Author Topic: Craftsman 3.7 won't pick up gas  (Read 1115 times)

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Offline 3000 FPS

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Re: Craftsman 3.7 won't pick up gas
« Reply #10 on: October 24, 2021, 10:27:28 pm »
That diaphragm in the bottom picture where those reed valves are does not look correct to me.   I would get another kit and try all the diaphragms to find which one fits all the holes and such the best.    That particular diaphragm is the one that pumps the fuel.   The other diaphragm on the opposite side of the carb is for metering the fuel.  If that one is not correct then it is possible it will not lift the needle correctly and allow fuel for the carb. 

But like Cut4fun has said it is really hard to tell from pictures.   

One other thing to check is to make sure the impulse coming from the crankcase is open and not blocked in any way.   
You can take the carb off and shove a small wire into the hole to make sure it goes all the way into the crankcase and also make sure the gasket is lined up correctly for the impulse to the carb. 
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Offline pmeyers

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Re: Craftsman 3.7 won't pick up gas
« Reply #11 on: October 25, 2021, 11:21:58 am »
Thanks 3000 FPS The gaskets and diaphragms from the after market kit matched those that I removed from the carb, but it maybe an issue of quality. Also I had someone work on it unsuccessfully so don't know what they did. I have a walbro oem kit coming. I  did verify that the impulse ports are open into the crankcase and that the carb gasket port is aligned. I'm wondering if  there is something different that I need to do with the vent line on the fuel tank, last picture? Otherwise stumped.

Offline pmeyers

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Re: Craftsman 3.7 won't pick up gas
« Reply #12 on: October 25, 2021, 11:58:01 am »
Cut4fun, in your description of your craftsman 3.7 that you are selling you say "New tank vent with new duckbill." I am trying to repair a 3.7 and you have offered advice in another thread. Could you please tell me what the vent should look like on that saw? If that is set up wrong could it result in no fuel be lifted by the car? Thanks

Offline 3000 FPS

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Re: Craftsman 3.7 won't pick up gas
« Reply #13 on: October 25, 2021, 01:36:54 pm »
If someone worked on the carb before it could be that they installed the wrong diaphragm in it so you need to check and see if there are any other diaphragms that could be a better match.   
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Offline Cut4fun .

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Re: Craftsman 3.7 won't pick up gas
« Reply #14 on: October 25, 2021, 02:38:26 pm »
I was wondering if the saw would start and somewhat run before you pulled apart?  If not could be like Roger is saying too.
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Offline Cut4fun .

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Re: Craftsman 3.7 won't pick up gas
« Reply #15 on: October 25, 2021, 02:43:43 pm »
Cut4fun, in your description of your craftsman 3.7 that you are selling you say "New tank vent with new duckbill." I am trying to repair a 3.7 and you have offered advice in another thread. Could you please tell me what the vent should look like on that saw? If that is set up wrong could it result in no fuel be lifted by the car? Thanks

Merging threads.  Cant keep up where they are all being posted.

Pull up into top of tank inside.  Same as this one I did on a 3.3.

Missing that duck bill wont stop it from drawing fuel like Roger said.

That crack IMO might be the culprit for sure.



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Offline pmeyers

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Re: Craftsman 3.7 won't pick up gas
« Reply #16 on: October 25, 2021, 03:10:40 pm »
It would fire if I drippeed gas  in but not continue to not run. Was  wondering, probably a stupid question but the vent tube does not have a duckbill, is that only to prevent leakes or can it affect the ability to lift fuel?

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Re: Craftsman 3.7 won't pick up gas
« Reply #17 on: October 25, 2021, 06:23:49 pm »
It would not be the vent.  Usually if a vent is not working it does not stop the fuel to the carb until it has ran for a little bit.   Then as soon as you open the gas cap it would repeat the process again.    You can always just leave the gas cap off and see if it starts and draws fuel. 
PP 505, 475, 445.
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Offline pmeyers

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Re: Craftsman 3.7 won't pick up gas
« Reply #18 on: October 25, 2021, 07:17:33 pm »
Thanks 3000FPS, that's good to know. So I might have found the problem. I found a small crack in the plastic fuel connection on the carb. It might be sucking air. I went over it with JBWeld and I'll let it sit overnite and try it in the morning. I'll never undertsand why they used plastic on a part like that.

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Re: Craftsman 3.7 won't pick up gas
« Reply #19 on: October 26, 2021, 06:56:36 am »
If the plastic part crack ed I never tried to seal one. I removed the plastic part and just grind down the metal nipple left in and used it or replaced the whole fitting altogether.

GL on sealing it if that works. Let us know.

They sell all metal or the plastic and metal still.

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