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Discussion Starter · #1 ·
Anyone know the recommended fuel pressure for the P220 Onan engine I recently bought a 4020ps that the gentleman replaced the original fuel pump with an electric one and it's flooding itself out possibly due to the pump being too powerful I'm wondering if I should go back to the og configuration with a new pump or get a lower pressure electric one thanks in advance.
Yeti
 

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I believe that 1-1.5 lbs is enough.
 

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Electric 12 V fuel pumps with 1-1.5 PSI output is the most pressure that the carb float valve can handle as has been mentioned. P series Onans don't have the combined fuel pump/carb as many B43 and B48 series engines do which is where the fuel pump problem exists.
I recommend removing the electric pump and restoring your P220 back to the OEM fuel pump configuration. The OEM pump mounts on the blower housing, its pulse hose goes thru a hole in the housing. The pulse hose is short and connects to a nipple on the engine. As the clamps on the pulse hose can be difficult to access, I modify the hole in the blower housing so the clamps on the pulse hose on the rear of the OEM pump will pass thru this hole. This makes removing/installing the OEM pump much easier as the pulse hose and clamps are already installed onto the pump. The other clamp can be placed onto the hose up a little bit and the pulse hose can be pushed onto the nipple and the clamp moved into place. This all can be done with the with the cylinder cooling baffle removed from the cylinder and no need to remove the blower housing which is a major deal.
After restoring the fuel system to OEM, you will need to do several engine oil and filter changes to get rid of the fuel diluted engine oil which can destroy and engine.
I am aware that OEM pulse fuel pumps are in short supply, but they can be found. :cool:
 

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The only other problem with P series Onans is the later models have a carb with an accelerator pump added to them. There is a diaphragm in the accelerator pump that isolates it from the carb fuel bowl. When this diaphragm ages and cracks, fuel from the pump side will leak into the carb throat both during engine operation and shut down causing fuel dilution of the engine oil. The only source of these parts in in an OEM carb kit from Onan. Two kits are needed, the carb kit and the accelerator pump kit. If anyone does this repair, bear in mind the order in which you disassemble the carb and some old parts may be needed to finish the rework of the carb. Referencing the Onan part number on the carb and the parts manual will guide you to the correct carb kit part numbers. If you do this job, you will need two new intake manifold gaskets as removing the carb along with the intake manifold is the recommended way to do this.:cool:
 

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Discussion Starter · #7 ·
I don't see an accelerator pump in the parts diagram anywhere thr OEM pump is still attached to the engine so gonna try and clean it today and see if it is just dirty but seems as tho caseingersollparts.com has new ones for $50
 

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Discussion Starter · #14 ·
That's gotta be one beast of a machine sir that is the same pump on mine but alas I tried cleaning it and reinstalling and it doesn't appear to be working is there anything else I should check before trying to order a new one?
 

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Pulse pumps have a diaphragm that moves with engine crankcase pressure causing suction and pressure in the pump. There are two check valves, one on the suction side and the other on the pressure side. you can test the pump by pulsing the pump with your mouth and feel the slight suction and slight pressure with your finger.
 

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You do have another option. The DEP required pulse pumps to be standardized long after Onan engines went out of production. Why the DEP got involved with this I have no idea!
The pumps on all small engines are now the same item. These pumps mount differently from Onan pumps and the pulse fitting is on the outside of the pump. I installed one on a customers Onan with a minimum amount of difficulty as he needed the machine running that same day. I don't have a pic of it however.
 
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