520H fuel pump question

[formariz 11,849]

My 520 runs fine without any surging. However, at startups when cold it needs choke on for a little while otherwise it will surge. One kind of has to release it slowly over a period of about one minute or less. Although I know that it does not mean that fuel is not going through it, at that point one does not see any fuel  in the filter. Once initial surging goes away one then sees small amounts of fuel coming into filter.

My diagnosis, is that at startup with high throttle it is getting fuel starvation because fuel has possibly backed up down line and perhaps also  pump is not as strong as it should be.I have already obtained another pump and will change it any way. Is this a typical attitude of 520's? I am not familiar with this type of pump, but it seems to be more efficient than the typical mechanical ones in the engine like the Kohler's from what I read. I also wonder if installing a one way check valve which I also obtained will help in reducing fuel back flow when stopped? I am just concerned as to how much more resistance such a valve would place on fuel movement from this type of pump. Any thoughts and suggestions appreciated as always.

Edited November 25, 2018 by formariz

[953 nut 51,536]

I have them on a couple of mine and they help at start up. Take the check valve and blow on it in both directions, hardly any resistance in flow direction.

[lynnmor 6,762]

Air in the fuel filter is common, not an issue.  I believe your problem is a dirty carburetor.

[gwest_ca-(File Mod) 10,485]

Air in a fuel filter on the suction side of a fuel pump has always bothered me. A good portion of the vacuum produced by the pump is lost to it thinning out the air in the filter. That leaves very little vacuum to draw up fuel since the pulses are so short in duration.

If the air could be totally eliminated from the filter will bet pump performance would increase at least 5x.

Anyone that has experience using an electric vacuum pump which pumps much faster to place a vacuum on a system knows it takes a long time to remove the air.

With air in the filter it is a wonder the short fuel pump pulses draw any fuel at all.

 

Air can be compressed and the opposite is expanded.

Fuel can not.

 

Garry

[953 nut 51,536]

10 minutes ago, gwest_ca said:

Air in a fuel filter on the suction side of a fuel pump has always bothered me.

That had bothered me until I rationalized it as being a cushion for the pump. If the fuel pump were delivering all it is capable of delivering it would overwhelm the engines needs. If the system were liquid solid and the carburetor needle and seat were doing their job well the fuel pump would be internally hemorrhaging unless there was a re-circulation valve and line like is used on fuel injection systems.

[formariz 11,849]

So it looks like my original diagnosis was correct. Installed a new fuel pump along also with a one way check valve. Immediately the difference was obvious. Not only was I able to lower choke completely right after start but even though Tractor worked correctly otherwise (so I thought) the difference specially at idle is incredible. It idles extremely smooth and throttle response is 100% better. I can see also fuel flowing clearly into filter and surely enough filter is now slowly but steadily getting filled with fuel. As for the check valve it also works well . One can see that when shutting off tractor. I can see the fuel in the filter stem. It does not go back down the line immediately as it did before. Old fuel pump still works but it definitely lost a lot of its strength. I think it is still the original one since its a Niki made in Japan?

[WHX?? 46,694]

Is that the check just below the pump? What's your source on them? Looks like a nice one. I should put one on my 520's always have problems re-priming if they sit for even just a week.

[formariz 11,849]

Yes it is. All aluminum body nicely made and not expensive . 2 for $10.00.

https://www.amazon.com/gp/product/B01C3PD06K/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

[WHX?? 46,694]

Excellent Cas will give them a crack...thanks

[cschannuth 3,795]

On 11/26/2018 at 2:48 PM, formariz said:

So it looks like my original diagnosis was correct. Installed a new fuel pump along also with a one way check valve. Immediately the difference was obvious. Not only was I able to lower choke completely right after start but even though Tractor worked correctly otherwise (so I thought) the difference specially at idle is incredible. It idles extremely smooth and throttle response is 100% better. I can see also fuel flowing clearly into filter and surely enough filter is now slowly but steadily getting filled with fuel. As for the check valve it also works well . One can see that when shutting off tractor. I can see the fuel in the filter stem. It does not go back down the line immediately as it did before. Old fuel pump still works but it definitely lost a lot of its strength. I think it is still the original one since its a Niki made in Japan?

 Based on your link I bought a couple of these check valves. Does anyone think it would matter if it was upstream or downstream of the fuel filter? Depending on the tractor it may work better at different locations from an installation standpoint.  Thank you for the link.

[WHX?? 46,694]

I don't think it would matter Craig I am going to put it right where Cas did... plenty of room.

Good spot for that charger plug in too, My 110 charger outlet is right where that is in her stall, don't know why I put it way on the other side!

Edited November 30, 2018 by WHX21

[formariz 11,849]

I decided that location not only because it is convenient without too much plumbing but more important so pump would not lose prime if sitting for a while. This way no fuel will flow out of pump when sitting.

[cschannuth 3,795]

55 minutes ago, formariz said:

I decided that location not only because it is convenient without too much plumbing but more important so pump would not lose prime if sitting for a while. This way no fuel will flow out of pump when sitting.

 

I put one on the C-161 and the 314-8 tonight and took them for a spin. It’ll be interesting to see the difference next time I start them. 

[chip61 655]

I need to get one of those-if my 314 sets for more than a week I don't even try to start it without pressurizing the tank first-otherwise I have to crank forever to get it to pick up fuel. 

[cschannuth 3,795]

17 minutes ago, chip61 said:

I need to get one of those-if my 314 sets for more than a week I don't even try to start it without pressurizing the tank first-otherwise I have to crank forever to get it to pick up fuel. 

 

My 314 is the same way. I hope this helps. 

[GrandpaRay 6]

great link for the check valve.  thank you.  I've got the same problem on a 520 and 314.  the 520 takes forever to prime if it sits more than 10-14 days.

[formariz 11,849]

I now started putting those valves directly underneath mechanical pumps such as on the C series and they proved to be a major improvement.

[WHX?? 46,694]

On ‎11‎/‎28‎/‎2018 at 10:03 PM, WHX21 said:

Excellent Cas will give them a crack...thanks

I did and huge difference . Put one on 520 #2 and she fires right up after a lengthy sit. 520 #1 cranks forever so she'll get the 2nd of the 2 for 10. They are no restriction in the fuel line.

 

 Grampa Ray

[SylvanLakeWH 24,093]

Interesting thread and excellent input.

 

Just wondering, on my C105 I have cold weather start up issues as well. Have read another thread about putting a boat tank pressure bubble in line as an option for assisting with starting and pressurizing the system. Would that help with your issue and mine?

Edited January 25, 2019 by SylvanLakeWH

[WHX?? 46,694]

I've heard tell of guys using the boat motor bulb primer thingys with some luck Jim. I never have just don't care for the look of it hanging ther.

Edited January 25, 2019 by WHX21

[formariz 11,849]

Essentially that also acts as a check valve with the added feature that you use it as a primer. A matter of preference I guess. Personally I also don't care for them and unlike the small aluminum valve placement is more limited.

[lodestonefarm 41]

@formarizI like this idea too.  My 520 surges at idle.  Thanks for the suggestion and the link to the check valve.  Can I ask where you got the new fuel pump?  

[WHX?? 46,694]

They're on fleabay Stone Farmer.. just search or Onan fuel pump. Very resonable... too should be around twenty bucks.

My bad jungle site https://www.amazon.com/149-1544-149-2187-01-149-1982-149-2187-Generator/dp/B01KZ97H9C/ref=sr_1_2_sspa?ie=UTF8&qid=1548466582&sr=8-2-spons&keywords=onan+fuel+pump&psc=1

[lodestonefarm 41]

@WHX21- who knew it could be so easy!  Thanks.  I just assumed (without actually searching, I admit it) there'd be too many choices and/or not enough info to know if it fits my machine.  Much appreciated.

 

[WHX?? 46,694]

No problem guy your , this fuel pump was used on quite a few of the Onan gennies as well. Now made offshore I would guess. Still at that price compared to other Onan parts doesn't kill a guy to have a spare "on the shelf".

BTW your surging may be caused by a dirty carb as you might know. There is more info on that here than carters got pills. 

Edited January 26, 2019 by WHX21