no spark

[enduro1978]

Im new to motorcycles and I just got a 1978 Yamaha DT 175 Enduro, its pretty beat up but fixable, I hope. Well, I cleaned the carb and changing the battery/spark plug. Go to kick start it, and it comes back to life but only for a few minutes, then just dies. Don't know whats wrong, I changed the spark plug/plug cap/cleaned carb again but still no use. It kicks over but no spark. I know the fuel is alright, and there is good compression, so that leaves the electrical part. How to I check to see if nothing is damaged, (i.e. the CDI box or Ingition coil..?)? Or could it be the magneto? I am stumped and getting fustrated, any information would be greatly appreciated, thanks.

 

[helio lucas]

the electrical system seems to be fine, otherwise you shouldn´t even get the engine to start...

the jetting is a good place to start:

Main jet 160
Pilot jet 25
Needle 5G4 clip in the middle slot
Needle jet O-2

see if your jets are too far away from this spec...

to test your ignition system normaly you check it with a omh tester or a multimeter in omh scale and compare the values with those listed in the service manual...

 

[eagles22793]

it could be the battery so you have to test the battery or it is the coil

 

[enduro1978]

Thanks for replying,
The bike won't start at all, I have kicked it probably over 20 times, with the choke in/out. I think the carb is in working order but I'll check it again, cause when i take out the spark plug, there is gas on it. I have also tried taking the spark plug out of the cylinder head and putting it in the cap, then laying it on the head to see if i get spark and there is none. Also, I have checked the ingition coil with a multimeter and it seems to be good. Not sure how to check the CDI box, though. Or could it be the Voltage Regulator? And unfortunately I do not have a manual.

I've tried push starting it, but I don't think I was going fast enough. Would that even work with no spark?

Thanks.

 

[2strokerfun]

I've tried push starting it, but I don't think I was going fast enough. Would that even work with no spark?

Nothing will make it run without a spark. Good luck, it can be frustrating.

 

[jcarautos1]

Have you tried the fuse close to the battery?

 

[helio lucas]

if you are never getting spark check every conection for rust, damage or unfit...
check the cables for damage and continuity... this can be done with a multimeter or with a batery and a ligth... this is very tedious, i know...
the stator is included in this quest...
if everything is ok then you have to buy the service manual and check the coils and cdi... and by the way, check you ignition timing too...

http://www.clymer.com/SearchResults.aspx?c=MOTORCYCLE&y=1978&mid=337&mn=Yamaha&

 

[enduro1978]

Thanks for everyones input.

I just used the multimeter to check for ohms on the ignition coil..the smaller wire(primary wire?) it read 1.2ohms but the wire leading to the sparkplug(secondary wire?) reads nothing, could this wire be the problem? :whoa:

I also tested a brown wire from the CDI box to the magneto, getting a 0.02-0.05 ohm reading on it, not sure if thats good or bad. And a orange wire from CDI to the ignition coil(primary wire?) reads the same.

 

[enduro1978]

I'm leaning towards the ignition coil is the problem and needs replacing, but does anyone else think it could be something else?

Don't want to spend money on something that isn't broken.

 

[james33333]

How to Test a Magneto Coil With a Multimeter? - ElectronicsHacks

If You’re Not Sure Your Magneto Coil Is Working Properly, You Can Test It With a Multimeter. This Guide Will Show You How to Do That Quickly and Easily.

electronicshacks.com