RE: Onan 4000 micro quite questions

I put on here a couple of weeks ago about the above generator not starting. Thanks for all the in put last time it helped!!
I put a new pump and filter on it this weekend and got it started. It runs with the air filter off but it surges. Some gas is spitting out of the butterfly where the air filter goes while running. I put the air fitler on and it will eventually die. I did take carb off to clean but looked good to me, but I am not much of a mechanic. I do have some stp in gas as well as a can of sea foam thinking it would clear itself up but no luck running for about an hour surging that way.
DO you guys have any more sugestions? Should I be looking at the carburator again? ???

Thanks for all the help as always.
Matt

When its running and surging, is there black smoke coming out the exhaust?? If so the problems TOO MUCH FUEL instead of not enough, that will eventually gas foul the plug and she will die. HOWEVER if shes surging n hunting cuz shes too lean (NOT black exhaust smoking) and the governor keeps bumping her up n down then Id say shes NOT getting enough fuel.

Those tiny carb jets can be clogged up even if a simple look inside the carbs bowl all looks fine. If she has good fuel to the carb (pump n filter all okay) but she hunts n surges and isnt blowing black exhaust smoke, I still suspect the carb.

Is this in an RV?? The gas inlet tube in the tank (that serves the genny) isnt at the bottom so they cant run the tank out of gas ya know..

ALSO the EXPENSIVE control board in those MicroQuieTs can casue all sorts of weird problems.

Again, just cleaning out the bowl area on those carb isnt enough as its the teeny jets and passages (maybe flaot level too low????) are what get gum n varnished n clogged up

PS wasnt there a certified Onan tech who posted before?? Do what they tell ya not me

I HATE the noisy single cylinder 3600 RPM so called Micro "Quiet" yeah right and their exotic expensive control board, give me the old Emerald 2 cylinder 1800 rpm quieter unit anytime

John T NOT any Onan expert but have fixed several of them

John T is correct. You most likely have a varnished carb. You need to take it apart and clean it. It is running lean. Very common problem on this model. If you do not run it as you should. Onan will not sell you a rebuild kit. Because you are not supposed to clean them(EPA) but it can be done. I use the spray can and some low air pressure to clear out the carb passages.Sometimes letting it run without load. With cleaner in the gas will clear it up.

Most fuel pickup tubes cut off at 1/4 of a tank.So make sure you have plenty of fuel.The control board can cause some odd problems.Some times what it shuts down for. Is not the real problem.

It is a good unit for what it is. But I prefer the old 1800 RPM units.

Onan tech since 1980.

Silly Me, I forgot the most basic simple try first grrrrrrrrrrrrr.

Ifffffffff your Onan carb has this (mine all did) at the bottom center of the carb is a mixture adjustment (how rich or lean) perhaps also called an "Altitude Adjustment"

Turning it out RICHENS the gas/air ratio (needed if its surging and not black smoking) while turning it in LEANS the gas/air ratio (needed if its black smoking) IT OFTEN JUST TAKES 1/8 TO 1/4 TURN TO FIX A PROBLEM DONT GET TOO EXCITED.

Have it running preferably under a load n try turning that screw first out then in a bit n see if she smoothes out n runs n stops surging or black smoking????????????????

NOTE Ive had some when I had to remove the plastic stop turn preventer then I got enough adjustment out of the screw for the correct mixture BUT NEITHER ONAN OR ME RECOMMEND THAT LOL

I hope Billy can correct me and/or add to this if Im all wet, it wont be the first time and he wont get any cherry lol

John T TRY THIS FIRST IF IT HAS THE BOTTOM OF CARB ADJUSTMENT SCREW and Billy says its ok

System will not let me give you an answer. You have a solenoid under your thing. Not the screw John is thinking about. But he is correct on the other units.

If fuel is comming out the air intake and getting the air filter wet, then air must be going the wrong direction throught the carb. That might mean the intake valve is set too tight or carbon isn't letting it close completely. Check valve clearance.

This will cause the engine to run rich, black smoke, black carbon on spark plug.

Had this happen on two briggs engine back in the day of flat heads, intake valve seat recession. Had to grind the valve stem off to adjust valves then.

Seems with overhead valve engines, the exhaust valve clearance increases making them extremely hard to start because the exhaust valve doubles over as a decompression valve when starting.