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73 CT3 175 itermitent spark

  • tsmitty1958
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73 CT3 175 itermitent spark was created by tsmitty1958

Hi Guys,
73 CT3, intermitent spark. When I took this engine apart, I did not touch the carb or the strator assembly. I figured it ran well enough so why mess with that. Replaced the bearing and seals. Put it all back together and the spark is white and intermitent. Replaced the points, same issue. Timing is set where I beleive it should be as I have 2 other CT3's that I have done the same things to and they run great. 

Any thoughts on the "intermitent" spark?

Tsmitty
The following user(s) Liked this Post: Reed valve Richards
18 Mar 2026 17:06 #1

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Replied by RT325 on topic 73 CT3 175 itermitent spark

Without being there it sounds like a condenser issue. Can alway mount an external condenser like honda do with it up at the coil--or buy a honda copy coil ready to go.But first look closely at your condenser. Engine mount bolts tight. Run an earth wire from motor up to the frame earth at the coil just to try. I'm guessing a lot. Nothing pinched behind the stator.
18 Mar 2026 19:14 #2

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  • Reed valve Richards
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Replied by Reed valve Richards on topic 73 CT3 175 itermitent spark

I feel for you, it's funny how stuff misbehaves just because you 'move' it. Had my neutral light decide to die on me while I was switching my stator out - these old bikes can be over sensitive sometimes ;)
Yo Joe, Go Joe
19 Mar 2026 00:42 #3

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Replied by Schu on topic 73 CT3 175 itermitent spark

I’ve had this happen which caused various spark related issues/quirks.

youtube.com/shorts/Po_I7u_D8gs?si=nNwfiBOZFfJ3owkn
Schu

CT1B, CT1C, JT1, JT2, CT2, RT3, DT360A, GT80B, DT100B, DT125B, DT175B, DT175C, DT250B, DT400B, Z50

Someday, you'll own some Yamahas
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19 Mar 2026 07:52 #4

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Replied by tsmitty1958 on topic 73 CT3 175 itermitent spark

Thanks guys. Getting spark that seems more white than blue. I'll give it a kick here shortly. If no start then I'll replace the condenser.
19 Mar 2026 12:27 #5

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Replied by tsmitty1958 on topic 73 CT3 175 itermitent spark

Changed the condenser, no spark. Put on a new coil. Same. The condenser is NOS so new one could be faulty I guess. I'll buy another and see.
19 Mar 2026 14:44 #6

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Replied by RT325 on topic 73 CT3 175 itermitent spark

Run the mag loom black direct to the plug coil to eliminate the main loom.
19 Mar 2026 17:42 #7

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Replied by pabdt on topic 73 CT3 175 itermitent spark

Who wants an old 73 CT3 anyway...just sell it to me inop. : ) ah hahahahaha. Ok, maybe not...

I agree w/RT352. time for analysis. note you could have bought a junk coil too. Trust me, almost all of them from
one particular country are JUNK. I know I tried buying about 6 of them and 100% failure rate even w/good resistance checks. buyer beware on coils.

One time I mounted a set of points and dial pin was NOT in the hole on plate. Verify they are flush.
________________________________________________
1969 Yamaha CT1 175
1974 Yamaha DT125A
1974 Yamaha DT360A with SP96 Exhaust
Next…196x-197x Yamaha something.


19 Mar 2026 17:53 #8

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Replied by tsmitty1958 on topic 73 CT3 175 itermitent spark

Ran direct to plug coil. Same, intermittent spark. The loom has continuity on all wires. This what I get for trying to make a "great" bike out of a good bike. :-)

The good news is that I'm back to intermitent spark although not sure why.
20 Mar 2026 08:34 #9

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Replied by tsmitty1958 on topic 73 CT3 175 itermitent spark

This is bike #2. I have 3. I have "Babe" #1 with the spark issue. #2 "The Beast" took it out yesterday for a spin around the neighborhood. It also had a spark problem and wound up replacing the stator. #3 is in the shed. Finished it up in December. Got it to run but needs some carb adjustment. Haven't named it yet.

imgur.com/a/IVzM9so
20 Mar 2026 08:59 #10

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