Possible SS180 air leak, looking for ideas on how to check

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colin
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Possible SS180 air leak, looking for ideas on how to check

Postby colin » Tue Jun 11, 2013 6:52 pm

Posted on scootrally if you like replying there:

http://www.scootrally.com/phpBB3/viewto ... f=2&t=2499

Have an SS180 that's had it's head rehoned and piston cleaned up, new rings and base gasket. Carb rebuilt, new gaskets, rubber, etc. Old pipe, not clogged up bad but not dranoed out or anything. Stock jetting (and everything else).

After fixing a leaky carb top due to a bad (new) gasket and possibly old crud, and making sure everything is properly and evenly snug, I get the following behavior:

Starts real easy with choke on and idles fine with choke on. Pushing in the choke it revs up a bit and unless I feather the throttle, will die.

My first thought is "air leak", but I'm wondering if anything else would cause this exact behavior. Exhaust is snug, no apparent leaks. Carb is snug and on good, no apparent leaks or looseness. Idles great and sounds fine with choke in.. can leave it there forever. Turn off the choke, one second later revs up and dies. Very repeatable.

Since it's an SS180, there's no view-port in the flywheel so I can't spray anything in that way to check for fly-side seal issue. Just wondering if there's another good way to check seals on this engine to be sure it's that before I break the whole thing down. Can't remember if you can change out the clutch side seal without splitting cases... I probably need to change the original clutch plates anyway so I'll be in that side....

Thanks for any ideas. I might try rigging something up to check pressure using the breather hole...
Skyyywalker

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imjuanpablo
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Re: Possible SS180 air leak, looking for ideas on how to check

Postby imjuanpablo » Wed Jun 12, 2013 10:08 am

Typically only running on the choke is indicative of an air leak somewhere.............

However, did you do a complete rebild of the carb and soak all the bits (including jets) in one of those soaker-type pant can carb cleaners? I swear by them.......many many running issues miraculously go away after using it, and blowing compressed air through the carb channels and jets.......

edit***************

the carb soak method worked when normal rebuild/clean jobs didn't fix my problems, was the point I was trying to make......
Last edited by imjuanpablo on Wed Jun 12, 2013 1:25 pm, edited 1 time in total.
John F.

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Zeets
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Re: Possible SS180 air leak, looking for ideas on how to check

Postby Zeets » Wed Jun 12, 2013 12:01 pm

I'm with John... tear the carb down and check for a clogged idle circuit or air jet. On a Vespa, it's not really a choke as much as a enrichener or primer, since you're essentially just letting in more fuel to richen the bike up for starting purposes, you could also check for an air leak by starting the bike with the carb box lid off and then using your hand to partially cover the carb mouth (choke off or in). If the engine settles down and idles, then you're looking at an air leak, if it still refuses to run then the problem is in the carb.
Zayretow

70' Vespa Sprint (2009 LML power)
74' Yamaha RD350 (pinger)
2008 Suzuki DRZ-400SM (thumper)

dirtyhandslopez
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Re: Possible SS180 air leak, looking for ideas on how to check

Postby dirtyhandslopez » Fri Jun 14, 2013 4:31 pm

What they said on the air leak business.
How did you "re-hone the head"? Never heard of that before.
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colin
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Re: Possible SS180 air leak, looking for ideas on how to check

Postby colin » Mon Jun 17, 2013 4:28 pm

dirtyhandslopez wrote:What they said on the air leak business.
How did you "re-hone the head"? Never heard of that before.


Meant rehoned jug, with new head (old one had pitts in the ignition area).

I had rebuilt and cleaned the carb twice already, but the result was the very tip of the pilot (or starter... forget which) jet has a hole through it and although I hit everything with vinyl brush and cleaner and soaked things, was still clogged. Gotta poke a strand of old cable through that apparently! All good now at idle and running well.
Skyyywalker

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Zeets
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Re: Possible SS180 air leak, looking for ideas on how to check

Postby Zeets » Tue Jun 18, 2013 9:20 am

These work extremely well for cleaning jetting out, I have a set I bought an autoparts store years ago.
Zayretow

70' Vespa Sprint (2009 LML power)
74' Yamaha RD350 (pinger)
2008 Suzuki DRZ-400SM (thumper)

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Mikeh
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Re: Possible SS180 air leak, looking for ideas on how to check

Postby Mikeh » Mon Jun 24, 2013 11:29 pm

Remove the exhaust, drain the oil, and plug the exhaust with a rubber stopper.

Then fill the carb with diesel or keroseen. If the fluid leakes out anywhere you will see it drip from somewhere.. I got this tip from here; (but wmasa cuts images off.. so go here; http://home.comcast.net/~toodoo2/leaktest.jpg
Image

dirtyhandslopez
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Re: Possible SS180 air leak, looking for ideas on how to check

Postby dirtyhandslopez » Sat Jun 29, 2013 1:28 am

Mike, reading between the lines is one thing, guessing what's on the outside of the lines is another :shock:
Yes, it's late and the wine did flow tonight :)
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