1973 65 hp Johnson Carburetor Problem

[abales12]

I have a 1973 65 hp Johnson. 105 psi compression on all three cylinders. I was having diffuculty starting and poor idling. Slow speed performance was poor. Mid-range and wide open was excellent. I rebuilt the carburetors using OMC parts. No gauge was provided for the float drop. So I did my best guess. I adjusted all of the linkage according to the manual. Now, it starts immediately. Idles perfect. Up to 75% power is perfect. When you apply full throttle the motor slows down. Applying the choke at full throttle does not help. I think it might be starving for gas. Suggestions on what to look for?

 

[fireman57]

Re: 1973 65 hp Johnson Carburetor Problem

I would bet that you dropped a cylinder. You might have a powerpack that is weak and shorting out at high rpms. It's tough to check by yourself. If you have buddy you can trust then take the cover off and put a timing light on each plug wire one at a time while you are running full throttle and let him check for spark. If he gets to a wire with none then I would change that powerpack. You might make sure that you have fresh plugs in it and that they are gapped properly. Check all your plug wires for any bad spots and make sure they are securely on the plugs. Undo the ground wires from the packs and clean that connection good.

 

[dolluper]

Re: 1973 65 hp Johnson Carburetor Problem

Did you change the float setting it was probably right when you dismantled the carbs sounds like you have dirt in the high speed jets ,it sucks lots of gas now if so rebuild the re build

 

[ddaigle]

Re: 1973 65 hp Johnson Carburetor Problem

Look at the throttle plates in the carbs when the throttle is at full speed( motor off) they should be perfectly horizontal. You may have messed up the linkage or sync. adj.

 

[ledgefinder]

Re: 1973 65 hp Johnson Carburetor Problem

Sure sounds like fuel starvation to me. Try squeezing the fuel bulb at WOT.<br /><br />Did you check whether the fuel tank vent is open? (Sounds obvious, but gets me all the time..). Any lines get pinched off? Fuel pump?<br /><br />The floats should be parallel to the carb body, when carb is inverted.

 

[fireman57]

Re: 1973 65 hp Johnson Carburetor Problem

Are you sure you got the high speed jet absolutely clean? The reason I don't think it is fuel starvation is because when he pulls out the choke it does not help. I have been wrong before. Okay, I've been wrong lots of times. That might come from being married for my entire life.

 

[ledgefinder]

Re: 1973 65 hp Johnson Carburetor Problem

I think you're right - clogged main jet on one of the carbs.<br /><br />If it were clogged fuel lines instead, it'd bog after running WOT for several seconds. He says it bogs right away, as soon as you move the throttle lever.

 

[abales12]

Re: 1973 65 hp Johnson Carburetor Problem

New spark plugs. Using the recommended one that do not require a gap. Installed new floats that came with the rebuild. Floats are parallel to carb body when inverted. Throttle plates are horizontal. This was my first thought. I have checked and rechecked. Fuel tank vent is open. No pinched lines. Will try squeezing the bulb. I thought applying the choke would help if it was starving for fuel.<br /><br />I think also think it is a blocked high speed jet. Was hoping not to have to take them all off again. Oh, well. Guess I will afte I finish the roof. Three hurricanes have put a damper on the boating.