Topic: 1960 Scott 7.5 hp fuel purge? – Antique Outboard Motor Club,Inc

This topic has 11 replies, 3 voices, and was last updated 2 years ago by Buccaneer.

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May 2, 2023 at 10:26 pm #275824
Buccaneer
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I tried today to get the subject motor running after going
all through it in March. The “fuel pump / carb” assembly
had a new kit installed, and all new hoses.
I’m not able to get gas into the carb to keep it running.
Initially, I took the fuel inlet hose off the fuel pump, and
using the tank’s primer bulb, got gas that far.
The carb is diaphragm operated as well as the fuel pump.

The manual mentions that some of these Scotts used two
different “purge” mechanisms, to purge out air and get gas
into the motor. One I believe was activated by the choke lever,
the other by the twist grip. Neither of my Scotts with the same carb setup
seem to have any purge valve.
Where a purge line “would” hook up, there’s a barb, but the end
is not drilled out.

I did manage to get it to run a few times, maybe 5 seconds, but
spraying fogging oil in the carb intake.

There’s a tiny plug on the carb, between the Hi and Low speed needles,
that goes into a passage on the “fuel” side of the carb diaphragm,
that I removed, and attempted to squeeze the tank’s primer bulb,
hoping to get some gas moving, but I got “nothing”.

It’s impossible to get at the fuel pump “to” carb fuel line, without removing
the powerhead.

I have a spare, unrestored carb, from a parts motor, that I may attempt
to hook up to the fuel tank and play around with on the bench.

Anyone mess around with one of these motors in the last decade
and have any suggestions?
Also, Is the bailer hose barb suppose to be “capped off” when not
bailing out the boat?
Thanks!

Prepare to be boarded!
May 3, 2023 at 5:37 am #275831
billw
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I really can’t help too much here. My McCullough 9 has a float type carb. (I doubt mine will run either, because the float has an assist spring holding the float up, which would shut the fuel off.) What I would like to say, though, is on mine, there are two holes in the lower cowl/midsection, that are directly over the two, hard-to-get, intake manifold screws. If I remove the flywheel, I can take my whole carb and manifold assembly off without removing the power head. I’m not saying it’s easy, but at least it can be done. The two holes have paint in them and appear to be OEM. If you don’t have these holes, you might consider drilling them.

Long live American manufacturing!
May 3, 2023 at 8:45 am #275835
Buccaneer
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Bill, thanks for the suggestion, but I’m about 90% sure
I don’t have the holes you’re talking about, and yours
being a “float” type carb, perhaps it mounts different.

I was thinking in the twilight hours this morning that
perhaps I could rig up an elevated gas tank to help
fuel work it’s way into the carb. If that’s what it takes,
God forbid if one runs out of fuel on the lake.

Prepare to be boarded!
May 3, 2023 at 11:43 am #275844
frankr
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I think I commented on this subject before, but here goes a recap. As you are aware, that carb was designed to run on a chainsaw, so the saw can work in any position, even upside down. But on a chainsaw, the gas tank is right tthere to supply a steady supply of gas. Not so with an outboard with the tank several feet away.

Anyhoo, the diaphragm carb works much like a float feed carb. The diaphragm chamber is air tight and as the engine sucks gas from the diaphragm chamber, it pulls the diaphragm toward the carb body, which opens the spring-loaded inlet valve, much as a float valve would be opened. Diaphragm moves the other direction, allowing the inlet valve to close. Herte is the important difference. The diaphragm chamber being airtight, there is no vent for an air bubble to get out, other than being pulled through the jets into the venturi. And as the air is going through the jets into the venturi, gas is not going through, and the engine cannot run. The only way to get the air out is pulling the starter 40 or 50 times, or purge what you can, thus the purge valve to get the air out of the line at least up to the carb entrance fitting.

If this is clear as mud, you can deduce that that system cannot tolerate air bubbles in the fuel supply.

Add to all that, the fuel pump is a lousy air pump.
May 3, 2023 at 3:18 pm #275845
Buccaneer
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Frank, thanks again for your input. I’ve been gone most of the day,
buy may play with the motor yet today. I had the motor running
briefly on fogging oil several times, and was hoping that would
get the fuel system purged.
I guess I’ll try rigging up my rotor tiller gas tank, elevated above the
motor, and hope that “gravity” helps to get the system working.
I’m afraid I already pulled the motor over 50 times and that
accomplished nothing, but the rewind spring repair letting go
after about 30 pulls, lol.

Prepare to be boarded!
May 3, 2023 at 10:17 pm #275855
Buccaneer
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I got the Scott started finally, using a gravity feed tank, and it still
was a lot of monkeying around, giving it shots of fogging oil, until
finally it took off.

It seems to run okay, but not sure I’ll be able to get it started with
the normal gas tank and hose hooked up to it, and I’m afraid
to think what would happen with the gas tank in the bottom of
the boat.

I had to “over fill” the barrel with water as to what should have been
enough, to even get it to pump water at all. What is pumping does
not seem adequate, and the bilge pump impeller isn’t doing anything.
Both had brand new, spendy impellers.

The motor really winds up, and seems like it has plenty of power, but
I couldn’t wind it up more than a couple of seconds as the water
flees the test tank.

https://youtu.be/yYExy8eQWIk

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May 4, 2023 at 5:40 am #275857
billw
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That motor has the water pumps at the normal level, right? Around the level of the top of the gear case, NOT high under the power head?

I noticed that on my 9 hp, there is a water tube that goes up into the mid section, as you install the lower unit, that doesn’t seem to have a provision for any kind of grommet. It just seemed to go into aluminum. I was wondering how that was going to seal. I put some perfect seal on it when I put it together. I wonder if this joint is the source of some of your water woes? By the way, it was a good time putting that lower unit back on, wasn’t it? Said no one.

Long live American manufacturing!
May 4, 2023 at 9:47 am #275858
Buccaneer
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US Member
Bill, In reviewing my photos when I had this little jewel
apart, but I see that I gooped up around one line.
And “yes”, both pumps on this one are “back to back” and below
the water line.

The replacement impeller has less vanes, but I can’t say what
difference that might make?

Black RTV around the supply water line.

billw wrote:

That motor has the water pumps at the normal level, right? Around the level of the top of the gear case, NOT high under the power head?

I noticed that on my 9 hp, there is a water tube that goes up into the mid section, as you install the lower unit, that doesn’t seem to have a provision for any kind of grommet. It just seemed to go into aluminum. I was wondering how that was going to seal. I put some perfect seal on it when I put it together. I wonder if this joint is the source of some of your water woes? By the way, it was a good time putting that lower unit back on, wasn’t it? Said no one.

Prepare to be boarded!
May 4, 2023 at 6:17 pm #275884
Buccaneer
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US Member
I got the motor to run on the normal remote tank now, instead of the
elevated “roto tiller” tank I rigged up yesterday.
I notice with the normal gas tank hooked up, the hose’s “quick coupler”
would drip a little when the primer bulb was squeezed hard, hence
it was probably sucking air.
So I switched it to another coupler I had. I believe both couplers are
Sears / Ted Williams style.
The motor then started on the 4th pull with the normal tank.

I still an issue with it pumping water. It pumps “so so” at idle, but when
you rev it up, it quits pumping. Normally it’s the other way around!
It’s impossible to switch the water lines (normal pump and bailer pump)
around on the “top side”, as the bailer line takes a 90 degree bend
half way up to the power head.

While running the motor today, I had a hose on the ‘bailer” fitting, and
hanging down in the water in the test tank.
I didn’t think about this until “after” I pulled the motor out of the tank,
but I should have pulled the bailer hose out of the water while the motor
was idling, and pump some water out the tell tale, to see if the flow
changed or stop.
Not sure if it’s possible to switch the pump lines on the bottom side.
Hope I sleep tonight…… or don’t have nightmares!
VIDEO
https://youtu.be/nDFxAZ74mPk

Prepare to be boarded!
May 4, 2023 at 6:35 pm #275885
Buccaneer
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US Member
In looking at my “apart” photos, it does NOT appear possible
to switch the water lines around on the pumps, either top nor
bottom side.
Not sure what to do now.

Prepare to be boarded!
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