Craftsman Weedwacker flooding

[plpitts1]

Hello, I have a Craftsman Weedwacker Model 306.794400. Starts and runs about 10 seconds and dies. Seems to be flooding itself. When I pull the plug it is soaked. I dry It off and it does the same thing. I have cleaned the carb., set Metering Lever, fresh gas, good filter, set L&H screws at 1.5 for starters. The other thing that seems odd to me is that if I prime it, gas come out the back of the carb. Its my understanding that the primer only pulls fuel through the carb and back to the tank. So I don't know why it comes out the back when priming. All this is going on with the choke open.
Thanks,
Pat

[StarTech]

Unable using the model given, Please double your numbers.

Now with that out of the way. If you or someone else installed new fuel lines or has removed the lines it is a good possibility that the primer bulb assembly or fuel lines are connected backwards. This is assuming you have a separate primer setup. I have straighten out several chainsaws this year for this problem and a string trimmer is no different plumbing wise.

[bgsengine]

Sounds like you got a leaking check valve in the carburetor - probably time to spring for a new carb. (In most cases, new carb is same price as an OEM Rebuild kit) But as KE4 said- that model number does not come up so , could not identify which carburetor you have - Might be a 356. prefix?

[plpitts1]

oops, Model 316794400, somebody else did do the fuel lines, but I think that if they where hooked up wrong, it would not run at all or pump gas from what information I have. Check valve sounds most likely, I appreciate your fast responses.
Pat

[StarTech]

Actually it would as the primer if connected backwards would fill the diaphragm side and then push fuel out the main nozzle causing the problems your describing.

The lines normal connects where the fuel with the fuel filter goes to carburetor fuel pump side then a line from the port near the metering diaphragm to the suction side of the primer and a line from the discharge primer port back to the fuel tank.

[bgsengine]

Actually it would as the primer would fill the diaphragm side and then push fuel out the main nozzle.

No - you're thinking float carb - This is a Cube Carb - MTD built Ryobi branded as Craftsman 753-05133 is the carburetor

And turns out THOSE are pretty pricey items (I was guessing at it being a Husqvarna-Poulan-Weedeater built one)

if I recall, you'll have a Walbro WA carburetor, and in some cases (depends on your carb numbers) they do have replaceable check valves.

But, if check valve can't be had, and at the price of a new carburetor, may as well toss it in the scrap heap and buy a new Homelite from Home Depot for the same price (Which will pretty much be a Ryobi, as MTD sold that part of the business to TTI, which now builds them under Homelite, Ryobi brands.)

[StarTech]

Brian hate to disagree here but if you look at the setup is highly possible. I know for sure as I have already more than 4 units in the this month alone that were the lines were connected backwards by operators unfamiliar the setup of the remote primer.

BTW: I was editing my previous the explain the actual line setup when you posted your last comment.

[bgsengine]

Brian hate to disagree here but if you look at the setup is highly possible. I know for sure as I have already more than 4 units in the this month alone that were the lines were connected backwards by operators unfamiliar the setup of the remote primer.

BTW: I was editing my previous the explain the actual line setup when you posted your last comment.

They still have a high speed nozzle check valve to prevent exactly that issue - If it pushes gas OUT it will leak air IN and either way the check valve is bad.

The rest of it is a closed circuit between the fuel filter and the return line - no matter which way the fuel moves, it is still not supposed to push any fuel out into the carburetor venturi which you seem to imply - If it does, then it ain't working right.

The purge system is only for the purposes of removing air space that may reside in the carburetor, allowing for easier starts - if the carb leaks gas out, or air in, it is going to have problems, whether or not the lines or purge system are hooked up right.

It is pretty simple - With a cube carb, for best performance, you do not want ANY air in the fuel circuits unless or until it is metered in (control) - purpose of the high speed check valves is to prevent air from contaminating the fuel charge before it is pulled (not pushed) into the venturi. Pressure on the fuel in the carburetor should *NOT* inject any fuel into the venturi Otherwise, you'd have no hope of properly tuning the engine as pressure will vary depending on heat and fuel tank vent, etc. - only negative pressure (vacuum) in the venturi should be pulling fuel into the carburetor.

So , either way, if it is getting fuel into the carburetor throat by any means than a negative pressure area (in relation to atmospheric) in the venturi, then the carburetor is not working properly.

[StarTech]

It basic fluid flow with check valves...Put them in backwards and they operate backwards.

Not going to say another word on this other than think about it or try it...

[bgsengine]

It basic fluid flow with check valves...Put them in backwards and they operate backwards.

Not going to say another word on this other than think about it or try it...

That's what Ive been trying to explain - If you have a check valve in backwards (if it was even possible to install backwards), the carburetor isn't gonna work right either.
Trust me, I have *tried* it many many times. I used to actually recondition these *Specific* carburetors (back when parts were cheap, carbs were expensive, and rebuilding was worth while- made some money selling "Reman" carbs.. new carb cost as much as a new trimmer - I could rebuild those carburetors and re-sell then with warranty for half that. ) - the only ones that leaked as described under pressure tests were the ones with bad check valves.

Already thought about it, trying to see what you must be thinking, and all I can figure is you're thinking about the purge system - but in no case should the purge be able to push gas through the carburetor so that gas is coming out the venturi - not in a cube carburetor... no matter which way they are applying pressure, pressure in the metering chamber should NOT be able to push gas into the venturi. *think* about it. - if line pressure or purge pressure (regardless of what direction it comes from) were able to push gas into the carburetor nozzle and dribble out the carburetor throat, the engine would be impossible to properly tune.

If you get gas coming through the main nozzle in the venturi by using the purge bulb, something definitely ain't right, and line hookups will have nothing to do with that. The high speed check valve in those carburetors is the final point which fuel can reach un-aided. Do a teardown of enough of these carburetors, and really look at the check valves and how they work, it's easy to see. Now, if the check valve is bad, then, YES it is easily possible for the situation you describe, (and a backwards check valve is a bad check valve) - But otherwise, no.