Hercules Misfiring When Hot

[Jim N]

My OC4 with a Herc IXB3 starts misfiring and sometimes backfiring  after it gets hot. Its really noticable when pushing hard and almost to the point of stalling. Also noticing  a black build up on the air cleaner side of the carb. Anybody have some ideas?  I think I've tried all the obvious stuff. Thanks

[Eric Severance]

Jim,
       It sounds like your ignition is breaking down. It may be time for a complete magneto rebuild. Weak magnets, and or coil will cause those symptoms under load. Make sure whomever you have rebuild it addresses those items. Faulty condensers can do weird things once they are heated up also. You might want to check compression and make sure you don't have worn valve or ring problems also.
                          Good luck

[Jim N]

I replaced the plugs, wires, points, condenser,rotor, rings, ground the valves, and cut new seats.
The valve springs, valve guides, and  coil in the mag were not replaced.  I guess the coil would be the next logical step??

[thecatskinner]

Jim, I have to agree with Eric.  It sure sounds like something electrical is breaking down when it gets hot.  since you have replaced most of the obvious things it points to the rest of the mag.
One thought--I have met bad condensers along the way.  Also, make sure your ground connection is good on both the condenser and points.

[JOHN HILL]

Back in the '50s I worked for a magneto repair shop and overhauled hundreds of Wico and Fairbanks Morse magnetos. The following are some of the things I would check:
1) There is a seal on the mag. shaft. If this becomes weak or defective, moisture can find its way from the crankcase into the mag. when the engine gets hot. The moisture can condense on the inside of the bakelite cap. This can cause spark tracking and cross firing. Remove the cap and clean thoroughly with a rag soaked in methyl hydrate/ wood alcohol. Dry well before replacing. Check the cap for spark tracks. Be sure to use a clean rag or paper towel for cleaning.
2) Moisture can also cause a bit of rust to form between the coil core laminations and the laminations in the mag. housing. These mating surfaces must be free of rust and clean to get a high level of magnetic transfer to the coil.
3) Replace the capacitor or have it checked for capacitance and series resistance. You might find a local electronics hobbyist who can do this for you. Points on battery operated systems pass quite a bit of current and tend to run warm or even hot and are to some degree self cleaning. Mag points don't pass much current, run cool and can easily collect crud. Remove points to clean them. I use crocus cloth or in a pinch 1000/1500 grit silicon carbide paper. After the contacts are shiney, clean with alcohol and don't touch with fingers or anything else.
4) To check the quality of the spark, arrange a 1/4 spark gap to the high tension terminal of the coil. This can be done on or off the engine (easier off the engine). When the mag is rotated the spark should be thick and blue. If the spark is yellow, thin or ragged, there is something wrong with the mag.
5) As aq last resort you might want to have the rotor magnet charged at a magneto repair shop.
6) It is hard to get the mixture adjusted perfectly when engine mechanical condition is not near 100%. My IXK tends to run rich when under heavy load and fouls plugs. Sometimes carbon fouled plugs look ok when tested under no pressure conditions. When I was in the business we used a Champoin cleaner tester. When a plug was being tested at 150psi you could look through a window and see the spark running down the insulator to ground. When I have these missing/ backfiring problems the first thing I do is clean the plugs with my handy baby sandblaster @ 40-60psi.
Hope this might help some.

[Jim N]

WOW!!  I had no idea there was so much going on with magneto ignition! I can see that I have much to learn. I can also see ordering a good book on mags.

In the meantime, could you tell me what the resistance in ohms, I should read across the cap??

Also, here is a pic of the Green Machine.  ( I hope.....)

[John Schwiebert]

You have gotten some good advice on the mag!. You might want to take a vaccum reading too . This will help look for internal engine problems such as week springs, etc without taking the engine apart.

[Jim N]

I have a vacuum gauge but am not sure where I'm supposed to check vacuum at.  I'm guessing somewhere on the intake manifold.  ....and  what kind of reading am I looking for?  Or should I use a vacuum gun in each spark plug hole???

I am am definitly getting into some advanced engine trouble shooting here. That's fine  because this is one of the toughest engine troubles I've ever came up against.  Rest assured, that when it's finally solved, I will bring everybody up to speed on everything I did.  Tonight , the mag is coming off after I finish moving  a small brush pile.  Thank you.

[JOHN HILL]

Jim
You don't measure any resistance on the cap. You measure the resistance between the lead and the case of the capacitor(condensor). Set your VOM (test meter) on the highest range. The closer the resistance is to infinity the better. Any resistance reading in the hundreds of thousands of ohms or less indicates leakage or a partial short in the capacitor.
Probably be hard to find abook on mags. In my years I never saw a book. I learned from the guy ahead of me. The mag. manufacturers didn't give out much info except to their distributors & dealers. Trying to protect their turf I guess!
If your engine is similar to mine (IXK) you probably don't have a vacuum fitting. I drilled and tapped the intake man. just above the carb. mounting flange. But its hard to get decent threads in that "cast iron". If you muff it you can always put a rubber expansion plug in yhe hole.
Good luck!
P.S. Also use your VOM to make sure you don't have any resistance in your plug wires

[Jim N]

Well, so far I've found  a major problem:     oil inside the mag; all the way into the cap.  I cleaned out everything the best I could. (Q-tip and spray contact cleaner).. Did the "off tractor"  spark test and am not sure what I'm seeing. Got  spark going across 1/4 inch, but not sure if I should be seeing any yellow at all.  The  spark looks blue on both ends but not in the middle some of the time.

Next question: should there be oil on the  governor side of the mag ( at the coupling)?? There appears to be some drain holes in the engine casting  for this.   And also ,the  mag shaft seal that you mentioned earlier needs replaced too.( How difficult??)  At some point,  I will have to get a rebuilt  mag.  Am I there yet or is there a resonably expensive way to repair it??

[JOHN HILL]

I wouldn't get the mag rebuilt yet - very expensive. Yes, there should be oil on the drive side of the mag. The best way to work on the mag. is to mount it ina big vice with styrofoam or something else soft on either side. Tighten the vice just enough to hold the mag in place-don't want to distort the housing.
The strength of the spark sound like it might be ok. Get the plugs cleaned and tested under pressure. If you decide to pull the mag. apart, let me know and I'll give you some instuctions. Is the mag. Wico or F.M.?
John

[JOHN HILL]

Some of that oil might be getting on the points and causing that "I CAN'T TELL LOOKING SPARK".

[Blake Malkamaki]

When you pull the plugs, let us know what color they are before cleaning. Are they sooty?

One thing I don't think anyone mentioned so far... a miss under load could be caused by a lean fuel mixture. If your plugs are sooty, that should indicate a mixture is not the case.

Blake

[Jim N]

Number 1 plug looks almost white. #2  looks like its  rich with black deposits. #3 has oil on it . #4 looks white too.

 I think I'm in trouble.

 I have a 130K .jpg  picture of the plugs but I do not know how to post it or link to it. Email me with some instructions would be greatly appreciated.

[thecatskinner]

Jim, store the picture on your harddrive--or a floppy. Open a new reply post here, then type what you want and move down on the page.  You will see "Attachment" a box and "Browse".  Click on Browse and go to the file where your photo is stored.  Highlight the file and then click on "open".
Click on "Post Reply" and it should be there.