Tankman 3,520 #1 Posted April 20, 2017 Having problems starting my 520-8 20 hp Onan. With a short shot of carb cleaner or either in the carb, starts 'n runs great. I'm thinking, "Vacuum fuel pump. Maybe." If not the fuel pump, thinking, "Why not replace the old pump anyway?" Was Looking at partstree.com's diagram. Without tearing the fuel pump off today, what is item #25 in the diagram? Where does it go? Do? Necessary? Share this post Link to post Share on other sites
pfrederi 18,035 #2 Posted April 20, 2017 I am not an Onan guy but that third hose looks like it provides the pressure pulse from the crankcase needed for the pump to work. Share this post Link to post Share on other sites
Tankman 3,520 #3 Posted April 20, 2017 pfrederi I'm not Onan knowledgeable either but, my '90 520-8 runs and handles great. Always preferred Kohlers the most. We'll see what the Onan gurus come up with. Not panicky. That's my reasoning excuse to have a herd not one poor, whimpering, lonely Horse. Share this post Link to post Share on other sites
boomers_influence 106 #4 Posted April 20, 2017 tankman yes, that is the pulse hose. the early P had the line coming from the gear case cover. the later P had its port above the oil filter adapter i always make that hose about 1" longer than original, that way the pump can be changed without removing the side tin. thank you. boomer ( the used onan engine parts guy, also NOS and new ) 2 Share this post Link to post Share on other sites
SylvanLakeWH 26,232 #5 Posted April 20, 2017 6 hours ago, Tankman said: That's my reasoning excuse to have a herd not one poor, whimpering, lonely Horse. Now wait just a minute there Tankman...Them's of us in the One Club simply realize the utility of these fine machines and have addressed our addictive behaviors vicariously by humoring ourselves at you collectors' expense through ... at a much more reasonable price I might add... 3 Share this post Link to post Share on other sites
Tankman 3,520 #6 Posted April 21, 2017 All here at Red Square just love our Horses. 1 Share this post Link to post Share on other sites
Tankman 3,520 #7 Posted April 23, 2017 On 4/20/2017 at 5:37 PM, boomers_influence said: tankman yes, that is the pulse hose. the early P had the line coming from the gear case cover. the later P had its port above the oil filter adapter i always make that hose about 1" longer than original, that way the pump can be changed without removing the side tin. thank you. boomer ( the used onan engine parts guy, also NOS and new ) Boomers do you think a check valve in the fuel line might do the trick? I did order a pump but thinking, and what do I know(?), a fuel check valve might help also. Inexpensive, ordered a check valve also. Right now just a squirt of carb cleaner and I'm off to the races. Makes me think pump draining gas back to the fuel storage tank. The fuel check vale would eliminate that possible problem. Share this post Link to post Share on other sites
