Vintage Dirt Bike Q & A

Glad I found this forum, been using the old Clymer manual the past week but it's not much use.

I put on new points, condensor and ignition coil. Got spark on the points but no spark on the spark plug.

Ran a direct wire from the output of the magneto to the power side of the ign coil - no spark. I removed the spark plug cap and inserted a needle in the wire still no spark. If I disconnect the wire from the ign coil, get spark on the points.

It appears anytime I hook anything up to the output wire on the mag the spark on the points stops.

I measured the voltage coming from the output wire on the magneto and its -13 to -18 volts depending on how hard I kick it over. What I find strange is the voltage output is minus volts??
I have my meter +probe on the output wire and the -neg prob on the engine block.

Any suggestions what to do next??

I should have also explained when I referred you to this site that it is a bit slower to get answers than over at DRN. Hopefully Ray or someone else that is more knowledgable about all things electric will soon help you. Unfortunately, anything electrical might as well be astrophysics math to me. The only thing that occurs to me is possibly a grounding problem. Here is something I found in a search from another poster (olddirtrider):

1) Check the continuity from the points to the coil, There is a inline connector between the wires on the stator and the coil. Its usually located near or just below the air cleaner box tied to the frame. BeIts not a good connector,,,,,so carefully examine it. If its loose or has has any corrosion on it your spark suffers greatly. To check to see if its the connector, pull it apart and check continuity in each direction. a)From the connector to the points. b)From the connector to the coil. If its good in both directions then the connector is suspect and you may want to replace it with a 2 prong trailer light type plug.

2) Take the points out and make sure they open and close electrically. Again use the ohmeter and dont worry about values just make sure you see a sharp change. (if they dont then go to 4 and 5)

3) The Clymer fails to tell you that light never really goes out it just goes dim on the MR175. It wont because of the of the pickoffs on the stator windings for the MR175 which doesnt have a battery but uses the pickoff for the lights. Sooooooooo just look for a change in brightness when you hook it up, rotate the rotor clocwise and watch the index line on the rotor, when the T aligns with the index on the cover it should dim. If it doesnt open your points with the two marks aligned and try again. Trust me the manual is spot on except the light does not go out 100%. .

4) Look at the nut on the points where the stator wire connects. You may have to reverse it. That is if the nut is facing out it could be grounding to the stator, Take the whole screw, insulators, (dont loose them) and put the nut on the inside of the point assembly.

5) If you happen to take the electrical connection screw off the points you may of lost the insualtor and that screw is now intermittely grounded to the points chassis.

1) Continuity checks on all the wiring. I now have a direct wire from the stator to the ign coil.

2) will check

3) no light installed or wiring for it.

4) don't understand this one?

5) interesting, will check

thanks for the info, I'll keep stumbling along.

These are correct, brand-new Honda parts?

With a good coil, condensor, and wiring, you should never have spark on the points.

The stator output voltage isn't easy to measure correctly; it's a short pulse waveform. Using a good meter adjusted to read pulse peaks, a mid-70's CR125M stator puts out about 60 VAC when kicked hard.

Is the kill switch completely out of the circuit?

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

New Honda parts, except for the condensor which is aftermarket (its not avail from Honda)

I must be getting old, I always thought there was spark between the points when they opened.

Kill switch is out of the circuit.

If the stator is putting out AC voltage what converts it to DC voltage to fire the ign coil?

Occasional points sparking is no big deal, but continuous sparking will eat them up in a hurry - that's why the condensor is there, to equalize the AC potential across the gap.

Magneto-type ignitions generate AC voltage to fire the plug. It's also common to rectify AC to DC to power lights, etc. if needed, but the stator/points/coil/etc. use AC pulses.

I would try disconnecting the condensor for now, as it seems it isn't really working right anyway. It's a made-for-ignition-service unit?

I'd also check the coil resistances just for grins. The primary (input from stator) should read less than 1 ohm, and the secondary (plug lead to ground) should read about 10,600 ohms or so.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I always thought ignition coils took DC voltage to fire. The original ign coil is long gone and I picked up a dirt bike coil from the local dealer. Possible I have the wrong ign coil???

I'd suggest getting the correct coil and condensor. These are still available as a set new (Honda P/N 30500-358-003) or on eBay.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thanks, just ordered it. What's the proper points/condensor to use?

These are the 3 ign coils I have, new one is the white one.

I'm very sorry - I made a mistake. I've been thinking so much lately about the MT250, I forgot your bike was the CR250. The correct coil for your bike is 30500-357-003. The coil I suggested should work fine, but the connectors and physical mounting setup may be different - and since it already has the condensor, you may not need that.

The original Honda/Kokusan 30210-357-003 points are still available as aftermarket parts (Sudco P/N 616-019) from Retrobikes (http://www.olypen.com/retro/, phone (360) 452-9043, E-mail retro@olypen.com). I would also ask them about the 30280-357-003 condensor (Sudco P/N 617-023), they can probably get that too.

http://www.olypen.com/retro/30210-357-003.htm

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thanks, called them but no answer, so I sent an email to see if all the parts are available. Update: They only have the points available.

Time to bring this bike back to life after a tour in Afghanistan.

Got spark now, found a hairline crack in the spark plug cap, new cap and nice fat spark.

Reading the manual and it says to use a dial indicator and a timing wheel. I dont have a dial indicator but do have a Motion Pro degree wheel. What can I used in place of a dial indicator and will the degree wheel work??