Onan Problems

[johnjbc]

Well I spoke too soon when I posted about how well my Onan was running. Went to cut something yesterday and it won't idle unless I turn the speed screw clear in. Did some checking and the back plug isn't firing.
Swapped the plugs twice When I reversed them the same cylinder missed.
Changed the plug wires and even reversed the coil terminals feeding the missing cylinder and the same cylinder still fails.
Checked the compression and seeing a bit over 100 in both cylinders.
Cleaned the carburetor again, no help

What am I missing?

[coldnorth]

I don't know much about the Onans, but had a B&S Vanguard 2 cylinder with OH valves that had a push rod fall out of the socket on the rocker.  Intake valve never opened.  Simply put the rod back in the socket on the rocker arm and it worked good. 

Good luck
Lamar

[poolman]

Try A timing light or a spark tester first to be really sure the coil is good.You might have already done it, but if not I would.I will ready your reply and keep trying to think of somthing to help.  Brian

[Magicman]

How long has it been since you ran it.  The first thing that I wondered about was a valve stuck open.

The simple thing would be ignition, but it seems like you gave that a good test.

[johnjbc]

Thanks for the replys.
If an intake valve was struck or not opening wouldn't it affect the compression?
I can pull the Plug Wire off of the bad cylinder, put a screw driver in the boot and watch a 3/8 inch spark jump to the plug. So I don't think its igniton.
Going to out to spray Starting Fluid on the side of the intake Manifold.
John

[36 coupe]

Your plugs may be the wrong heat range.Unleaded gas needs a plug 2 steps hotter.

[poolman]

Like Coldnorth said a closed valve could give you compression but not let fuel in.If you have fire and fuel it will combust.Starting spray would only be needed if the carb did not work .Your carb feeds both pistons so it would not run at all if that was it. Brian

[ladylake]

Stuck shut, bent push rod, you'ld still have compression.  Stuck open, none.   Steve

[Chuck White]

I had problems with my Onan a while back and the trouble was dirt/sawdust in the fuel system.

My engine wouldn't run unless the throttle was opened well above an idle.

Cleaned the carb and the fuel pump and the problem went away...... for a while.

Then the problem reoccurred and I ended up replacing the fuel pump.  One of the diaphragms was puckered and out of place.

I put a DR® equipment fuel pump on the engine and it works beautifully.  Ended my problems.

[Buck]

Tgat "dang" fuel system and carb. You have missed something.  Ethanol is the enemy!

[TreeBones]

Try good gas again. I ran my Onan 24 HP through around 800,000 bdft with little to no problems except gas. Fuel filters and oil changes is all I did and no problems with the fuel pump. Don't know the hours but I got my moneys worth, good engine. It just finally wore out most everything at once and seized up. California wont let us order the same style any more. I now have a Kholer 25. Good so far.

[johnjbc]

I sprayed starting fluid on the end of the intake manifold next to the failing cylinder and the engine speed up. This leads me to think that that air is leaking into the manifold, and making the mixture to  that cylinder lean. I see Blue RTV on the joint between the Two half's of the intake Manifold. >:(
I think the valve covers are under the manifolds so I will have a look at the valves while I have it apart.
I ran out of daylight so I couldn't take it apart tonight
John