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Discussion Starter · #1 ·
Hey guys

I'm having trouble with a little S90 i just picked up as a project
I've sort of hit a wall with it.

When i plug in the battery, turn the key and go to kick it i get no spark. (its a new plug gapped to .6mm)

I've pulled out the motor and checked out the ignition coil and it looks okay. (but i was thinking of ordering a new one anyway as it's the original coil with a 1964 date stamp on it)

the points look pretty good when i pulled the cover off.

I'm thinking maybe theres something wrong with he wiring to the ignition switch? i was thinking about trying to bypass the switch to see if that might do it but I'm not sure!

anyone have a suggestion on what i should do?
 

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If you own a test light or a multimeter and have a general idea of how to use it we can help you to determine what the problem is. It's a lot cheaper that way than replacing one part at a time until you stumble on to what the problem is.

Welcome to the group.

Got pictures?:p
 

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Discussion Starter · #4 ·
i do have a multimeter and general idea of how to use it!
perhaps you can help me out!

I did find a mouse nest on top of the motor (complete with dead mouse) which is why i was thinking of replacing the ignition coil they chewed up a couple wires that i fixed but i wasnt sure of how extensive the damage could be.

where on the points would i place the test probes?

I'm pretty new to this (sigh)

photo (5).JPG
 

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Nice looking little S90 ! Put the test leads on the wire terminal which attaches to the points(+) and the negative on the bare cylinder metal for (-) ground and the slowly spin the engine over w/o the spark plug installed.
 

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Discussion Starter · #6 ·
alright cool! I leave the wire thats hooked into the points in place right?

what should i look at incase im not getting power to the points?
 

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Discussion Starter · #8 ·
I fixed a loose wire coming off the ignition coil. And remounted the motor.
so I plugged the multimeter into the points and it is giving me power.

... Also for good measure I grabbed the end of the high tension cable and kicked the starter and it's giving me a good jolt to the hand.

Alas but still no spark.

I'm not sure how to adjust the points but could that be the reason?
 

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Discussion Starter · #10 ·
I put a new plug cap on and still no spark.

I know I'm getting power through the tension wire.

Could the coil be bad?

Or do the points have anything to do with it?
 

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Sensei
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I fixed a loose wire coming off the ignition coil. And remounted the motor.
so I plugged the multimeter into the points and it is giving me power.

... Also for good measure I grabbed the end of the high tension cable and kicked the starter and it's giving me a good jolt to the hand.

Alas but still no spark.

I'm not sure how to adjust the points but could that be the reason?
That Jolt to your hand means it IS getting spark (at least that far..)....
With a new boot/plug cap on the end of the HT lead, it SHOULD fire the plug...If NOT, bad plug....
 

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What does the plug look like on the business end? My S90 would foul the plug very easily and if you've been cranking it over for a long time I'd bet it is fouled. If it is black and sooty or oily looking on the electrode you can check resistance between the center electrode and the plug body. Anything under about 10 mega-ohms means the plug is fouled. Check out this explanation - http://www.ngk-sparkplugs.jp/english/techinfo/troubleshooting/03/index.html

Plugs are cheap for these things, buy a couple of spares.
photo (4).JPG

BTW - nice bike! I traded the black and silver one in the picture for a running, driving '75 CB400F.
 

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Discussion Starter · #13 ·
I readjusted the points and got it running! I put in a new plug for good measure solid consistent blue spark.

However I'm having trouble getting it to idle. It will run for about 15 seconds revs really high. Then dies.

Maybe something in the carb?
 

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Sensei
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When you "re-adjusted" the points, did you actually gap them and re-set the timing to specs, or did you just "play" with the adjustment until it would fire the engine?
Changing the gap changes the timing.....
Have you disassembled and cleaned the carbs, checking all the jets and passages?....For starters, High revs could mean the slide is set too high, or indicate an air leak, or indicate it's running out of fuel....
We need to know what you've done so far.....
 

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Discussion Starter · #15 ·
When I readjusted the points I set the flywheel to the f position and set the points gap to .015" then it started giving me a consistent spark.

When I bought the bike the guy I bought it from said he sent the carb out for cleaning but I didn't chance it and I pulled it myself and cleaned it out. (It's only a single carb. Little guy) the jet was clear.

Although the slide seems to be kinda screwy it was set in there the right way and should be down all the way. Is there something I can better lubricate the slide with?

I don't think it's running out of fuel. It seems to have a good flow from the tank into the carb.
 

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Discussion Starter · #16 ·
Alright so I put a whole new carb on it.

And it worked great for the first few fireups.

I went a worked on a couple other cosmetic things and came back to fire up and now it idles SUPER high. The throttle doesn't seem to do anything and when I turn the choke on it seems to kill the engine.

The screw that sets the idle on the side of the carb doesn't do anything either. I can pull it all the way out and it still idles crazy high.

Does anyone know what could be the problem?
 

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Discussion Starter · #18 ·
Just whatever ones came with the new carb.

Also it seems to lower rpm the choke is ON. I thought it might be an air leak or something
 

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Discussion Starter · #19 ·
What does the plug look like on the business end? My S90 would foul the plug very easily and if you've been cranking it over for a long time I'd bet it is fouled. If it is black and sooty or oily looking on the electrode you can check resistance between the center electrode and the plug body. Anything under about 10 mega-ohms means the plug is fouled. Check out this explanation - PLUG STUDIO / NGK

Plugs are cheap for these things, buy a couple of spares.
View attachment 46191


BTW - nice bike! I traded the black and silver one in the picture for a running, driving '75 CB400F.
Hey John, im finally to the point with this that i can hook up the original gas tank and get er rollin. when i got it the tank was already dis assembled.
I see there is a second fitting on the left side of the gas tank annnnd I'm not sure where thats supposed to hook up to. maybe my petcock is missing a piece for it to hook into?
I'm not really sure..

do you recall how this tank hooks up?
 

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Sensei
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When I readjusted the points I set the flywheel to the f position and set the points gap to .015" then it started giving me a consistent spark.

This is NOT how the points are set and timed in.....It will be close, but NOT EXACT....
Set GAP first at the highest part of the breaker-cam lobe (widest opening),
THEN, with the crankshaft rotated to, and held at the "F" mark alignment on the COMPRESSION stroke, rotate the entire points plate until the points JUST break......
You method likely set the timing slightly advanced.....

Overtightening the carb can also cause the revving (slide sticks) as can undertightening (air leak)...
Did you replace the O-rings (or change to flat gasketing as I often recommend?)

Note that the carb has TWO jets, (pilot and main) and the float height must be set correctly for the engine/carb angle.......
IS your replacement a Keihin or a "cloned" version?
 
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