need some help diagnosing a fuel problem - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 9 (permalink) Old 07-01-2009, 01:08 AM Thread Starter
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need some help diagnosing a fuel problem

hello vulcanites.

my bike has had a recurring problem which i'd like to solve. about 50% of the time, the bike won't idle and will lose power and sputter at low rpm's. the other 50% of the time, it's absolutely fine and idles perfectly around 1500 rpm. when the problem is occurring, the bike displays all the symptoms of the 'phantom out of gas' syndrome, but i've tried opening the gas cap while the symptoms are occurring with no positive effect. if i slow down, the bike will die unless i keep the engine revved at about 3000 rpm. if it does die, it absolutely will not start until i use my magic trick.

the magic trick is removing the vacuum line which connects the petcock to the carbs. once i remove this tube (by disconnecting at the carb), i hit the start button and after about four turns, the engine starts and will continue to run. while it's running, i'll put the vacuum line back on the carb and the idle will instantly pick up (as now fuel is being actively sucked into the carbs). ok... good... and the bike will be fine for an indeterminate amount of time... maybe only a minute, maybe for half an hour depending on how fast i'm going... and then it happens again. the bike dies at low rpm's and won't start until i disconnect the vacuum line.

i use seafoam religiously and the carbs have been cleaned. the vent line going to the right side ear is cut at 45 degrees. the bike is a california model with two vent lines coming out of the gas tank. this past weekend i made sure that the left vent line which terminates at the gas cap was unobstructed... and now the bike won't start at all, even with the trick. doesn't seem like any gas is getting to the carbs. my plan was to eventually cap the right vent line and then just run a line from the left vent to the ground (bypassing the whole ca emissions thing), but yeah... the bike won't start now.

i don't know what is going on. seems like something simple, but i need some help.

any ideas? sorry for the long post.

paul
1991 vn750: 'for great justice'
http://www.globalrecon.org
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Last edited by global_recon; 07-01-2009 at 01:11 AM.
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post #2 of 9 (permalink) Old 07-01-2009, 01:57 AM
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sounds like the diaphragm in your petcock is damaged or has a hole in it and is sucking gas thru the vacuum hose ito the vacuum port on your carb and flooding your engine,I 'd got to the Items for sale on ebay and order a petcock repair kit and see if that solves your problem ,actually you should draining the tank and disassemble the petcock and hold the diaphragms up to the light and see if you can see any visible damage,and if you have one of those little vacuum pumps you could plug the line going to your carb and put some vacuum on a longer hose attached to the petcock where the one you take of the petcock and zip tie the little hand pump out of the way and test ride your bike and it would let you know if it ere flooding out by either running right or running right for a while and dying like it is out of gas until you give a pump a squeeze or two ,and it could be your float valves not shutting off and allowing the fuel level to get too high and when you remove the vacuum you are in effect shutting off the fuel and it burns the excess and starts running better until you put the line back on again letting gas flow freely into your carbs again if this is your problem I and a lot of others on here would recommend seafoam in the tank and maybe it will clear up then on its own.




If you see it on my bike I did it
VROC#30324
92 vn750(sold)
Current ride 05 1500 Classic FI
lovin' the new scoot



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post #3 of 9 (permalink) Old 07-01-2009, 07:00 AM
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X2 as above.

02 honda sabre 1100
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post #4 of 9 (permalink) Old 07-01-2009, 09:58 AM
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Have you pulled your plugs to see if they're wet? If the bike won't start, I'd go through the routine checks for spark, fuel and air filters etc. I've seen the vacuum port on the petcock pulling fuel before so that is definitely something to look for. Its interesting that your bike will run with the vacuum tube off the carbs as this would cause a very lean condition, but it makes sense if you're flooding out, maybe from float valves getting stuck open, that generating a temporary lean condition would allow the bike to start. But now that it won't start at all, it sounds like you need to cover all the basics for combustion, fuel, spark and air...

Fergy
Kyle, TX VN750.com member #707 VROC#19556
2002 VN1500 Classic
Spline Lube Procedure, with photos, R/R Relocation and Coil Mod
Rusty Tank Cleaning!
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post #5 of 9 (permalink) Old 07-01-2009, 08:48 PM Thread Starter
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thanks for the responses, guys.

i pulled the petcock off and disassembled it. i'd done this about six months ago and it all checked out... and again today the diaphragm looked fine. no holes at all. still, i ordered a petcock kit off of ebay, so i'm sure that won't hurt.

i haven't pulled the plugs yet, fergy, but i'll check them out too.

thanks again.

paul
1991 vn750: 'for great justice'
http://www.globalrecon.org
follow my rides on twitter: http://www.twitter.com/globalrecon

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post #6 of 9 (permalink) Old 07-03-2009, 10:34 PM Thread Starter
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i got the petcock rebuild kit (diaphragm and o-rings) today and installed it and after the no reserve filter conundrum referenced in post https://www.vn750.com/forum/showthread.php?t=11696 i installed some inline fuel filters and got the bike started. so far, so good... idles at 1100rpm. i never consider these issues solved because something always crops up, but i'm hoping this is the last fuel problem for a while.

fergie... we need to hook up for a ride at some point. anyone else in the austin area?

paul
1991 vn750: 'for great justice'
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post #7 of 9 (permalink) Old 07-04-2009, 12:23 AM
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There are a few of us in Austin. My son who bought my 750 and I are meeting in the morning and riding up to Buda to the Dan's Hamburgers there close to Cabelas for breakfast, maybe meeting another guy who just took the course with my son a few weeks ago. We're planning to meet there at 8:30am. You're invited to meet us if you can. We might go for a short ride out to Devil's Backbone before the heat sets in. Hope you can make it, but I know its short notice!

Fergy
Kyle, TX VN750.com member #707 VROC#19556
2002 VN1500 Classic
Spline Lube Procedure, with photos, R/R Relocation and Coil Mod
Rusty Tank Cleaning!
Electrical Fault Finding Flowchart
SEAFOAM JUNKIE!


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post #8 of 9 (permalink) Old 07-17-2009, 01:31 AM Thread Starter
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just wanted to post a quick update. my problem has been completely resolved since replacing all of the petcock rubber. big thanks to denny for the suggestion and thanks to everyone for their input. much appreciated. ride safe.

paul
1991 vn750: 'for great justice'
http://www.globalrecon.org
follow my rides on twitter: http://www.twitter.com/globalrecon

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post #9 of 9 (permalink) Old 07-17-2009, 01:41 AM
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you are very welcome gr, I am just another blind squirrel that occasionally finds an acorn.




If you see it on my bike I did it
VROC#30324
92 vn750(sold)
Current ride 05 1500 Classic FI
lovin' the new scoot



Quote:
"When all is said and done,usually more is said than done" UNK
Click on one x and drag to the other to read between them.

Psalm 40:1...
XI waited patiently for the Lord; and he turned unto me, and heard my cry. X
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