Engine Quits

[billmo]

I own a1973 70 hp JOhnson until recently it ran fine, last trip out it started and ideled fine. The engine also ran well up to half throttle, when Imoved the throttle control to full it died out andthe same thing on many outher attempts it will nor run full, I checked the fuel lines and pump, cleaned and regaped the plugs it also has a good spark.Need some direction where is the timing screw that I have been reading about in this forum ? Thanks billmo billmogayzel@aol.combbfrancis@iboats.com null

 

[Down South]

Re: Engine Quits

I'd leave the timing be for right now. You might check all the linkages and cams to see that none are damaged and all are in place. It sounds like to me your problem in the carburetion. When is the last time you rebuilt the carburetors.

 

[12Footer]

Re: Engine Quits

I still think it is fuel delivery problem.<br />The timing will rarely move out of adjustment on it's own,unless an adjuster backs out, or linkage breaks.<br />The symptoms you describe are almost allways due to fuel starvation. Check the tank's pickup tube for an obstruction, and make sure the vent screw actually allows the tank to vent.<br />Check the carb.<br /><br />The fuel pump on your motor operates off of compression,so check the compression. The check valves in the fuel pump can leak-by, and only supply enough fuel for idling sometimes. So if the compression test checks good, rebuild the fuel pump. The kits are only about 15 dollars, and the pump is not complicated....The only cautions are, make sure the check valves go back in the right way (they can be put in backwards on this pump), and clean. You may also find the diaphram half-eaten by time and alcohol additives in modern fuels. Also, use locktite or other threadlocker on the fuel pump screws, as engine vibration has been known to back these screws out,and if you try to overtighten them,they will strip out.<br />Good luck.

 

[billmo]

Re: Engine Quits

Thanks to both of you, I will recheck and try your suggestions first thing in the AM.

 

[JB]

Re: Engine Quits

Hi, Billmo. The point is probably harmless in this case, but the fuel pump operates off of crankcase compression/vacuum, which is unrelated to cylinder compression. You check cylinder compression when you do a compression check (which is never a bad idea in any case). <br /><br />Don't expect a cylinder compression check to tell you anything about crankcase sealing, reed valves or crank seals.<br /><br />Red sky at night. . .<br />JB

 

[Walter]

Re: Engine Quits

Start with the simple things first. I'm in total agreement with 12 Footer in believing (based on what you've described) that your problem is fuel related. Are you running off of a buit in fuel tank? If so, do you have a remote fuel tank (with hose) full of fresh 50:1 gas/oil mix that you could run your engine on to see if anything improved?<br /><br />I realize how easy it is to believe the problem is serious/complicated...but so often the opposite is true.<br /><br />Good luck!<br /><br />Walt