Primestart; for Webfootga

[boscoe99]

Be careful about what you look for. You might get it.

PRIME START CARBURETOR
Most of the current 40 to 90hp engines are equipped with Prime Start carburetors. A conventional choke is not required on these carburetors. Fuel enrichment for starting a cold engine is provided by the Prime Start System. To control fuel enrichment for starting and warm-up, an electrothermal valve/enriching fuel pump assembly is mounted on the carburetor. The enriching fuel pump is actuated by pulses from the crankcase. The electrothermal valve is heated by power from the lighting coil. The enriching pump draws fuel from the carburetor float bowl and pumps it to the electrothermal valve unit which controls the amount of enrichment fuel. This fuel is then drawn into the intake manifold with the assistance of intake vacuum to enrichen the fuel mixture entering the combustion chamber. The electrothermal valve is normally open, with the amount of valve opening determined by ambient temperature. After the engine starts, power from the engine’s lighting coil begins to heat the electrothermal valve. The valve expands as it is heated, so its valve seat starts to close, con*****ing the amount of enrichment fuel passing through it. The electrothermal valve heater is energized as long as the engine is running. Therefore, the valve opening is continuously reduced, which restricts enrichment fuel flow once the engine has warmed to normal operating temperatures. The valve assembly also has a three-position manual override valve. This valve can be set for automatic or manual enrichment or set to turn off the enrichment.

Automatic Enrichment
With the manual override valve set in the automatic position, enrichment of the engine will take place depending on the temperature of the engine and the electrothermal valve. Enrichment will take place automatically as outlined previously and as long as the throttle valves remain closed during cranking.

Manual Enrichment
When the manual enrichment lever is at the open position, the fuel is drawn by the enriching fuel pump and led directly to the intake manifold through the passage selection valve. Air will not be drawn for primary mixture in this setting. When starting the engine with the manual enrichment lever open, the lever should be turned to the closed position immediately after the engine has started.

Manual Enrichment Closed
If the power source for the electrothermal valve should fail with the valve fully open or the electrothermal valve fail to close, the manual enrichment lever should be turned to the closed position. After starting, the engine can be run normally with the valve in the closed position.

[dark_star]

My F60 carburated engine has prime start, but I would prefer a manual or key
choke.
The prime start can be quite finicky when the engine is cold.

[99yam40]

as long as the carb and prime start passages/jets are clean and set to specs the motor should start and run properly.
If it does not, then the systems need to be cleaned/repaired

[boscoe99]

My F60 carburated engine has prime start, but I would prefer a manual or key
choke.
The prime start can be quite finicky when the engine is cold.

Not if it is working properly. It should not be so.

My Yamaha F225 (like my Ford truck) had Primestart as part of the EFI system. Started instantaneously at all temperatures. If it ever got to be a bit finicky then the solution would be to fix the problem and not long for the good ole days of yesteryear, when men were iron, ships were wood and chokes had knobs.

[pstephens46]

Seems to very straightforward technology.

[rodbolt17]

***.

manual and automatic chokes ALWAYS sucked.

you may be you young to remember the issues with fast idle and chokes sticking but I am not.

prime start on the F motors with the electrothermal valve worked wonderfully and are easy to fix.

back in the day when I started this only a hand full of US produced motors used a transistorized ign and none used any EFI.
closest thing was the rochester mechanical FI but was never coupled with any electronic ign systems.

points sucked.

modern fuel/ign systems work well.
require minimal maint and are easy to fix.

[pstephens46]

Points absolutely sucked.

Wasn't there a Corvette late 50's or early 60's that was fuel injected? Not electronic....Not sure how that system would work. Maybe it didn't.....

[boscoe99]

Points absolutely sucked.

Wasn't there a Corvette late 50's or early 60's that was fuel injected? Not electronic....Not sure how that system would work. Maybe it didn't.....

It worked and worked pretty well. State of the art at the time.

Many aircraft motors use mechanical fuel injection today. Simply a pump that varies speed with the speed of the motor. The faster the motor spins the faster the pump spins. The faster the motor spins the more fuel that is needed. The faster the pump spins the more fuel that it delivers. And it even has an adjustment so that fuel flow can be diminished when the aircraft is at altitude, keeping the air/fuel ratio at the setting the pilot wants. It is a continuous flow system with fuel flowing constantly out the injector nozzles whenever the motor is running.

[pstephens46]

What creates the pulse for the injector timing? Manifold or fuel control?

[boscoe99]

What creates the pulse for the injector timing? Manifold or fuel control?

There is no pulse. It is a continuous flow system. The injector is all mechanical. It is really just a device with a calibrated hole. More fuel pressure = more fuel flow. Less fuel pressure = less fuel flow. The fuel pressure varies to meet the demands of the engine.

[99yam40]

no pulse or timing needed if sprayed into manifold,
valves take care of getting fuel and air into cylinders, just like a carb motor would.

I guess the old vets did it the same maybe?

Seems like they had injector lines running out of a distribution system to ports close to cylinders.
I never did work on any of those old systems

[pstephens46]

no pulse or timing needed if sprayed into manifold,
valves take care of getting fuel and air into cylinders, just like a carb motor would.

I guess the old vets did it the same maybe?

Seems like they had injector lines running out of a distribution system to ports close to cylinders.
I never did work on any of those old systems

10-4 on the manifolds. I was visualizing injectors mounted top of cylinders.
Thanks for the info. Always like to learn.

[throrope]

boscoe - thanks for the awesome description! A great system that proves good old stuff still works.

I had a 1977 Audi with Mechanical fuel injection, a real POS that I never got running right. Even Consumer Reports gave it a black eye. When I owned it they ran "art of engineering" adds. My dad and I joked it it sure was art since it included no science.