Jonsered 70E no spark - help!

[Ironhand]

I picked up a 70E from a co-worker. Ran fine until one day it quit sort of story. The first thing I checked was the spark. No joy. New plug. Nothing. I pulled the starter cover and checked the wire that runs from the coil to the contact where the cover mates with the crankcase. Everything appears to be intact. Seems like with an electronic iggy, the potential problems should be limited. I'm looking for advice troubleshooting this old girl.

 

[Cantdog]

OK...first does your 70E have a plastic or alum fan?

 

[Ironhand]

Plastic

 

[Cantdog]

OK ...the early models with the plastic fan and the recoil mounted coil have a large module under the flywheel. This is the SEM unit and they go bad.....however there are a couple things to check before reaching complete depression...first is make sure your kill switch is not shorted by disconnecting the wire from the switch and then checking spark again....Any luck??? If not the next place to look is the connection between the recoil and case...on the right hand side of the recoil you will see a boss with a brass deal in a hole...this matches up with another brass deal in the case. Some times these will get dirty, corroded or worn and just not make the connection. Clean these both up and try the spark again......how about now??.......if not pull the recoil again and use one of the washers that goes on the recoil bolts between the connectors with a small dab of grease to hold it on place, make sure it isn't touching the recoil or case, reassemble and try again.....any luck?? If not then you are on the hunt for a new module......and right now you are in luck, for right on Ebay there is the only NOS SEM module I 've ever seen on ebay with a BIN.....or you look for a used one or a parts saw...the NOS one is very pricey...but they are so rare new that he WILL get the price. Question is how nice is your 70E?? Is it mint? Do you plan on using it for a long time yet?? You'll have to figure that stuff out but if you still have no spark after doing what I mentioned you will need to pull the flywheel (which is steel only the fan itself is plastic) and replace the module...and no I have nothing to do with the one for sale on ebay just trying to give you all the options that I see now.......these parts have been NLA for yrs.

 

[Ironhand]

Thank you for that! I'll check everything tonight. The contacts did look clean and apeared to be making contact. You mentioned that they are brass - should they be silver? I'm wondering if something is missing.

If nothing you suggested works, I was going to pull the flywheel to verify no broken wires around the SEM unit. Looks like the plastic fan has to come off to get a puller on the flywheel. With the 4 small bolts removed, should it lift off. I was afraid to break it.

Is it possible to test the secondary coil to rule that out before dropping $100 on the primary?

 

[Cantdog]

Thank you for that! I'll check everything tonight. The contacts did look clean and apeared to be making contact. You mentioned that they are brass - should they be silver? I'm wondering if something is missing.

If nothing you suggested works, I was going to pull the flywheel to verify no broken wires around the SEM unit. Looks like the plastic fan has to come off to get a puller on the flywheel. With the 4 small bolts removed, should it lift off. I was afraid to break it.

Is it possible to test the secondary coil to rule that out before dropping $100 on the primary?

They may be nickle plated brass. Yes the plastic fan should come off first, as you said, then there are three threaded holes in the flywheel which you can thread screws into and use a three-way bar puller to pull the flywheel off. Not sure if a jaw type puller will fit in to get a straight pull. I made a plate puller out of a piece of 1/4" plate with a number of three bolt patterns to fit the clutch and flywheel on nearly all the old Jreds. You should screw the nut onto the crankshaft top protect the threads and also that can give some adjustment if you use the three screws to pull with. Make sure you don't thead the screws past the thickness of the flywheel top as the unit is directly under there and can be damaged by using to long a screw.

As far as testing the coil you can do a search on this site for coil testing, though in my experience, I have not seen a coil failure on the 52E, 66E or 70E which all use the same components. The 52E carries a different part number for the coil and SEM because the wire lengths are different from the 66E/70E. Other than that they are all the same units. Also make sure you have a known good plug and that the connection between the plug and plug wire is sound. If it's stock the spring connector actually screws into the end of the wire core for the connection. These can gain resistance over time/corrosion. These are just a couple more things to rule out before replacing the SEM.