9n acts normal but won't start

zaximus84

New User
I was mowing the other day when my 9n suddenly died on me. I haven't been able to start it since. It sounds normal when turning over, so I'm stumped as to what might have suddenly gone wrong. I did the following after it died:

1. Put more gas in it. It definitely wasn't empty, but might have been low.

2. Drained the carb and confirmed that gas is flowing to it.

3. Fully charged the battery.

4. Tested two of the spark plug wires and they're sparking. I didn't bother testing the other two because I'm assuming they're also fine. Spark plugs were just replaced a couple of months ago, so I'm assuming those aren't it.

If it's getting gas and spark that only leaves air, but I don't know why it wouldn't be getting air all of a sudden. I tried removing the oil cup on the air intake and it didn't make any difference. Am I overlooking something obvious here? I was mowing a ditch right before it happened, so the tractor was tilted a bit sideways for a couple of minutes. It has died on me in this ditch before. Is it possible that some kind of vapor lock occurred?
 
It is important for you to tell us if your tractor has a 6 volt or 12 volt electrical system. The troubleshooting is different based upon the configuration of your engine.

It takes three things for an engine to run: spark at the right time, compression, & fuel/air in the right mixture. For the moment, forget about compression & concentrate on narrowing the problem down to spark or fuel.

There are three very important tools you always need to have in your N tool box: a 3 inch piece of wire w/ alligator clips on each end, a spark checker w/ an adjustable gap (* see below) and a 7/16 box end wrench. (see tip # 50 at the link below) And, you really do need a working ammeter on the tractor; it is a very important diagnostic tool. With these tools, you can quickly narrow down most N problems to spark or fuel.

First, check for fuel**. Get a can & put it under the carb. Remove the bolt in the bottom of the carb; as long as the fuel is turned on, you should see gas flowing out of the carb. Let it run for at least 30 seconds. If it’s a dribble, or runs for 5 seconds & stops, or none at all, you have solved half the problem: it’s fuel related. If gas flows well out of the carb & only stops when you turn it off at the sediment bowl, chances are very good it’s not a fuel problem. So, next, turn the key on, crank the engine & look at the ammeter. What is the needle doing? Does it show a constant discharge, no movement at all, or does it move back & forth slightly? Next, hook up your spark checker, turn the key on & crank the engine. If the spark jumps the 1/4” gap, you probably don’t have a spark problem. If it won’t jump the ¼” gap, you have a spark problem. If the ammeter needle shows a constant discharge, or doesn’t move at all, that also tells you that you have a spark problem. Jump the ignition switch w/ your jumper wire & see what happens. If it runs, you found the problem. If it doesn’t have spark after you jump the ignition switch, post back for more info on further troubleshooting. (and do not forget to turn the ignition switch off; see tip # 38)

If it does not have gas coming out of the carb at a steady stream w/ the bolt out for at least 30 seconds, you have a fuel problem. First, remove the gas cap. Your vent could be clogged & it vacuum locked. If that doesn’t work, tap the carb bowl w/ a hammer handle in case the float is sticking closed. (don’t whack it w/ the head of the hammer; you can crack the bowl). If you still don’t see gas flowing, the N has three fuel screens; one in the brass elbow, one in the top of the sediment bowl & one on the stem of the sediment bowl in the gas tank. Check the screen in the elbow & the screen in the top of the sediment bowl. (don’t worry about the one in the tank) Both probably need to be cleaned. If you have the fuel knob turned on all the way, & 1 gallon or less in the tank, it may be trying to feed off of the reserve inlet which is probably clogged. Only open it 2 full turns. Put at least 2 gallons in the tank. (and do not forget to turn the gas off; see tip # 9)

There are ways to check for spark & fuel that work & ways that don't. For example, having gas to the carb is nice, but having it past the float is what counts! That’s why removing the 7/16” bolt in the bottom of the carb is the way to check for fuel. And, same thing w/ spark at the plugs. Some folks think that checking for spark means pulling a plug wire off & looking for one. Well, it's the distance the spark jumps at the plug that gives you the info you want. It takes about 17kv to jump a 3/16" gap & 22kv to jump ¼” in the open air. Remember, it’s 14psi outside of the engine & about 90psi at a 6:1 compression ratio in the cylinders & compressed air creates electrical resistance, so you really need the 17-22kv to fire the plugs when the engine is running. A store bought plug checker (in the picture) will work better than an old plug because it won’t shock the snot out of you like an old plug might!

Post back with results or more questions.



*If you don’t own a spark checker w/ an adjustable gap, buy one. In the meantime, an old spark plug w/ the gap opened to at least ¼” will work. Ground it to a rust & paint free spot on the engine turn the key on & look for a spark.

** On most gas engines, you would check for spark first. But, the N gas tank has a pin-hole size vent that easily clogs, causing vacuum lock. By the time you check for spark, the vacuum lock will dissipate w/ the engine off
75 Tips
 
if it making spark.. see if it will pop on start fluid. if so.. you have a fuel issue.. even if you have fuel TO the carb...
 
It's a 12 volt system. Gas flows freely from the bottom of the carb when I have the fuel turned on. When I turn the tractor over the needle on the ammeter wiggles slightly from side to side, but barely off of zero. I've never seen much movement on that when starting and running the tractor, so I'm not sure if it is in working condition.

I did get a spark tester, but unfortunately I didn't read your recommendation closely enough before shopping and I didn't get an adjustable one. However, the spark tester did light up in a very steady rhythm on the 2 spark plugs I tested. I did hook an old spark plug up gapped at 1/4" and it seemed to jump the gap just fine.

Just for kicks I've been trying to start it about once a day. After about 7 seconds on the starter it does sputter a little like it's trying to start, then the starter disengages. I've noticed the carb leaking a couple of times after trying to start it. It seems to be leaking at the seam between the top and bottom pieces (opposite of the main fuel mixture). I don't know if that may be from turning it over too long.

A friend of mine said it might be the points or the condenser, but I've still got no idea. The symptoms definitely don't seem very clear.
 
You've done well eliminating the usual suspects. Now for some more detailed diagnostics.

Yes, you could have a points or condenser problem, but try some more easy to do checks first.

Replace the plugs. You flooded it, they're fouled & it will be it next to impossible to start. You don't need to toss them; heat the tips for a few seconds w/ a propane torch to burn off the invisible spark-robbing deposits from today's additive filled gasoline........or wash them in lacquer thinner.

Next, charge the battery. All that cranking w/o starting isn't helping your spark.

You need a strong battery to:

1. Spin the starter

2. Engage the bendix

3. Provide voltage to the coil.

As the battery gets weaker, the first thing to fail is your spark.

In addition to charging the battery, don't forget to clean all the grounds, to include the mating area between the starter & the block.

The more current you use to spin the starter, the less you have for the ignition.

Finally, remove the breather hose, turn the key on & spray starting fluid in the carb throat (no choke) while you crank the engine.

Post back w/ results or more questions.
75 Tips
 
(quoted from post at 17:19:02 07/07/14) It's a 12 volt system. Gas flows freely from the bottom of the carb when I have the fuel turned on. When I turn the tractor over the needle on the ammeter wiggles slightly from side to side, but barely off of zero. I've never seen much movement on that when starting and running the tractor, so I'm not sure if it is in working condition.

I did get a spark tester, but unfortunately I didn't read your recommendation closely enough before shopping and I didn't get an adjustable one. However, the spark tester did light up in a very steady rhythm on the 2 spark plugs I tested. I did hook an old spark plug up gapped at 1/4" and it seemed to jump the gap just fine.

Just for kicks I've been trying to start it about once a day. After about 7 seconds on the starter it does sputter a little like it's trying to start, then the starter disengages. I've noticed the carb leaking a couple of times after trying to start it. It seems to be leaking at the seam between the top and bottom pieces (opposite of the main fuel mixture). I don't know if that may be from turning it over too long.

A friend of mine said it might be the points or the condenser, but I've still got no idea. The symptoms definitely don't seem very clear.

Any time that I am having trouble getting one of these to start, one thing that I do right away is to remove the air intake tube from the carb so that I can better monitor the fuel situation. It is the nature of an updraft carb that if it is drawing fuel but doesn't start in about two revs that when it stops cranking that fuel that has been drawn up will run out of the carb intake. How long you keep cranking determines weather or not it floods. If it fires right away on just one cyl. it is likely to release the starter drive from the flywheel anyway so likelihood of flooding is low, and getting another good plug in there to help the one that does fire will usually do the trick.
 
I cleaned the spark plugs with a butane lighter and some emory cloth. They were pretty black, though #4 seemed to be much worse than the others. I fully charged the battery and cleaned the grounds. I tried to start it with the starting fluid directly into the carb with no choke. It came closer to starting than usual. It sputtered and the starter disengaged pretty quickly. After a couple of attempts I tried it with a slight amount of choke and it seemed to come a little closer. Then I tried a little more choke and I actually thought it was going to start for a moment, but the starter disengaged.

I am concerned about the carb leaking. As soon as I turned the gas on it started leaking quite a bit, though it was difficult to tell where from. I'm assuming having the breather hose off shouldn't cause this. I did adjust the fuel mixture the day the tractor first died on me (dumb move since I didn't know what I was doing). I read that I should put it all the way in, then back it out 1 full turn as a starting point. That's where I've got it now. Does that seem correct?
 
" As soon as I turned the gas on it started leaking quite a bit"

That's because you've got a stuck needle valve. Tap the carb bowl w/ a hammer handle & maybe it will loosen up. (don’t whack it w/ the head of the hammer; you can crack the bowl).

Start over.

Clean the plugs again. (skip the emory cloth)

Screw the main jet out 1 1/2 turns & don't touch it again.

Recharge the battery.

Now.....this is the hard part.....keep your hand off the choke!

Get ready w/ the starting fluid. Turn the key & gas on, crank the engine & use the starting fluid ONLY.

Post back w/ results or more questions.
75 Tips
 
I had to tap the bowl quite a bit, but the leak finally seemed to stop. After charging the battery and cleaning the plugs I tried again. I tried starting it while spraying the starting fluid and it wouldn't start. I made one last effort from atop the tractor so I could put the clutch in (though I couldn't reach to spray starting fluid), and it reluctantly started. I ran it for about 15 minutes and finally brought my finish mower in from the side of the road. However, the tractor doesn't seem to be running normally. It's sputtering quite a bit, like something is firing out of rhythm. Does this help narrow the original problem? Is it possible I caused some sort of problem when removing the spark plugs?

Thanks for all your advice Bruce.
 
" It's sputtering quite a bit, like something is firing out of rhythm. "

It will do that if you have the plugs wires crossed.

Firing order is 1-2-4-3, CCW. #1 is closest to the radiator.

You'll need a carb rebuild too. If you're not skilled in that sort of thing, try GB in MT. If he's not open yet, try:


Automotive Manufacturers Inc
2400 N Lombardy St Richmond, VA 23220
(804) 321-6861

They do mail order work. And they also rebuild clutches, pressure plates, water pumps, alternators, generators, starters & reline brakes.


By the time you buy a complete carb kit & the cleaning solvent, the $80 they charge for a rebuild is worth it.
DSC03473.jpg

75 Tips
 
Thanks for the info. I'm still a little unclear on the findings of our science experiment. What's the indication that the carb needs to be rebuilt? Is the basic idea that running it with the starting fluid proves that the carb is the weak link in the system?

Also, I removed the plugs one at a time to clean them and I put each wire back on before moving on to the next plug. It's extremely unlikely that I got them crossed, though I'll double check tonight. Are there any other possible explanations for the sputtering?
 
" What's the indication that the carb needs to be rebuilt?"

You got good fuel flow to the carb (as you said) but it leaks gas because the float is stuck.

And, you said " I was mowing a ditch right before it happened, so the tractor was tilted a bit sideways for a couple of minutes. It has died on me in this ditch before."

That's because the float got hung up on the side of the bowl.

" Is the basic idea that running it with the starting fluid proves that the carb is the weak link in the system?"

That & a sticky, misadjusted float.

" Are there any other possible explanations for the sputtering?"

Yes.

A dirty carb.

Or it could need a tune up. Or both.

When's the last time you replaced the points/plugs/condenser/rotor & cap & set the timing?
75 Tips
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top