Onan Generator starting issues

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cougsfan

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Joined
Aug 2, 2009
Posts
21
Location
Eastern Washington
Hi,  I recently bought a "98 Minnie Winnie 31 WM with very low miles and in incredibly good condition.  It has a couple of problems though and I thought I would ask about one of them now.  The Onan 4000 micro lite generator (250 hrs on the meter) starts very difficultly.  According to the old owner, it has always been that way.  It starts, but it takes a special drill.  You run the starter (either local or remote) for 5 seconds or so and let off.  Eventually it fires and runs for a second or two or three or four, then dies.  I have found it works better if you wait quite a while (15 seconds or so) between tries.  It may take a dozen or more attempts before it takes off and catches, then runs absolutely fine from there on out until I shut it off.  If I restart it right away, it starts fine.  If it sets for any amount of time off (maybe 15-20 minutes), you have to go through this ritual again.  The previous owner acted if it were normal.  I don't buy that.  The motor home is always kept full of fuel, The gen set has plenty of fresh oil, and my all my batteries are good. 
  I changed the spark plug and fixed the broken air filter mount (God only knows how long that has been broken). Put a new air filter on too.  None of this made any difference.  I have visually checked the fuel line (it looks OK), and I can't find a fuel filter (if it even has one.)  I cant find the fuel pump (if it has one) either
  After reading tons of threads I am coming to believe that it is either a bad fuel supply or a bad voltage regulator.  I don't know which and don't know how to check either in more detail.  With what I have described, can someone rule one or the other (or both) out , then point me in the right direction?
Thanks   
 
My guess is that the electric choke probably is not functioning correctly, especially if once being warmed up, it runs okay. Check for a corroded or loose wire at the choke. When starting there should be 12 volts there I believe.

Most models of Onan generators will not start at all if the circuit board doesn't sense AC voltage being produced. That would kind of rule out the voltage regulator. If it was a fuel supply problem, it should run poorly even after finally starting.
 
Sounds to me as if you're losing prime. Check the rubber hose going into the generator for leaks. FYI the pumps for these are low pressure and even the slightest leak will cause starting and running problems. I found that mine had what looked like very minor cracks, but turned out to be leaks. Interestingly, it started and ran fine with a full tank, but half tank and it became very difficult to start.
Hope this helps,
Ernie
 
I have the same generator and I had nothing but problems with it for the first year and a half. I paid to have it fixed several times and I fixed it myself a few times including rebuilding the carb. I finally took it into a shop and they had another 4000 that they swapped with mine. Cost me $650 and it now works every time just fine.

So if it keeps on flustering you I would suggest watching Craigslist. I see 4000s for sale frequently in the $400 range. It only takes a competent mechanic an hour or two to change it out.
 
I had a problem with mine. It was doing something similar. I pulled the fuel tank and found the short piece of 1/4" hose from the steel line to the tank was split.

Dewey
 
Perhaps it gummed up. Do you have a fuel shutoff valve near the gen? Use that for shutting it off when you leave it for more than a day. "Dry bowl" wont gum up. 

Get a can of onan brand crud buster carb cleanout. It creates a hideous cloud of steam and black gunky waste product out the tailpipe but it's REALLY good for your generator. It degums the works. Mine now starts great. This is a good time to use your GenTuri.

Thereafter you do need to run the starter for a bit but only to get fuel back into it, but then it starts great.
 
If you think it's a fuel delivery problem in either the tank or the fuel line, take a short piece of new fuel line and hook one end directly to the fuel pump and stick the other end in a gas can and see if it starts and runs normally.
 
Thanks for all the ideas!  I will mess around with the fuel supply this weekend.  I feel more confident fixing mechanical problems than electrical ones!  Will let everyone know what I find.
 
I am not sure it is a fuel problem.  First I disconnected the hose that feeds from the gas tank into the fuel filter at the filter. The line had not lost it's prime. With the generator not running , a steady, healthy stream of  fuel runs out. (Fills a 16 oz pop bottle in probably 20 or 30 seconds). So I hooked it back up, then disconnected the fuel line at the carb.  Nothing came out, but the moment I hit the start button, fuel then gushed out of the hose.

I put that back together, then I played with the choke and throttle linkage while trying to start it.  It is not obvious to me what way is open and closed on each, but holding either of them fixed one way or the other just seemed to keep it from starting at all.  (Left alone, the linkages kind of fly around a bit when it tries to start then settles down to a fixed position once it starts)  (I think it is a bimetallic choke, not an electric choke.  Don't see any wires to the little box that the choke linkage goes into.  Also the manual indicates it is bimetallic)

Again, After 8 to 12 starting attempts, it stayed running and ran smooth as a kitten until I shut it down.

Am I missing something?  What is next to try? 
 
The bimetallic choke most likely requires an electrical heater to make it function.
 
Because it runs smooth once you get it started I would also be looking at the choke and also the + coil voltage. Check the coil voltage when the engine is cranking to make sure the mag is working. I seem to remember them having trouble suppling enough start voltage at cranking speed (hard start), but Ok when they are running (higher RPM).
If coil volts are the same at crank as compared to running I would investigate the choke adjustment further. Once the engine starts you should see the choke linkage move towards the open position as the engine warms up. Before you start it mark the linkage so you know where it is, then start and check it again once it runs a while. Let us know what you find.
 
According to the manual that John gave me a link to, and according to what I see, It does not have an electrically heated choke.  It heats up the bimetallic coil with hot air that is ran across the exhaust manifold.  (I have never heard of such a thing!)
I tried it again and didn't play with the linkage this time, just watched it.  I must have released something before because it doesn't bounce around now while starting.  It holds a position.  When it starts, the choke slowly opens up, just like you would expect it too.

I found out something else interesting too.  After the third try,  I held the start button 
 
Ooops, i pushed the send button as I was typing

Anyhow, I held the starter button in until well after the engine fired.  Maybe a second or two, And it started right up and kept running!  I will try that again, tomorrow morning after it cools down and see if that is the trick.  Don't know if that is hard on the starter though. 
I will let you know if that is the solution.
 
After reading Cool Daddy's post on his starting problems, and Waterdogs Pdf on an Onan Starting sequence, I am even more apt to think I am simply not holding the starter button long enough to allow the electrical circuitry to go through it's sequencing!  Hope it is as simple as that!  Onan should put a tag somewhere telling people that.  Wonder how many people struggle with that?
 
Started on second try this cold morning!  I am now pretty sure that was the problem all along.  To think my previous owner and hard telling how many others have just dealt with this stupid little situation.  If this is normal operations, I wonder how many needless trips to and dollars spent at a small engine shop have been made?  Seems like Cummings could have put a timer to a relay  to do the same thing. 
Thanks to all for helping me solve this.
 
If your remote switch is anything like mine, It has a pilot light in the start position of the switch. When the generator is running and will continue to run, the light comes on, and that is when you release the switch. At least it was an easy fix.... ;D ;D
 
It's not normal to have to hold the start switch on any longer than it takes for the engine to fire.  I'd look at the oil pressure - maybe it's low and takes longer than it should to build up to normal, or the oil pressure sender is defective.

As a test, locate the oil pressure sender on the engine and temporarily remove the wire and make sure it's not touching any metal.  Removing the wire disables the low oil pressure protection.  See if this changes the starting behavior.
 
Yea, I agree that you shouldn't have to hold the starter engaged after the engine starts. The overrunning clutch will drop out the drive gear but will still have pressure against the ring and cause damage in a short time. You are inadvertently bypassing something by holding the start switch, probably the low oil safety as Lou mentions. You would see this on a voltmeter as explained above or just bypass it for a test. IMO I'd keep looking.
 

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