1998 Onan MicroLite 4000 Weak SPARK

Sounds like symptoms of low battery voltage while cranking.
Or more properly, low voltage to the engine while cranking.

Could be that the starter is drawing high current too.

Test the batteries and all of the main connections.

Test the voltage AT the starter when cranking versus the voltage at the battery to see if you have excess loss due to a bad connection.

If a jump to another good battery makes the cranking speed perk up and then it starts.....or tries to.....it's a good bet that you have a supply voltage problem. If you do that, be VERY careful about polarity and do NOT have the other vehicle running.

P.S. Unless you are dumping liquid fuel into the cylinder, it won't "put out the spark".

X2 sounds like you have a cranking problem to fix first.

Please see this video I just took: https://youtu.be/ngCta0D-0UE

I have to keep it throttled to start it and keep it throttled for a while till the automatic throttle control kicks in. It seems to do a fair job at keeping her at idle until you either manually touch the throttle arm or try put her under load. I know it powers the 110 because I put my A/C on (fan only) and it the generator ran fine, but when I switched the A/C on she died immediately. It seems that the automatic throttle control is not working properly, it should compensate for the load and throttle up and when starting it should adjust the throttle on its own but it is not doing either.

I think I have a bad ground somewhere and I will look into that. With the truck running I get a lot more power to the generator to start her. I did not realize the generator used the truck battery verse my campers deep cycle battery to start it.

HELPPPP

Usually the generator is started from the house battery. If you have a weak battery or a poor connection to it, running the (main) engine will engage whatever sort of battery combiner/isolator system you have and the generator will be using both electrical systems to start.

The generator starter needs quite a bit of current, somewhere around 100A. It doesn't take much to cause a voltage drop at 100A that is all but unnoticeable for typical RV usage.

The starter should be able to easily and energetically spin the engine. If it struggles to get over the first compression, besides the ground and power connections it could also be a bad or disconnected brush in the starter motor. The starters are permanent magnet DC motors, with four poles and four brushes, and if one of the four brushes is not working they will still operate at about half power. In my case, that was just barely enough to get over the compression cycle...most of the time...until it didn't on a cold day and I burned out a couple windings in the starter trying too long.

I don't think you have a spark issue, but rather a carburetor issue. It seems the engine dies when the throttle is opened, which may mean a clogged main jet possibly? It looked to me like the governor was attempting to govern the engine speed properly, i.e. it moved the throttle in response to engine speed changes, but the engine did not respond properly.

heebeha wrote:

I have to keep it throttled to start it and keep it throttled for a while till the automatic throttle control kicks in. It seems to do a fair job at keeping her at idle until you either manually touch the throttle arm or try put her under load.

I did not realize the generator used the truck battery verse my campers deep cycle battery to start it.

Now we have a different story from the original "won't start".

But all of the stories point to a carb problem (way too lean or choke not working) and my Onan dealer replaced my carb for about the same price as a removal and cleaning which doesn't always work. Highly recommended.

And as for the batteries: The gen starts off of the house batteries BUT when the truck is running a solenoid closes to connect both sets together.

My guess is that you need a new carb on the gen AND you have a bad connection from the house batteries to the gen OR the house batteries are getting old and weak......or are not being charged properly.

I disconnected the Cut Off Solenoid Valve red connection and it died. Then I connected a straight positive lead to it and it fired up after again having to play with the throttle. I tried disconnecting it and reconnecting it when it was running to see the effect and the throttle killed it but when I reconnected it the generator came back to life. Does that Cut Off Solenoid Valve work in conjunction with the governor to keep her running during a surge ?

Could it be my problem?

I really appreciate everyone's help here. Anyone know about the cut off solenoid on the carb?

https://www.youtube.com/watch?v=EeOkNi5F78c

I took a video of what I am referring to and you can se how when I remove the power lead to the solenoid it cuts off the fuel as it should. When I reconnect it the Gen fires right back up. So it seems strange that it wont start unless I manually give it full gas and keep it throttled until the governor kicks in on its own.

I'm thinking what ever the positive lead connects to is not working properly. What does it connect to and what are your thoughts?

You need a new carburetor.

Why do you think I need a new carb? A new carb is expensive. Seems that the carb is working correctly, see the video.

heebeha wrote:
Why do you think I need a new carb? A new carb is expensive. Seems that the carb is working correctly, see the video.

This is possible and YOU must be the final judge of what you do next but at least two of us now have told you that from all the symptoms we can see it all points to a carb problem.

And experience tells me that even the professionals can't effectively clean them once they get gummed up and an amateur has even less chance.

IIRC, a new carb, installed, cost me about $250 at the Onan/Cummins dealer. Things that go bad don't always have a cheap fix.