Low Compression, other causes before I rebuild?

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mitsukid124
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Low Compression, other causes before I rebuild?

Post by mitsukid124 »

I have an 86 spree that I am trying to get running and before I swap piston rings I want to make sure that is actually the problem.

Currently the spree will start and idle for a little bit and then die. Originally I thought it was just running rich because the plug was wet.

What I have done so far:
- Pulled it out of the shed and started it up just fine and would idle no problem. Gave it any gas and it'd die
- Pulled the carb off to clean and reassemble. Also put in a new plug. No change
- Pulled out the petcock and cleaned the fuel filter. Starts no problem but will not stay idling anymore
- Pulled the spark plug and did a compression test. Test reads 95 psi.

I want to try adding a little oil to the cylinder and redo the compression test. Also, I will be draining the oil and cleaning everything out to rule out that, but I don't think that is a problem because the plug seems wet with oil and gas.

The other problem is what could be causing the plug to be wet/ flooded engine? And is it related to the low compression reading?

Last year this thing ran perfect for me up until I took a digger messing around in the yard with a buddy.

If any of you guys have ideas or suggestions on what to check I will give it a shot. I just don't want to replace rings if its not the actual problem.

-Cole
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Meatball
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Re: Low Compression, other causes before I rebuild?

Post by Meatball »

Could be a few things, as you know.

The "digger" may have tweaked the muffler to cause an exhaust leak. Proper seal is vital. The motor needs the back pressure from the exhaust canister to operate correctly.

The "digger" may have caused an air leak. Check every possible spot from stem to stern. Carb, intake, airbox connection, etc...

May be a stuck reed valve. Its possible that its opening enough to idle but not allow it to revv.

Air filter. The Foam air filter element is just as important to the system as anything else. You wouldnt think something as simple as a piece of foam could wreak havoc but it actually serves two purposes. It keeps particles out of your motor but it also provides resistance to the incoming air to create the vacuum needed to operate the petcock.

Bad gas? How long was it sitting?...

Try cleaning the carb AGAIN. Blow compressed air through every hole and follow the instructions HERE: http://hondaspree.net/wiki/index.php5?t ... ture_Guide
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jakubman1
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Re: Low Compression, other causes before I rebuild?

Post by jakubman1 »

Crank seals ?
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Wheelman-111
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Re: Low Compression, other causes before I rebuild?

Post by Wheelman-111 »

Greetings:

Assuming you held the throttle wide open (or removed the carb) for the compression test, it should run at 95psi, though maybe not well. It's a pain to remove the manifold and you'll need gaskets to reassemble, but bad reeds could be another reason for low compression.
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eclark5483
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Re: Low Compression, other causes before I rebuild?

Post by eclark5483 »

Polymers age. The reeds are a polymer. When a polymer ages, it tends to get dry and brittle. As Wheelman stated, that could be one cause of low compression. Ideally you want a compression of 100+. Yours is low, but not quite to ring job levels. Best to check something simple first like reeds before tearing into the head. Kill 2 birds with 1 stone here at this point, by possibly porting your intake and reeds for better performance while excluding them from being a reason for low compression.

And easy quick fix that is very common to do, is just unscrew the reeds from the cage, then flip them around. Don't worry about replacing them just yet. Hit noiseguy up for gaskets. See if things can't be improved without spending a dime or too many hard earned bucks first... fixing these gets expensive. Best to tackle intake right now before moving along to the next step.
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