I don't recall any crankcase bleed valves on a Big Twin 30hp. You've got the big reed plate behind the intake manifold, and there are a couple of small reeds that send crankcase pressure to the pressurized fuel tank.
To upgrade to a fuel pump setup, you'll need to remove one of the intake port transfer covers and drill out the large hole that's cast into the side of the cover. Drill all the way thru, use a drill that's the correct size for a 3/8"-NPT tap. Then, tap the hole to 3/8-NPT. Screw a fitting in there and this becomes the vacuum and pressure pulse supply for a separately-mounted fuel pump.
A good one for the BigTwin is one that was used on '70's V4 engines. Some V4s had a pump that mounts directly to the block and that won't work. You need the pump that has an In and an Out, plus a third fitting for the hose going from the crankcase to the pump. The vacuum and pressure pulses from the crankcase act upon the back of the fuel pump diaphragm to create the fuel pumping action.
Just make your own mounting bracket and mount wherever it'll fit. You'll also need a single-hose fitting, one a later-model 70's-or-so Johnrude should fit fine.
I checked on eBay and there are a lot of 0438559 fuel pumps for pretty reasonable prices. There are some for less than $13.00 but they are aftermarket and I expect are made of Chinesium. A new OMC pump is over $100 so maybe it's worth taking a shot. I checked one vender and they've sold 225 of the cheap pumps, that's a pretty good track record. I can't post eBay links here unless I break them up. So check this out, it's a search for the P/N, and it'll pull up a bunch of pumps to choose from.
Just copy the link and paste in your browser. Then remove the spaces around "ebay" and it should work.
The P/N for a single-line fuel fitting that will bolt right up in place of the pressure tank fitting is 0376154 or 0393334. Both numbers have been discontinued. This fitting accepts 5/16" line which should be plenty to supply your 30hp. IIRC the V4 fuel pump uses the same size fuel line. You can find used and some new old stock on eBay.
Pics are attached, post any questions you may have. Hope this helps.........ed
Cballer wrote: a while back I posted question on single line fuel pump. I’m curious does anyone know the output pressure of these single line pumps (EMP 1399-07352) not been able to narrow output pressure down.thank you!
I can't recall ever putting a pressure gauge on one of these, but I'd be very surprised if they operated on more than 5 psi or so. Doesn't take a lot of pressure to feed the carb of a small 2-stroke engine such as these. You could put a "tee" in the line and measure fuel pressure that way.
BTW I forgot to mention what to do with the pressure fitting off the intake manifold, that feeds the tank, when you delete the pressure system and go to a single-line tank with a real fuel pump. Just plug the end of the small brass fitting, you don't have to take the intake manifold apart and do anything to the little reeds.
A vacuum line cap for an automotive carb would work well, and you may be able to use the old bendable-type hose clamp to affix it. Or use a tie-wrap to keep the cap from blowing off. A chunk of hose with a bolt or screw in the end is also a crude but effective fix!
Thanks for all that but I’m working on different project now. That fuel pump install is complete.
Now trying to safe the planet (ha) by collecting the spent oil/gas from crank case. There are actually two more reed valves on this powerhead, little ones that drain into leg.
My fuel pressure question was in relation to crank case pressure. Basically I wanted to feed the spent gas/oil back into fuel (but my tank is at bow not transom) in order to do this it has to tie into fuel line which most like won’t work because fuel pressure is greater than crank case pressure if that all makes sense..
The picture of gauge is proof at .300psi from crank case, I still don’t know what fuel pump pushes but certain it exceeds 5.000psi?
Here’s what I did after first initial question on dual line to single line conversion.
As well the oil/gas recovery cover
So the right way is plug one of the reeds if you are using barbed outlet pressure to feed a fuel pump, plugging one valve gives you a pulse just like transfer port cover.
I plugged both… going with transfer port cover fuel pump..
Crude way doesn’t work if you don’t plug holes ha I learnt that the hard way.. the pressure builds from reed valves and eventually will blow hose off and good chance causes issues with motor I would think. It’s a exiting pressure with fuel/oil present. Pretty easy to plug off from back side of reed plate, also easily enough removed if a guy wants to go back to dual line or use one valve for different fuel pump single line conversion.
As for fuel pump pressure I didn’t ever find out been down different rabbit hole, but there’s no manufacturer specs on any of those pumps that I can find and no one seems to really know. I get the same answer as you said gotta be around 5psi.. one day I will check by doing what you said just tying into fuel line after pump..
Very low pressure. Usually around the 2psi range. Anything more than around 5 psi will blow the needle off the seat in the carb.
Be careful with what you do around the small reeds. One of the passages is a lubrication supply to the lower bearing.
An easier way to recirculate the fuel is to install a tiny nipple on the one that drains into the exhaust and route it to another nipple you can drill into the carburetor mount flange. Only suction there. I have done this on several 35hp engines for folks and it definitely reduces the rainbow on the water surface around these old engines. An OMC primer niipple is perfect for this. PN 327706