spark plug wire problem

i know this is a tractor forum ....but i have gotten a lot of help here before on engine electrical......i have a double bug welder 225 with a oran engine two cylinder......i have a starting problem......i have never ran into before.....it wont start unless i pull one of the plug wires and ground it to the frame.....it will start but not run well......thanks for any help....keith

I've worked on alot of Onans over the past 20 plus years and though I've seen them do some strange things, I've never recall having seen that particular problem either. First I'd check the plug wires. I know some of the older engines had resistors built into the wires and if one of them went bad it would cause strange things to happen. If you rule that problem out, next check/change the condenser and see what happens. From there move to the coil itself and check/change it.

Give that the dual coil fires both plugs at the same time, every time the ingition systems on these engines can do strange things that a 'normal' ignition system won't do, so they are often hard, if not impossible to troubleshoot. I've always just chalked it up to the engine being an Onan....when they run, they run great, when they break, they really screw up and break...... A such, in the past, I've found it's often more economical AND FASTER, to simply change the cheap parts (ie the plugs, wires, and condenser in that order) one at a time and with those problems ruled out you can then turn your eye to the expensive part, the coil. I wish I could be of a little more help but given the way the Onan's are designed this is about the best I can do for you without me being there. Good luck.

In the past I have seen engines that (1 Clyinder) would not start and run unless you pulled the plug wire off and held it away from the plug to make the fire jump to the plug. I guess the extra resistance helped a fouled plug to fire.

The spark is too weak to jump both gaps. Gap the 2 plugs closer. Put in new points & condenser. Check & make sure the plug wires are good. Non resistor wires. Those coils fire both plugs at the same time.

thanks for the input guys......i did replace the plugs when it first started giving me trouble....
will try wires and condensers next.....this engine is for a bouble bug welder 225.....it does not have a tipical starter. i think it uses the generator to turn the motor over.....it has bad Constant Force Spring holding the brushes in place.....i have to aply pressure to get good contact at the amature to get her to turn over......wonder if this could be a problem....
boy try and find info on a double bug welder....

that makes sense teddy will try it

You need to replace the spring holding the brushes in. Using the armature as a starter requires a good hot battery to start. It can also effect the voltage needed for the ignition system. Check your points,they may be burned. But I would get the starting problem fixed first. In time you are going to burn out the starting side of the armature.Last time I looked the spring was still in the system. Onan tech since 1980.

Mag or ciol type ignition??? If it is a mag check clean and gap the points. If it uses a coil and a battery ignition then the starter generator maybe pulling to many amps and that will cause one not to start like it should because of not having enough amps to feed both the starter and the ignition

Keith - I had the same issues with an Onan twin in a garden tractor. Problem turned out to be a failing (weak) coil.

The Onan twin has the plugs connected in series. High voltage goes from the coil to one plug, passes thru the block to the other plug, then returns to the coil via the 2nd plug wire.

By grounding one plug wire, full coil voltage is applied to a single plug rather than being shared. Thus a weak coil may still fire one plug but not both plugs together.

Hey, OLD....!!!

Got a question for ya...!

My old Bolens QT 17 (Big Bore Onan) was giving me fits last year..
Long storie-short, an electric fuel pump has sure cured that problem..!!
Second....ever since I installed this Onan Bobcat engine, I cannot figure how to wire it so it will shut off without choking it to kill it..even with the switch off and battery dis-connected...!!
Tried it every way I can figure..should I install a Diode in the charging circuit or something..???
Once the engine stops, there is no current draw on the battery, even if I leave it hooked up (which I don't)..

Thanks...!

Ron..

Sure sounds like the alternator excite circuit is still hooked up and is causing a back feed in the system so the engine will not shut down. Be very careful if you unhook the battery with it running you can let the smoke out of the alternator and or your self if you get hold of things wrong. Alternator can put out well over 50 volts at more then 30 amps and tat is more hen enough to smoke test your heart. You big problem will be figuring out where you need to put the diode and I do not know the wiring on that one well enough to help much with out a diagram that is. If it would help you can e-mail me and I'll give you my home phone number if that would help you any.

The gap lets the spark voltage climb higher than normal.Its not extra resistance.

The commutator gets an oxide film that tends to insulate the copper.

uploading a pic of the engine.....i did find a few problems with the engine.......1st was like billy said.....brush springs were bad......(25 bucks apiece) replaced the condenser.....found a bad wire going to the points.....
one reason of hard starting i found is its getting flooded....i pulled the carb....cleaned it .....but i am not sure how to adjust the float....do you turn the nut with the wings on it in or out to lower the float level.....

its a mag type coil....points looked good.....is it hard to get to the mag coil.....on these....

Points can look good but still be bad or dirty. If it is a fair bank mag send me an E-mail and I'll send you a manual for it. Cost is just your time since I have it in the computer and some one gave it to me years ago so I just pass it on to others now

(quoted from post at 02:12:43 03/19/11) i know this is a tractor forum ....but i have gotten a lot of help here before on engine electrical......i have a double bug welder 225 with a oran engine two cylinder......i have a starting problem......i have never ran into before.....it wont start unless i pull one of the plug wires and ground it to the frame.....it will start but not run well......thanks for any help....keith

Click to expand...

It's a wasted spark ignition system that always fires both plugs together. Allows the use of a twin cylinder engine without a distributer.
The path for the spark is not back through the engine castings to the coil. The spark jumps plug to plug with the path across the engine from plug to plug. Then back though the coil wire to the coil.
Test the high voltage sid eof the coil with a ohm meter or even better a megger. Odds are the coil is breaking down and shorting to chassis.
You can change plugs, condensors and wires ten times but that won't fix the coil.

ok i did clean the mag and points.....like old sugested ....replace wire from mag to points......and it starts and runs good now.....but will only start if i pull the throttle almost closed.....not sure why.....
is it a carb adjustment?.....or govenor problem...


funny my case 3414 wont start either unless the thottle is closed.......or pulled to low
thanks so much for all the info guys.....
best site ever.... keith




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