1978 200 20hp running bad

[Nturp]

I am working on a 1978 200 20hp motor. It starts good but will die if the choke is open. It will run with the choke half open but as soon as you open the choke it dies. I've cleaned the carb and replaced the fuel bulb and connection at the tank. I have also tried pumping the bulb will it is running but it still dies. Any help of suggestion would be appreciated.

 

[racerone]

Re: 1978 200 20hp running bad

Is the plastic " boost venturi " in place on the high speed nozzle?----Have you confirmed that it is running on both cylinders ?----Is this something that started suddenly ? ------How long have you owned the motor ?

 

[Nturp]

Re: 1978 200 20hp running bad

I believe that the "boost Venturi" is in place. I don't know how exact they have to be. I checked the spark and each spark plug fires when the motor is turning over. I am working on the motor for a buddy. And he claims that it was running fine. I replaced his kill switch with a newer style and a new starter.

 

[Texasmark]

Re: 1978 200 20hp running bad

Didn't say if under load or not. Does make a difference and we can only guess!!!!!!!! It takes fuel to supply the energy for combustion. If the fuel air mix is less that about 1:12 the engine has a hard time running on it's own and surely won't accept a load. Your choke manipulation is suggesting that you are high on air and low on fuel. Figure out why you are low on fuel in the combustion process!

Mark

 

[Nturp]

Re: 1978 200 20hp running bad

It has the same problem if the motor is in a tank or if I put it on a boat and run it on the lake. Do you think that it is a fuel leakage problem or a problem with the jets? I can pump the primer bulb and it seems to die faster. By pumping the bulb I would think I would be by passing the fuel pump diaphragm if that was the problem. But it dies still. I've taken the carb off several times taken it apart cleaned it with no improvements. I'm stumped at this point.

 

[Texasmark]

Re: 1978 200 20hp running bad

It has the same problem if the motor is in a tank or if I put it on a boat and run it on the lake. Do you think that it is a fuel leakage problem or a problem with the jets? I can pump the primer bulb and it seems to die faster. By pumping the bulb I would think I would be by passing the fuel pump diaphragm if that was the problem. But it dies still. I've taken the carb off several times taken it apart cleaned it with no improvements. I'm stumped at this point.

Interesting comment. Runs both places suggests adequate fuel which includes the jets performance/low speed adjustment....high probably is fixed...only one spring loaded screw on carb.

Pumping the bulb makes it worse also speaks of adequate fuel. Both comments are contrary to your having to have the choke part way out to run.

When you cleaned the carbs did you use carb solvent like Berryman's Chem Tool or equivalent, did a good soak, and use compressed air to ensure all the ports were clean and open?

Your answers to others questions will help too!

Mark

 

[Nturp]

Re: 1978 200 20hp running bad

Yes, when I cleaned the carb I used a carb cleaner similar to Berryman's. Then blew air through the various holes and jets. I also let the carb dry out on its own before re installing the parts and putting gas to it.
I am confused also to why it doesn't run without playing with the choke. With the choke off it runs great for about 5 to 10 seconds and then acts like it doesn't have fuel and dies. this is what lead me to pump the bulb to try and feed it fuel but it still dies and like I said sometimes quicker.
Also the motor starts up fast often within a few seconds of bumping the starter. But, after it dies it then takes some time to start back up.

 

[racerone]

Re: 1978 200 20hp running bad

When you pump the bulb you put fuel right through the pump and into the carburetor.------------If the pump diaphragm has a hole then fuel will go straight into the motor and flood the motor ( slows down ) as well.-----Do a compression test and check for spark on both cylinders that will jump a gap of 3/8" or more.---------How does the motor behave / sound when running and you disconnect the fuel hose ?-----Does it run for a while ?-Does it smooth out ? does it quit right away ?

 

[Nturp]

Re: 1978 200 20hp running bad

I did a compression test and had had 120 on both cylinders. It also has good spark. The motor sounds like it is running great right until it dies. I haven't noticed any change when I disconnect the gas hose. When I did pull the plugs today I noticed the top spark plug had some oil on it.

 

[racerone]

Re: 1978 200 20hp running bad

Will spark jump a gap of 3/8" or more ??----Have you checked reed valves?

 

[Nturp]

Re: 1978 200 20hp running bad

Yeah the spark will jump a gap 3/8 or more. I haven't checked the reeds to see if one is cracked.

 

[Nturp]

Re: 1978 200 20hp running bad

Would it hurt the motor to run it at half choke for extended periods?