTECTION and try shooting carb cleaner (from pressurized can) through the overflow circuit, both ways, (1) into floatbowl tube orifice to exit from floatbowl outlet, and (2) into floatbowl nipple to exit from floatbowl tube orifice. Then also check the drain tubes themselves for clear passage throughout and escape to open air underneath the bike.

Imo, it's unusual for the float valves to be functioning so poorly (for whatever reason) that the volume of excess fuel being allowed into the floatbowl exceeds the volume allowed to escape through the overflow circuit.

Good Luck!

Whenever I have a problem with my carbs I always use Seafoam in the gas tank first. Start the bike up for a few minutes even if gas is spewing (get a rag or something). Let the bike sit overnight and try again. Does wonders for stuck floats.

If that doesn't work, then I give in and start troubleshooting.

Best of luck.

Timebomb's suggestion of the #120 main jets really did my bike some good. I checked all the floats again and made a few small adjustments, and sprayed some seafoam on a few different parts to make sure nothing was sticking. I let my bike sit around and idle and never had any gas spewing out of the vent, and my #4 cylinder seems to be closer to the other cylinders in temperature.

I took the bike for a few short trips and it finally pulls through the RPM's all the way to redline. I don't know if it has ever ran this good in the two years that I have owned it. Thanks everyone for all your input- I think my bike is finally running how it should!

I spoke too soon. After getting a full tank of gas tonight and returning home, I let the bike idle on the kickstand only to find that gas was yet again spewing out of the vent. I noticed that when gas is coming out of the vent, the idle drops down a few hundred rpms- leading me to believe that one or more cylinders are getting flooded out. I'm almost positive gas was coming out of the #2 and #4 overflow as well, so this must be some sort of float issue. I'm just going to have to break down and do the wet float test, even though its sort of a pain.

Do the old Gringo trick. Take a "q" tip and some brasso and shine/clean the seats.
Have you measured the float height? Roy