cb 750 - timing woes

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Monkey man
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cb 750 - timing woes

Post by Monkey man »

Hi guys i’m still having problems with my honda cb750 k5 1975

It’s reluctant to start even after cleaning the carbs so i have turned my attention to checking the points and timing

Trouble is try as i might i can’t get the firing marks to line up and the points open about 6mm from where the lines on the timing plate line up - there is no more adjustment available on the back plate as the slotted holes where the screws sit are at the limit of their extremities .

Anyone got any ideas what is wrong ?

will new points rectify it or even electronic ignition ?
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jabcb
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Re: cb 750 - timing woes

Post by jabcb »

Have no expertise on engines with those valve thingies.

But that being said, your points may open too wide or not wide enough, depending on if the points are 6mm early or late.

Take a look at the condition of the point contact surfaces. They may be pitted & causing you to get a false reading with your feeler gauge. With the bad reading you set the point gap wrong & then can’t adjust the timing correctly.
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gammakeith
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Re: cb 750 - timing woes

Post by gammakeith »

Yes, new points should fix it as its likely a worn heel. You can try widening or narrowing the points gap slightly as needed as its not very critical. I did nearly 80,000 reliable miles on my old 750K6 with points so I don't think you need the expense of electronic ignition. Many bikes don't have much backplate adjustment so it can be a pain when things wear. I think I did widen the slots on my back plate which is always a bit of a botch though. Lastly, has the engine been recently "rebuilt"? If so, there is always the worry that something silly has been done.

Good luck!

Keith
Monkey man
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Re: cb 750 - timing woes

Post by Monkey man »

Thanks guys - so new points it is then - time to get the cheque book out 😃
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