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Starts w/o plug, but not with - why?

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Hank NWO

06-16-2005 08:17:41

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I have been trying to fix a Farmall BN that is hard to start. I took out a spark plug to check for spark, and the engine started when I cranked it, holding the spark plug against the block. It turns out it will start with any one of the spark plugs removed, but will not start with all of them in.

What does this mean?

Thanks for any suggestions.

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buickanddeere

06-17-2005 06:49:40

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

Higher system voltage after skipping a cylinder. No compression to slow the starter down and cranking rpm speeds up. By the time spark is needed on the next live cylinder, the system voltage is still high enough to jump a spark. What is the voltage measured between the batteries + & - post while cranking? What is the voltage measured between the starter body and the post going into the starter? What is the voltage across the coil when the points are closed and the engine cranking? What are you using for a battery?

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T_Bone

06-17-2005 06:20:18

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

Hi Hank,

When I have a hard starter, I reach for the propane. I let a small amount of LP flow into the air intake and adjust LP flow until the engine runs smooth.

If the engine runs smooth then it's a fuel related problem.

If the engine runs ruff while using LP, then it's an electrical or mechanical problem.

It sounds like you have a fuel problem.

T_Bone

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Paul Shuler

06-16-2005 20:12:08

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

I know this is way out there, but any chance the plug wires could be in the wrong order. Done that before and I would have sworn I put them back on correct. Might run better with one off if two of them are crossed. Just a guess. Keep us updated.

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Hank NWO

06-16-2005 22:55:29

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Re: Starts w/o plug, but not with - why? in reply to Paul Shuler, 06-16-2005 20:12:08

Thanks, but that is not it. I have checked that a number of times to make sure!

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Hermit

06-16-2005 19:12:11

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

Re-check point gap. If right on then close gap on all spark plugs by .005.

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ANSWER MAN

06-16-2005 15:52:35

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

All of the guys below are totally out to lunch. If it starts and runs OK with one plug out then it's a NO-BRAINER ..... take all of the plugs out and it'll purr like a kitten and start even easier. You really should've known !!!

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Hank NWO

06-16-2005 17:51:15

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Re: Starts w/o plug, but not with - why? in reply to ANSWER MAN, 06-16-2005 15:52:35

I bet the gas consumption will be a whole lot better, too! I was just waiting for someone to make that suggestion . . .

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frankiee

06-16-2005 14:15:48

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

The angle I am going to suggest is this:(Maybe)
It starts with one plug out because it turns over faster and the heat of compression stays in the cylinder lond enough to ignite the mixture.
The engine has a fault that is causing it not to start with slower RPM. Do you think the cranking RPM's are the same as allways or a bit slower?
Do you have a tack to put on it.
Another theory would be that when the plug is out and you crank the engine that it is not making contact to ground and directing all the spark energy to the other plugs. In you car at nite if you make sure it is pitch black, look at how the plug wires have a glow around them at places. Stop the engine. Now remove 1 spark wire and start the engine again and notice that the wires are glowing more now that the wire is disconected. More electrical energy is available at the other plugs. Maybe try and keep the plugs in and just remove 1 wire and see if it will start.
There is a problem and I am just tring to give you some ideas as to why an engine would start with a plug removed and not start with it in.
Good luck and please reply if you find the problem. It is interesting.
frankiee

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Hank NWO

06-16-2005 18:08:37

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Re: Starts w/o plug, but not with - why? in reply to frankiee, 06-16-2005 14:15:48

Thanks for the suggestions.

It does not SEEM to turn over faster with a plug out, but I do not have a tach to actually check that.

When I have started it with a plug out, I have been grounding the plug (I started doing this to check whether or not I had spark). Perhaps there is enough difference in the grounding to change the resistance and spark strength for the remaining plugs.

Today it did start and ran briefly, then started to sputter out (it has occasionally done this). When it sputters, I can sometimes keep it going by somewhat wildly moving the throttle; but it will only run for a relatively short while. After that, I usually cannot get it started again unless I wait a day or two to try.

I did just try one of your suggestions and removed a plug wire (leaving the plug in) - it started, then ran erractically. I tried that a few more times; it started a couple more times (with plug wires removed) but later would not start at all.

I've got new plug wires and coil wires. Would this indicate needing a new coil? or new plugs??

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frankiee

06-17-2005 04:44:21

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 18:08:37

I would try another coil. Should have an old one laying around someplace A 12 volt car or truck coil should do it. I have done this in the past and it worked for me.
Too bad you could not put it on a scope. It has a function of measureing Kilovolts of output to each wire. The voltages raise when you short one out.
So I ask you. When one plug is completely out then it starts and runs fairly smooth??

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Joe (Wa)

06-16-2005 18:42:08

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 18:08:37

Sounds like you have a fuel restriction problem. In the time it takes to pull the plug or what ever else you are doing to the ignition, enough gas gravitates into the carb to start it.

Joe

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Hank NWO

06-16-2005 22:52:18

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Re: Starts w/o plug, but not with - why? in reply to Joe (Wa), 06-16-2005 18:42:08

I have suspected this also. I have checked/cleaned the screen in the fuel line elbow at the carb, replaced the screen in the sediment bowl, blew out the fuel line to the carb, and checked the flow in the line - all appear ok. I wonder about the carb itself - it is a Zenith with no mixture adjustment. I have taken it apart and blew out passages, but have not rebuilt it.

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Redmud

06-16-2005 13:36:31

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

Sounds like a bad condenser to me.

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Ludwig

06-16-2005 12:40:56

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

What if you pull start it with all the plugs in? If it started easy that way I'd have another look at the starter...

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Jon H

06-16-2005 11:31:31

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

Does the tractor run well with good power when started ? I have seen an engine with a clogged exhaust system act exactly this way,it would start with a plug removed ,but not fire a pop with the all plugs installed. The engine was a 2 cyl Onan genset. we had run through monsoon rains in the south and returned home to ND in early winter. I wanted to change oil in the motorhome and genset before storing it for the winter, This was early winter and below freezing. tried to warm up the genset before changing oil. It would crank fast,but not run. Had good spark and plenty of fuel,turned fast but would not fire. Finally tried starting it with one plug removed. It started instantly on one cylinder with exhaust pouring out of the plug hole on the other cylinder. Then it dawned on me what had happened. The rain we were running through had run down the back of the motor home and into the genset muffler,filling it with water. This was a below freezing morning and the water in the muffler was frozen solid. I put the torpedo heater on the muffler and reinstalled the plug. After 1/2 hour of heat the genset cranked right up and blew about a quart of Oklahoma rain water out the exhaust pipe. The genset ran fine after that.

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Hank NWO

06-16-2005 12:34:47

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Re: Starts w/o plug, but not with - why? in reply to Jon H, 06-16-2005 11:31:31

Interesting - I don't think I have actually looked closely at that. It has a muffler with a rain cap, and it is stored inside. I do know the rain cap moves up when I crank it, so I doubt that is it.

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LPGASONLY

06-16-2005 10:36:10

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

DON'T USE CHAMPION PLUGS!!

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Vern

06-16-2005 12:54:35

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Re: Starts w/o plug, but not with - why? in reply to LPGASONLY, 06-16-2005 10:36:10

I have used nothing but Champion plugs in my Super A for over 20 years with great results.
What's your problem?

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RAB

06-16-2005 09:02:43

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

So, we have a couple of suggestions. Personally, I would go with Allan. Try starting it with one of the plug leads grounded like you are doing, but with a plug in situ. If it won"t start, it"s probably not cranking fast enough. Possibly only a weak spark or none at all at that cranking speed.
Have you checked the spark colour? and strength? Could indicate poor points, wrong gap, poor coil, poor condensor, poor battery, poor battery connections.....
Just don"t keep throwing money at it unless you are sure what the fault is...
Regards, RAB

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Fawteen

06-16-2005 08:40:44

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

Might be a coil too. Holding the plug against the block doesn't provide as good a ground as having it screwed in, which increases the resistance, which can make the spark hotter.

Try pulling a wire off and holding it a quarter-inch or so from the plug terminal. If it starts and runs that way too, I'd replace the coil and have a look at the points and wires while I was at it.

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elcajonfarms

06-16-2005 11:31:57

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Re: Starts w/o plug, but not with - why? in reply to Fawteen, 06-16-2005 08:40:44

Because it's a red tractor.

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Hank NWO

06-16-2005 12:15:16

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Re: Starts w/o plug, but not with - why? in reply to elcajonfarms, 06-16-2005 11:31:57

Actually, you are probably right! This is the black sheep of my collection - my REAL tractors are a different shade.

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Hank NWO

06-16-2005 08:45:07

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Re: Starts w/o plug, but not with - why? in reply to Fawteen, 06-16-2005 08:40:44

Thanks for the suggestion; I will try that. I have already replaced the secondary wiring (and the primary wiring to the coil also). The coil tested 1.7 ohms. Points and condensor are relatively new (last year).

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Mike M

06-16-2005 09:45:02

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:45:07

Make sure you use spark plug and coil wires with wire in them and not the carbon fibers.

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Hank NWO

06-16-2005 10:36:44

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Re: Starts w/o plug, but not with - why? in reply to Mike M, 06-16-2005 09:45:02

Thanks - Fortunately, I have been following these discussion boards enough to have already known that one.

Even with all the suggestions, I am still confused why it starts BETTER with any one plug OUT. I don't know how that changes things enough to make it start better with a plug out - that doesn't change valve clearance, wire condition, coil, or much else I can think of. I doubt it changes starting speed much if any. Would it affect fuel intake mixture some way?

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supergrumpy

06-16-2005 08:36:09

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

don't know your particular model

but kinda sounds like intake valves set too tight or leaking real bad back into intake manifold

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Hank NWO

06-16-2005 08:47:33

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Re: Starts w/o plug, but not with - why? in reply to supergrumpy, 06-16-2005 08:36:09

Thanks for the reply.

I did check the clearance on all valves (although the engine was cold when I did so) and set them to spec.

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Allan in NE

06-16-2005 08:29:11

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:17:41

Sounds to me like it isn't spinning fast enough; tired battery or starter?

Dunno,

Allan

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Hank NWO

06-16-2005 08:48:56

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Re: Starts w/o plug, but not with - why? in reply to Allan in NE, 06-16-2005 08:29:11

Thanks for the suggestion.

Battery is new and charged; starter was rebuilt a few years ago and it seems to spin pretty well.

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MLP

06-17-2005 03:17:19

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Re: Starts w/o plug, but not with - why? in reply to Hank NWO, 06-16-2005 08:48:56

I do not see how it can be electrical since only one plug fires at a time so it should not mater how many plugs are in it.
I would guess it has some thing to do with fuel. With one plug removed that cylinder will not create much of a vacuum so the available gas gets sucked up into the the other three cylinders which now have a fuel to air ratio that will allow it to fire. May be when you had the carburetor apart a gasket may have been put in wrong blocking a passage or perhaps something got lodged while blowing it out.

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TimS

06-17-2005 08:33:44

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Re: Starts w/o plug, but not with - why? in reply to MLP, 06-17-2005 03:17:19

Have you tried using small squirt bottle of gasoline to add some extra gasoline to the carb intake while cranking?

If adding a bit helps, then you may have a clogged fuel passage or two....the carb may need to be solvent dipped to clean them out.

I agree with you that the electrical system seems to be working correctly as you get spark .... still not sure why having one plug out makes a difference.

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