SAM58 30 #1 Posted April 30, 2011 Looking for a solution for a 520H 1992 model. it starts easy, runs good but after about 5 - 10 minutes of mowing, it starts acting like it is out of gas. It doen't do it until the fuel gets to a half full. fill the tank back up and it runs great until the fuel get around a half tank again.... I have blowed the fuel lines out with an air hose, replaced fuel filter. Shut it off and let it set about 3-5 minutes and it will run again for 2-3 minutes. Fill it up with gas, it will run strong until the fuel level gets to around a half tank, then it starts staving for fuel again.... Are the 520H's bad to vapor lock? could it be the fuel pump? maybe something floating around in the tank and plugging off the flow? I haven't been able to find anything. Any ideas?? Share this post Link to post Share on other sites
Kelly 1,028 #2 Posted April 30, 2011 Try loosing the gas cap, maybe a plugged vent, if that don't help it may be a weak fuel pump, and with a full tank there is more pressure pushing gas to the engine. Share this post Link to post Share on other sites
SAM58 30 #3 Posted April 30, 2011 thanks Kelly, I did check the cap vent, seemed to be open. I have a fear in the back of my mind that it is a weak fuel pump. Are they available? Onan stuff is not cheap.... By the way, is there a vaccuum hose on the back of the pump? I did not see how the pump gets vaccuum from the engine... Share this post Link to post Share on other sites
300zx 7 #4 Posted April 30, 2011 Yes, it is on the back of the pump. I'd loosen the hose on the discharge of the pump and see if it is still pumping gas the next time it quits. If it isn't, then fill the tank and see if it does. If it does, it may be a weak pump and gravity is helping it feed the carb until you are at half a tank. I am just guessing. For me, pumps usually worked or failed. I haven't seen one do this. Share this post Link to post Share on other sites
Cody 275 #5 Posted April 30, 2011 I would check or replace the vacume line on the back of the pump, you will have to remove the head shroud to get to it. I have seen many with bad lines and it causes the pump to suck air instead of gas. Also check the oil and make sure it does not smell like gas, iv seen a few pumps with a pin hole in the diaphram which allows gas into the crank case and the pin hole will cause the pump to be weak. Share this post Link to post Share on other sites
SAM58 30 #6 Posted May 1, 2011 Thanks everyone for the input... :thumbs: Share this post Link to post Share on other sites
SAM58 30 #7 Posted May 2, 2011 I would check or replace the vacume line on the back of the pump, you will have to remove the head shroud to get to it. I have seen many with bad lines and it causes the pump to suck air instead of gas. Also check the oil and make sure it does not smell like gas, iv seen a few pumps with a pin hole in the diaphram which allows gas into the crank case and the pin hole will cause the pump to be weak. change the hose on the back of the pump.... you can see the fuel pumping into the filter at first, when running it is hard to see. runs for about 3 minutes and them it dies. After it dies, let it set for a minute and it will start back up. Could the carb float needle be sticking closed? It will run longer setting still, when you start driving it, it will dies sooner. Any Ideas? GOING TO TRY A NEW FUEL PUMP.... WILL POST THE RESULTS. Share this post Link to post Share on other sites
SAM58 30 #8 Posted May 7, 2011 UPDATE.... AFTER A WEEK OF TRYING TO FIGURE THIS ONE OUT, I STARTED AT THE CARB AND REPLACED THE FUEL HOSE, THE NEW OWNER BORROWED A USED FUEL PUMP THAT MADE IT RUN FOR A LITTLE LONGER. LET IT SET STILL AND IT WOULD RUN FOR AN HOUR, MOVE IT AND DIES. WENT TO DRAIN THE TANK AND IT LOOKED LIKE AN OLD MAN AT THE URANAL... DRIBBLE...DRIBBLE... DRIP... DRIP. PULLED THE VALVE FROM THE TANK AND THE SCREEN WAS PACKED FULL . CLEANED AND FLUSHED THE TANK, SOLVED PROBLEM. THEN SENT A NEW FIRST TIME OWNER HOME WITH (HIS NEW TO HIM) TRACTOR. STARTED BIG, 1992 520H, 60" DECK. THIS IS WITH A 48" DECK RIGHT AFTER I FINISHED PAINTING. THANKS EVERYONE FOR YOUR INPUT I HAVE LEARNED A LOT ABOUT THE 520 FUEL SYSTEM. Share this post Link to post Share on other sites
