Bike will / won't start

krikster · L Plate Warrior Joined: 05 Dec 2015 Karma :

Ok here it goes.....I have a bike that I have gone through with a fine tooth comb trying to figure out the problem. The bike has a new battery, new plugs, new fuel, new stater, and new switch. However if I use the switch to try and crank it, it will try to crank, but no start. Yet if I roll it off it cranks in the first 5 feet of a small roll. So that tells me the engine is easy to start, but for some reason will not fire up when using the switch.

P.S. Tried checking to see if the starter was weak by using jumpers with a car and still did the same as just the battery itself! Evil or Very Mad

What could possibly be the issue in this freaky situation? Confused

NJD · World Chat Champion Joined: 11 Mar 2015 Karma :

Telling us what bike you have may be a good place to start. Rolling Eyes

krikster · L Plate Warrior Joined: 05 Dec 2015 Karma :

Sorry about that......84 Kawasaki 750cc Vulcan

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

The fist test is to find out if the problem appears to with the starter or its connections, or with the rest of wiring leading up to it. You can test this by shorting out the starter relay.

Find the starter relay, probably next the battery. It will have a couple of thick wires going to it, and a multi-plug with some smaller wires. There should be some rubber boots covering the connectors for the thick wires.

Peel back the rubber boots. Using an insulated screwdriver, and probably wearing gloves as well, bridge the two connections. Expect some sparks.

If the engine turns over when you bridge the connectors, the problem is likely to be with your starter relay, starter button, or the wiring between the two. If the engine fails to turn over, the problem is with the starter motor or its connections. Check the thick wires for a good connection before pulling the starter apart.

Pete. · Super Spammer Joined: 22 Aug 2006 Karma :

are you saying that it will crank over on the button but not fire up but if you push it and bump-start on the clutch it will fire up easily?
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy

krikster · L Plate Warrior Joined: 05 Dec 2015 Karma :

P.addy · *Formerly known as* P. Joined: 14 Feb 2008 Karma :

More power. Got a car battery to hand?

Polarbear · Super Spammer Joined: 24 Feb 2007 Karma :

krikster · L Plate Warrior Joined: 05 Dec 2015 Karma :

Luckyfish13 · Renault 5 Driver Joined: 30 Nov 2015 Karma :

When you shorted out the different parts to the circuit did it act as expected?
Eg. When you connected starter directly to battery did it still spin? If not the starter motor is finished.

Assuming all the tests you have done came back negative, I'd be checking the compression next.

If not, the alternator probable isn't making enough AC power to run the starter motor. Get the multimeter out and do a voltage test at the alternator while the bikes running...it should stay steady around 14V. Any higher and the regulators screwed. Any lower and there could be discontinuity in the circuit to the battery...
For discontinuity check the resistance as follows:

Remove ONLY negative lead from the battery
Put multimeter in OHMS mode
Touch either of the terminals to the connection where the main wire comes out of the alternator to the reg/rec, then touch the other end to the middle of the positive terminal on the battery.
If the OHMS reading indicates continuity (0.5 OHMS or infinitely open reading) then the alternator is finished.

Check the compression first though, I bet that's the problem...
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krikster · L Plate Warrior Joined: 05 Dec 2015 Karma :

P.addy · *Formerly known as* P. Joined: 14 Feb 2008 Karma :

Could do what Pete did on my blackbird. Give the starter, JUST the starter 24v.

Pete. · Super Spammer Joined: 22 Aug 2006 Karma :

Yep we worked all day on that bike and couldn't find a solution. The only cure to hand was to wire a second battery between the starter solenoid and the starter and it was on the button every time after that. I think it was a fault in the loom personally but without stripping the whole loom apart we'd never know.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy

Luckyfish13 · Renault 5 Driver Joined: 30 Nov 2015 Karma :

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

It takes very little electricity to make a spark, it takes a lot to crank an engine.

However, if the battery is weak - or the starter motor resistance is very high - then the starter motor seems to take all of the power, not leaving enough to make a decent spark.

So, questions:
1. Start motor cranking. You say it cranks the same whether it is using the bike battery or using the bike battery and an additional car battery. Does it crank good and fast, or is it a bit sluggish?
2. New battery. Did you charge the new battery, or just fit it? Have you charged it since doing all of this experimenting? Always diagnose problems like this on a good condition battery that has been on a charger overnight.

If the battery is charged then the next place to look would be the thick wires between battery and starter motor. The red wire should go from battery to solenoid and then solenoid to starter motor. The black wire will only go part of the way, using the frame/engine as a general ground.
The bike is 31 years old so corrosion is going to be a problem, particularly where dissimilar metals meet. Check where the thick earth (black) lead meets the frame or engine for corrosion. If you find any, clean it up. Also see if any of the thick leads are frayed near their ends. For a real shortcut, run an additional thick earth lead from the starter motor back to the relay.
If none of that works, I would be stripping down the starter motor.

Also, you keep saying you replaced the stater - I assume you are referring to the stator plate and not the starter motor. It's a misspelling which could lead to very different advice being provided.

krikster · L Plate Warrior Joined: 05 Dec 2015 Karma :

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

My money is on a bad earth, try applying 12v straight to the start as others have said.
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331X2 · Crazy Courier Joined: 10 Jul 2013 Karma :

Not sure if it's relevant but I'd be stripping the starter motor and checking the condition on the commutator and brushes, carbon build-up can short the segments and rob power leading to slow cranking, as can arcing as a result of stuck or worn brushes.