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Fuel in cylinders

Old 07-28-2015, 09:27 AM
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Fuel in cylinders

Hey guys, been doing a lot of work to my Hawk over the last two years and am almost done with it and have it road worthy. However hit a huge road block yesterday.

Basic carb setup done, 48 jets, needles shimmed, a/f screw 2.5 turns all that stuff done. Hooked the airbox up and tank fuel and vent lines. Started the bike, runs great no bogging anywhere through the powerband. However, I noticed my choke assembly was leaking, so I let the bike warm up a bit more to see if the leak would go away, it didn't. Shut the bike off, waited 5 minutes, tried to start and it wouldn't crank. Pulled the tank/airbox off and noticed a bunch of fuel in the aribox, also pulled the carbs and BOTH the cylinders where full to the top of the carb boots with fuel, almost hydro-locked the engine. I had the bike running last weekend without this issue, I find it difficult to believe that both floats/needle seats took a dump on me in a few days so i'm being directed to the petcock on the tank. Any ideas/advise???
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Old 07-28-2015, 09:53 AM
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Sounds like the vacuum diaphram in the fuel tap/petcock has failed. Time for a new un and an oil change.
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Old 07-28-2015, 11:07 AM
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Originally Posted by Wicky View Post
Sounds like the vacuum diaphram in the fuel tap/petcock has failed. Time for a new un and an oil change.
Already have a rebuild kit on order, however im confused wouldn't the float bowl needle/seats prevent this fuel from getting further down through the carbs if this happened?
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Old 07-28-2015, 11:46 AM
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Originally Posted by bbancsov View Post
Already have a rebuild kit on order, however im confused wouldn't the float bowl needle/seats prevent this fuel from getting further down through the carbs if this happened?

Not if they too, have a problem. Or if your tank is full, gravitational pressure is strong enough to open them up.
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Old 07-28-2015, 12:07 PM
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Originally Posted by bbancsov View Post
Already have a rebuild kit on order, however im confused wouldn't the float bowl needle/seats prevent this fuel from getting further down through the carbs if this happened?
Your float valves are worn or not seated correctly. I ran for ages with no diaphram in my petcock and had no trouble. Only way for this to happen is float valves.
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Old 07-28-2015, 01:54 PM
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Originally Posted by NZSpokes View Post
Your float valves are worn or not seated correctly. I ran for ages with no diaphram in my petcock and had no trouble. Only way for this to happen is float valves.
I'm struggling to understand this because wouldn't BOTH front and rear carb float valves or seats have to be damaged/disturbed abruptly at the same time for this to be the outcome? Keep in mind I ran the bike fine for a few days prior now, this just happened abruptly. I'm going to disassemble tonight and post pics, hopefully they are okay and it was just the gravitational pull/diaphragm being damaged on the petcock that caused this.
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Old 07-28-2015, 02:39 PM
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possibly the screen on the petcock is compromised permitting debris to flow into both carbs.
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Old 07-29-2015, 04:54 PM
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So I pulled the carbs off and looked at the float bowls and needles. Both were clean with no signs of wear and checked the floats for leaks they are good. Checked the petcock on the tank with a vacuum tool and that also seems to be working fine. Really at a loss for what could've caused all this fuel to dump into the cylinders when all looks well
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Last edited by bbancsov; 07-29-2015 at 05:03 PM.
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Old 08-02-2015, 12:09 PM
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Rebuilt the petcock. Now I only get a slow drop leak in the front cylinder but the rear is good. So I swapped floats and needles from the front to the rear to see if they leak would follow it. Well it didn't it's still leaking in the front carb from the needle so I guess the last thing to do is take a shin out of the front needle to see if that helps. Front is shimmed to 0.0425 and rear is 0.06875
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Old 08-02-2015, 08:17 PM
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Are you sure the float height is set correctly?

I'm not understanding how a needle shim would affect a fuel flow issue with the bike off.

You should be able to remove the needle and it wouldn't matter. In fact you should be able to remove everything in the carb except the float, float needle, and float needle seat, and it wouldn't make a difference.

The float/float needle/float needle seat are what cuts off fuel from the petcock (unless there is something about these carbs i don't understand, which is entirely possible). When the bike is sitting, engine off, no fuel should flow past the float needle/seat, assuming the floats are set to the correct height.

You could have 20 gallons of fuel directly above the carbs and the float needle/seat would stop it from flowing.

James
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Old 08-03-2015, 05:29 AM
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Originally Posted by thedeatons View Post
Are you sure the float height is set correctly?

I'm not understanding how a needle shim would affect a fuel flow issue with the bike off.

You should be able to remove the needle and it wouldn't matter. In fact you should be able to remove everything in the carb except the float, float needle, and float needle seat, and it wouldn't make a difference.

The float/float needle/float needle seat are what cuts off fuel from the petcock (unless there is something about these carbs i don't understand, which is entirely possible). When the bike is sitting, engine off, no fuel should flow past the float needle/seat, assuming the floats are set to the correct height.

You could have 20 gallons of fuel directly above the carbs and the float needle/seat would stop it from flowing.

James
So made some progress on this issue this weekend, here's what's been done:

- Fuel tank petcock rebuilt with new diaphragm
- New choke system installed
- Carbs taken back to stock?
- 175 Front - 178 Rear, needle shims removed, a/f screws 1.5 turns out
- Front and Rear float bowls, needles and float needles swapped to see if problem follows float: Runs lean but no leak
- Carb needles shimmed (0.0425 Front and 0.6875 Rear): Runs a bit lean with no leak
- Carb a/f mixture screws adjusted (2.25 Front and 2.5 Rear): Runs seemingly rich, backfire and front carb now leaking

I'm perplexed that an a/f screw seems to be causing this since that's the only adjustment I made on the front (1.5 ->2.25 turns) before it started leaking again. In my mind this doesn't make any sense... I swapped the needles because the front initially looked like it had a weird wear pattern to it but that nor the floats seems to make any kind of difference. I 'm going to slightly adjust the front a/f screw in this afternoon a bit after work and report back. Video of fuel accumulation below...

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Old 08-04-2015, 04:42 AM
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So last night I swapped the a/f screws from front to rear carb, and also installed a new oring because they looked a bit worn and sandwhiched. Well, started the bike and let it warm up cracking the throttle every now and again, no leak in the front cylinder. Took the bike for a rip up and down the road, shut it off and let her sit for 5 minutes. Immediately the front cylinder started filling up with fuel all the way up to the stack. I'm really at a loss here, the only thing I have left to change are the needle/seat and float.
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Old 08-04-2015, 05:53 AM
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Your floats look old, the plastic floats can get saturated and not do their job correctly, not saying this is or might be the problem but I would swap them out because they are cheap and... well... your probably gonna swap out everything anyways
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Old 08-04-2015, 07:13 AM
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Originally Posted by scottiemann View Post
Your floats look old, the plastic floats can get saturated and not do their job correctly, not saying this is or might be the problem but I would swap them out because they are cheap and... well... your probably gonna swap out everything anyways
They look old? How can you tell? I did the dunk test in water with them with no bubbles. I tried looking on ronayers a coworker was saying it might be the seat where the float needle sits but I can't find a diagram or part number
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Old 08-04-2015, 08:10 AM
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just the color, new ones are a very light off white, after sitting for a while my bike started dumping fuel out of the vent tubes, turned out to be dried up old gas siezing the float needles but while I was in there I replaced the floats. And I wasnt saying your floats are leaking but the plastic itself can get saturated with fuel. Again, Im not saying this is the problem, just basic maintenance for an old bike...
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Old 08-04-2015, 08:32 AM
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Originally Posted by scottiemann View Post
just the color, new ones are a very light off white, after sitting for a while my bike started dumping fuel out of the vent tubes, turned out to be dried up old gas siezing the float needles but while I was in there I replaced the floats. And I wasnt saying your floats are leaking but the plastic itself can get saturated with fuel. Again, Im not saying this is the problem, just basic maintenance for an old bike...
Hmm, well perhaps I will order a new set then even though they don't seem to be the culprit. Anyone have a line on the float needle brass seats that are threaded into the carb body? I'm assuming there is an o-ring beneath that but I cant seem to find a part number. I'm going to try and remove them and take a look to see if there is something strange going on.
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