Could a bad starter *only* spin the engine with the plugs removed?

[LowercaseJake]

Humor me here please, because there's a lot going on at once... Bike is a carby M600.

I've been having symptoms that made me suspect vapor lock (and other clues that led me to this hypothesis, but more on that later). The bike sputtered and died in busy traffic, and I was lucky enough to cross 3 lanes before rolling to a stop. After a few moments the bike fired up again, but the starter was laboring to turn the motor over. Got within a mile of home, happened again only this time no go. Would barely turn 3/4 of a revolution. Assumed my Chinese battery was junk, pushed it the last mile home (which sucked). Installed a brand new fully charged Antigravity. To make sure I wasn't hydrolocked I Pulled both spark plugs before cranking again - abracadabra, the starter spins the crank over... Except, not as fast and strong as I'd have liked. The old "finger in the spark plug hole" method of compression testing was unimpressive, it didn't blow me away (get it? Har Har).

All this babbling is to ask - can a bad starter be just bad enough to not be able to overcome the motors compression? But good enough to spin with the spark plugs removed?

Also want to add that when cranking the bike with the plugs removed and grounded, everything sounds healthy... No metal on metal/grinding/loose parts clanking etc. Flywheel, belts, rods and pistons seem fine. And as for hydrolock - no gas, oil, or other fluid spurted out of the holes, and the plugs are a decent looking mocha color. The crankcase is not overfilled, and there is no smell of gas in the oil. The mechanical fuel pump also checks out OK.

I've just never heard of a Ducati starter failing in such a way (where it's "weak"). Usually they either do nothing, or work intermittently.

I have triple checked my power cables from the battery to solenoid, solenoid to starter, and I have a big beefy 4g ground strap from a lug on the motor directly to the negative terminal. This setup has always spun the engine up fast and strong.

I also suspect  I have an excessive amount of crankcase pressure, but I'll get into that after I determine whether or not I need a new starter.

Sorry for the rambling post... I guess I was hoping there was something else I could investigate while waiting for my eBay starter to arrive.

Thx...

[Howie]

Yes, it is possible, but rare.  Shorted armature could cause this.  Or a really bad bushing.  Before going any further try jumping it with a known good battery.  A lithium battery that went flat while in storage could be permanently damaged.

You also want to confirm the starter circuit is in good order.  This is done by testing for voltage drop caused by high resistance in connections or a component, in this case, starter solenoid.  Don't forget the ground side.This video is for a car, but same thing and it saves a lot of typing.  Easy shade tree method - known good battery to positive on the starter positive and ground directly to the starter body with suitably sized cables.  The bike must be in neutral since you are bypassing everything. 

After you get the bike running check charging system performance, as it could have been your stalling problem.

Oh, fully charge that "junk" Chinese battery and have it load tested.  It might be good.  Never ass u me.

[LowercaseJake]

Thanks Howie

This would be the 3rd battery I'm on (decent customer support, sketchy product - there are 2 in my bin, one stuck at 3 volts the other too dead to register, neither accept a charge). According to my multimeter and my Optimate charger/tester/maintainer, the current battery is OK tho. Swapping in a known good battery yielded the same results.

Several months ago after my second battery failure, I followed the method posted on the Electrosport website to test the charging system with a quality multimeter (after installing the fully charged replacement). Obviously I can't do it again properly since the bike won't start, but at the time everything checked out (the voltage output of both the stator and RR, at idle and while revving). I've also thoroughly  checked the power and ground wiring (both have been upgraded as well). There *could* be a potential flaw somewhere in the stator > RR and RR > battery wires, but that wouldn't explain why a known good battery wouldn't at least temporarily solve the issue.

I will bypass the solenoid and apply power directly to the starter today, thanks, I feel silly for not having thought to do that already.

If we briefly assume the battery, charging components and starter are all OK - what else could be preventing the motor from turning over with the plugs in? I tried starting it with one plug in each cylinder but no luck, it'll give a little extra "chuff", but will not spin at all unless *both* plugs are removed. I'm a little concerned about forcing the issue and making my problems worse. There's no sign of water or fuel in the crankcase but I'll be draining and changing the oil today regardless.

Thank you for taking the time to address my post, Howie.

[Howie]

If you remove the spark plugs and turn the engine by hand how does it feel?  No tool, on a rear stand turn the engine engine by the rear wheel in gear.

In theory the starter can be bench tested, the problem is no published specs I know of so all you can do is apply battery voltage and hear how it sounds.

[LowercaseJake]

If you remove the spark plugs and turn the engine by hand how does it feel?  No tool, on a rear stand turn the engine engine by the rear wheel in gear.

In theory the starter can be bench tested, the problem is no published specs I know of so all you can do is apply battery voltage and hear how it sounds.

I just moved out if a house with a garage and into an apartment so I've been shuttling back and forth for tools. Pain in the arse. I'll grab my Pitbull stand today and turn it via the rear wheel.

I'm very worried this is something serious and expensive. All of the anecdotes I find when googling this problem are either bad starter or hydrolocking. But there's no sign of the latter, no gas shooting out the holes. I mentioned in my OP I suspected excessive crankcase pressure because after a ride a couple weeks ago I discovered a good amount of oil leaking from both the breather and the forward valve cover, despite both being well sealed. I don't wanna let my mind run wild before I rule out the starter and charging system, but this is very, very concerning. I keep telling myself if a rod or valve was bent or broken, the engine wouldn't turn at all, or at the very least I'd hear obviously alarming sounds if it did, but I'm sure that's not necessarily the case.

[ducpainter]

How's the oil level?

[LowercaseJake]

How's the oil level?

Exactly in between the bottom of the sight glass and the line of the sight glass, that's with the bike directly upright. I've always been fanatical about oil levels, I check to be sure they're neither too high or too low prior to every 3-4 rides.

[ducpainter]

Exactly in between the bottom of the sight glass and the line of the sight glass, that's with the bike directly upright. I've always been fanatical about oil levels, I check to be sure they're neither too high or too low prior to every 3-4 rides.

Then it isn't hydro-locked.

Check all the grounds like howie suggested, and put voltage direct to the battery.

[LowercaseJake]

 things I want to reiterate - A: with both plugs out, the starter spins the engine steadily, but compression is  extremely low using the crude finger test. However, it feels the same in both cylinders. B: the engine *does* turn with the plugs in, it just labors to do so... I can hear it struggle getting through each full revolution before pausing to give it a break. Again  no alarming sound of broken parts... The symptoms are 100% identical to that of trying to start a car or bike with a weak or dying battery. Except I've now tried 3 different batteries, all fully charged with a reliable charger. I won't have the means to bypass the solenoid or turn it by hand till I can get to my garage later today.

[LowercaseJake]

Then it isn't hydro-locked.

Check all the grounds like howie suggested, and put voltage direct to the battery.

Ducpainter - how do you know it isn't hydrolocked by the oil level? Or are you saying that because I've never over filled the crankcase? In theory, if something was causing excessive crankcase pressure, this could have theoretically forced oil into the cylinders, causing hydrolock? Again not trying to get ahead of myself here, I'm just agonizing a bit since I can't bypass the solenoid or turn the motor by hand right at this moment.

[ducpainter]

Most engines hydro lock due to overfilled cases...usually fuel, not from liquid in the cylinders. It takes a lot of liquid to lock up a motor. The amount forced in by excessive crankcase pressure would most likely just burn. Your oil level isn't low, which indicates crankcase pressure isn't pushing it anywhere.

You've had the plugs out, and didn't mention them being soaking wet, so I'm saying your issue isn't mechanical, but electrical. Again, it takes a lot of liquid to lock up a motor.

Of course you're closer, and my crystal ball has limited range these days, so I could be mistaken. My experience tells me that your issue is likely very simple.

You'll feel better if you stop imagining everything that 'could' be wrong, and wait until you can diagnose the problem.

[LowercaseJake]

Points well taken Ducpainter.

Confirmed the following are fine: solenoid/switch. Power and ground wiring. Battery. Motor turns by hand via the rear wheel, in all gears, with no noticeable scary sounds.

A few months ago while the bike was on my old lift, I attempted to start it - thumbing the button produced only rapid whirring sound. Bypassed the switch and same result. I'd heard that a weak/worn starter could have "dead spots", where the brushes were worn. Since this was a newer Rick's starter I thought it to be a bit flukey, so I pushed the bike back and forth a few times, clicked up and down through the gears, afterwards the bike fired right up.

Well, last night as I was troubleshooting it happened again as I was testing/cranking, testing/cranking. . I think it's obvious I have a bum starter, and the current situation has hastened its demise. Best way to describe the sound coming from the starter is a radio controlled toy revving/whirring.

Now if you guys would humor me once more:

I already explained I'd been experiencing issues with sputtering / stalling that I'd written off as heat soaked fuel hoses.

Now, each time the bike died it would start up relatively easy almost immediately afterwards. This time, during a 3 mile ride from A to B it stalled 3 times, becoming more and more difficult to crank/ start each time until it finally would barely crank at all then of course not start. And, I was getting a flickering oil pressure light at traffic lights which would go away with a gentle twist of the throttle.

Also, remember how I've now gone through 2 lifepo4 batteries which I originally attributed to being "cheapo Chinese batteries". Plot thickens.

Pull the left cover and investigate the stator? I do have a spare OEM stator in excellent condition. And what's in there is an aftermarket Electrosport.

As a reminder I've thoroughly investigated the power and ground wiring, the health of the battery, confirmed I'm getting fuel/spark, turned the motor over by hand, and also attempted to bump start the bike, which didn't even come close to working.

[Howie]

That spinning noise you hear is a bad sprag, not the starter  The sprag is not allowing the starter to turn the engine, therefore the radio controlled toy revving/whirring. 

With all the problems you are having maybe it is time for professional help.

[ducpainter]

That spinning noise you hear is a bad sprag, not the starter  The sprag is not allowing the starter to turn the engine, therefore the radio controlled toy revving/whirring. 

With all the problems you are having maybe it is time for professional help.

I'd add that changing parts is not an effective method of diagnosis. Why change a stator without knowing it's faulty? Have you put a meter on the battery, or the leads from the stator to determine whether it's charging?

Check the hoses under the tank to make sure you didn't kink the vent after looking around under there. That could explain the sudden stalling issue.

[LowercaseJake]

That spinning noise you hear is a bad sprag, not the starter  The sprag is not allowing the starter to turn the engine, therefore the radio controlled toy revving/whirring. 

With all the problems you are having maybe it is time for professional help.

LOL, I don't blame you for saying this. Unfortunately I need to ride or die (no pun intended) on my own efforts.

Thanks for clearing up the issue with the sprag gear, that saves me a lot of frustration Howie. I have a light flywheel and a light clutch basket - professionally installed - could the lack of weight be mimicking a bad sprag? Especially since it's intermittent?

You're correct about impulsively changing parts. I certainly would've inspected the stator before simply installing a new one, but the starter motor was something I was ready to assume was faulty.

I don't think I need professional help, I just need to get *some* of these issues solved so the entirety of these issues is less overwhelming. I do appreciate the help from both of you.