# Carburetor Spitback Causes



## Haywire Haywood (Nov 16, 2008)

My 076 seems to spit a lot. I've read that worn piston skirts can be one cause. What are other possible causes for excessive spitback and... what is "normal" for a well used 076?

Ian


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## GASoline71 (Nov 16, 2008)

When my saw was chewin' snoose... it spit a lot too...

Heh, heh... 

Gary


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## blsnelling (Nov 16, 2008)

I think all saws spit some but the only cause I know of excessive spitting is a worn intake skirt on the piston. Can you hear it slapping the cylinder wall?


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## litefoot (Nov 16, 2008)

Brad,
Can you explain how a worn piston skirt causes the blowback? I guess I'm not the sharpest knife in the drawer on this stuff. I'm just trying to get a visual of what's happening.


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## Haywire Haywood (Nov 16, 2008)

GASoline71 said:


> When my saw was chewin' snoose... it spit a lot too...
> 
> Heh, heh...
> 
> Gary



Hey Hey... I'm the class clown... You're the oil guy. Stick to your assigned duties... LOL

Ian


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## GASoline71 (Nov 16, 2008)

HAHAHAHAHA!!!



Gary


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## Taxmantoo (Nov 16, 2008)

In a four stroke, it's a leaky intake valve. In a two stroke, a reed valve or the piston holds the charge from blowing back up the intake. Trimming the skirt or enlarging the intake port can do it, as can wear on the skirt.


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## eba1225 (Nov 16, 2008)

Can it be fixed / replaced?


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## jeeptj19992001 (Nov 16, 2008)

eba1225 said:


> Can it be fixed / replaced?



get a new pistton to fix it


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## RiverRat2 (Nov 16, 2008)

litefoot said:


> Brad,
> Can you explain how a wotn piston skirt causes the blowback? I guess I'm not the sharpest knife in the drawer on this stuff. I'm just trying to get a visual of what's happening.



I think Gary's explanation is pretty good!!!!!!

LOLOL!!!! Just kidding,,,,  


this phenomenom is more prevalent on piston ported two strokes,,,, or reed valve motos that have reed/piston wear issues,,,


with the piston rocking in the bore the worn skirt can no longer effectively seal the Lower compression zone below the rings in the fuel charge area,,,
so not all of the fuel charge is pushed into the transfers as designed,,,

so as you give the tired moto more throttle it tends to spit back through the carb because it has become inefficient from excessive wear,,

which in turn causes the airfilter to get soaked and the motor can actually run too rich,,, become hard to start fouls plugs,,, etc. etc.

A new piston and fresh rings will work wonders!!!!

on a reed valve moto piston/rings and reeds!!!!!

Hope that helps,,,,,


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## Busmech (Nov 16, 2008)

*spitback*

A plugged exhaust will cause that, check the arrester screen if you have one.


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## barkies (Nov 16, 2008)

:hmm3grin2orange: better check that muffler for suckback while your at it 

My pistons prefer pants over skirts 


opcorn:


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## Taxmantoo (Nov 16, 2008)

RiverRat2 said:


> which in turn causes the airfilter to get soaked and the motor can actually run too rich,,, become hard to start fouls plugs,,, etc. etc.



I always figured it was a guarantee of too rich, because some of the air goes through the carb forward, mixing it with gas, then goes through the carb backward, mixing gas into it, then goes through once more forward, picking up a third dose of fuel.


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## Musclenut (Nov 16, 2008)

My little poulan was spitting real bad. Practicly squirting. It had a blown cylinder gasket. The cylinder was moving up and down a 16th". It has a reed valve by the way. It will still squirt if it's runing extremely rich. I found that out tinkering with the carb.


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## Haywire Haywood (Nov 17, 2008)

I'm thinking it may be a combination of a couple things.. It was hard starting yesterday come to think of it. I checked the air filter and it was oily and fairly clogged with fines and dust. I switched filters and it started right up, so I suspect it was running rich in combination with maybe some skirt wear. I'll have to check that filter more often than the 372 I suppose.

thanks,
Ian


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## computeruser (Nov 17, 2008)

Haywire Haywood said:


> I'll have to check that filter more often than the 372 I suppose.



Understatement of the day award goes to...Ian!


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## Haywire Haywood (Nov 17, 2008)

Hehe... what the heck, an award is an award I suppose. It's just like the certificates of appreciation at work. Doesn't affect my paycheck at all. LOL

Ian


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## computeruser (Nov 17, 2008)

Haywire Haywood said:


> Hehe... what the heck, an award is an award I suppose. It's just like the certificates of appreciation at work. Doesn't affect my paycheck at all. LOL
> 
> Ian



Yup. That about sums it up.


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## RiverRat2 (Nov 17, 2008)

Haywire Haywood said:


> I'm thinking it may be a combination of a couple things.. It was hard starting yesterday come to think of it.* I checked the air filter and it was oily and fairly clogged with fines and dust. I switched filters and it started right up, so I suspect it was running rich in combination with maybe some skirt wear.* I'll have to check that filter more often than the 372 I suppose.
> 
> thanks,
> Ian



yep!!!!!! Thats what they do!!!!!! its double edged sword!!!!!!

Keep a couple of plugs handy,,, if you are running the mesh type filter they are notorious for letting fines by which are not good for your moto,,, probably helped accelerate the wear on the intake skirt

We need to put a piston kit in that puppy and get a flocked filter!!!!!!

That piston slapping the bore isn't helping things BTW!!!!!!


:monkey: :monkey: :monkey:


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## Haywire Haywood (Nov 17, 2008)

It is a flocked filter....  I haven't noticed any slapping sounds either.. Ran it this afternoon in some 30" hickory. I need to go check the filter again and pull the plug to see what it looks like. I got hot and sweaty, then wet then cold. I retreated indoors when I got back and got into some dry duds. I'll do some maintenance on it tomorrow after work and see what it looks like.

Ian


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## woodyman (Nov 23, 2008)

If the skirt is worn how long can you run the saw before any damage(besides just replacing the piston)happenes.


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## Lakeside53 (Nov 23, 2008)

The skirt wears from day one.... at some point it's just too slappy and spitty.. Collateral damage? Little...


I've seen blowers (and some saws) where the skirt is razor thin and big chunks broken off.


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## woodyman (Nov 23, 2008)

Would a worn skirt lessen the compression and what else besides running rich would make a saw spit fuel out the carb?


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## Lakeside53 (Nov 23, 2008)

Compression isn't necessarily affected... Often a worn skirt is an indicator of high hours, but I often see slappy pistons on saws with decent compression - poor filter maintenance (crap sucking past around the edges of the filters) .. or more usual holes in the filters (mainly flocked types...


Other reasons - bad main outlet valve check valve.


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