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Registered Badass
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102 Posts
Discussion Starter #1
Guys I really need you help on this one. Been troubleshooting every day for like two weeks now.

It idles fine, and if I can get it over 5K RPM's it'll handle the freeway just fine.
The moment it hits 4K RPM's it starts sputtering. Once that begins it'll continue until I get it over 5K or I can get it to idle without stalling completely.


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A little history in case it's relevant:

Within two weeks before this started happening I did an oil change (Mobile 1).

Replaced the O-rings in the deep spark plug tubes.

I removed the sidestand switch because the bike wouldn't start at all. Those wires are shorted now. I've tested this connection at the junction box. Bike starts fine after this.

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Bike ran excellent for about two days after those things.
Then on my way home from work (this is my commuter), after getting off the freeway and lowering my RPM's it sputtered and stalled. And such has been my world every day since.


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Things I've tried:

Checked all wiring/plugs/connections. Cleaned contacts etc.

Changed the oil filter since I hadn't when I did the oil change. Topped up the oil again.

Gaped the spark plugs. Tightened the screw-on connectors (I don't have stock wires).

Checked/cleaned air filters and airbox/hoses/boots.

Pulled the carbs and cleaned them out using gumout.

Blasted the jets with gumout followed by compressed air.

Checked the vent hose, fuel hoses and vac hose for cracks/kinks.

Rerouted the vent hose to face the rear of the bike. I do not believe it was in it's holder when this happened. It's possible something may have been sucked in.

Checked the air mix screws. They were one turn out. I set them to two turns. No noticeable change.

Synced the carbs.

Used excessive amounts of Sea Foam throughout this time (and had on occasion previously).

There may be few other things I did and forgot. Feel free to ask. It's been a long couple weeks.


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A little info about the bike.

It's a 94. I've had it for about 5 years and put about 20K miles on it.

K&N Air Filters, MF Battery, Iridium NGK Spark Plugs, new spark plug wires, coastered (still have the air box though).
The "pumpkin" is off an 86. Had my splines turn to dust about 6 months ago. They've since been replaced and lubed proper.
Headlight device (switches from high to low and vis verse when one goes out) has been removed.
Regulator has been replaced with another used one. It's possible the original was fine. That was years ago though.
Added a handlebar voltage meter.

Think that's about it. All of those mods were done 6 months or longer ago.


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I'm assuming it's a carb problem since it happens Right at 4K RPM but I've blasted the jets so many times I just can't imagine anything still being in there.
I didn't see anything horrific inside the carbs when I had them out. Some minor tarnish on the needles but no real buildup on anything. Float needles were fine.

I had the carbs off and cleaned a few times when I first got the bike (about 4 to 5 years ago). I've always been good with the Sea Foam since then.

I'm not sure what else would cause this behavior though.


-Bean
 

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The Professor
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3,147 Posts
Ckeck the gas cap vent, petcock diaphram, fuel filter and make sure the fuel vent is clear.
 

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Registered Badass
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102 Posts
Discussion Starter #4 (Edited)
I've ridden it with the tank's cap open and the petcock on reserve. No change.

How would I go about checking the diaphram?

edit:
Forgot to mention, I've also inspected (with a flashlight) the tank. Didn't see anything scary in there. Also took a swap to the bottom. Seems clean.

I've also drained the crabs a number of times during all this and the gas has always come out clean.


-Bean
 

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Kawika
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441 Posts
The tank would have to be empty or removed, and set on side to keep fuel leaking while petcock is removed and dissassembeld and checked.
I think you could put a vac pump on the vac nipple to the petcock and after applying vacuum, fuel should flow through the lines to the carbs. I would try this before removing the petcock.
 

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Registered Badass
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102 Posts
Discussion Starter #7
If it idles fine and runs at high speed fine wouldn't that rule out a petcock issue?


-Bean
 

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The Professor
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3,147 Posts
If it idles fine and runs at high speed fine wouldn't that rule out a petcock issue?


-Bean
If it consistantly hapening from 4000-5000 rpm you may have an electrical problem and not fuel. I would start with the side stand wires since you bypassed the switch. If the wires have a loose connection at certain speeds the wires can resonate and temporarily loose connection and cutting the ignition circuit.
 

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Undercover Sportbiker
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1,097 Posts
I think I have a side stand switch in my parts box if you wanna try a fix that won't cost a whole lot.

On my Ninja 250, after I rejetted for a new pipe, I had a stumble exactly like you described aroun 9K (14K redline) that was due to the jetting being too rich. The bike pulled fine up to there, and once past, ran fine as well to redline. Would also start and idle fine. What are your jetting numbers? Also - have you checked the rubber on the vacuum slides for small tears / leaks?
 

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Registered Badass
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102 Posts
Discussion Starter #10 (Edited)
I think lance is on the right track. I've been trying some things. I'll post my findings in a day or two. Thanks for all the suggestions everyone.

As for the side stand. I'm beginning to think that was a symptom of the real source of the problem. i.e. a bad wire/connection or something grounding out, something along those lines.

I got some electrical contact cleaner. Sprayed down all the connections and brushed then with a wire brush. I also grounded the side stand wire right at the junction box to eliminate the possibility of the wire being bad along the way to the side stand.
I haven't had a chance to thoroughly test ride it yet though.


-Bean
 

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and the Adventure Cycle
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6,141 Posts
The only time my bike spuddered and had no power around 4k rpm's was when I took a ride with the covers off of the air filters.
It idled fine and ran fine up until then, but once the tach needle hit 4k, it was like riding in 2 foot deep mud. :(
But it wouldn't get better after that, like yours does, so I guess I'm just rambling on without being much help :doh:

Hope you get it figured out.
 

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Registered Badass
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102 Posts
Discussion Starter #12
I visually inspected the air filters and they looked fine but it couldn't hurt to give them a good cleaning. I've got the K&N oil kit so there's no reason not to. Maybe I'll try that tomorrow if it's not raining.


I looked over the wiring harness under the seat. Like the part that gets smashed anytime you put a battery in. Thought that may have been a trouble spot. Took the covering off and all the wires in there looked surprisingly good.

Bike's still running crappy but I've noticed the charging system is doing better since cleaning all those contacts. About a week before this all started I had replaced my brake lights with LED lights. I noticed those made a difference too (nice ha ving a battery meter right on the handlebars). I only need maybe 12K RPM's to be charging the battery. And at speed it holds a solid 14V.

Anyway, I'll post anything new. Feel free to through out other suggestions. I'll be monitoring this thread. And thanks again.


-Bean
 

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Registered Badass
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102 Posts
Discussion Starter #13
Well damn, it's running excellent now.

I had it idling last night and the engine was plenty hot yet I noticed I still had the choke about half way. That obviously wasn't right so I started turning the pilot screws out. To bring it up to where it should be (my normal idle adjust screw is fixed in place due to a previous adventure years ago).

Now it idles where it should while at running temp and the choke off. What worries me is I now have my screws out 3 full turns. That seems outside of the typical ranges I see posted here. So I'm wondering if that's simply masking the real problem (perhaps air related).

I'm still going to clean out the air filters and monitor things. I wouldn't be surprised if one day it starts idling at 5K or something.

I just filled my tank. I'll be monitoring my gas/mileage as well.
The charging system is still working excellently since cleaning the electrical connections. Bike runs smooth as butter too. I just want to make sure it's for the right reasons.


-Bean
 

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The Professor
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3,147 Posts
Well damn, it's running excellent now.

I had it idling last night and the engine was plenty hot yet I noticed I still had the choke about half way. That obviously wasn't right so I started turning the pilot screws out. To bring it up to where it should be (my normal idle adjust screw is fixed in place due to a previous adventure years ago).

Now it idles where it should while at running temp and the choke off. What worries me is I now have my screws out 3 full turns. That seems outside of the typical ranges I see posted here. So I'm wondering if that's simply masking the real problem (perhaps air related).

I'm still going to clean out the air filters and monitor things. I wouldn't be surprised if one day it starts idling at 5K or something.

I just filled my tank. I'll be monitoring my gas/mileage as well.
The charging system is still working excellently since cleaning the electrical connections. Bike runs smooth as butter too. I just want to make sure it's for the right reasons.


-Bean
I would not worry about 3 full turns, as long as it is running great, just ride and enjoy. :beerchug:
 

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Registered Badass
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102 Posts
Discussion Starter #15 (Edited)
Well it's been a couple weeks so I thought I'd update.

As I expected, the work I had done improved the bike's running a great deal but it had not solved the real problem. After two or three days of it running great it started having problems again.

For the past two weeks it would either run smooth as butter or experience the sputters and tach jumping in lower RPMs.
After reading many threads here and studying the bike's wiring diagrams I finally narrowed it down to the wires connecting the pickup coils to the IC Ignitor. Moving those around made the bike run great again.

So today I cleaned out all the gunk that had built up in the area (these wires come out of the left side of the engine next to the alternator wires, then between the frame and drive shaft). Once I had a clear view of everything, there it was, plain as day. The wires were against a hot.. something, exposed and grounding out.
It was just a matter of re-insulating the wires and routing them safely with zip ties so that they don't come into contact with anything scary.

Baby runs like a champ now. Although I need to re-adjust the idle and probably tweak a few other things due to all the work I've done on it the past month+.

Thanks again to everyone on this board!
 

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The Professor
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3,147 Posts
Glad to hear you got her sorted out, now you can ride and enjoy it. :carryflag
 
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