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Discussion Starter #1
Hey!

Well, it's my first post, but I've been lurking for a while! Great place!

I picked up my 1990 Vulcan about 3 weeks ago, and it's in great shape! Was 100% stock when I got it, 19k original miles on it, ran very good and was very well maintained and clean.

The bike ran great, except for a hard to start when hot problem, which searching around I found much info on. I put in an AGM battery, and iridium plugs. This immediately solved my issue, and it started each and every time with no effort after this! Ran great! Previous owner just did wires not long before he sold it to me, and he had the carbs cleaned and everything about a year ago. Along with changing out the battery, I tore most of the bike down and checked ALL of the electrical connections, and changed the oil. Everything lookin good!

Well, I've been cruising on this, loving it for like I said, almost a month now. Bikes been running great! Not a problem with it once the battery and plugs were switched out, however now I have my first problem.





Today, I rode up to my girlfriends work, bike ran perfect the entire way up there. Nothing out of the ordinary. Upon pulling into the parking lot, I started to park, and the bike started sputtering and died on me and wouldn't idle. I started it back up, didn't want to idle, died again. Well, I managed to find out that I could get it started and then give it enough gas to keep it idling, and once I got it about 2k rpms it ran perfectly fine as usual. I decided I needed to get it home before I got stranded, so I ran home quickly with it. Along the way, no problems aside from keeping it idling. If I was sitting at a stop light, I would have to hold the gas to keep the revs up, and it would take a little work to get it going in 1st, but then again no problems.


I pulled it into my garage, checked everything. Fuel tank is FULL. Now, mind you I don't have my experience with bikes or carbs, but I do have a lot with car engines and fuel injection. My understanding is that these carbs are gravity fed correct? I noticed the main fuel line coming STRAIGHT down from the petcock had a crack near the top, but it didn't look under the nozzle, so I replaced that line no change. For kicks, I left this main middle fuel line disconnected, and turned the petcock down to ON. No fuel came out?! Shouldn't fuel be coming out of this pretty good? Like I said, the fuel tank is full all the way.

I didn't pull the other 2 lines on the left and right sides of the petcock, because I ran out of time before I had to goto work, but I'm assuming on our bikes gas should freely pour from here when the petcock is turned to the on position. I'm guessing there's a little screen in there as well. A couple days ago I put some SeaFoam in the gas tank, maybe it clogged this screen?




So...Could this be causing my problem? Maybe it's too clogged at idle, but under some throttle the vacuum is enough to suck past this? Or am I wrong in asuming gas should be pouring out of this petcock with no lines attached under ON?

Also, the previous owner told me these bikes have no reserve. Is this true?

Any insight on this problem would be appreciated! I love my baby and I want to get it runnin again ASAP!

Thanks guys!
 

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The Professor
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The petcock is vacuum operated, the engine has to be runnung for fuel to flow. :beerchug:

The center line is the vacuum line, the ones left and right are the main lines to each carb.

The vacuum leak may have caused your problem, not enough vacuum at idle to open the petcock diaphram.
 

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Discussion Starter #3
Crap.......and I thought I found my problem :(

I should mention, I adjusted my idle screw as well, and this didn't solve the problem either *tear*
 

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The Professor
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Check all four clamps on the carb boots and make sure they are tight.

Try adjusting your idle knob on the left side, set to 1100 rpm when engine is warm.

Make sure your choke is fully closed.
 

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Discussion Starter #5
Choke was the first thing I checked, I need to check it more, because when I got it started, it still smelt like it was running very rich for some reason.


When I had it idling in my garage by hand, I put my ear very close to the right side of the carbs and heard nothing out of the ordinary, but on the left side I could hear air being sucked in rythem with the carb, the carb was slightly moving a little. I'm not sure if this sucking sound is normal either. I tried spraying some WD-40 around, but it didn't change much.
 

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Love My Baby
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... the previous owner told me these bikes have no reserve. Is this true?
There is a reserve in the tank. Acutally, the RESERVE position on the fuel selector switch (petcock) just allows fuel to flow from the tank via a shorter intake line, meaning that line originates inside the tank from a lower position than the line that's connected to the ON position of the fuel petcock. So when the fuel level falls below the height of the fuel line when the petcock is in the ON position, no fuel will flow to the carbs until you select the RESERVE position. There's not really a reserve section of the tank separate from the main section.
 

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have you tried running the bike in the reserve position your petcock may be messing with you.And check the vent hose from your float bowls that goes in the back side of the right air filter it doesn't attach it just fits there to keep it from flopping around and also have you tried running it with the gas cap unlatched so the tank can breath if the cap breather is stopped up?
 

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The Professor
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Choke was the first thing I checked, I need to check it more, because when I got it started, it still smelt like it was running very rich for some reason.


When I had it idling in my garage by hand, I put my ear very close to the right side of the carbs and heard nothing out of the ordinary, but on the left side I could hear air being sucked in rythem with the carb, the carb was slightly moving a little. I'm not sure if this sucking sound is normal either. I tried spraying some WD-40 around, but it didn't change much.
Set your pilot screws at 1.75 turns from closed, they may be turned out too much. That will cause it to run rich at idle and up to 2500 rpm.

Drain your carbs into a clean container and check for sediment. The openings on the pilot jet are very small and can clog easily.
 

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Discussion Starter #9
I forgot to mention, that vent hose was flopping around, and I put it back behind the air filter in that little spot that it's supposed to go, didn't seem to help :( I did notice the end smelt like fuel and was a little wet for some reason!!! That worried me!

I will try the gas tank thing, I never thought of that.


Set your pilot screws at 1.75 turns from closed, they may be turned out too much. That will cause it to run rich at idle and up to 2500 rpm.
I'll try this. These are the little brass adjuster screws on each carb right? The flat head ones? I looked for those today, but they looked tight to fit a screw driver in, and I didn't wanna mess with em without being sure what to set them at.


Drain your carbs into a clean container and check for sediment. The openings on the pilot jet are very small and can clog easily.
Is this difficult to do? I've never really worked on carbs before, only fuel injection.



On a separate note, I can't thank you guys enough for the help so far! I never expected this much help! You guys are awesome!
 

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The Professor
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Stick a small hose on the bottom of the jet cover nipple and open the drain screw. :carryflag

The pilot screws are beside the vacuum ports. You need a tiny screwdriver.
 

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One thing I noticed in your first post was that you mentioned that your tank was full. You've been riding this bike the past month with it running great and suddenly you have this problem, with a full tank. This means you just filled the tank and suddenly have problems. Catch my drift? It sounds like you got some bad gas, maybe some water in there, who knows. The split in the vacuum line would definitely give you problems, glad you replaced that line. The carb vent hose would also cause problems when you are up in the higher revs going down the road. The fact that the end was wet with gas shows you it was drawing gas through the hose the wrong direction because of the air pressure since it wasn't in it's home position. Pull it back out and trim the end at a 45 degree cut so it can't bottom out in the air box. Then put it back in. Your carbs need this hose to maintain stable air pressure so the carb bowls can draw the right amount of air to keep fuel flowing in the right direction. With it dangling out, with wind rushing past it, it will draw air and pull fuel the wrong way. Shouldn't have any effect on idling though.
Draining the carbs to get any crud out is a top priority, and I would definitely put in a half can of seafoam in the tank to try to get the crud or water to burn out and clean things up!
 

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Discussion Starter #12 (Edited)
Well......I've got updates. I came home from work and started on the bike.

I drained both carbs like you said, and I did find some crap in there, although to be honest the hose was in the garage, but it looked like a decent amount, almost like rubber though so it makes me think maybe it was inside the hose.

I drained them both, closed them, started the bike, let it run for a while, drained it again. I did this 3 times to make sure what was coming out was perfectly clear, and it was. I also removed the seat, and used wire to clean out that gas tank vent. I didn't feel any restrictions, or see anything come out though. I also cut the carb vent tube at a 45 degree angle and stuck it back into the right side air box.

As you mentioned, I adjusted the air/fuel screws 1.5 turns, they were like a hair over 2 turns before I started.

After this, I started the bike, let it warm up, seemed to start ok. Adjusted the idle, perfect, started idling really really good! I did notice white smoke coming out, but as a last ditch effort lastnight before I posted, I put about 1/2-3/4 can of seafoam in the gas tank....

I took it for a ride, and immediately I thought the problem was fixed! It ran like a champ! Idled down perfect, strong power, everything.



However, about 1/2 way though my route, I started *thinking* I was feeling slight power surges going 55. Sure enough, when I came to a stop at the sign, I almost killed the bike and it was stumblin pretty rough again at idle and trying to get through the gears. However, above 35% throttle, power came back strong and it ran like it should!

I'm at a loss here : / I checked the wires, both are tight on the battery as well. looked for fried connections, none found. I don't get it. It's like a switch suddenly flipped outta no where. I love my bike and just want to be able to ride it again. I still smell like it's running rich at idle for some reason.



On a side note, yes I did fill at a gas station I seldom do, but the times I've had no problems, but that was in my car as well. The thought had occurred to me as well of possible bad gas, but I don't know why it would run good up high and not down low? I really hope these plugs aren't fowled already, they're brand new and ran like $38!



Maybe I should pull the tank, empty it out, and pull out the petcock to see what that looks like and while I'm at it, get some gas from the local Mobile I've never had problems with. I dunknow. I hope this isn't a serious problem.
 

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In the grand scheme of things, draining your tank and the carbs again, and putting in fresh gas is still a pretty inexpensive way to go. You can always use the drained fuel to run your lawnmower! With the tank off I'd definitely check the petcock while you're at it.
 

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Discussion Starter #15
I'm still wondering if it's normal to hear a suction noise from the left side of the bike down by the carbs. I hear and feel suction from both air inlets, I know that's normal.

I'd like to check the other screws that hold the carb to the bike, but it looks like you must have to remove a lot of stuff to get a screwdriver in that far.
 

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My bike was doing the same exact thing before I had crobins do my carbs....

some people may not agree and I could be wrong but check these things.

Air filters (don't just look at them be sure to touch them and make sure they are not rotted, they can full you very easily)
Plugs (all 4) if they are flaky rotted a little then I would def replace filters and do the carb brake down and clean them. make sure if you replace the air filters to treat them with a air filter type oil. I used PJ-1, this will prevent the grit from the filters getting into the carbs.

My bike never had this problem til I did a seafoam treatment and took it for a good 30 mile ride. and then did the same exact problem you are having now.

Seafoam is great however it is so great that it will free up gunk in the fuel system and clog jets,lines ect.... so you may be on the way to brake down the carbs and give them a good cleaning.

And remember when you buy a used vehicle/PO (previous owner) they will tell you anything you want to hear.

Good luck, and please keep us posted on progress and steps you take to fix the problem.

Oh yeah and Welcome to the site!!!
 

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It's not a popular mod on this forum because the strainer screen on the petcock should filter out most contaminants, but I placed clear in-line fuel filters on the hoses just below the petcock. This pretty much eliminates anything in the tank (rust, varnish, other contaminants) from reaching the carbs. It's not easy getting those things in that small space, but I figure it beats pulling the carbs any day!

There is a strainer screen on my other bike, and I have found junk it didn't stop in the filter. Haven't had any reason to check those on the VN750 yet, but I figure if it can get by one screen, it can get by another.
 

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Discussion Starter #18
Well, got some MAJOR updates and possible solution! I drained the tank, cleaned it out, looks clean as a whistle. Took the petcock out, screen was clean, functioned perfectly, no rust or anything, drained the carbs again, nothing out of the ordinary...


and then.......


I found a mysterious plug sitting on top of the carbs that wasn't stuck in anything, upon further poking around I found a huge open hole in the bottom of the air box!! This plug was def not ment to be in there, and I don't know how it was even stuck in there but I'm guessing this could have been my problem.


I've got pictures, I'll post them in a bit, I gatta get ready for work, but I can post them there. I want to know what this hole is there for, and why it's not got something attached. I got a freeze plug for it, and I found another vacuum cap that was rotted, so I replaced that as well.

Pictures to come!!!!
 

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Discussion Starter #19
Here's pics!



This is what I found sitting on top of the carbs upon further inspection:



I found this hole when looking up at the underneath of the air box from the right side of the engine. Here's 3 pics of it.








I pulled this rubber grommet in the hole that I pulled out:





I'm guessing that this cap went into the grommet like this, but it does NOT screw in there, so it was obviously not meant to be there, it's so loose, he musta had to glue it in there to hold it some how:







My solution was to get a freeze plug for the grommet like this:






I also found this vacuum port cap rotted, so I got a replacement today, it goes here:



A better shot of where the vacuum cap goes on this nozzle:










I ran out of time before work. Tomorrow, hopefully someone will know what this hole is, why there's nothing in it, and if this could be causing my problems. I'm stumped as to what was supposed to go in this hole! I'm glad I found this, it very well could be causing my problem. Hopefully putting this freeze plug in will work, and fix my problem, but I'd still like to know why it was there to begin with. I also got a tank of new good gas from my usual place today, and cleaned the whole tank and petcock out. They were NOT dirty.
 

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Discussion Starter #20
I stumbled upon this picture while searching through your forums here.




It looks like from the picture, that the hole and grommet I found belong to #92071. What I can't figure out is:

a: What this hole is for? What should it be connected to?
b: Why it appears to have been plugged on my bike with something that shouldn't have been used to plug it?
 
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