Craftsman weed wacker carb floods on prime

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  #1  
Old 04-28-16, 06:37 PM
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Craftsman weed wacker carb floods on prime

Hello group,
I recently rebuilt the carb on my weed wacker. I carefully cleaned all passages and blew them out with compressed air.

This style of motor has the prime bulb seperate from the carb.

When I reassembled it, and when I prime it, It floods the engine with raw fuelmwhen I pump the prime. It has never done this before. When I prime it, huge quantitys of raw fuel squirt into the carb via the main jet passage in the carb throat. raw fuel runs out all over the carb and floods the engine so that it will not start.

Does anyone know how these carbs work so I can try to diagnose this problem? Ive had the carb off several times inspecting it and I cannot find a single thing wrong with it.
Thanks
 
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  #2  
Old 04-28-16, 07:32 PM
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It sounds like you have the fuel lines connected wrong.
 
  #3  
Old 04-29-16, 04:10 AM
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I would bet on Cheese on that one. The primer is pulling gas from the tank from what should be delivering gas to the tank and the discharge side of the primer is forcing fuel into the reservoir overflowing it through the main jet. The primer is pumping gas the wrong direction.

Try swapping the lines on the fittings at the primer.

When you stick it back together, the gasket on the reservoir side (under the four screw cap) goes on first, then the diaphragm with the disc. On the other side (the pump side) the diaphragm goes on first, then the gasket.
 
  #4  
Old 04-29-16, 10:35 AM
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Cheese was right about the fuel lines. It's amazing that it never ran before. I am looking into it more
 

Last edited by hotrodjohn71; 04-29-16 at 10:55 AM.
  #5  
Old 04-29-16, 01:12 PM
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Still problems.
I found a youtube video of a guy changing the fuel lines on a unit exactly like mine:
https://www.youtube.com/watch?v=bVw9G5XVLxE

So with new fuel lines, a new primer bulb and a cleaned carb, My problems now are that first, I dont get a pressurization in the primer bulb like it used to when priming.

I hear a air sound in the carb when I prime the primer like air escaping. It wont start.
I have a gasket and diaphram kit now on order which I got a good deal for 3.99+ free shipping, but all of the gaskets and diaphrams look fine so I dont know what else it could be. The needle seemed to be seating fine when I did the blow test.

Still puzzled on this one.
 
  #6  
Old 04-29-16, 03:44 PM
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I think you got gremlins
You might be able to get a new carb for under 20 bills. I am convinced sometimes even the most simplest carbs have internals that sometimes are un repairable and un diagnosible.
Your metering diaphragm doesn't look that bad but if it is stiff could be an issue. Also your valve diaphragm should be pliable.
 
  #7  
Old 04-29-16, 05:51 PM
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If you have the diaphragms as described above and the fitting on the top of the carb hooked to the line going to the filter and the filter submerged in the gas, you're good there. Now from the bottom side of the carb hook that line up to one of the fittings on the primer and pump the primer. If it doesn't fill with gas, move that line to the other fitting and pump it. It should fill and force fuel out the other fitting.

Then hook a line to the side you're getting fuel out of and run that line back to the tank and you're in business!
 
  #8  
Old 04-29-16, 07:02 PM
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In your 4th picture, you can see a silver round piece with a hole in it pressed into the carb body at 10:30 or so. That piece is supposed to have a tiny thin rubber disk in it. If you try to blow compressed air or poke a wire through this check valve, it ruins it. If the other side of that valve is where gas was coming from, then it got damaged while cleaning the carb.
 
  #9  
Old 04-29-16, 10:04 PM
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Yes I agree with Cheese ~~~

Your check valve is ruined. I have a chainsaw carb with the same problem. It just dumps fuel in the throat of the carb ~!~!

That is one reason we say blow air across the body of a carb and not in it.

Well I say that at times.

New carb may be in order for you ~!~!
 
  #10  
Old 04-30-16, 07:13 AM
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Hi guys. I think we were all thinking about the check valves at the same time and I think I found the problem but not confirmed yet. There are actually 2 check valves. There's the one in the picture that cheese spoke of. I actually took a tiny screw and extracted that plug with the tiny hole in it. The check valve is a tiny rubber disk. That one is OK as I checked it with a rubber tube dooing the suction/blow test after reassembly BUT I think the problem is in the second check valve which is in the main jet. Zama calls it the Nozzle. I didn't know there was a check valve in there but it makes sense since fuel was pouring into carb throat through main jet when priming.
Here's a response I wrote before I read your guys replies:

Well, I am almost sure I have this figured out and I hope this helps someone with a similar problem even though these carbs are cheap and easy to throw away.
After persistently learning all of the ins and outs of this carb over a couple days, I have discovered that Its probably whats called the main jet check valve which Zama calls the Nozzle. There is actually a check valve inside this main jet which if stuck will NOT allow vacuum in the metering chamber hence the lack of fuel in the primer bulb and the air escape sound in carb when priming.
There is also another check valve in the priming system for the idle circuit, but on my carb that has tested good.
If one or both of these 2 check valves are not working, the priming system wont work and the motor will either not start or wont run well at all.
Heres a link to a guy who changed that main jet check valve. It might also be cleanable.

http://www.lawnsite.com/threads/zama...h-pics.326826/
 
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