1997 520h Onan EPA compliant carburetor

[TheReDStAnG 4]

I recently picked up a 1997 520H with 450 hrs. When I bought it, the idle speed on the governor was set really high. I want to say around the 2200-2500 rpm (ball park), which is a little high for my blood on a cold engine. So I adjusted the it down to about 1100 rpm. Then I began to notice it have a slight hiccup every so often, almost like a misfire. Replaced plugs (gapped and all), hooked up a timing light to verify spark wasn't cutting out, took the carb apart cleaned all necessary ports (I have two late 80's 520h's so I know these carbs pretty well), and still no dice. Ok, so I took off the muffler shroud to get to the idle adjustment screw, pulled everything off, and to my amazement found there to be no idle speed adjustment screw along with some type of "accelerator pump" attached to the carb. What gives? Did these come from the factory high idle due to EPA compliance? It didn't appear the governor idle adjustment was ever messed with before me.

[Crown Vic P71 20]

I would imagine thats what it is about... I have a newer tractor as well with the same deal.

[Kelly 1,033]

I just bought a 97 520 but it runs great, idle is about 1000 and smooth, throttles up very good, so I have no reason to mess with it, (yet) now my 95 520 needs some carb work, I haven't looked at it yet but it runs very rich at idle, and starts with no choke but still puffs black smoke at start up, and runs ruff for 30 sec. after start up.

[zieg72 209]

MY 97 HAS THE NORMAL SET UP, JUST ADJUSTED MINE AS LOW AS IT WOULD GO FOR IDLING.

[Brian K WheelHorse 28]

I recently picked up a 1997 520H with 450 hrs. When I bought it, the idle speed on the governor was set really high. I want to say around the 2200-2500 rpm (ball park), which is a little high for my blood on a cold engine. So I adjusted the it down to about 1100 rpm. Then I began to notice it have a slight hiccup every so often, almost like a misfire. Replaced plugs (gapped and all), hooked up a timing light to verify spark wasn't cutting out, took the carb apart cleaned all necessary ports (I have two late 80's 520h's so I know these carbs pretty well), and still no dice. Ok, so I took off the muffler shroud to get to the idle adjustment screw, pulled everything off, and to my amazement found there to be no idle speed adjustment screw along with some type of "accelerator pump" attached to the carb. What gives? Did these come from the factory high idle due to EPA compliance? It didn't appear the governor idle adjustment was ever messed with before me.

I have a low hours 1997 520H now too and mine was the same way when I got it - really high idle and it has the accelerator pump so I also assumed it was set up for California emissions or something. I have to pull my carb to clean it. I am getting quite a bit of gas up through the carb on low idle and it smells like it burns really rich on the low end when it isn't under load. It otherwise runs great at higher rpm running speed - smooth and tons of power.

I already had the heads off and decarboned them along with the pistons. I set the valve lash (strangely enough it was set in too far) and the valve seats were snug. Replaced the plugs and fuel filter. The only reason I didn't take the carb apart is because I needed to mow the lawn - lol.