How well do you know Onan?

[luvrbus]

Sure the timing is adjustable they retard those for propane use

[Jim Blackwood]

I don''t see how. The magnet is in a fixed position on the flywheel. There is only one keyway. The magneto bolts into the end bell in a single fixed position. There are no further electronic controls other than shutoff. How could you possibly adjust it?

Maybe on the propane models they use a different flywheel. I think in the manual it says the timing is not adjustable, set at 25*BTDC (specifications).

Jim

[Jim Blackwood]

I have an issue with the choke linkage, it won't let the engine start unless it is dead cold and no adjustment of the bi-metal spring helps that. Overly rich.

On the carb, the choke flapper has a tab that engages a cam on the throttle arm to hold the choke open while running. a separate arm engages the choke linkage to the bi-metal. There is a light concentric spring that  nudges the choke plate towards the closed position. I'm attempting to attach 2 photos but they might be too big, we'll see.

What happens is that the choke needs to be open to start once the engine has run just a little but the spring urges it closed. Intake pulsations make it flutter around a little but it's still too much. Once the governor begins to back off the cam holds it open but for starting it is just way too rich if there is any heat in the engine at all. Cold it works just fine, in fact backing off the bi-metal makes it too lean to start.

I know these normally work correctly so what gives? Is the concentric spring supposed to move the choke tab the other way maybe?

Jim

[eagle19952]

Can of dust-off on hand....?

[Jim Blackwood]

Dust-off for Onan's sister? Man, you are a cold one.

Anyway here's a shot showing how I think the spring is supposed to go. Seems to work anyway. One more test tomorrow to set the choke for cold start and it should be done and dusted. You should be able to see in the first photo how the spring position was different.

Jim

[Jim Blackwood]

Does it ever end?
How do things get so weird? Now I've discovered that the bi-metal is somehow set up so that it closes the choke when the engine gets hot! ??

That's right, I didn't make that up, and I do know how it is supposed to work. After sitting overnight the choke was open but the motor started fairly easily. After running five minutes the throttle cam was holding the choke open but once I stopped the engine it went fully closed.

I'v got to wait for it to cool down before I can get in there to disassemble and see what's up with that. Maybe the bi-metal was put in backwards.

Jim

[TomC]

All this gobbliegoop will continue as long as you have an Onan gasoline. I have a Powertech 10kw Diesel gen with about 1,200 hrs on it. Brushless altenator, 4 cylinder Kubota. Except for changing the coolant and oil, have done nothing else to it. Get a Diesel genset-you'll be much happier. Good Luck, TomC

[luvrbus]

I thought the choke always went back to the closed position it does on my Onan,then when starting when hot it opens when you try to start

[eagle19952]

All this gobbliegoop will continue as long as you have an Onan gasoline. I have a Powertech 10kw Diesel gen with about 1,200 hrs on it. Brushless altenator, 4 cylinder Kubota. Except for changing the coolant and oil, have done nothing else to it. Get a Diesel genset-you'll be much happier. Good Luck, TomC

Tom, it's gasoline for a good reason.

[eagle19952]

Does it ever end?
After running five minutes the throttle cam was holding the choke open but once I stopped the engine it went fully closed.

I'v got to wait for it to cool down before I can get in there to disassemble and see what's up with that.

Jim

ok. ice cubes, to trick the choke ?

BTW. just kidding.

[Jim Blackwood]

Thanks guys, all suggestions gratefully appreciated, even the funny ones.

As it turns out, and often the case it's a good idea to take pictures before disassembly even for apparently simple things. After going to the trouble of removing the choke bi-metal and choke stove (and yes, it can be done while leaving everything else intact including the case but it isn't exactly fun) and then testing the bi-metal with my lighter, I though to myself..."Self, don't you think maybe there could be some other cause..."

And sure enough, right there it was right on top of the carb. Now mind you it wasn't obvious which is why nobody picked up on it from the photos and pointed it out to me but that little tab that the choke rod connects to is supposed to be back BEHIND the shaft, not in front of it. It reverses the operation. And there is a strategically placed dimple in the air cleaner base that will not let it be rotated from one side to the other without loosening that plate from the carb. So, whatever side it is on when the carb is bolted up, it's stuck there.

After putting it on the back side, amazingly enough the little limiter tab on the choke tab lined up and functioned as a choke pull-off and the concentric spring now fit into the holes and appears to function as it should. Such wonderfully brilliant engineers they had at Onan to come up with alternate ways to put their parts together. It makes such a delightful puzzle.

So anyway, warmup tests are good and I think the cold test tomorrow will be as well.

And then I'm done with it. Not my genset, not my RV. Dave's problem after that. (Of course, being my oldest son he might be inclined to ask dear old dad for help and that being an excuse for a visit I might be inclined to take a look. But we'll see.)

Jim

Were those ice cubes for Onan's sister? I've heard about that trick...

[chessie4905]

What made the exhaust glow red? Retarded timing?

[Jim Blackwood]

Lean mixture. I suspect it might have had something to do with alcohol in the gas these days but who knows? Richened it up and it worked fine.

Jim

[luvrbus]

We had a resident Onan expert and dealer in DaveG here that answered all our question about Onan, even where to buy the boards at a huge saving but  Dave passed away a few years ago.

[chessie4905]

Check the mix at full load. Adjust to be  ever slightly rich.