No spark on ST90 Help !

bcuda

bcuda

Member
I just bought this ST90 and cant get any spark to the plug.
I have a brand new battery in it and fully charged from what I understand a fully charged battery is very important on this bike the in line fuse on the hot wire is good the on off switch is in the on position, no ignition switch so I took the red and black wire and connected them together (or do I need them disconnected ). I checked the points cleaned them and gapped them at .016 has a new spark plug (is the gap to much). I did remove the tool carrier and it has what looks like to be a flasher for the turn signals on one side , (does this somehow need to be connected to get spark) or what are some tests I can do ?
Thanks!
Dave
 
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bcuda

bcuda

Member
I have 6 volts to the black and white wire on the coil have 6 volts to the points but no spark to the plug. I have rechecked the points I took them off and made sure they were clean and not burnt and used a point file on them. I rest the airgap on the points to .012 and still no spark to the plug.
 
bcuda

bcuda

Member
Update I re checked and do not have 6 volts to the points not sure what is going on it is more like .6 volts
 
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b52bombardier1

Well-Known Member
Hello Dave,

No need to regret buying the bike. It takes a while to undo 40 years of neglect and bike abuse at the hands of previous owners. That's why we are here . . . to help undo that abuse. You have probably found the reason why this bike got discarded but you have us now and we will get this bike going.

OK - unlike a CT70, a healthy battery on a 90 CC bike is just about essential but you already know this. .6 volts at the points??? Are you sure your multimeter is reading on the correct scale? Does it have a no kidding six volts at the leads coming out of the battery? How about six volts on the far side of the fuse away from the battery?

The next analysis can be done two ways - towards the points from the battery or towards the battery from the points. I like to backtrack my way up the points wire to find out where I get my six volts back. The likely culprits are a broken points wire at the square grommet headed into the points plate area or a broken wire at the points wire bullet connector. If not either of those, head on up the wire to the kill switch looking for six volts.

Your ignition switch wiring also worries me. Do you have six volts on both sides of the new connection you just made?

Turn signal relay?? Has nothing to do with the ignition.

Do you have six volt power in the headlight bucket on the four-way black wire connector?

Rick
 
bcuda

bcuda

Member
Rick thank you so much!
I have been at this all day and its driving me crazy. I just went and did some more checks I have 6.2 volts from the battery hot wire to ground. I just checked my voltage at the points when open it was 5.2. volts There is a connection about 6 inches back from the points and I checked here and was still 5.2 volts. I then disconnected the wire and ran a jumper wire straight to the points and got 6.2 volts with the juper wire and I still do not get spark to the spark plug. I checked the brand new plug to make it is good and put it on my CT70 and it has good spark. I took off the headlight and checked the black 4 way connector in the bucket it also has 6.2 volts I checked voltage at the kill switch and it is 6.2 volts.
Feel like Will Robinson (Lost in Space)
 
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b52bombardier1

Well-Known Member
But no "Danger, Will Robinson" here. Only Dr Smith lamenting "the pain, oh the pain". But we will get you through the pain.

So now I suspect the spark plug cap and high tension wire. Spin the plug cap off and then cut a quarter inch of the wire off. Before you put the cap back on, check the cap for continuity with your multimeter. The caps sometimes fail open.

Rick

Two CT90 and two ST90 bikes
 
bcuda

bcuda

Member
Cap is good I just switched them with my CT 70 and both work. I just cut back the plug wire and that solved it ! I got nice blue spark !
Thanks so much for the help Rick !
Next up Carb rebulid and to see if it will run .
Dave
 
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b52bombardier1

Well-Known Member
Just don't forget to disconnect your battery tonight. With no ignition key and those two wires twisted together, your battery could be deader than Millard Fillmore by tomorrow.

Rick
 
birdmannn101

birdmannn101

Member
Dave, It looks like Rick took you through everything. Let me tell you about my friends ST90. I did all the things you did and still no spark. Checked the points at 16 and spark. Checked the points voltage and it was good. Here is where I went astray ... I "thought" I checked the voltage on the other side of the points when they were closed. Guess I didn't. Took the bike to a shop where they fixed it the next day. They said that they took the points off and ground them down and now the bike has spark. Just my 2 cents worth....Dan
 
bcuda

bcuda

Member
Dr Frankenstein said its Alive !
Got it running tonight!

The problem on the points been there before with my CT70 so I made sure the points were real clean with my points file

Rick I did remember to disconect the wires to the battery last night . Thanks for everything!

I had found the original key switch still sitting inside the frame whenever they lost the key and put a toggle swich it it and had looked up the key code and found one on line it came in the mail today and fits perfectly tomorrow I will splice it back onto the wire harness and take care of that.
 
cjpayne

cjpayne

Well-Known Member
bcuda said:
Dr Frankenstein said its Alive !
Got it running tonight!
.........I had found the original key switch still sitting inside the frame whenever they lost the key and put a toggle swich it it and had looked up the key code and found one on line it came in the mail today and fits perfectly tomorrow I will splice it back onto the wire harness and take care of that.
Click to expand...
That is so cool that you found that. Did it feel stiff or move smoothly?
 
bcuda

bcuda

Member
Im pretty sure the switch was cut off cause the key was lost.
You could see where somone tried to remove the gas tank under the seat and had a hard time with all the small dents and pry marks on the gas tank , I would think they tried to remove the gas tank so they could install a new switch or something but I am sure they didnt get the gas tank out cause if I had not watched a you tube video on how to do it I would have given up myself and the original ignition switch would not have been just left on the inside the frame. The key switch worked smooth and it is already back in its spot. I took it for a few test rides and it runs pretty good got it up to 40 mph still needs some tuning prett sure it still needs a carb I went thru this extra one a friend had and it just dosent want to run right and hard to get it to idle down. Anyone have a carb ?
 
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b52bombardier1

Well-Known Member
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Mark A

Mark A

Member
That idle problem may be something as simple as an air leak. Perhaps between the carb and manifold. Happened to me.
Mark
 
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