Got a trailblazer with a onan 20 performer. 850 hrs. Idle is "suddenly" erractic, idle up is fine. Flushed the fuel first thing. Plugs were worn looked lean, replaced them. Checked the solenoid it is locking in and holding good. Moved the solenoid and raised the idle but it is still missing and stumbling. Fuel lines are ok, return to tank line ok. Checked for intake leaks with starting fluid, nada. The only thing I can think of is trash in the carb, looks like you have to unbolt the intake manifold to break the carb down, looks like it bolts in from the bottom of intake. Cleaning out the carb is my next option as far as I can guess.
Am I missing anything other then weird little fuel pressure regulator thing on the side of the carb?
Any help appreciated
By rcwelding 
Date 01-05-2011 04:06
Edited 01-05-2011 13:52
I have a Bobcat that gave me the same problem.. It turned out to be water in the gas.. Look close at your in line filter and see if you can see any separation... If not I would still change the filter before you get to excited about bigger things... Filters are $5
Another time it was pulsing and my filter looked ok but it wouldn't run right so I got an air hose and gently blew air down the hose into the tank then blew air through the hose up through the carb and it worked great... I found some spiders in my fuel filter... NO Clue how they got in there but the only thing I could figure is that something was plugging the hose out of the tank..
Just my 2cents worth
RC
I had the same problem with my Trailblazer when it got low on fuel ,and I changed the fuel filter and it was go to go.
Should be able to take the 4 screws off the top of the carb to look inside. Sounds like the low speed jet is clogged. Be careful not to drop the needle when popping the top off. And yes, if you need to replace the carb you have to take off the manifold as the carb is bolted on from the bottom. My experience, I just replace the carb and move on. Good luck.
My Ranger with the Kohler would do that once in awhile. New plugs sometimes would fix it, other times not. Next on the cheapo list was a fuel filter. Between those 3 things one would cure the problem. I would carry extra plugs and filters in the truck and have changed them out on the right of way when she started acting funny. If the filter don't get it running right refer to Regmanager's post above. I know on some other small equipment I have around here taking the carb off and shooting carb cleaner thru all the tiny holes yields some good results, especially when you find one that is not letting the carb cleaner pass thru.
