1988 520-HC will not start when hot

[cafoose 3,354]

My 1988 520-HC (I did get lots of snow that's an old picture) starts up great at first but after running it awhile it will not start back up. It cranks over fine it just does not start. I sprayed starting fluid in the carburetor and that does not help. When I let it sit for a few hours and come back to it, it starts up fine. Today I was cleaning up some snow and it worked great while it was running. I ran it out of gas earlier today   and when I filled it up it did not start until a few hours later.  I put it back in the shed when I was finished with it and when I shut it off I tried starting it back up in a couple minutes and it did not even attempt to fire up. Does anyone have any ideas what might be wrong with it?

[ericj 1,578]

ignition module, when it shuts off get a meter and put it on the negative side of the coil and the negative battery post, spin the motor over by hand and you should see the voltage go from 12 volts to 1 1/2 volts and back to 12 volts if it doesn't then it is it is bad if it does then you have another problem.

I see your in york pm me and load it up and bring it over and i'll help you figure it out

 

 

 

 

 

eric j

Edited March 19, 2017 by ericj

[cafoose 3,354]

31 minutes ago, ericj said:

ignition module, when it shuts off get a meter and put it on the negative side of the coil and the negative battery post, spin the motor over by hand and you should see the voltage go from 12 volts to 1 1/2 volts and back to 12 volts if it doesn't then it is it is bad if it does then you have another problem.

Don't you think if it was the ignition module it would quit running on its own? It will continue to run as long as I don't shut it off but when I do shut it off it doesn't start until after it sits for a long time.

[cleat 5,771]

You will need to check out the power to the coil and verify you have +12 Volts when the key is on and also in crank position.

 

If not then start bactracking to figure out why.

 

If so then verify the negative side is pulsing when cranking to verify the module.

 

If negative side stays constant at ground or +12 volts then the module is likely bad.

 

If it is pulsing and you have 12 volts on the positive side of the coil then the only thing left is the coil itself.

 

Cleat

[elliot ness 1,916]

I have had that problem before and it was the coil. changed the coil and presto all better.

[ericj 1,578]

the onan service manual does a real good job telling how to trouble shoot almost any thing wrong with an onan motor. I'm sure it's on here for down load if nit I can email it to you.

 

 

 

 

 

 

eric j 

[cafoose 3,354]

This is directly out of the Onan service manual. I am going to run it until it is warmed up and go through these steps.

 

1. Check all electrical connections to be sure they are
clean and tight. If all connections are good and
wiring is intact, go to step2 .

2. Pull spark plug wires off spark plugs and remove
spark plugs. Connect an approved spark tester to
each of the spark plug wires and ground them away
from spark plug hole. Turn key on and crank engine
over for 5 seconds while watching for spark. If a
spark occurs regularly, the problem is not in the
ignition system. If no spark occurs, go to step 3.

never put jumper leads to the negative coil terminal this
will cause failure of the electronic ignition module.
3. Connect a jumper lead directly from the positive
battery terminal to the positive (+) coil terminal
(smaller diameter of the two threaded posts). Crank
engine over while watching for spark. If spark
occurs, the problem is in the low oil pressure cut out
switch (if equipped) or related wiring, the lubricating
system (low oil pressure), or in the other circuitry
bringing voltage to the coil. if no spark occurs, go to
step 4.
4. Refer to IGNITION COIL section to test coil for
proper resistance. If coil checks out good, go to
step 5.
5. Connect positive side of voltmeter to negative (-)
coil terminal (larger diameter of the two threaded
posts) and negative side of voltmeter to engine
ground. Turn key on and rotate flywheel slowly by
hand while observing voltmeter. Voltage should
switch between battery voltage and 1-1.5 for each
revolution. If voltage does not switch properly,
replace ignition module.
Never put B+ lead to the coil negative terminal
This will cause failure of the electronic ignition module.
6. Install spark plugs and wires. If ignition module is
being replaced, be sure to connect red lead from
new ignition module to positive(+ ) terminal of coil,
black lead from module to negative (-) terminal of
coil.

 

IGNITION COIL
To test primary and secondary windings within the
ignition coil first make sure the ignition power is off and
coil is at room temperature of 70°F (21 "C).
1. Use a Simpson 260 VOM or equivalent.
2. Place a black lead on negative (-) coil terminal and
red lead to positive (+) coil terminal. Primary
resistance should read between 2.90-3.60 ohms.
3. Change resistance setting on ohmmeter. Place
ohmmeter leads inside of spark plug cable holes
(Figure 3). Secondary resistance should read
between 14,500 - 19,800 ohms.
4. If either of the above resistances are not within specifications,

replace the coil.

 

Edited March 19, 2017 by cafoose

[cafoose 3,354]

I left it run for 10 or 15 minutes and it starts right back up. It seems to be fine now. I heard Onans are temperamental    and expensive. I'm thinking of a repower and trading or selling the Onan for a Kohler or Honda. How many modifications to fit a K-341 16hp and is it powerful enough?

 

Edited March 22, 2017 by cafoose