Starter gears getting locked up

[SVracerjosh]

Here's a strange one... I just picked up a 32k mile '10. Normally the bike starts great. Occasionally though, when I hit the start button the starter motor engages but something seems jammed and won't turn the motor over. If I 'bump' the engine from the rear wheel it seems to free whatever the problem is then it starts ok.
Since I'm doing a bunch of work anyway I popped the alternator cover and nothing looks amiss. it's clean, gears look good, everything rotates smoothly by hand.
I suppose there's a chance its the starter motor itself, but doesn't seem like it.
Any thoughts in what might cause this?
Thanks everyone!

[DannoXYZ]

Hydrolocked cylinders from leaky petcock dripping petrol through carb's leaky float valves into engine when it's parked. Next time it locks up, remove spark-plugs and crank. Does it spin easy and send spray of liquid petrol out?

[SVracerjosh]

Fascinating theory, and you may be spot on. I had left the petcock on prime by mistake after I drained out the old fuel and refilled the tank with fresh + seafoam to start clearing the carbs. So, it was slowly dripping fuel in the same timeframe as when I had the starting problem - and I only noticed the next morning when there was some fuel on the floor.
Cleverly deduced, Holmes :-)

[Triple Jim]

Check your carb float valves if you haven't already, since leaving the petcock in "prime" alone won't fill the cylinders with fuel.

[DannoXYZ]

Yeah takes 2 failures lining up: petcock flow when OFF, leaky or set to PRI. AND non-sealing float valves. But not uncommon to have both with age.

Hydrolocked cylinders will cause starter gear to work extra hard to compress liquid petrol. If you have enough liquid petrol in cylinders, it will win over starter ring-gear. Had this happen to my race-bike when I 1st got it.

[SVracerjosh]

You're completely right, both prime + float seals leaking to get the fuel to drip through.
Fingers crossed that the float seals is just the goop from sitting for a couple years & it will clear itself with the carb treatment.
Worst case I'm not afraid of taking the carbs off, but it looks like a giant hassle with the airbox in place!
Back in the day I used to swap stock carbs and exhaust to Keihin & Muzzy between prod. twins and supersport races on my EX500. No airbox :-)

[DannoXYZ]

Even with airbox, it's possible to extract carbs in about 5-10min. I did write-up somewhere. Maybe I'll update procedure with video...

In meantime, run through some PEA-based fuel-system cleaner.

[SVracerjosh]

Well, most everything is back together & overall we're in pretty good shape. Except, it still stumbles a bit at low RPMs. I'll run it a few times a day for a while and if the seafoam does its thing, if it doesn't improve I'll pull the carbs next weekend. Thanks everyone for the suggestions!

[Triple Jim]

The chance of Sea Foam doing anything helpful is near zero. It's 10 to 30 percent isopropyl alcohol, which I wouldn't want in my fuel system. You have a better chance with a PEA based cleaner that Danno suggested above, but it's still not a sure thing. Chevron's Techron is one.

https://seafoamworks.com/uploads/pub...210608-sfi.pdf

[DannoXYZ]

The isopropyl alcohol in Seafoam is similar to ethanol in modern petrol. Absorbs moisture from air, causes separation and all sorts of corrosion and clogging problems.

You'll want to use fuel-system cleaner with heathy dose of PEA:

- Red Line SI-1
- Techron Concentrate Plus
- 3M Max Strength Fuel System Cleaner #08814
- Royal Purple Max Atomizer 18000
- Gumout All-in-One (might be off list soon due to lowering amounts of PEA)

If you've ever done any carb scrubbing and cleaning with Seafoam, then tried PEA cleaners, you'll notice they work A LOT better.

[SVracerjosh]

Perfect, thanks. Saved me the trouble of searching for which are PEA products :-)