First Water Choke

[bill-mcnamara]

I am going through a friend’s RDS-24, trying to revive his late Dad’s gently used motor.
It has the "automatic choke" feature,of which I have no experience.
Were these chokes reliable? Should I just leave it alone until I see if it functions?
I will be replacing or repairing the choke’s vacuum line though, as it appears that a mouse had a little snack on it at some point!
The water lines to the choke seem soft and pliable, and look quite usable.

Fuel lines are a different story as expectedl, hard and brittle and will definetly be replaced.Too bad our little "rodent snacker" hadn’t taken a chew on these lines instead?

Any advice or opinions gratefully received.

Bill.

[rvpapasso]

Bill,

I am running the water choke on my 1960 40Hp Johnson and love it! However it must be in working order in order to fall in love with it. The vacuum pull-off must be checked to ensure it releases the choke. The thermal spring must also be free to move as the cooling water gets warm and of course a proper working thermostat. I picked up my 1960 40Hp over 19 years ago and never had to fix anything regarding the water choke.

[frankr]

Well, I can’t argue with a success story like that. However…an awful lot of those things did not work that well. Most people wound up opening the door and put it on auto choke or manual choke to start, then flip it to choke off position after it starts. Maybe our sub-tropical climate has something to do with that?

As a side note, the cooling water thermostat has to be working if there is to be any hope of the automatic choke working.

[rvpapasso]

Frank, I may have a theory on why many people with the automatic water choke set it to manual for starting based on my experience with it. If you understand how the choke works and where it is positioned in the carb relative to the throttle butterfly and the main jet my theory may have credence.

Typically in a carb with only 1 jet, main jet, “choking” is to pull raw fuel out of the main jet and into the engine. The maximum amount of raw fuel will be pulled with the air inlet of the carb blocked and no restrictions to air flow between the main jet and the combustion chamber.

The choke provides the blocking of the carb air inlet. However if the throttle butterfly is closed and not open there is a restriction of the airflow and not as much suction is at the main jet to pull raw fuel out of it.

Due to the vacuum pull-off with the water carb the choke will flutter some due to some vacuum produced when the engine is pulled through. This flutter does not allow the choke plate to completely block the air inlet reducing the blocking action of the choke. This is most apparent with electric starting.

To get max suction at the main jet the throttle butterfly has to be opened as far as it can be in neutral. With electric starting the mercury switches sometimes are not set properly to allow the starter solenoid to be energized at max throttle in neutral.

Both of the above combine to make a hard starting engine for a cold start. The fluttering of the choke plate and inability to have the throttle opened as far as possible reduce the amount of fuel that can be pulled from the main jet.

My electric start engine was hard to start on a cold start at the beginning of the day due to the above. Slightly tweaking the mercury switches to allow starting at max throttle in neutral resolved it. Converting to the safety switch under the flywheel to eliminate the mercury switches will alleviate the problem entirely.

As for manual starting the engine does not turn over as fast or continuously as the electric starter will do. Any flutter of the choke plate is a real detriment to pulling raw fuel. In the occasion I had to manually start the engine I always had to manually set the choke, open the throttle as far as it will go in neutral and pull it over a few times with the ignition off. Then bring the throttle back to a fast idle position, turn off the choke, ignition on and pull it through. It started every time.

My opinion is the water choke was really designed for electric starting engines and the convenience of not having to leave the driver’s seat to start the engine. For manual starting you have to be back at the engine and manually operating the choke is the best way and not relying on the automatic choke.

Once started if you have the thermal warm up set correctly the engine will run smoothly without lean sneezing.

The above is my experience with simple carb engines. The same rules apply to cold starting with my 1943 Harley. As you can imagine if you don’t get the starting drill correct you will have a heart attack jumping up and down on the kick starter like a monkey on a pogo stick. Same starting drill; close the choke all the way, open the throttle all the way, ignition off and a few prime kicks. Then choke off, throttle cracked, ignition on and a swift kick and it starts on the first kick every time when cold.

Can’t say for sure if my theory is correct but trial and learning (i.e. error) has found it works.

[frankr]

I have no problem with your theory. Amazing, how many people don’t know how to start a motor, especially the throttle setting. A friend of mine invited me to go on the maiden voyage of his new boat and motor. Well it wouldn’t start. Out of respect, I held my tongue. Then I offered a few suggestions, and he was kind of perturbed, so I kept quiet again. When the battery was nearly shot, I offered to try it, and he was so mad by then he didn’t care so he agreed. I sat in the drivers seat, raised the throttle warm-up lever, pushed the key to choke it and it started right up. Now, the rest of the story is I had earlier suggested he set the warm-up lever and he told me bluntly that the dealer told him never to mess with that!!! If the dealer doesn’t know how to start it, how can we expect the customer to?

Back to the water choke, the main problem we had was blubbering, slobbering and smoking due to too much choke after starting. With out warm air and water, they just didn’t need all that choke. Yeah, I’m aware of the importance of proper set-up.

[legendre]

@RVPapasso

Sounds like an ‘interesting’ system they had then.

Question.. if the motor is cold and the choke is set ‘on’, why would it flutter as the engine is cranked? If the vacuum operated choke pull-off has a thermally controlled valve, why is there vacuum signal when cold?

Shouldn’t the valve be closed at that time, only to begin opening later and pulling off the choke when the temperature of the cooling water begins to rise?

[rvpapasso]

There are two parts to the choke, the vacuum pull off and the thermostatic spring. The vacuum pull off closes the choke plate in the absence of intake manifold vacuum. When vacuum is present the vacuum pull off releases the choke plate. When the choke plate is released the amount the choke plate is open is dependent on the thermostatic spring.

Given the above when the engine is not running the vacuum pull off forces the choke plate closed regardless of the position of the thermal spring. However any vacuum in the intake manifold during cranking will tickle the vacuum pull off slightly releasing the choke plate and then forcing it shut between vacuum pulsations. This is where the flutter comes from. Once the engine is running and there is steadier vacuum in the intake manifold the vacuum pull off completely releases the choke plate to be controlled by the thermostatic spring.

The amount of choke is then dependent on the thermostatic spring based on the temperature of the water passing through it. When at proper operating temperature the thermostatic spring will hold the choke full open. This part of the choke is adjustable to be leaner or rich during warm up. If adjusted properly the engine will run smooth from cold to operating temperature. Once the engine is stopped the vacuum pull will close the choke fully regardless of the temperature.

Carter had a similar choke setup for cars that was called a "climatic control". It also utilized a vacuum pull off and thermostatic spring.

[legendre]

So how exactly does the thermal spring control the position of the choke plate, then? A better question might be, how does the vacuum pull-off close the coke with no vacuum signal – does it have a second spring? Are these thermal and second springs in opposition to one another?

An annotated diagram would save a thousand words.. 😉

[frankr]

OK, this is getting complicated. Let me give everybody my recollection of the choke system without having one in hand. The main part of the automatic choke is the bi-metal spring, part of the choke cover, item 56. It is a coiled-up flat spring that winds/unwinds as the temperature changes. Very common on old cars if anybody remembers them. When the motor (and spring) are cold (let’s say room temperature or less) the bi-metal spring is putting pressure on the choke shaft lever, holding the choke closed. As the motor (and choke) warms up, the bi-metal spring unwinds, allowing the choke to open.

Now: The above described system would continue to choke the motor after it is started, causing it to flood out. So, two ways of preventing that are provided. The first is the vacuum pull-off diaphragm. item #55. Mainfold vacuum pulls the diaphragm downward against the spring, which pulls the choke shaft in opposition to the bi-netal spring. The tug-of war is slightly won by the pull-off which allows the choke to open part way. But the bi-metal spring is still trying to close it. This provides a partially closed choke for the warm-up period. As the motor and bi-metal spring warm up, the bi-metal spring unwinds enough to allow complete choke opening. There is a second device that helps open the choke, and actually is what is causing the fluttering. That is the fact that the choke shaft if not centered on the choke butterfly plate See the screw holes on the plate, #91. Since it is off-center, vacuum within the carburetor venturi is sucking on the plate’s off-center side, pulling it open like a swinging door.

Hope this is clear as mud, or better. The system actually is pretty well thought out. Too bad it didn’t work better. It was re-designed in 1964 to operate on hot air with an electric assist solenoid. That worked much better.

[legendre]

@FrankR

Part #91 in the diagram is the choke valve, correct? The shaft is notably off-center of the valve plate..

Yes, then that all makes sense.. as to why it would flutter during cranking and while running in general, if it were being held in the closed position.

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