1982 Onan 4K Genset won't start

[randini]

That sounds more like it. Is it generally worth the work to get a better look at these things?

[Dave78Chief]

When the engine is stopped, the oil pressure switch should be open. When the engine starts and builds up oil pressure the oil pressure switch closes thereby energizing relay K3. I suspect the oil pressure switch is either stuck closed or is closing to early resulting in k3 being energized to early and disconnecting the K1 start solenoid before the engine can start.

Dave

[randini]

That's actually about exactly what I thought might be going on if you look back a few posts in the thread. I thought the oil switch might be stuck closed or the wire from it might be shorting to ground and tried disconnecting it during the crank and then connecting it after the gen started.

Tonight I took it a step further and connected the oil switch connection from the control box to a switch and then to ground. With the switch off the gen cranks and eventually catches and if I turn the switch on it tries to run. I think the oil switch might be bad, closing early as you described.

But I also think I might have a new problem. The gen sometimes cranks for a long time before it catches and then at best it runs for maybe ten seconds, hunting up and down from full down to almost a stall and then eventually dying. Is it possible with all this cranking I killed the fuel pump? Also, I noticed a pretty big crack in the exhaust downpipe. This seems like a long shot, but is that engine sensitive enough to backpressure that running it on a straightpipe would make it stumble?

[Dave78Chief]

Exhaust pipe would only be an issue if it is plugged up.

This is a points based system. Have you verified the condition and adjustment of the points?

Valve lash should also be checked.

Fuel pump could be defective and/or you could also have an old rubber fuel line that is cracking and sucking air.

Dave

[randini]

Weird thing is if anything like that is wrong it just changed. Two weeks ago when this thing would start it ran fine if a bit loud.

[PlayItForwrd]

Back to the fuel pump, and I'll expound on what I mentioned previously-

When these pumps are dry, they clack LOUDLY-

When they pick up fuel and start pushing it to the carb, the clacking gets quieter-

When they start building pressure, the clacking is almost silent--

When the carb is full and the pump is holding pressure, the pump quits clacking altogether, and then just "thumps" a few times every so often to replace the fuel the generator is using.

Because the Onan's only run the pump when the starter is engergized or the engine is running, it's kind of hard to troubleshoot the pump. I've been troubleshooting a fuel problem with the Westerbeke generator on our houseboat for the past month (which is why I'm VERY familiar with the clacking!), but the nice thing about the Westerbeke, it has a separate switch that turns on the pump to prime the carb, so I can turn on the pump by itself any time and wait for something to happen. (for what it's worth, I couldn't get 3 different electric pumps to fill the carb, and it turned out to be crap caught in the sediment filter in the carb!)

ANYWAY-- I would suggest running a simple 12 volt hot wire from someplace handy so you can just run the fuel filter. If it just keeps clacking and doesn't quit, it's either (A) same problem I had, it can't push fuel into the carb, (B) it can't suck fuel from the tank, or (C) the pump is plain bad-

To troubleshoot (A), remove the fuel line from the carb, and run the pump- if you get gas, something's up with the carb. Otherwise, you then need to determine if the pump is working, and/or if you're sucking air from a bad fuel line...

How much gas is in the tank? If it's around 1/4 tank or less, the genny's fuel intake may be out of reach--

[randini]

I'll pull off the fuel line and see if I get anything out of it. Might also remove the filter and see if that makes any difference. I might just replace the sucker with a generic solenoid pump.

On the exhaust thread, I'm leaning toward building something instead of dropping a fortune on Onan's parts. Looks like even the shortest stock downpipe costs a fortune (I was thinking of buying that and welding on from there). Anyone know if that flange is standard? Know the dimensions?

[randini]

OK, the original parts manual says the gasket for the exhaust header is part 154-2061 which has been superceded by 154-2800, which I found one online vendor for that has the dimensions on it, 1.5" ID and 2.75" centers on the bolt holes. Can anyone confirm this? Anyone know if this sized flange is an easy part to find?

[randini]

Took the fuel pump apart and removed the filter element and installed a glass inline filter before the pump.

Took off the carb and doused it with gumout and blew it out with compressed air as best I could without taking it all apart; didn't want to have to find a rebuild kit and a full rebuild is a stretch of my skills.

Put it all back together and it ran possibly slightly better but was still hunting way up and down. I also called my father in law who was much better wrenching skills than me and he asked "do you have a load on it?"

Doh. On an 1982 RV there's no cutover, you just take the shore power connector and plug it into an outlet just inside the cable door. In fact, all this time I had the shore power hooked up to my driveway outlet so the converter could keep a charge on the house batteries I've been abusing with the cranking.

Plugged in the rig to the gen and with the bare load of the converter it ran slightly better. Started the AC and it smoothed right out. Same for the microwave. It's hard to tell how rough or smooth it's running with the exhaust noise, and it still hunts a bit every ten or twenty seconds, but I claim it's running within normal limits for a thirty year old machine. Maybe at the end of the season I'l replace the plugs (it has fresh oil and with only 114 hours I don't know that I need to mess with the points yet).

So. The starting problem behaves correctly with the switch hack until the oil switch arrives. This resolves the hunting problem. I picked up some exhaust pipe tape that will hopefully reduce the noise until I get a new exhaust figured out.

Any feedback on the exhaust flange size question a few posts back? Can anyone confirm the flange from the header is 1.5" pipe wth 2.75" between the bolts?

[randini]

Tried the tape on the cracked pipe but the leak is right at the 90 deg bend and the clearance against the fan housing is too tight to get the tape tight around the pipe. Not much help there.

Also, now that the thing is running I'm finding it's running pretty rough,bogging down hard if I turn the AC on, for example. We've established it's getting clean fuel. I'll blow out the air cleaner. Other than changing out the plugs and checking the points, any other suggestions on smoothing this thing?

[Dave78Chief]

Normal Onan Tune up:

Valve Lash (page 53)
Points adjustment (page 24; replace if necessary with condenser)
Plugs
Carb Float level Adjustment (page 15)
Carb mixture screws (page 18)
Choke adjustment (page 20)
Governor adjustment (page 23)
Check Generator brushes (replace if necessary; page 43)
Clean slip rings

Note: rubber hoses between fuel tank and carb dry out and crack with age. This results in air being sucked in such that the engine is fuel starved. This is a very common situation for systems > 20 years old.

Dave

[Stan.Birch]

Originally Posted by randini

When I hit the start button, I hear a rapid "small" click from inside the beast, and only intermittently a "big" click from the main relay. When the main relay clicks, the starter turns, and if I get lucky it starts.

If I short the two main connections on the main relay it cranks great, and if I also hit the start button (with my third hand) it fires right up."

Those symptoms are completely consistent with pitted contacts on the starter solenoid. The heavy duty contacts tend to get burned and pitted over time.

1. So . . . the bad contacts in the solenoid are bypassed when you put a jumper across the main connections, allowing the starter to turn;

2. but it doesn't supply the needed starting voltage to the fuel pump and ignition.

3. When you press the start button, that supplies 12 volts to the fuel pump and ignition, allowing the engine to start.

4. Once the generator starts, you can release the start button, because the generator is now supplying the 12 volts needed to keep the fuel pump and ignition with power.

Thing missing here is a solenoid with good contacts. Even when contacts are burned, the solenoid may randomly work sometimes and not others.

[randini]

But I got the thing with a replaced main solenoid that hadn't solved the problem. I'm pretty sure the new oil switch will solve the starting problem, as the bypass switch solves that problem.

And I'd be surprised there was significant wear on any of the "consumable" parts with only 114 hours on the thing. Which are the things that are likely to go wrong after sitting for thirty years minus a hundred hours?

BTW, now it doesn't start. Spends a minute trying to catch, lumping along and eventually backfires and stops. It really does act a lot like it's fuel-starved.

The fuel line I saw was slightly cracked but seemed sound. At one point I cycled the pump with the carb line disconnected and it squirted gas pretty good.

Traced the line back toward the tank and it disappears above the tank. To replace it do I need to drop the gas tank? That'd be a drag even if the tank wasn't full (which it is right now).

Checked the air filter and it's pretty pristine. We have a new fuel filter on. I also put in new plugs.

So unless it's a fuel line problem or that pump sounds fine but doesn't have the kick it needs, I'm thinking I need to bite the bullet and open up that carb. Seems like a long shot that I can get it open, clean the jets, and get it back together without trashing a gasket, but the only place I can find the rebuild kit (146-0290) is on EB and it's $98. Ouch. Anyone have a line to a cheaper option? Or just the gasket? If I search on 146-0220 I don't find it, but if I look at pictures on EB I find a listing for a gasket that sure looks like it and shows the 146-0220 part number on the bag but the listing is for 146-0792. And it's still $32.

[Stan.Birch]

Probably no need to disassemble the carb. Seafoam carb cleaner has a great reputation for getting guck out of clogged up carbs.

1. Prepare a pint of gasoline with the recommended amount of Seafoam added;

2. Disconnect the neoprene fuel line from the fuel pump inlet, and connect a 1/4" ID clear plastic hose to the fuel pump and the other end into the Seafoam mix;

3. Disconnect the power connection to the fuel pump, located about 8" up the line from the fuel pump;

4. Connect a jumper from the main 12 volt stud to the fuel pump connector and observe if fuel being drawn from the Seafoam mixture;

5. When the carb is no longer drawing mixture, turn over the engine for a few seconds to draw the cleaning solution through the jets and passages;

6. Let the solution in the carb sit for 12 hours or so, and then try to start the engine. You may have to repeat this procedure two or three times before the engine runs smoothly.

BTW: Sometimes crud will accumlate in the float bowl. It's easy to remove:

1. Pry off the plastic altitude knob exposing the main jet making a note of the setting;

2. Loosen off the nut holding the float bowl, and try to leave the main jet screw undisturbed;

3. Dump out any crude and reassemble;

4. If the engine runs, but runs rough, try adjusting the main jet:

a. Turn the main jet out until the engine runs smooth;

b. Turn the main jet back in until the voltage drops a volt or so, OR listen for the engine start to slow down.

c. then back out the jet until the voltage is at peak, OR the engine is running smoothly at max speed and voltage;

d. back out the main jet another 1/4 turn;

e. replace the plastic altitude knob pointing at your current elevation.