Starting a sleepy Onan Microlite 4000

[Red_Cobra_10]

Hello Travelers. I've got a tip for many that own an Onan 4000 Microlite that has been sitting for a few months without being started. I take the cover from the generator and manually start the unit out side. A repairman showed me a trick one time how to get the generator to fire up within a few seconds. Have you spent 20-45 seconds cranking before yours fire? An easy tip is to push the choke over and hold it until the unit fires. About 5 seconds of crank time and she running. Try it , you'll love it and so will the starter on your generator. I'll see you around the camp fire.

[ron_dittmer]

As some here have shared, I too learned about priming using the start rocker switch in reverse. What had thrown me off was the light that came on some seconds after starting to prime. I thought the light meant "It Is Primed, Now Try Starting". But the light going on means "The Pump Is Now Priming, So Keep Pressing It".

After a long hibernation of many months, I learned to prime (with the light on) for 10-15 seconds for that first attempt. Less light-on priming time on the second attempt if needed. Crank-over time at 5 second duration.

I also agree to make sure the altitude adjustment on the carburetor is set to your altitude. But that thing is such a sloppy adjustment. It seems to have 3 general considerations.
- sea level to ~5000 (set it all the way to zero)
- ~5000 to ~10,000( set it half way between zero and max)
- ~10,000 on up (set it to max)
Do your best figuring out your altitude and then "wing" the adjustment. This is one place where a simple electronic fuel injection system with an altitude sensor would do real good. But then Onans would be even more over-priced.

[leeper]

parkmanaa wrote:
I have a Onan 4000 Microlite, but it runs on propane.
This rig sat for a year with engine only being started every
week or so, but never started the Onan.
Now it just has a high clicking noise when I attempt to start
it.
Any clues?
Thanks,

The most common problem with Propane generators not starting is that the vent hose is plugged with bugs. Bugs are attracted to the smell of propane, so they crawl in the vent hose and stay there. Clean out the tube or replace it. Onan has a foam sock that fits over the hose end keeping bugs out. Works good for me. You can only get it at an Onan parts shop.

[Snowman9000]

I got around to trying the OP's suggestion, on a 30 degree day. YES! The typical Onan 4K hard starting is a choke problem. I don't know if it's a poor design or just adjustment.

When cranking, the spring loaded linkage lets the choke flap closed and then wide open repeatedly. Whether the oscillation is as the engine shakes, or sucks air on the intake stroke, I don't know. Whatever, it's not closed long enough to be effective. When I just held the actual choke lever closed, it started instantly.

In a couple of weeks I'll be camped in warm weather and will have time and comfort to check to see if it is adjusted to spec. I suspect the spec is lean for some reason, though.

Oh, and thank you, OP!! Big time.

[pnichols]

Whether or not an Onan needs to be choked to start it may also have something to do with it's altitude setting.

Our Class C motorhome's Onan generator has an altitude adjustment knob on it. Having that knob set to a high altitude by mistake when trying to start it at a lower altitude will of course make it too lean at the lower altitude. This may make a choke necessary to start it if one doesn't notice the too-high setting of it's altitude adjustment knob. Also, running one's Onan at lower altitudes with it's altitude knob set by mistake at a high altitude runs the risk of burning out it's valves.

[Bobbo]

Snowman9000 wrote:

Bobbo wrote:

Snowman9000 wrote:
I can prime the genset for 60 seconds or more and it still won't start without a lot of cranking. I'll try the choke suggestion and see if it makes a difference. I bet it will.

This describes mine, but I am too lazy to go outside, open the compartment and take off the ONAN cover. I will continue to just crank it 3 or 4 times even after priming for 60 seconds. It is just quicker and easier. Even 4 cranking sessions of 5 seconds on/5 seconds off takes less than a minute.

Yeah, well, I'm taking the problem personally. 🙂 I don't like poor designs and I can't resist trying to improve them.

If you find a way to install a manual choke control next to the remote start switch, let me know. :B

[Snowman9000]

Bobbo wrote:

Snowman9000 wrote:
I can prime the genset for 60 seconds or more and it still won't start without a lot of cranking. I'll try the choke suggestion and see if it makes a difference. I bet it will.

This describes mine, but I am too lazy to go outside, open the compartment and take off the ONAN cover. I will continue to just crank it 3 or 4 times even after priming for 60 seconds. It is just quicker and easier. Even 4 cranking sessions of 5 seconds on/5 seconds off takes less than a minute.

Yeah, well, I'm taking the problem personally. 🙂 I don't like poor designs and I can't resist trying to improve them.

[Bobbo]

Snowman9000 wrote:
I can prime the genset for 60 seconds or more and it still won't start without a lot of cranking. I'll try the choke suggestion and see if it makes a difference. I bet it will.

This describes mine, but I am too lazy to go outside, open the compartment and take off the ONAN cover. I will continue to just crank it 3 or 4 times even after priming for 60 seconds. It is just quicker and easier. Even 4 cranking sessions of 5 seconds on/5 seconds off takes less than a minute.

[Snowman9000]

j-d wrote:
Using the "Prime" function for gasoline-fueled ONAN genny's (as Phil noted) is a very good idea, and something many of us didn't know was available till recently. I prime ours till I hear the pump stop its tapping sound. Then I attempt a start. It sometimes actually does start. If not, I repeat the priming and listening, the do a second attempt. It always starts then.
OP - Fully closing the choke is a good idea and I've done it in the past. I do NOT think the Microlite will cause this possible hazard, but... Be sure it's the Choke and not the Throttle. The older ONAN's would go right to 160-volts-plus if you tweaked the throttle. The one that did that with me had no electronics, just a mechanical governor. I think Microlite won't allow that much voltage. I'm just not sure and I just don't feel lucky.

I can prime the genset for 60 seconds or more and it still won't start without a lot of cranking. I'll try the choke suggestion and see if it makes a difference. I bet it will.

[Bobbo]

When my gas powered ONAN did that, it was a loose negative connection on my house battery.

[DrewE]

parkmanaa wrote:
I have a Onan 4000 Microlite, but it runs on propane.
This rig sat for a year with engine only being started every
week or so, but never started the Onan.
Now it just has a high clicking noise when I attempt to start
it.
Any clues?
Thanks,

That sounds like a dead or low battery or a bad 12V electrical connection. A propane fueled generator won't be likely to have the same carburetor problems that gas powered ones do since there's no varnishy residue left behind from propane evaporating.

Very often the generator starter is powered by the house battery, not the chassis battery. It may help to start the main engine so that the alternator and chassis battery are tied into the house 12V system. The Onan starter needs a lot of current, somewhere around 90A or so on my motorhome.

[j-d]

Using the "Prime" function for gasoline-fueled ONAN genny's (as Phil noted) is a very good idea, and something many of us didn't know was available till recently. I prime ours till I hear the pump stop its tapping sound. Then I attempt a start. It sometimes actually does start. If not, I repeat the priming and listening, the do a second attempt. It always starts then.
OP - Fully closing the choke is a good idea and I've done it in the past. I do NOT think the Microlite will cause this possible hazard, but... Be sure it's the Choke and not the Throttle. The older ONAN's would go right to 160-volts-plus if you tweaked the throttle. The one that did that with me had no electronics, just a mechanical governor. I think Microlite won't allow that much voltage. I'm just not sure and I just don't feel lucky.

[parkmanaa]

I have a Onan 4000 Microlite, but it runs on propane.
This rig sat for a year with engine only being started every
week or so, but never started the Onan.
Now it just has a high clicking noise when I attempt to start
it.
Any clues?
Thanks,

[pnichols]

I've also discovered - using the Onan remote start rocker switch on the panel inside the coach - that holding the Onan start rocker switch in the position opposite from "Start" for a few seconds runs just the Onan fuel pump so as to fill/prime the Onan gas line and carb float fully. Then hold the Onan start rocker in it's Start position for a fast start in all kinds of conditions.

I didn't discover this dual action of the Onan's remote start rocker switch until owning our motorhome for quite some time. The rocker switch is labeled as "Start" for it's engine starting position, but is not labeled for it's fuel pumping/priming position. I've never had to go outside and use the Onan's local controls under the cover. I just have used the dual action rocker switch for quick starting over the last 9 years.

[Snowman9000]

AHA! So it IS a choke adjustment issue. I suspected as much. I've owned two of these gens; the current one was brand new. Both cold start like crud. I figured Onan had to lean out the jetting for emissions reasons, and maybe the choke too? I don't know, but one of these days I'll print the choke adjustment out and richen the choke setting. (I downloaded a service manual from somewhere or other.)

Thanks for the tip.