Tach not working and engine firing erratically - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 27 (permalink) Old 01-01-2013, 07:56 PM Thread Starter
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Tach not working and engine firing erratically

Hi,

First of all I would like to wish everyone a Happy New Year. I have an 89` model and from time to time I like to log in and read new posts here. Am not much of a mechanic or an electrician but managed through some problems quite well with the help of this site. Now to the problem,recently I was riding and suddenly the tachometer stopped working and the engine lost alot of its power. I immediately turned off the bike and checked for anything unusual. When I tried to restart the bike, it backfired like a boss and ran erratically. Luckily I was not far away from home and managed to drive it back. Now I read some posts here and assuming its an electrical problem and having a few spare parts I did the following. I changed both coils and the ignitor box. Checked the spark plugs and HT cables, voltage on voltmeter looks normal, checked for any loose connections and wiring and all seems ok. I have a good MF gel battery. Problem still there and am running out of ideas. Does any one have any more ideas on what to check?
Cheers, Alan

89` Vulcan 750 - a.k.a HellRaiser

Last edited by malteser66; 01-01-2013 at 08:02 PM.
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post #2 of 27 (permalink) Old 01-01-2013, 08:07 PM
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I think the first thing I would look at is my grounds. Battery to frame & engine to frame. Do not just visually look but like wire brush clean and add a little dialectric grease. Faulty grounds will cause the elect system to do strange things. Go for the easy stuff first!

04-3,200 miles bought July 2011 with 928 miles. Loaded with acessories to many to list here, see my albums for more details! I also make a custom tank bib specific for the 750 if anyone is interested, ck my albums for some pics.
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post #3 of 27 (permalink) Old 01-01-2013, 08:16 PM
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Most common cause is a loose battery connection.
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post #4 of 27 (permalink) Old 01-01-2013, 08:28 PM Thread Starter
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Thanks for your replies, but correct me if I am wrong,as regards to ground wires on this bike, there is one from the battery to the frame, one from the battery box to the engine and the one from the starter to the frame. I have a couple of others for the accessories but I guess these won`t affect the engine. Not sure cause I havent` inspected these well but I will remove, clean and grease properly each and everyone of them. As regards the 2 thin wires feeding the coils, what kind of voltages should these show and are they +ve and negative, I have one red and one green on each coil. Should there be a constant voltage or is the voltage continoously changing depending on the spark needed? Sorry for all the questions but I am trying to learn a bit more as I am trying to avoid further damage and the Stealership...

89` Vulcan 750 - a.k.a HellRaiser

Last edited by malteser66; 01-01-2013 at 08:34 PM.
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post #5 of 27 (permalink) Old 01-01-2013, 09:08 PM
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Don't remember the starter having a ground wire to frame, think it is grounded by bolting to the block.

04-3,200 miles bought July 2011 with 928 miles. Loaded with acessories to many to list here, see my albums for more details! I also make a custom tank bib specific for the 750 if anyone is interested, ck my albums for some pics.
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post #6 of 27 (permalink) Old 01-01-2013, 10:06 PM
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The 2 red wires are always hot when the key is on. The other 2 go to the ignitor.
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post #7 of 27 (permalink) Old 01-02-2013, 12:00 AM Thread Starter
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Ok RomeoBravo172 and Dariv, I will have to check the wiring better and will come back to you......hopefully with a resolution to this problem. Thanks again for your quick input!!

89` Vulcan 750 - a.k.a HellRaiser
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post #8 of 27 (permalink) Old 01-06-2013, 05:49 PM Thread Starter
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Unhappy

Hey,
I`m back, unfortunately bike is still the same, removed and cleaned earth wires from battery box to frame and from battery box to engine, checked the voltage in thin red wires on coils, voltage shows 12.58v, i noticed that voltage on volt meter keeps showing 12.xx volts where before it used to go up to 14v as i revved the engine. I hope it has nothing to do with rectifier or stator, I have changed to a shindengen mosfet rectifier about 1 year ago and eliminated the bullet plugs on all wiring and used soldering and shrinking pipe + taping properly to make sure to have proper insulation and protection.. Bike was working excellent till a few weeks ago. Guess I have to go to stealership as I really wouldn`t want to remove all the taping and wiring and work i did before and maybe for nothing...... sheesh

89` Vulcan 750 - a.k.a HellRaiser
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post #9 of 27 (permalink) Old 01-06-2013, 06:29 PM
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Any checks for good connection on the pick up coils?

02 honda sabre 1100
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post #10 of 27 (permalink) Old 01-06-2013, 08:29 PM
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Quote:
Originally Posted by malteser66 View Post
Hey,
I`m back, unfortunately bike is still the same, removed and cleaned earth wires from battery box to frame and from battery box to engine, checked the voltage in thin red wires on coils, voltage shows 12.58v, i noticed that voltage on volt meter keeps showing 12.xx volts where before it used to go up to 14v as i revved the engine.
You initially said your tach stopped working and the bike lost power.
The tach runs off the front ignition coil output, so it could be a bad or weak coil.

These bikes need a strong battery voltage to run properly...it is possible that the coils are OK but your charging system is weak.

When you rev the engine the voltage at the battery should rise. The bias voltage(from the battery) in the coil should be the same voltage you see on the battery. MOSFET R/R's usually read a steadier 14 volts even when not revving the engine.

I suspect your R/R is weak.....it may be weak due to a weak stator output.

Before bringing it to the stealership....try using Slim's charging system spreadsheet and run ALL the tests. you can post the results here so we can help you decipher it.

Here is the thread: https://www.vn750.com/forum/showthread.php?t=21206
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