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Next On The List Of Gt18 Frustrations

onan b48 b-48 carb sears gt18

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#1 Utah Smitty OFFLINE  

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Posted June 24, 2012 - 07:49 PM

Well, I resolved one issue with my mom's GT 18, but another one has resurfaced.

When we bought it, the PO said he had to run the tractor with the choke pulled out slightly (about 1/4") and that every once in a while it would just stop, but that it would start up again okay.

When I got it, I cleaned out the carb and disassembled the fuel pump on the side to see if the diaphragms were bad. They didn't have holes in them and were still pliable, so I re-installed them.

Now, the tractor will be running fine, then cut out and stop. Sometimes it will start right away, and sometimes it has to wait for a while. I don't have a lot of experience with the carbs on the Onan B48, but it looks a lot like the one on a B&S 18 hp twin I used to repower a Snapper mower--which also has problems even with a new kit.

I suspect this is a common problem for these carbs... can anyone give some insight as how to correct it? I have heard of people putting low pressure electric fuel pumps on--do you just connect it to the fuel inlet on the carb, or do you have to do something else?

Thanks in Advance,

U.S.

#2 KennyP ONLINE  

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Posted June 24, 2012 - 08:07 PM

I made a plate out of aluminum to replace the pump. This is a little blurred, tomorrow I can get a better pic and some measurements.
Image0031.jpg
Here's the same pic I pulled the above from:
Image003.jpg
Here's another to give you an idea:
Image008.jpg

I am using a pump I got from Napa for small engines.
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#3 olcowhand ONLINE  

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Posted June 24, 2012 - 09:16 PM

Yes, you can just hook the line from an electric fuel pump to the inlet on the carb's fuel pump. The vacuum pumps tend to retain junk, but you've already cleaned that out, so you're good to go. Make sure it's a low pressure pump, 1 1/2 to 4psi max.
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#4 Utah Smitty OFFLINE  

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Posted June 24, 2012 - 09:48 PM

I made a plate out of aluminum to replace the pump. This is a little blurred, tomorrow I can get a better pic and some measurements.

I am using a pump I got from Napa for small engines.


Thanks, Ken,

Do you have a picture of the pump and the model or part number?

#5 KennyP ONLINE  

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Posted June 25, 2012 - 06:20 AM

I found a pic of the pump, finally! I have since remounted it under the battery tray, so it's a bit hard to get a pic of right now.
Image002a.jpg
Not sure if I can find the receipt for it.
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#6 MH81 ONLINE  

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Posted June 25, 2012 - 06:33 AM

Sorry to hear of your recurring troubles Smitty. Any chance it's something floating around in the gas tank causing this?

#7 KennyP ONLINE  

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Posted June 25, 2012 - 06:55 AM

It's been close to 15 years since I took the vacuum pump off. If I remember correctly, the mechanic at Onan/Cummins said it was best to remove the old pump and make the cover plate. Then you don't have to cap the vacuum port out of it. I had access to the aluminum plate, so I just made the plate to fit. As soon as I get enough light outside to get a decent pic of the plate, I'll get it and measurements of where the fitting is. I haven't had any problems with the plate, had to replace the original pump with this one. But the tractor had set for about 5 years.

#8 KennyP ONLINE  

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Posted June 25, 2012 - 07:18 AM

Got a better pic of the plate:
Image034a.jpg

From what I can measure, the fuel fitting is 5/8" over and 5/16" higher than the right mount bolt in the pic. That is 1/2" thick aluminum plate I made it from. I think I used the original pump gasket to seal it up, been a long time since I did this.
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#9 Utah Smitty OFFLINE  

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Posted June 25, 2012 - 05:12 PM

I found a pic of the pump, finally! I have since remounted it under the battery tray, so it's a bit hard to get a pic of right now.
Image002a.jpg
Not sure if I can find the receipt for it.


Don't worry about the receipt, Kenny. That looks identical to the Mr. Gasket pump I bought for my mom's IHC 2400 tractor. It's been bypassed, now and run to a regular fuel pump, so maybe I can use it.

Regards,

U.S.

#10 olcowhand ONLINE  

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Posted June 25, 2012 - 06:28 PM

You'd want to use the Mr Gasket #42S pump, as it's low pressure...2 to 3 1/2psi. Their model #12S is 7psi & will overpower your float & needle. Other than the numbers, these two pumps look identical.
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#11 MH81 ONLINE  

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Posted June 25, 2012 - 10:04 PM

You'd want to use the Mr Gasket #42S pump, as it's low pressure...2 to 3 1/2psi. Their model #12S is 7psi & will overpower your float & needle. Other than the numbers, these two pumps look identical.


Thanks Daniel, been thinking about one of these for my GT 5000. Nice to have the part number.

#12 Utah Smitty OFFLINE  

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Posted June 26, 2012 - 01:04 PM

I can't remember which pump mom's used, but we put a fuel regulator on it to keep the pressure low--seems to me it overpowered the needle on the carburetor if we didn't.

U.S.

#13 olcowhand ONLINE  

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Posted June 26, 2012 - 02:14 PM

I can't remember which pump mom's used, but we put a fuel regulator on it to keep the pressure low--seems to me it overpowered the needle on the carburetor if we didn't.

U.S.

Even with a 42S mounted with a TJD Wisconsin, I had to use a regulator also.

#14 KennyP ONLINE  

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Posted June 26, 2012 - 02:28 PM

No regulator on mine. Works great!

#15 Utah Smitty OFFLINE  

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Posted June 27, 2012 - 10:52 PM

Thanks Daniel, been thinking about one of these for my GT 5000. Nice to have the part number.


I've found these pumps all have no more than 4 or 4.5 psi pressure. They're also priced about the same as the Mr. Gasket 12S, but have higher review scores:

Carter P60504. One plus with this pump is that it comes with an inline filter (removable). There's some on eBay right now for about $45 incl freight.

Airtex E8016S

Airtex 110E8251

Regards,

U.S.
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