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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 15281
Experience:  Certified on Onan and Generac generators
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Onan Marquis 5000 BGM spec F will not run the Air. can you

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Onan Marquis 5000 BGM spec F will not run the Air. can you help?
Customer: replied 2 months ago.
New Carb, fuel filter,air filter,plugs,and fuel line from frame to genny pump.

Hello, my name is ***** ***** I am going to assist you with this.

Could you please provide some detail here?

Is the genset running well, good and smooth?

Running rough?

Is the A/C the only thing that is not being powered, or are there other things that are not being powered?

What happens when you try to turn the A/C on?

The more detail you provide, the easier and quicker it will be to find the problem.

Customer: replied 2 months ago.
Genset is a little hard to get started. once it starts it will run all day no problems at all with out a load on it. Everything is getting power and since i put new carburetor on it will run 1 of the a/c units but it showing around 115 to119 volts on an inside outlet with fluke meter. If i try to start the 2nd a/c unit it stalls and dies. Also have a cherry red exhaust at night with bay door open.
Customer: replied 2 months ago.
It's late here and would not be able to trouble shoot tonight.
Customer: replied 2 months ago.
Both a/c units run on shore power with no problems. Manual states that they can both run off generator.

If it is running that hot, it is not good.

It indicates that the engine is running too lean, either a bad carb, or an air leak, or the valves may be out of adjustment, or the muffler is restricted.

Check the altitude adjust on the carb, and if it is not already open all the way, open it up.

Since this is a new carb, we will assume it is good, but still keep in mind that it may not be.

I would also recommend adjusting the valves before going on.

Let's see what happens with that.

Customer: replied 2 months ago.
Do i have to remove genset to adjust valves? Exhaust blow out plug has been removed from muffler and it seems to be fine. No junk or carbon coming out of the hole while running for ten minutes. Blow out plug has since been reinstalled.
Customer: replied 2 months ago.
Altitude is set to 0.

It depends on how the genset is mounted in the coach. Sometimes they have to be removed, sometimes they do not.

The intake manifold has to come off to be able to adjust the valves.

Customer: replied 2 months ago.
The genset is mounted parallel to the coach frame. Gen to right and engine to the left. I think i can get the intake off if that's all that needs removing. Do you think its possible the fuel pump is going bad?

Side clearance doesn't matter - it is overhead clearance that you need.

If the gen will run all day with 1 A/C, it is extremely unlikely that the fuel pump is the problem.

Customer: replied 2 months ago.
You misunderstood. It will run all day without a load from a/c. It will run the single a/c but it does shed power often and seems to do better driving down the road. But will still shed power from time to time.
Customer: replied 2 months ago.
i have about 9 inches clearance on top.

What do you mean by "shed power" exaclty?

And how often is "often"?

You need to be specific and detailed. Remember, I can't see or hear what is going on, and I only know as much - or as little - as you tell me.

Customer: replied 2 months ago.
The a/c control panel inside the coach has a green light and red one. The way the manual for a/c says is it will shed power if it is not getting enough power. Thus green and red blinking back and forth. When green is on it runs. When hooked to shore power it's always green, not shedding power. Before i changed carb it would try to start 1 a/c and the power would keep falling and falling. I could hear genset bogging down until the meter showed around 105 volts then it would just die. Also i have cleaned both slip rings and brushes look good.
Customer: replied 2 months ago.
Often is when i slow down while driving.

Get the valve adjustment done, and lets see what happens.

Hank F. and 2 other Small Engine Specialists are ready to help you
Customer: replied 2 months ago.
ok. i have not used this service before. how do i get in touch with you once i get the valves adjusted? do i need to do the 7 day trial thing that keeps popping up?
Customer: replied 2 months ago.
do i rate you now?

To get back to me, just log in with your user name and password, then click on the My Questions link.

Or you can simply click on the link in the emails that you receive every time I reply to you.

No, you do not need to do the 7 day trial thing if you do not want.

Customer: replied 2 months ago.
Did some checks today. Checked the plug wires, coil primary and secondary and all checks good. Started checking module and ran into some difficulty. Removed wires from + side of coil, black, white and red. Made a jumper from red wire down to positive post below start switch. Attached red wire from meter to negative side of coil and black meter wire to a good ground. Turned engine with 3/8 allen wrench counter clockwise several revolutions. I could only get a reading of .6 vdc. What is weird is that I checked for spark at the plugs and they both have spark although it was a weak looking spark. Did the spark check first with the start switch. Any ideas you might have would be great.

Not sure why you are testing the ignition system. If the engine will start and run, the ignition system is working.

But if you are testing it, it is best to disconnect the ignition module wire from both sides of the coil, and just test the module. It is possible for the coil to interfere with getting an accurate reading.

Customer: replied 2 months ago.
Which wires on the coil are for the module? Positive side of coil has three wires, black white and red. Negative side has two wires, black and white. I'm just going through the trouble shooting in the repair manual. Also checked compression on cylinders, both equal 120 psi.

The ignition module only has 2 wires - red and black. They both go on the coil, red on positive, black on negative.

Customer: replied 2 months ago.
Ok will let you know the results tomorrow. Just checking this stuff because it's hard to start most of the time. Would compression check rule out the Valve adjustments. It isn't very noisy.

No, you can still have good compression even if the valves are out of adjustment.

Customer: replied 1 month ago.
Have done all that I have told you and also adjusted the valves today. Poured seafoam in both valves and let it sit for an hour. It did not leak out so we know the valves are seating. Did same thing on the other side and it didn't leak out either. Pulled plugs and spun it to get all the liquid out of cylinders. Put them back in and started it up. Let in run out of a three gallon jug of non ethanol fuel, to rule out the coach tank. It will run only one A/C with fan on high and compressor not on. Any more load and it still bogs down and dies. Will run forever with no load.
Customer: replied 1 month ago.
Only had to adjust intake valves a .003 as they were to tight exhaust side was fine.

That's different. Usually it is the exhaust valves that come out of adjustment.

Since everything else is checking out, it is pointing to a lean running condition - either you have an air leak somewhere in the intake, or the carb is not set up properly, or is bad.

Customer: replied 1 month ago.
Could you tell me how to check the timing on this engine? The exhaust is getting cherry red. Going to do some more work on the carb also.

Timing is not adjustable. It is either in time, or the engine won't run.

The hot exhaust is due to the engine running too lean - either an air leak at the intake, or not enough fuel going through the carb.