Thank-you for this web site; marvellous and helpful!  I am repairing a friend's 86 savage.  He had taken it apart, reassembled it and got scared when "it made a loud noise"!   I've been repairing motorcycles for over 50 years, predominantly British , Italian ,spanish and older Japanese; this 86 Suzuki is a new bike to me!  As you may have guessed, I am having trouble with the device known as the electric starter!  Upon your recommendations, I upgraded the system by fitting a starter limiter gear; I modified the original outer case cover to suit.  I also set up the starter decompression solinoid according to your recommendations. Upon reassembly, the bike started right up.  Now, it does not. Upon pushing the starter button, the decompression solinoid clicks, I can see the exhaust valve rocker arm go down with the valve cover off. With a fully charged battery, the engine will only turn one revolution, it will not spin the 500 rpm suggested.  I have tried boosting the battery; no change in starter performance.  Do these starter motors get weak? Yes, the connections are tight! The bike has less than 10000 miles on it and is completely original.

From your post I have to believe you completely understand that a battery can show 12+ volts and have no ability to produce the amps needed. But that is the first thing my head went to. If it's trying to push against what has to be zero compression,,
You got it in neutral?
Clutch in, does it roll easy in gear?
How old is that battery?
I'm really fond of my $20.00 battery tester from Harbor Freight.

The ground on the right rear of the engine, clean and tight?
If you try to start it and touch that ground, if it's hot,it's resistive.

don't worry... be happy  

Yeah, pretty much, I'm thinking it's a timer circuit in the board that fires the decomp.
You Can manually activate the decomp, some people have removed the decomp solenoid and they manually make the decompression happen by pushing on a lever.

If you were to get it in gear and roll the motor to get the piston at close to BDC of the end of the power stroke, the starter would just be pushing through the exhaust stroke followed immediately by the intake stroke,, maybe you would learn Something that would help us
Sorry for your troubles, but, that is kinda the reason for this place to exist.


Upon reassembly, the bike started right up.

You didn't get to hear that loud noise and it started after that scary loud noise?


Maybe get ahold of the decomp lever and hold the exhaust valve open and see if the starter can handle that?

I'd jumper twelve volts straight to the starter. If it spins it over, then you can dig deeper.If you can get it past compression and on the down stroke, you will be giving it a chance to get spinning good before it hits compression.
I can't wrap my head around a solenoid that pulls the contacts together and carries the current to spin the thing One Turn and then drop out.

Just to be certain I understand how you are describing the situation, you heard it run, it ran with no drama or excitement, and after that, no joy?
Or did you start it and it made a loud noise and after that, it would not start?

IDK why it would or if it can, but I would want to get something, maybe a stiff wire with a hook, on the decomp solenoid cable and see if the thing stops turning the starter at the same time the decomp solenoid times out. If you feel the cable relax at the moment that starter stops, it would be interesting.

Just tried jumping the starter directly,as suggested; the starter spins the engine over even through the compression stroke! It does sound slow to me but it does work! I am now suspicious of power loss through the solenoid...does this seem feasible?

IDK how old the battery was before you did that, but it's a Lot older now.
This is where the battery tester can come in handy.
If you charge it and it doesn't take a good amount of time before it's showing the 12+ a healthy one does, but you can hear it slowing down, sometimes the you can use the tester to hit it with some real quick loads,on off on off quick, till it recovers to around ten volts, charge it, torture it,I'm really not sure exactly why it helps sometimes, the article I read said something about it knocking some kinda oxide or something off the plates. I've rejuvenated a few that way. It's not a solution that works in five minutes. Takes a few
Charge,/ Challenge cycles and sometimes it's just time for a battery.