engine missing, I've tried everything - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 24 (permalink) Old 07-21-2016, 01:56 AM Thread Starter
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engine missing, I've tried everything

1988 Vulcan 750

My new bike has one tiny issue I've spent all day on and I can't figure it out...... It's missing.

Symptoms: Front plugs have carbon on them, engine is missing. Plugs are not wet at all. Rear plugs are clean.

What I have done:
- Swapped CDI
- Swapped Junction box
- Swapped front and rear coils
- Swapped tanks and petcocks
- New fuel line
- Plug inspection
- Verified power coming from ignition on all wires
- Ohm tested pickup coils (500 ohms right, left side of 4 pin plug)
- installed new carbs

On the chance it is a jet, Just to eliminate any possibilities, I'm going to ride the bike tomorrow and see if I can get it to behave or misbehave above 3500 RPM.

Side note of odd occurrence: With both Junction boxes the bike wouldn't start unless I jumped B/R to Y/R, but when I went back to the original Junction box it started without the jumper. (electrical gremlin causing this missing perhaps?).

So as a seasoned VN owner and having built 5 bikes from a frame I've done the usual. The ONLY thing I haven't swapped is the RR. Could it be giving me a voltage issue perhaps that is causing one cylinder to miss?????

Give me some ideas on where to stick my meter and find the missing link.


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post #2 of 24 (permalink) Old 07-21-2016, 07:28 AM
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Your engine is missing ... how did you lose your engine?

When you say the front plugs have carbon on them, you mean they've got abnormal buildup? Like that's probably the cylinder thats missing (but still getting a dirty burn?)

The B/R to Y/R would not have anything to do with one cylinder missing. They're involved in the starter motor only, so once the bike is running they're out of the equation.

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post #3 of 24 (permalink) Old 07-21-2016, 08:30 AM
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carb, almost has to be carb issue with all the other testing done..

does not rule out internal issues tho.

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post #4 of 24 (permalink) Old 07-21-2016, 09:00 AM
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Since you have done all that stuff and it hasn't helped. Have you cleaned your ignition switch under your key? Sounds crazy but that thing wreaks all sorts of havoc.

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post #5 of 24 (permalink) Old 07-21-2016, 11:33 AM
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Quote:
Originally Posted by Thorn View Post
Your engine is missing ... how did you lose your engine?

When you say the front plugs have carbon on them, you mean they've got abnormal buildup? Like that's probably the cylinder thats missing (but still getting a dirty burn?)

The B/R to Y/R would not have anything to do with one cylinder missing. They're involved in the starter motor only, so once the bike is running they're out of the equation.
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post #6 of 24 (permalink) Old 07-21-2016, 11:51 AM
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post #7 of 24 (permalink) Old 07-21-2016, 11:52 AM Thread Starter
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Quote:
Originally Posted by Thorn View Post
Your engine is missing ... how did you lose your engine?

When you say the front plugs have carbon on them, you mean they've got abnormal buildup? Like that's probably the cylinder thats missing (but still getting a dirty burn?)

The B/R to Y/R would not have anything to do with one cylinder missing. They're involved in the starter motor only, so once the bike is running they're out of the equation.
The relevance of that was that the junction box seems to be malfunctioning but I had swapped to another one that was doing the same thing it was good just to be thorough in case there were two independent controls to the igniter from the junction box that had a known issue that resolves itself


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post #8 of 24 (permalink) Old 07-21-2016, 12:28 PM Thread Starter
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Here's a video.


When I let the choke off it goes down to a loping idle. Could this be a sync issue?


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post #9 of 24 (permalink) Old 07-21-2016, 02:52 PM
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Plugged pilot/idle jet?

Will it run down the road above 3500rpm or higher?

If it's only affected at idle, it's behaving the same as mine right now. Which I think has a plugged pilot/idle jet in the front carb. Will not idle without the choke, hot full choke puts it around 1100rpm. Low speed running is poor and the power is unpredictable from idle to mid transition, like low speed street corners. Runs pretty much fine at highway speed.

Pull both plug wires off one cylinder and try to start it. This will at least show which cylinder is dead. If it won't start, the cylinder you unplugged is the only one firing. If it starts, unplug the other cylinder and repeat.

Sounds like you did the Two-Wire mod with the jumper to get the start circuit going. There is a wire in that start circuit that runs to the IC ign., we just aren't sure what it does.

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post #10 of 24 (permalink) Old 07-21-2016, 03:56 PM Thread Starter
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That's the weird thing, I've had carb issues with plugged jets. This thing is solid, not unpredictable. Doesn't try to die, just idles SUPER LOW and lopes. Has a shake when revving, so I know it is missing. It's consistent though..... runs as if it thinks it should be running that way. No uncertainty, problems. My second VN I built a few months ago had plugged jets and it missed, but it would try and die and power was not smooth. This one is solid and runs well, but has that low idle, lope, shake to it and only runs at 1100 with the choke fully on. I'm going to bring the idle up and see what it runs like with the choke on then.


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