8n aggravation

John....ny

New User
48 8n runs VERY bad or goes dead after it"s been running
about 30 minutes. It"s converted to 12 volt, and does have
electronic ignition kit installed....(about 2 years ago). It ran fine
till just a couple months ago when this problem started. Under
a load (bush hog), and after it heats up the engine all but shuts
down. I can shut it down, with key off, and after two minutes or
so I can start it back up and get another 15 minutes or so. I
replaced the coil, didn"t work. I found the resister was busted
up so I replaced it thinking "I found the problem"...
Still the same....BUT....
That resister gets blazing hot and I think that"s what"s causing
the problem....but what could it be?
Please help...
 
(quoted from post at 11:17:55 04/20/14) 48 8n runs VERY bad or goes dead after it"s been running
about 30 minutes. It"s converted to 12 volt, and does have
electronic ignition kit installed....(about 2 years ago). It ran fine
till just a couple months ago when this problem started. Under
a load (bush hog), and after it heats up the engine all but shuts
down. I can shut it down, with key off, and after two minutes or
so I can start it back up and get another 15 minutes or so. I
replaced the coil, didn"t work. I found the resister was busted
up so I replaced it thinking "I found the problem"...
Still the same....BUT....
That resister gets blazing hot and I think that"s what"s causing
the problem....but what could it be?
Please help...
s soon as it stops, you need to pull a plug wire & see if you still have spark. Also, as soon as it stops you need to have wrench in pocket, so you can immediately remove drain plug from bottom of carb & verify that fuel will flow for two minutes into a pint bottle. should fill in under two minutes.
 
Sounds like your coil has too much current going thru it and running too hot. What kind of a resistor do you have? you may need a 1.0 ohm resistor in series with the original resister. the current thru your coil should not exceed 3.7 amps regardless if it is a 12 volt or a 6volt coil.
 
Thank y'all. I'm not sure at all about the resister size. I just had the parts store match the busted one. It's just a small, 2 terminal resistor. I just know that thing gets too hot to touch and I'm sure that's not right. Also, regarding resistor size, the tractor ran fine for a couple years now. What's confusing is what has happened for this to be going on now???
Excuse the ranting....I'm frustrated.
 
John,

The resistor should get a little hot. Anyhow, do as JMOR says and have the wrench in hand to check the fuel flow when it dies--don't waste time. Also, I would get a cheap spark tester from NAPA or Autozone and ground the tester on the block, and if it jumps a good gap say, 1/4 in, with a bluish or white color, you are in good shape on the spark. (You can take an old plug and do the same thing. I would widen the gap a bit though.)

My money is on the fuel flow if it has set up all winter with fuel in the bowl of the carburetor. Time for diagnostics.
 
Thank you very much. I will try that this afternoon. Fuel should
continue to run out? Or just what's in the bowl?
 
Question about funk in the carb....
Why does the tractor run fine until it gets hot? Then, after a
brief cool down, (about 2 minutes) cranks and runs for a few
more minutes then same problem. And that resister will about
blister you it's so hot....
(confused and frustrated)
 
Next time it stops, check quickly for fuel then spark. When I say quickly, I mean get off the seat, grab the tools & do it right then. Do not wait a minute or two. 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. Next, get an old plug, open the gap to 1/4", ground it to a rust & paint free spot on the engine, turn the key on & crank the engine. If the spark jumps the gap, you probably don’t have a spark problem. If it won’t jump the 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 will work better than an old plug because it won’t shock the snot out of you like an old plug might!
75 Tips
 
"And that resister will about blister you it's so hot...."
That's what they are suppose to do. Yes, they get hot enough to blister. I wasn't told that. I found out the hard way. The tractor came with a so called 6volt coil. But it is really a 4volt (More or less). When you first start it the resister is cold allowing 6 volt to got to the coil for better starting. As the resistor heat up the voltage drops to 4 volts thus protection the coil from melting down. If you convert to 12 volt you add an additional ceramic resister to step that voltage down to 6 volts. I would say you would need that resistor only if you kelp the 6 Volt coil and didn't change it out to a 12 volt coil. However, there is a guy on Ebay that sells a kit. and he shows the ceramic resistor and a 12 volt coil. I've asked about that her before and didn't receive a good explanation.
12 volt Conversion
 
That resistor looks just like the one in our old chrysler products. They also had a double set up which we used. Should 1 side fail, you switched to the other. Was much easier than searching for the paperclip in glovebox.
 
" I've asked about that her before and didn't receive a good explanation. "

The short answer is in tip # 30.

And the long answer........

Technology & materials being what they were in the 30's, that square coil would melt if it ran on much more than 4 amps for any length of time. (see tip # 38 for an example). In order to get a hot spark at the same time the starter was drawing max current from the battery, a ballast resistor was added in the ignition circuit. What that did was add about .3 ohms of resistance in the circuit, added to the 1.5 ohms of the coil. That got you 3.5 amps or so at start up. As the voltage increased when the engine was running to about 7.5 volts, the resistor heated up, adding more resistance in the circuit. 1.0 ohms hot, plus 1.5 ohms of the coil got you down to 3 amps or so to keep from melting the coil. The same rule (actually, Ohm's Law) applies to a 12v circuit. I= E/R. Current equals voltage divided by resistance.

Make sense?
75 Tips
 

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