CUPLA MINS THEN DIES - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
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post #1 of 16 (permalink) Old 09-09-2016, 04:50 AM Thread Starter
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CUPLA MINS THEN DIES

So, I am wondering, WTF? Having restored my '97 750 it looked great, ran great, and all was well. Took it on a few 100 mile rides, and around the area trips to the bank and such.

I let it set a few weeks, then rolled it out and started it, and let it set at an idle to warm up. After a couple of minutes, the idle started dropping lower and lower and then it died. As if it ran out of fuel. I tried to restart it but it wouldn't start. I switched it over to reserve, but still nothing. It didn't smell flooded, more like as if out of fuel. Yet there was still plenty of fuel in it.

I let it set about a half hour with the fuel cap open while I went to do something else. When I got back to it, it started right up. I let it set at an idle again, and again after a couple of minutes, the idle started dropping and it died again. Wouldn't start again either.

Frustrated I wheeled it back into the garage turned the petcock back to the off position and left it. Since then I have fired it up a few different times, and it did the same thing. If I let it set a little while it will start back up, but then do the same thing again.

The last time I started it, when it started to idle down again, I grabbed the throttle and with some sporadic twisting managed to keep it from dying. Until I let it try to idle again, and then it did the same thing.

During the restoration I rebuilt the carbs (with all new brass) rebuilt the tank petcock and acid washed the tank interior. I replaced all of the fuel and vacuum lines and synchronized the vacuums. I cleaned the tank venting (so it isn't POOGS I don't think) And like I mentioned, when I got it all back together, it ran great.

So has anyone else encountered this problem before? Anyone got any idea what is going on with it?

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post #2 of 16 (permalink) Old 09-09-2016, 09:38 AM
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Still sounds like weak fuel delivery.

Check flow from petcock and choke operation. Could be sticky float or dirty pilot jet/dirty passages in the carbs.

Sitting with ethanol gas doesn't take long to produce corn syrup.

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post #3 of 16 (permalink) Old 09-09-2016, 03:54 PM
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When you gave it throttle to keep it from dying, how did it behave?
Did it struggle to stay alive and stumbled or did it sound okay?

This is not addressing the real issue and is more like using a duct tape as band aid, but maybe you could increase the idle rpm to keep it alive.

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post #4 of 16 (permalink) Old 09-09-2016, 07:54 PM
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Poogs posibly?

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post #5 of 16 (permalink) Old 09-09-2016, 08:52 PM
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Rule out the gas tank vent for good by running for several minutes with the gas cap open to see if it dies the same way or not.

If a stuck float were causing the problem you could verify that by opening the bowl drain right after it died. Little to no gas should drain out, right? A clogged gas tank vent would do the same, so that needs to be ruled out first. The petcock would need to be set to 'prime' or a constant vacuum applied to the center line to ensure flow from the fuel tank.

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post #6 of 16 (permalink) Old 09-12-2016, 02:57 AM Thread Starter
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Quote:
Originally Posted by Spockster View Post
Still sounds like weak fuel delivery.

Check flow from petcock and choke operation. Could be sticky float or dirty pilot jet/dirty passages in the carbs.

Sitting with ethanol gas doesn't take long to produce corn syrup.
A sticky float might be possible, but I've just gone through the carbs so it's not a dirty pilot jet/dirty passages issue I wouldn't think.
It's also only had 90 octane Ethynol free fuel in it since I restored it. But it does seem like a like weak fuel delivery, your right.

Quote:
Originally Posted by evulcannibal View Post
When you gave it throttle to keep it from dying, how did it behave?
Did it struggle to stay alive and stumbled or did it sound okay?

This is not addressing the real issue and is more like using a duct tape as band aid, but maybe you could increase the idle rpm to keep it alive.
It struggled trying to bog down until I got the RPM up enough then it throttled alright until I let it back down all the way and it wanted to die out again.
I did try turning the idle up some but it would drop lower past it and die anyways.

Quote:
Originally Posted by OleDirtyDoc View Post
Poogs posibly?
No, it hadn't run long enough to suck all the air out of the tank before doing it. Plus I cleaned the vent system thoroughly during the restoration. Also even tried it with the fuel cap open...same thing.

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Originally Posted by Thorn View Post
Rule out the gas tank vent for good by running for several minutes with the gas cap open to see if it dies the same way or not.

If a stuck float were causing the problem you could verify that by opening the bowl drain right after it died. Little to no gas should drain out, right? A clogged gas tank vent would do the same, so that needs to be ruled out first. The petcock would need to be set to 'prime' or a constant vacuum applied to the center line to ensure flow from the fuel tank.
I did try it with the fuel cap open...same thing.
I will try opening the bowl drain right after it dies though see what that tells me.
As for the petcock, I had rebuilt if completely during the restoration. It was working fine. When it started this glitch though, I took it back off, pulled the vacuum diaphragm did try it with the fuel cap open...same thing.
I will try opening the bowl drain right after it dies though see what that tells me.
As for the petcock, I had rebuilt if completely during the restoration. It was working fine. When it started this glitch though, I took it back off, pulled the vacuum diaphragm out of it completely, made a flat gasket to replace it with. The vacuum line still goes to the petcock, but the flat gasket makes it like the vacuum line is capped off. Without the plunger (that is part of the diaphragm I did try it with the fuel cap open...same thing.
I will try opening the bowl drain right after it dies though see what that tells me.
As for the petcock, I had rebuilt if completely during the restoration. It was working fine. When it started this glitch though, I took it back off, pulled the vacuum diaphragm out of it completely, made a flat gasket to replace it with. The vacuum line still goes to the petcock, but the flat gasket makes it like the vacuum line is capped off. Without the plunger (that is part of the diaphragm) the petcock is open inside down to the valve and is functioning as a normal gravity flow, and just has the manual "off" "on" "res" valve settings.) the petcock is open inside down to the valve and is functioning as a normal gravity flow, and just has the manual "off" "on" "res" valve settings. out of it completely, made a flat gasket to replace it with. The vacuum line still goes to the petcock, but the flat gasket makes it like the vacuum line is capped off. Without the plunger (that is part of the diaphragm) the petcock is open inside down to the valve and is functioning as a normal gravity flow, and just has the manual "off" "on" "res" valve settings.

Thanks for the replies, and ideas guys. I am surprised that as thoroughly as i went through the fuel system that is would be causing problems, but.......Something is causing the bike to die out like it is.

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post #7 of 16 (permalink) Old 09-12-2016, 02:39 PM
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Quote:
Originally Posted by A6ULdv8 View Post
It struggled trying to bog down until I got the RPM up enough then it throttled alright until I let it back down all the way and it wanted to die out again.
Does sound an awful lot like a restriction in a pilot jet. Fuel starvation due to bad petcock or float would get worse as fuel consumption increased with rpms.

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post #8 of 16 (permalink) Old 09-12-2016, 03:02 PM
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Is your choke open? It gets hot and then there isn't enough air. Check that it is operating correctly when closed.

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post #9 of 16 (permalink) Old 09-28-2016, 05:36 AM Thread Starter
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I'm also starting to wonder if i could have a coil breaking down after it warms up a few minutes.

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post #10 of 16 (permalink) Old 01-21-2017, 01:10 PM Thread Starter
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OK so it's 4 months later and it hasn't healed up on it's own. Fired it up and it is doing the exact same thing. However, this time I found that it's not running out of fuel at all. It reaches that point (roughly 2 minutes of running) and the idle starts dropping right off. If I let it, it will drop to nothing and die. but when it is dropping if i twist the throttle, it revs right up. No hesitation, no bogging down, it's got plenty of fuel on demand.

No one has encountered this problem? Could it be electrical? perhaps a coil breaking down once warmed up a couple of minutes?
Any idea guys?

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