Riddle Me This: Possible Timing Issue? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 6 (permalink) Old 06-27-2018, 10:46 PM Thread Starter
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Riddle Me This: Possible Timing Issue?

Backstory: some may remember this a few years ago.

2 years ago my stator rotor warped and shredded my stator. I took the engine out and replaced the rotor and stator.

I put the engine back in 1 year later. It would not start. It would only back fire occasionally. Front block was back firing out of the carb and the rear block was back firing out of the tail pipe. All plugs were sparking, all had gas on the plugs. After much research and cans of starting fuild it was dead to me. I feared the worst, that being something with the timing was messed up but wasnt sure how or where I went wrong. And dreaded the thought of pulling the engine out again.

This last week I decided to look at it again as now i have more time. I Graduated. So the battery was swapped with a new one. And after a few attempts with starting fuild and new fuel it started up and ran for about 5 minutes before I turned it off. It ran very well, wasn't back firing or anything.

Today, it would not start again. It did the following:
-Rolls over and over and over..
-Rear Block is back firing out the tail pipe
-Front block is pushing white exhaust out the tail pipe
-Front block is pushing air through the carb about every 3 turns (hiccuping).. and it just blew flames out of the carb... actually catch the bike on fire for a brief minute. That's when I stopped. I think it's sparking on the wrong cycle (when the intake valves are open), but for only one cylinder? I'm confused how it could have started and ran yesterday.

Am I looking at a timing issue, a coil issue or something else?

If it's a timing issue, the only thing that was moved was the front balancer gear and the stator rotor. I'm confident that they were lined up right. I'm puzzled about what else it could be.

Any help would be much appreciated.

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post #2 of 6 (permalink) Old 06-27-2018, 10:58 PM
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It does have separate chains for the cams. One has slipped?

Compression and leakdown tests could show if the valves are amiss, and which ones. Don't really need a full leakdown reading, just get compressed air into the cylinder at TDC compression stroke.

Sitting a long time makes the carbs dirty and sticky, can make valves stick too.

White smoke can be raw fuel, as in stuck float, stuck valve, or valve timing off.

To know if the chain(s) jumped, you have to align the timing marks and see if they're right. Should involve pulling the valve covers.

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post #3 of 6 (permalink) Old 06-27-2018, 11:03 PM Thread Starter
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A year ago I got a cylinder pressure gauge that screwed into the plug ports and it was holding pressure... a year ago. Is that the compression test you are talking about? If so what psi should it be?

It's weird that it ran at all yesterday...

Thanks for the advice.

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post #4 of 6 (permalink) Old 06-28-2018, 12:35 AM
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Quote:
Originally Posted by duraholiday View Post
A year ago I got a cylinder pressure gauge that screwed into the plug ports and it was holding pressure... a year ago. Is that the compression test you are talking about? If so what psi should it be?

It's weird that it ran at all yesterday...

Thanks for the advice.

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A compression tester will hold pressure until you press the release valve. On a compression test 100 psi should be enough to run, but I think the 750 tends to be toward 130 psi in good condition. Should still run with 100psi. I don't think you could see 100 if the valves are leaking or far out of time.

With a leakdown, you pressurize the cylinder with compressed air and see if the cylinder can hold pressure and how slowly does it leak off. If the air just passes through, then see where it goes, into the intake, exhaust, crankcase, or all three. You use a gauge to actually do the leakdown rate test, but a simple air hose and fitting will show if the valves are leaking. You'll hear it in the carb, muffler, or the oil cap.

If the engine is tip top, the compressed air will try to make the crank turn.
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post #5 of 6 (permalink) Old 07-06-2018, 02:04 PM
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Is it possible you have a plug wire mis-routed?
IE, each cylinder has a wire from it's correct coil AND from the incorrect coil?
If you have crossed wires (one from each cylinder), you'd get one cylinder firing at 60 BTDC & 5 BTDC, and the other at 5 BTDC and 50 ATDC.
If you have all wires swapped to the wrong cylinder, you'd have one firing at 60 BTDC and one at 50 ATDC.

Or, it's backwards completely?
That'd certainly mess up the timing!

I believe (correct me if I'm wrong) that this bike runs on wasted spark, and sparks once per rev, per cylinder.
Normally, the extra spark comes at the end of the exhaust stroke and has no effect, thus is "wasted".

If that's the case, and both wires are swapped:
Then you'd have one cylinder firing with open intake valves (50 ATDC, between exhaust and intake stroke). If it didn't burn the charge at that point, it'd then fire again 50 degrees into the power stroke, giving incomplete burn (black smoke).
The other cylinder would fire 60 degrees BTDC (making it hard to start), and midway through the exhaust stroke (having no effect).

If only one wire is swapped, each cylinder would spark 4 times:
One cylinder would fire with open intake valves, at the proper 5 BTDC, late in the power stroke (50 ATDC), and late in the exhaust stroke.
The other cylinder would fire at 60 BTDC and again at the proper 5 BTDC. The third spark and forth spark would both be during the exhaust stroke and have no effect.


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post #6 of 6 (permalink) Old 07-06-2018, 03:41 PM
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Quote:
Originally Posted by Jason Pittenger View Post
Is it possible you have a plug wire mis-routed?
IE, each cylinder has a wire from it's correct coil AND from the incorrect coil?
If you have crossed wires (one from each cylinder), you'd get one cylinder firing at 60 BTDC & 5 BTDC, and the other at 5 BTDC and 50 ATDC.
If you have all wires swapped to the wrong cylinder, you'd have one firing at 60 BTDC and one at 50 ATDC.

Or, it's backwards completely?
That'd certainly mess up the timing!

I believe (correct me if I'm wrong) that this bike runs on wasted spark, and sparks once per rev, per cylinder.
Normally, the extra spark comes at the end of the exhaust stroke and has no effect, thus is "wasted".

If that's the case, and both wires are swapped:
Then you'd have one cylinder firing with open intake valves (50 ATDC, between exhaust and intake stroke). If it didn't burn the charge at that point, it'd then fire again 50 degrees into the power stroke, giving incomplete burn (black smoke).
The other cylinder would fire 60 degrees BTDC (making it hard to start), and midway through the exhaust stroke (having no effect).

If only one wire is swapped, each cylinder would spark 4 times:
One cylinder would fire with open intake valves, at the proper 5 BTDC, late in the power stroke (50 ATDC), and late in the exhaust stroke.
The other cylinder would fire at 60 BTDC and again at the proper 5 BTDC. The third spark and forth spark would both be during the exhaust stroke and have no effect.
Would it even run?

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