312-8 & 416-8 Fuel problems

[Tony in Australia 2 15]

My two wheelhourse's have the same issue, after sitting for 2 or more weeks without being started both take forever to get the fuel back up to the carby to get them started.  My guess is that the fuel is darining back to the tank. Is there a anti drain back valve in the system? One engine is the Magnum 12hp Kohler and the other is Power Plus 16 Onan. Both run great when used very regulaly. Any Ideas?

[wallfish 17,019]

That's a common issue

A 12v electric fuel pump or one of these should solve the problem

https://www.ebay.com/itm/New-Fuel-Line-Pump-Primer-Bulb-Hand-Primer-Gas-Petrol-Pump-Rubber-Aluminum-Sales/373229524942?_trkparms=aid%3D777001%26algo%3DDISCO.FEED%26ao%3D1%26asc%3D20160801204525%26meid%3Dcb9f1da1c6ef4ed49a923ef27838631e%26pid%3D100651%26rk%3D1%26rkt%3D1%26mehot%3Dnone%26itm%3D373229524942%26pmt%3D0%26noa%3D1%26pg%3D2380057%26algv%3DPersonalizedTopicsRefactor%26brand%3D&_trksid=p2380057.c100651.m4497&_trkparms=pageci%3Acafa3447-3b41-11eb-b2d0-2ef43906d994|parentrq%3A4f0ba8c01760a9c98cd5a284fffdf0c4|iid%3A3

[Tony in Australia 2 15]

What a great idea, would never of thought of a in line boat fuel pump. How simple. Thanks heaps Wallfish

[oliver2-44 9,767]

Both of your horses have the gas tank under the seat. With that design there’s not much or any gravity flow on the suction side of the diagram style fuel pump. There have been some threads about putting check valves and I let those folks speak about that. The other common option is too install an electric fuel pump In place of the mechanical diaphragm pump. I have a “Facet brand 1-2psi pump on my C-81 and A 313-8  The Facetvpump cost more than the Chinese brands but it will last. 

[Tony in Australia 2 15]

Thanks mate, I will see what I can find down this way. There are no issues once they are running. I think I will try a small in-line hand fuel pump like what's on an outboard motor first, if that fails I can step up to an ele pump. I am trying to keep these two are original as possible. Cheers Tony

[SylvanLakeWH 25,608]

Put an in line bulb on mine couple years back - no issues since! Works like a charm!!!

 

 

[Tony in Australia 2 15]

What a great idea, would never of thought of a in line boat fuel pump. How simple. Thanks heaps Wallfish

[953 nut 55,337]

1 hour ago, Tony in Australia 2 said:

Is there a anti drain back valve in the system?

The fuel pump on each model has a couple of check valves but over time they fail. When you install the fuel primer bulb or an electric fuel pump be sure it is located below the fuel tank.

[Tony in Australia 2 15]

That's what I will do bug I might try to put mine under the seat close to the tank and tuck it up out of the way, if that doesn't work I try under the battery area as you have done. I will try and get some pictures uploaded soon, cheers very one for the help and you all have a safe and Covid free xmass.

[sparkie333 265]

1 hour ago, Tony in Australia 2 said:

My two wheelhourse's have the same issue, after sitting for 2 or more weeks without being started both take forever to get the fuel back up to the carby to get them started.  My guess is that the fuel is darining back to the tank. Is there a anti drain back valve in the system? One engine is the Magnum 12hp Kohler and the other is Power Plus 16 Onan. Both run great when used very regulaly. Any Ideas?

It sounds like it is sucking air somewhere letting the fuel out and this making it take time to get the gas back to the carb.IMHO.

[Tony in Australia 2 15]

Thanks everyone, all good ideas. Cheers Tony out

[wallfish 17,019]

A primer bulb has a check valve in it and will also pull fuel up very well like for a boat tank, so no need to install one of those below the tank.

 

 

2 minutes ago, sparkie333 said:

It sounds like it is sucking air somewhere letting the fuel out and this making it take time to get the gas back to the carb.IMHO.

Correct, a fuel leak in the line could also cause the same symptom.

But the carb has a vent to atmosphere for the bowl so when the check valves in the fuel pump get weak, it allows fuel to flow back down through the fuel line to the under the seat tank. This is a common problem with the under the seat tank models when no fuel leaks are present. Then when the pump tries to suck fuel for starting there is air in there. Fuel pumps are great for pushing fuel but not so much for sucking fuel and especially so when the check valves inside aren't sealing properly. 

[sparkie333 265]

1 minute ago, wallfish said:

A primer bulb has a check valve in it and will also pull fuel up very well like for a boat tank, so no need to install one of those below the tank.

 

 

Correct, a fuel leak in the line could also cause the same symptom.

But the carb has a vent to atmosphere for the bowl so when the check valves in the fuel pump get weak, it allows fuel to flow back down through the fuel line to the under the seat tank. This is a common problem with the under the seat tank models when no fuel leaks are present. Then when the pump tries to suck fuel for starting there is air in there. Fuel pumps are great for pushing fuel but not so much for sucking fuel and especially so when the check valves inside aren't sealing properly. 

 

Yes you know more about this kind of carb's. I do understand about when they are older and the bulb would fix the problem.  Great fix.