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Fuel Troubles On Sears Gt18

carburetor onan fuel fuel delivery

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35 replies to this topic

#16 Cvans OFFLINE  

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Posted May 22, 2013 - 09:00 PM

This is starting to sound like a plugged vent in the gas cap. What happens if you leave the cap loose and run it?



#17 Utah Smitty OFFLINE  

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Posted May 23, 2013 - 02:37 PM

Smitty does the carburetor have a Fuel solenoid on it?  I've got one in the shop that has a bad one on it, it won't run with out the choke and even then it wants to surge.  But it does it all the time not just after a while.

The carb doesn't have a fuel solenoid... just the diaphragm type fuel pump on the side of the carb that runs off the crankcase pulses.  Another thing I've noticed is that it runs better when there's a full tank of fuel--which makes you think the pump is weak, but when I first started it, it only had about a gallon of fuel in it, and the pump quickly brought fuel up to the clear filter by the carb.

 

Smitty



#18 Utah Smitty OFFLINE  

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Posted May 23, 2013 - 02:39 PM

This is starting to sound like a plugged vent in the gas cap. What happens if you leave the cap loose and run it?

 

Thanks for your input.

 

That's what I thought earlier last year when I was trying to get it to run. The cap has the cork float and needle that shows empty or full, etc. It has venting to allow the flat rod to turn the needle.  Even so I ran it without the cap on--no change.

 

Regards,

 

Smitty



#19 olcowhand ONLINE  

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Posted May 23, 2013 - 02:49 PM

I forget, does this carb have the brass float or the old composite float?  The composite float is notorious for hanging up.


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#20 MH81 ONLINE  

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Posted May 23, 2013 - 04:26 PM

The carb doesn't have a fuel solenoid... just the diaphragm type fuel pump on the side of the carb that runs off the crankcase pulses.  Another thing I've noticed is that it runs better when there's a full tank of fuel--which makes you think the pump is weak, but when I first started it, it only had about a gallon of fuel in it, and the pump quickly brought fuel up to the clear filter by the carb.
 
Smitty


Smitty, do you have an old tank around? Something you could really set the neighbors off with by tying it to the hood and running it around for a while?

Something is telling me you should eliminate or confirm the pump as a next step.
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#21 Utah Smitty OFFLINE  

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Posted May 23, 2013 - 10:27 PM

I forget, does this carb have the brass float or the old composite float?  The composite float is notorious for hanging up.

I'm not sure, but I think it's the composite float.  That could be it... maybe I need to pull the top off the carb the next time I'm at mom's and see... I assume you can purchase a brass float for them...

 

Smitty



#22 Utah Smitty OFFLINE  

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Posted May 23, 2013 - 10:28 PM

Smitty, do you have an old tank around? Something you could really set the neighbors off with by tying it to the hood and running it around for a while?

Something is telling me you should eliminate or confirm the pump as a next step.

I'll try the tank thing... that will let me know if the pump is the culprit as you said.

 

Smitty



#23 olcowhand ONLINE  

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Posted May 24, 2013 - 08:40 AM

I'm not sure, but I think it's the composite float.  That could be it... maybe I need to pull the top off the carb the next time I'm at mom's and see... I assume you can purchase a brass float for them...

 

Smitty

 

 

Yep, on ebay: http://www.ebay.com/...=item4cf299c4f2



#24 Golden Hurricane OFFLINE  

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Posted June 14, 2013 - 06:37 AM

olcowhand may have hit upon an original thought with his comment that "sounds like the fuel level is dropping in the bowl"...if we think about this, it means that the bowl is being emptied faster than it is filling. So, the issue would be on the suction side of the bowl. Gee, this doesn't sound too promising. Back to where you started? I always start with the easiest and work toward the hardest or most expensive thing to change, replace or modify. I would begin with the fuel line. Are you sure it is the correct size? New or old? I think you have also cleaned out the tank. How about the fuel filter? Heck, I have forgotten everything you have done.



#25 Utah Smitty OFFLINE  

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Posted June 14, 2013 - 08:40 AM

olcowhand may have hit upon an original thought with his comment that "sounds like the fuel level is dropping in the bowl"...if we think about this, it means that the bowl is being emptied faster than it is filling. So, the issue would be on the suction side of the bowl. Gee, this doesn't sound too promising. Back to where you started? I always start with the easiest and work toward the hardest or most expensive thing to change, replace or modify. I would begin with the fuel line. Are you sure it is the correct size? New or old? I think you have also cleaned out the tank. How about the fuel filter? Heck, I have forgotten everything you have done.

Thanks for your input

 

I cleaned the tank and installed new fuel line from the tank to the carb.  The carb was rebuilt last year, including the pump.  The fuel cap is vented so it isn't creating a vacuum.  The pump works well... and the engine runs well sometimes... I suspect it has a plastic float and it's hanging up. When I get a moment, I'll drive up to mom's and pull the top off the carb and change the float.

 

Regards.

 

US



#26 Golden Hurricane OFFLINE  

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Posted June 14, 2013 - 10:54 AM

Well, UT Smitty, it sounds like you have been thorough. Please keep us informed as to what is your final solution. That way, we all benefit. Happy Trails!



#27 llskenandore OFFLINE  

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Posted November 15, 2014 - 12:08 PM

iam very new to this sight but I was reading the different posts on the sears gt 18 I have one and had the same problem , this is what I found. the plastic gas tank if not kept  full of gas will form water over a very short time I put a clear fuel filter on and didn't believe how quick water was forming in the tank I plan to install a sediment bole to help I hope, i


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#28 fxdb96 OFFLINE  

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Posted December 05, 2014 - 12:13 PM

Remove the fuel line from the carb and crank over to see if fuel pump is working well.  


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#29 Utah Smitty OFFLINE  

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Posted April 28, 2015 - 11:09 PM

Well... I gotta get after this again... mom's been using my GT18 for general duties around her place--hauling the weed sprayer, riding over the fields to the irrigation ditch when her water turn comes, etc.

 

She needs a large machine that can mow the grass on either side of her lane-approx 1.700 feet.  She's been using the little MF7 I repowered, but it's hard on that little machine... she sure loves it to mow the grass around the house, though.

 

Anyway, I'm not sure where to go from this point, but two things popped into my mind.

 

1. When I first removed the electric pump ('cause the engine still died out with it working), I ran new fuel line from the tank to the carb.--this was at my house.  I also put a kit in the carb and the pulse type fuel pump.  I started the engine and let her run about 1/2 throttle for almost an hour--no issues.

 

I hadn't noticed it, but the fuel line was lying against the drive belt and wore a hole through it, so I just put a piece o 1/4 inch copper tubing to splice it

 

--is it possible that the 1/4" copper tube is creating a greater restriction and the pump can't over come it?

 

2.  I put an automotive-style see through fuel filter on the fuel line to let me know if fuel is getting to it.  Is is possible that the fuel filter--which is about 1 1/2" in diameter and 2" long--is too big and the pump vacuum can't work with it??--maybe I need one of the smaller metal or plastic filters with it.

 

As I mentioned in one of my previous posts, the engine has about 85-90 psi compression on the two cylinders... a little low, but consistent.  Is the low compression likely creating a problem with the operation of the pump.

 

And, another question--if I put an electric fuel pump back on it, do I need to do something with the integral fuel pump on the carburetor, since the only fuel inlet nipple is on the pump?

 

Thanks for any input.

 

Smitty



#30 Alc ONLINE  

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Posted April 29, 2015 - 05:26 AM

When you had the electric fuel pump on was the filter before or after the pump ? Reason I ask is some fuel filters will not flow on gravity or suction side on these small engines . I've been using the yellow fuel lines to make it easier when you have fuel related problems , you can see if there's fuel , bubbles ect  







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