Ignition advice on '72 WR250

[rob kelly]

Hi, I'm after a bit advice getting a wr250 running. Its not run since i bought it.

I suspected the HT coil was to blame for an intermittent spark so following peoples advice on here i have bought an orange Emgo HT coil. Whereas before i had a sporadic spark i now have no spark.

What resistance should i expect from the femsa primary coil and what should the HT coil resistance be for it to work? I've fitted new condensor and points and have gapped the points. I'm now suspecting the primary coil.

Any suggestions would be appreciated.

Rob

 

[Crashaholic]

I don't know what the resistance value should be for a Femsa primary coil but I have heard many guys say that the 6v emgo ignition coil works well with Femsa. Strange that your sporadic spark turned to no spark with the addition of the new emgo.

While your looking for the primary coil resistance value you may want to check other things like an unwanted ground at the kill button, a good ground of the emgo to the frame as well as at the primary coil to the backing plate, look for a possible short in the lead between the coils i.e. primary to ignition. Some have even suggested checking the engine bolts for proper torque to ensure a solid circuit.

 

[rob kelly]

Ok cheers, I'll go through it all properly and make sure its all earthed well.

 

[rob kelly]

Hi chaps, thanks for your help, I cleaned all mating surfaces properly and inspected the wiring. The blade connectors on the wiring were particularly dirty and corroded, I cleaned these and have a good spark now. Am I right in thinking that points should open when the centre punched mark on the flywheel lines up with the top right hand cover hole?

 

[Crashaholic]

Am I right in thinking that points should open when the centre punched mark on the flywheel lines up with the top right hand cover hole?

You have spark now, that's great!

I don't know what you mean by the top right hand cover hole. Heres a PDF on setting the Femsa timing, has other good things to know. The photos shown in these instructions are of the Mag engine post 74 ML frame so the timing marks on your 72 250 may be in a different location.

Let us know when you get it running.

 

[rob kelly]

Sorry crashaholic, I meant top left. I've only noticed one centre punch mark but i'll have a look for another and give it a go.

 

[Crashaholic]

Its possible that your flywheel has only one punch mark. If it lines up with the case mark before the piston is TDC then that would be when your points must begin to open, i.e. timing mark. If the marks align at TDC then you'll need to find the timing mark by measuring on the flywheel counter clockwise 23.8mm +/- 1.2mm from the TDC mark, as outlined in the PDF tech sheet for the 72 250WR.

Even though the 72's have the MJ frame the timing spec is the same as the MK frame.

 

[rob kelly]

Ah that's great. I did wonder as the flywheel on it does only have one mark and that appears to be at TDC. So if I understand the manual and what you are saying correctly I simply just measure 23.8mm along the outside of the flywheel to the right (clockwise) of the current mark so the points would open before TDC.
I'll give that a go after work or tomorrow and let you know how I get on. Thanks again.

 

[rob kelly]

Right... either there is an art to this or I'm just being stupid. The punch mark is 23.8 in front of tdc so I've set the points to open when this mark lines up with the top left cover bolt hole. Still nothing, not even a pop or bang. I've put a bit of fuel down the plug hole to help, still nothing. The back plate is virtually turned fully anti clockwise which doesn't seem right.

 

[Richard Colahan]

OK...let's go over two ways to check the ignition timing...which is the exact point when the contact breaker points "open".
First, the flywheel gets re-installed and properly torqued. Before you do that, carefully remove that worn woodruff key and replace it. Also carefully dress that tapered crankshaft mating area with fine emery paper. Get it as smooth as you can. Do the same thing to the mating surface of the flywheel. Clean both with contact cleaner and re-install the flywheel with both components clean and dry.

Option 1: Use a metric dial indicator inserted into the spark plug hole. Bring the piston to tdc. "Zero" the dial indicator at tdc. Rotate the flywheel counter-clockwise about 3 mm. Slowly rotate the flywheel clockwise. If set correctly the points should open at 2.43 mm btdc. If not, rotate the backing plate until they do. I prefer an ohm-meter or a battery/bulb circuit to accurately detect when the points break. Or the analog method of tugging on a super-thin slip of cellophane inserted between the points.

Option 2: Use a degree wheel fastened (yes...I use a double-sided piece of duct tape to secure the degree wheel) to the flywheel nut flat surface. Fasten a piece of wire to the case that can be used as a pointer on the degree wheel. Bring the piston to tdc. Bend the wire pointer to match up to 0 degrees. Rotate the flywheel counter-clockwise about 30 degrees. Slowly rotate the flywheel clockwise. If set correctly the points should open at 20 degrees btdc. Adjust as needed.
For future use, carefully mark the flywheel and the engine case at that 20 degree setting.

That should do it...

 

[stormer254]

That's the way to do it, the only thing I would do different is to lap the flywheel on to the crankshaft taper with some fine valve grinding paste, certainly in need of a clean up on the mating surfaces.

 

[Richard Colahan]

That's the way to do it, the only thing I would do different is to lap the flywheel on to the crankshaft taper with some fine valve grinding paste, certainly in need of a clean up on the mating surfaces.

Yes! Good tip! After the fine emery paper use the fine (wet) valve grinding compound. Then get both surfaces squeaky clean before re-installing that flywheel...

Also...take a close look at the points cam surface of the flywheel. My guess is it's also a bit crusty. It must be smooth or else it will wear the points rubbing block. Polish with fine emery paper...CLEAN...then lightly lube. Oil the felt wiper also.

 

[rob kelly]

Ah ok, i didn't think it would be that critical, but it makes sense. The crankshaft end taper is a bit lumpy from previous corrosion so i'll emery it all smooth and lap it in. cheers for the tips. I've pretty much set the timing like you've described Richard so maybe its the flywheel not sitting square on the shaft thats causing it to be retarded. I would've thought i would have got a pop or bang at least though.

 

[Up-tite]

Try moving the backing plate to where the scribed line on the backing plate lines up with the 2 scribed lines on the motor case.
look at pic above,
When these ign were close will make a big juicy spark just by spinning by hand.
Later George

 

[rob kelly]

Ok cheers George i'll do that.
I've cleaned all the mating parts and have used valve grinding paste to lap it in. I'll torque it up and use new fuel and see how i get on, hopefully tomorrow.
Rob

 

[Arthur Smith]

OK...let's go over two ways to check the ignition timing...which is the exact point when the contact breaker points "open".
First, the flywheel gets re-installed and properly torqued. Before you do that, carefully remove that worn woodruff key and replace it. Also carefully dress that tapered crankshaft mating area with fine emery paper. Get it as smooth as you can. Do the same thing to the mating surface of the flywheel. Clean both with contact cleaner and re-install the flywheel with both components clean and dry.

Option 1: Use a metric dial indicator inserted into the spark plug hole. Bring the piston to tdc. "Zero" the dial indicator at tdc. Rotate the flywheel counter-clockwise about 3 mm. Slowly rotate the flywheel clockwise. If set correctly the points should open at 2.43 mm btdc. If not, rotate the backing plate until they do. I prefer an ohm-meter or a battery/bulb circuit to accurately detect when the points break. Or the analog method of tugging on a super-thin slip of cellophane inserted between the points.

Option 2: Use a degree wheel fastened (yes...I use a double-sided piece of duct tape to secure the degree wheel) to the flywheel nut flat surface. Fasten a piece of wire to the case that can be used as a pointer on the degree wheel. Bring the piston to tdc. Bend the wire pointer to match up to 0 degrees. Rotate the flywheel counter-clockwise about 30 degrees. Slowly rotate the flywheel clockwise. If set correctly the points should open at 20 degrees btdc. Adjust as needed.
For future use, carefully mark the flywheel and the engine case at that 20 degree setting.

That should do it...

Thanks. New to a '72 250WR. What device do you use to check the points opening. Since the flywheel is mounted, something has to connect through the slits in the flywheel. Also, can you rotate the backing plate with the flywheel mounted. Sorry for the elementary questions and appreciate you comments.

 

[Crashaholic]

What device do you use to check the points opening.

I use a Buzz Box. You can find one here but its pricey for someone who may use it only once or twice.
https://www.speedandsport.com/parts/tools/ignition-timing-buzz-box/

As mentioned above you can use an ohm meter or rig up a battery and light bulb. All of these methods connect one lead to the wire that goes to the secondary coil and the other lead to a good engine ground.

Once the timing is set make sure the points are opening to the required .35mm - .45mm as mentioned in the PDF in post #5.

 

[Arthur Smith]

I use a Buzz Box. You can find one here but its pricey for someone who may use it only once or twice.
https://www.speedandsport.com/parts/tools/ignition-timing-buzz-box/

As mentioned above you can use an ohm meter or rig up a battery and light bulb. All of these methods connect one lead to the wire that goes to the secondary coil and the other lead to a good engine ground.

Once the timing is set make sure the points are opening to the required .35mm - .45mm as mentioned in the PDF in post #7.

Thanks, appreciate it. And the wire that goes to the sec. coll is easily accessible with the flywheel on? And, the points can be set through the slits in the flywheel?

 

[Crashaholic]

And the wire that goes to the sec. coll is easily accessible with the flywheel on? And, the points can be set through the slits in the flywheel?

Theres a connector on the secondary coil hot wire (the black wire) where it exits the engine case. It goes directly to the points so it allows you to hook up your device to know when they break. And yes the slots in the flywheel enable access to gap the points. I use a feeler gauge thats been trimmed narrow enough to fit through the slots.

 

[Arthur Smith]

Theres a connector on the secondary coil hot wire (the black wire) where it exits the engine case. It goes directly to the points so it allows you to hook up your device to know when they break. And yes the slots in the flywheel enable access to gap the points. I use a feeler gauge thats been trimmed narrow enough to fit through the slots.

Thanks, the wire method. Perfect. And, the timing? I have the marks, but am a bit unsure about moving the backing plate. Crash, thanks for taking the time. I really appreciate it.