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Discussion Starter #1
Hi, my bike turns over freely with the plugs out, but as soon as the plugs are back in, it will struggle to turn over at all.
I have cleaned the starter and done a ground mod. Any help would be appreciated.
 

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With the plugs out the starter motor doesn't have to work against the engine's compression so I would be more concerned if it didn't crank faster.

If it is cranking too slowly to start with the plugs in, the first thing to check is whether the battery is fully charged. How long has it been sitting since the last start and if it was more than a few weeks what have you done to maintain the battery in between?
 

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Previous history can help with diagnosis. Is this a long standing problem or new? If new, what, if any, changes were made before the problem developed?

Knowing battery voltage would help, both at rest and while cranking with plugs in. It might also help to measure the voltage at the batttery terminals and at the starter terminal in case there is excessive voltage drop between battery and starter.
 

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Discussion Starter #5
I fully charged the battery over night, but I was going to give it a go from my van battery to see if that made any difference.
Its always had a problem really slow cranking when it's hot, but never from cold.
Is there any way to conclusively check whether it's the starter that's toast?
 

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When you cleaned the starter did you clean the commutator with some fine emery cloth followed by cleaning out between the commutator segments? I've found that this makes a world of difference on starter performance, especially if you install new brushes.
 

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If you use any sanding material to clean the commutator make sure you flush it thoroughly with Contact Cleaner afterward to remove all traces of grit. If a spec of grit becomes lodged in the copper it will dig a gouge in the brushes. Also, it is a good idea to burnish the edges of the commutator segments so that they don't have burrs that can accelerate brush wear. I find an old ball point pen is just about right to burnish the edges of adjacent segments (after you have cleaned between them).
 

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I've had a my starter motor full of motor oil in the past..
 

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Hi, my bike turns over freely with the plugs out, but as soon as the plugs are back in, it will struggle to turn over at all.
I just went through this with my new 750 build - even after a full cleaning the starter wouldn't turn the engine over, unless I took the plugs out. I was able to swap out another starter from another 750 and it worked. So the old starter just couldn't crank over the newly rebuilt engine, but it could crank over an old worn out engine. Try another starter.
 
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