Author Topic: Odd ignition problem on a '74 750  (Read 521 times)

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Offline korey

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Odd ignition problem on a '74 750
« on: October 14, 2014, 11:29:09 AM »
Hey guys,

To start off I consider myself pretty knowledgable about SOHC Hondas and in the past year have had atleast a dozen of them, all of which were bought not running or running poorly. So this is nothing new to me. I picked up a 74 750 the other day that I was told wasn't running very good anymore. It came with a box full of ignition stuff, so you could tell someone was chasing an ignition problem on it at one point. Popped the bowls off and found all the main jets loose, and even one that had fallen off and was sitting in the bowl. Popped off the ignition cover and found a new points unit under there. Took it off and checked that the advance to make sure it wasn't stuck, put it back together and static timed/gapped it. The bike fires up and idles and when I put a light on it the 2/3 is working perfect but the 1/4 seems pretty jumpy and the timing doesn't advance right. At idle it stays at F for the most part, but as you start giving it throttle it varies from jumping back to T and to advancing a couple degrees. I've never seen anything like this before on one of my bikes. I've tried another new coil and it doesn't affect anything. Any ideas? The only thing I can think of so far is that the blue wire from the coil is shorting on something and causing the weird spark, which I am about to test now.

Thanks in advance

Offline goldarrow

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Re: Odd ignition problem on a '74 750
« Reply #1 on: October 14, 2014, 11:37:23 AM »
When I work on my bikes, I like to do things in this order. 

Valves
Cam chain
Points gap
Ignition Timing - rev at 2500rpm

Ignition plate may have some play, especially if they're not TEC. try to shim it
Life Is Full Of Challenges - And My Backyard Is Full Of SOHC4's

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CB750 K0, K2, K23 JDM, K45, K5
And the little ones z50r, xr50r, st90


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KiefRichards

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Re: Odd ignition problem on a '74 750
« Reply #2 on: October 14, 2014, 11:38:33 AM »
Weird.
Have you checked the shaft from the crank to see if it's straight?
Just throwin that out there.

Offline korey

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Re: Odd ignition problem on a '74 750
« Reply #3 on: October 14, 2014, 12:24:06 PM »
^ Yep, thought of that too and checked it. Came out straight

When I work on my bikes, I like to do things in this order. 

Valves
Cam chain
Points gap
Ignition Timing - rev at 2500rpm

Ignition plate may have some play, especially if they're not TEC. try to shim it

I generally do ignition, carbs, then top end.

Offline korey

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Re: Odd ignition problem on a '74 750
« Reply #4 on: October 14, 2014, 12:25:45 PM »
Problem turned out to be a bad condenser. Noticed it arcing a lot across the points so I swapped out an old used condensor I had laying around the the problem is fixed. Thanks for the help guys