Why must my motor warm up first?

[mauzy]

I have a 1981 75 hp evinrude. Motor will not start without choke. Motor RPMs go up 3000 plus then back down and motor will shut off if I don’t re choke. I do this three or four times before motor will idle and warm up so that the motor will not bog down and die when I put it in gear and power up. If I adjust the idle lever during start up the RPMs go up high forcing me to put the idle lever back down. After warm up motor runs good. Start idle and run. After warm up motor idles at 1500 rpm and idle lever will adjust rpms smoothly. Why must I warm up first?

 

[martyscher]

Re: Why must my motor warm up first?

All internal combustion engines require a richer fuel mixture when the engine is cold.<br /><br />You probably just don't notice it on cars, etc, because the choke is automatic, or if fuel injected, the mixture is just richened, until the engine is warmed up.<br /><br />If it's any consolation, my 2001 Johsnon 40HP starts the same way. Very cold blooded until warmed up, then runs fine.

 

[mauzy]

Re: Why must my motor warm up first?

The choke is electric and is activated by pushing in on the Key. Maybe I need to hold the choke in longer than just till it starts. If so should I expect the motor to die if I hold choke to long and I am idling.

 

[martyscher]

Re: Why must my motor warm up first?

That's the same setup I have (new boat). I don't think it is a choke, per se, but is considered a "primer", that simply squirts in extra gas when pressed.<br /><br />I'm learning to just press the key some more after starting, to richen the mixture.<br /><br />I also disengage the gear and then speed the throttle a tad which helps it warm a little faster to get away from the dock easier.<br /><br />Too bad there is not enough patience from some fellow boaters on the ramp. I have recently heard of the term "ramp rage".<br /><br />You have fun.

 

[Dennis4b]

Re: Why must my motor warm up first?

Hi<br /><br />Firstly on a cold block the fuel will condense on the metal, there'll be moist etc, so you need to enrichen (via choke or primer) the mixture.<br /><br />Secondly the engine is combusting the fuel, if the cilinder walls are very cold it's harder for the engine to burn things properly. Hence the thermostat controlled cooling system, to keep the engine temp within optimum temperatures for combustion.

 

[Franki]

Re: Why must my motor warm up first?

The other thing about cold starts is the metal itself..<br /><br />a powerhead is made of many different metals.. and they all expand with head, and different metals expand different amounts and at a different rate..<br /><br />when an engine is first started, the alloy's will heat up first, the liner will take longer..<br /><br />so running a motor hard while cold reduces your engines lifespan considerably.<br /><br />if it a minute or two and it will thankyou with years of service.<br /><br />rgds<br /><br />Frank

 

[petryshyn]

Re: Why must my motor warm up first?

The reason engines must warm up to run properly is due to the nature of gasoline. Gasoline will not burn unless its a vapour. Vapourized gasoline can be achieved through evaporation or boiling of the liquid. Cold engines are not up to temperature to boil the fuel, so we must rely on evaporation. It takes alot of raw fuel spread over an area to evaporate enough to run an engine. Hence is the reason for the choke, primer or enrichment circuits in all gasoline engines. Deliver an extremely rich mixture in hopes of having enough evaporation to support combustion. Some vapourization takes place in the combustion chamber as well. This happens due to the increase in temperature caused by compression....<br /><br />In a nut shell......pour a ton of fuel into a cold engine and hope enough fuel evaporates to support combustion.<br /><br />Once combustion takes place, and the engine warms, vapourization occurs in the warm intake runners, crankcase and combustion chambers. Less fuel is needed, as the vapour is easier to come by.<br /><br />hope this helps......