How does the choke work on 1978 Johnson 85 HP?

[brettule]

I've got a 1978 Johnson 85 HP (85ETLR78C) engine with a key start, the COLD START guide here says there are two basic types of fuel systems to aid in cold starting. Solenoid activated Choke plates and solenoid primers. I think my engine has the push key primer?

From what I can work out this key-push injects fuel directly into the cyl to aid with cold starting. It basically injects extra fuel to enriches the mixture to facilitate starting. This is just a once off squirt of fuel per push isn't it? That's why the cold start guide says to "bump" the key to squirt some more fuel if the engine stumbles. Is there an automatic choke elsewehere on a thermostat or something to allow the mix to run richer when cold or not? Is that just what the idle lever is for, raise the rev's so it doesn't stall, the end?

 

[F_R]

Re: How does the choke work on 1978 Johnson 85 HP?

Pump up the primer bulb (tank hose)
Raise fast idle lever
Turn key on and push it in and hold it in while continuing to turn key to crank motor.
Release key.
If motor sneezes and snorts, "bump" the primer by momentary pushing the key in. Lower the fast idle lever to reasonable speed.
When motor runs smoothly, lower fast idle lever to normal position and shift into gear and go.
Priming is normally not needed when restarting a warm motor.

 

[brettule]

Re: How does the choke work on 1978 Johnson 85 HP?

Yeah I understand the starting process but I'm just wondering how the choke works. Does the push key just prime or does it somehow activate a warmup choke as well? One pime only squirts one measure of fuel into the cylinders, that's not enough for a choke warmup so I assume there is a proper choke somewhere as well. Is the choke completely automatic and even if I was trying to cold start and didn't push the key to prime it would be enabled somehow?

 

[boobie]

Re: How does the choke work on 1978 Johnson 85 HP?

According to the parts break down on this mtr you have just choke plates in your carbs and no primer. Push your key in when starting and this will close the plates. To check them pull the air silencer cover off, turn on your key and push it in. You should see the plates closing.

 

[wired247]

Re: How does the choke work on 1978 Johnson 85 HP?

Yep. You have a good old fashioned choke and not an injection solenoid. Choke plate closes and forces the engine to draw in a richer air/fuel mixture.

 

[brettule]

Re: How does the choke work on 1978 Johnson 85 HP?

Ok perhaps I'm not explaining myself very well. I'll try reword this. I have the 85ETLR78C model engine with an ignition push key feature. Given that I can push the key in I'm assuming it's the "Push to Prime" model, however I can't be sure. I do know that when I push the primer in a solenoid actuates an arm around the carburettor. From what I've read this tends to indicate it's the primer plunger mechanisim which injects some fuel stright into the cylinder to aid with starting.

This "priming" mechanisim which essentially squirts some fuel in to aid in starting is fine for those 5 secs starting. However usually what keeps an engine running smoothly when it's cold is a choke, this acts on the carburettor to change the mixture so that it's richer and so the engine can run smoother for the 10 or 15 minutes it takes to get to operating temp.

I didn't think a primer was a choke, aren't they two seperate concepts? If not, can you explain? If so, how does the choke work on my engine?

 

[rockyrude]

Re: How does the choke work on 1978 Johnson 85 HP?

Pushing the key in activates the solenoid that closes the choke butterflies. There is no squirting of fuel involved. The butterflies are closed only as long as the key is pushed in. Like Boobie said, verify this by removing the air silencer and look at the motor as you push the key in, you should see the butterflies close.

 

[eclark53520]

Re: How does the choke work on 1978 Johnson 85 HP?

Your engine does not have any priming system. Only a choke system.

Pushing the key in is what activates the choke. The engine does not need choke on for 10-15 minutes, only during starting and possibly right after starting to keep the motor running. Even then, you usually only have to bump it once if it starts to stumble right after cold starting.

 

[wired247]

Re: How does the choke work on 1978 Johnson 85 HP?

Ah. To go back to the innocent old days before fuel injection systems when everyone knew what a choke was.

 

[brettule]

Re: How does the choke work on 1978 Johnson 85 HP?

How come on a car you need the choke engaged not only for starting but until warmup has achieved but this engine only needs it for a moment when starting?

 

[rockyrude]

Re: How does the choke work on 1978 Johnson 85 HP?

Generally speaking, cars probably use the choke more than needed, an outboard runs at lower temps than a car and becomes stable much quicker.

 

[brettule]

Re: How does the choke work on 1978 Johnson 85 HP?

Ok. I guess I can live with that explanation. The thing is even my 2 stoke 49cc moped needs the choke enabled for a few minutes for smooth operation.

 

[wired247]

Re: How does the choke work on 1978 Johnson 85 HP?

A lot of it has to do with the fact the propeller has no solid link to the water. Its not like a car or moped where you have to push weight against the ground. Give it gas and the prop just revs somewhat cleanly through the water without a heavy load on the engine. Same reason you dont need an accelerator pump in a boat carb. It won't bog down. Once the engine has started as long as the ignition and carbs are working the way they are supposed to and the thermostats arent stuck open, the engine will warm up almost immediately and run without a richened A/F mixture. Put an outboard engine carburetor on a land vehicle and it will run like crap. Put a automotive carb on a outboard ( like a sidedraft weber or delorto ) and it will run well but use more gas.