Topic: Help with Timing issue, I hope

[TimboTec]

Trying to get my 76 750 back on the road after letting it sit for far too long. Runs rough at idle, backfires and pops with throttle, often sluggish response too, Then it will just bog down and die.

From what ive read on the forums, most issues seem to stem from electrical so I started with Timing and Ignition. Replaced all spark plugs, old ones were sooty and smelled of fuel. Then I moved on to the Timing plate and points. Followed along on a youtube vid on setting static timing for gapping the points and it seemed to go ok (set approx .012"). Then I moved on to the timing. Using a test/continuity light I placed the clip end on the screw for points 1-4 and the point end into the case for ground.  It lit up even when the points were open!!! It then did the same for points 2-3!!! (SEE PICS and VID below) Rotating the crankshaft all the way around caused no change to the light. There seems to be constant continuity which makes no sense. Im sure im not grounding out on anything else. What would cause this? Bad condensers? Bad coils? Some false ground somewhere?
How can the bike run at all? It does start up and run although rough.

Please help, Im dumbfounded.
Tim

[bryanj]

If you connect the light between points power lead and ground its supposed to be on with points open and ignition on, but off with points closed, sounds like you have crud on the contact surfaces built up when standing doing nothing

[newday777]

Trying to get my 76 750 back on the road after letting it sit for far too long. Runs rough at idle, backfires and pops with throttle, often sluggish response too, Then it will just bog down and die.

From what ive read on the forums, most issues seem to stem from electrical so I started with Timing and Ignition. Replaced all spark plugs, old ones were sooty and smelled of fuel. Then I moved on to the Timing plate and points. Followed along on a youtube vid on setting static timing for gapping the points and it seemed to go ok (set approx .012"). Then I moved on to the timing. Using a test/continuity light I placed the clip end on the screw for points 1-4 and the point end into the case for ground.  It lit up even when the points were open!!! It then did the same for points 2-3!!! (SEE PICS and VID below) Rotating the crankshaft all the way around caused no change to the light. There seems to be constant continuity which makes no sense. Im sure im not grounding out on anything else. What would cause this? Bad condensers? Bad coils? Some false ground somewhere?
How can the bike run at all? It does start up and run although rough.

Please help, Im dumbfounded.
Tim

We can't see the picture or video you posted.
This is what happened when I clicked on them.

[newday777]

You say the bike has 'sat far too long' 

Did you drain the tank and carbs of all the gas before you let it set? Or did you leave the gas in as if you were going to get back to it right away?

My 1st impression is dirty carbs from gas being left in them far too long(seen this far too many times over the years)

Here is a video on setting the points and timing.

[cooldrum]

Timbo,  You are on your way of doing a full service. Yes, pull the float bowls and that may give you a glimpse of what's in the carbs. If your bike has been parked for "way too long"  Time to go through everything, valve adjustment, carb sync, strong battery charge, etc.  All the little things add up on making these bikes run well.  Just takes time and patience.  Many good YT vids to watch and learn to get your bike in tune.  Keep us posted.

[TimboTec]

Apologies all, Ill try to re-upload the pictures so you all can see what Im talking about. The gist of it again is that with a test light im getting continuity with the points open and closed on both the 1-4 AND the 2-3 Points.

[bryanj]

How are you connecting the test light? It should be between contact spring and ground

[TimboTec]

It is, it is connected to at the same spot (wiring nut for points 1-4) as shown in the video that newday777 posted. Coincidentally it is the same video I used to follow to Gap the points and set the timing marks.

I have pasted a Youtube link to a video I took. I hope this clarifies the issue. Im probably missing something pretty obvious, but Ya dont know what Ya dont know. Ya know?

[newday777]

So do you have TEC on the points and condensers? Or are they aftermarket?

[TimboTec]

I cant recall the brand, I rebuilt the bike years ago. I believe I sourced them from 4into1.com, pretty sure they are just reproduction Points and Condensers.

[RAFster122s]

Not putting the insulating washer in the right spot on the connections can cause you to have no difference in open and closed points…

4 into 1 likes to sell the cheap Chinese crap daiichi points and condensers. The condensers are total junk out of the box. The points are not designed properly for the CB Fours and really should be avoided.
The Daiichi three propeller blade logo is usually on the points… but they should have came in a box…

4 into 1 might sell Oem Honda at higher than discount dealer prices…
(south sound Honda of Olympia WA)

[TimboTec]

Ok, I'll check out the placement of the insulating washer. But just curious, The bike ran fine before, and I haven't messed with points since it had been sitting. Would that cause the bike to start running horribly out of nowhere? It seems to me like it wouldn't even fire up at all if the points were getting constant voltage.

Would a bad condenser cause this? Or possibly a false ground somewhere that made contact somehow? Any ideas on troubleshooting?

[RAFster122s]

Ok, I'll check out the placement of the insulating washer. But just curious, The bike ran fine before, and I havent messed with points since it had been sitting. Would that cause the bike to start running horribly out of nowhere? It seems to me like it wouldn't even fire up at all if the points were getting constant voltage.

It wouldn’t fire, thought you had put new points in… often catches us on reassembly if not careful.
Disregard insulating washer comment. I didn’t read back far enough…sorry.

Are you getting voltage to the points?
Kill switches sometimes will get dirty sitting causing non operating condition. Corrosion build up in switch in the handlebar housing…

If it is running kill switch is working.

Have you tested your spark plug caps to see what they are Ohm-ing out at?
They can cause rough running

[TimboTec]

Haven’t put a voltmeter on it yet but it does fire up so the points are getting power. The question is why and why isn’t that test light turning off when the points are open.

The kill switch works fine, bike won’t start with it off, and will shut off when it is engaged.

[TwoTired]

The yellow or blue wires on the point’s post get grounded to the engine case when the points are closed.  Test light across those test points should be out when points closed and light up when the points are open as the blue and yellow wires connect to the coil whose other end of coil connects to the black key switch + 12 volts.

[TimboTec]

OK, thats good info. I think I had my logic backwards. In my tiny brain I thought that when the points closed the circuit was complete and the spark would fire. So what I SHOULD be looking for is a continuity light when the points "break open" aka the firing position?

Am I correct?

However this still does not explain why I have circuit continuity in all positions of the points. Open/closed, doesnt matter. I can rotate the crankshaft 360º as many times as needed and no change occurs in the test light.

[bryanj]

I cant watch any videos on my crapfone so all i can say is the test bulb/lamp should connect one lead to ground and one to thethe spring blade or screw where wires are, if bulb stays on all the time you have assembled the points wire area wrong

[Deltarider]

For reference

[TwoTired]

When points are closed, the coil circuit is complete and the coil stores energy ( this is called “dwell time”, the period of time when the points are closed).  When the points open, the stored coil energy is released to the spark gap.  Plugs fire when the points open at the F mark if crank revs are low.

I don’t know the design of your test light.  An ordinary single filament type bulb should only light when it has a voltage applied to its two terminals.  If attached across the point contacts, it should only light when the points are open and key switch on.

I made my own test light by taking an instrument lamp and soldering two wires with alligator clips to it. 

I have an old test probe with three lights in it, one lights for logic high, one lights for logic low, and one lights when logic high and low are actively switching.  I mention this as evidence that there are different designs of “test lights” out in the world.  When I was still writing documentation on the circuits I designed, included in the documentation was the test equipment make and models used to obtain measurements of circuit operation.  This was so test results could be obtained and verified by anyone reading the documentation.  Test equipment design can vary among manufacturers and calibration. 

Yes, I’ve had my ass bitten a few times.

[TimboTec]

Thanks, I think im really learning a lot. So it seems like I may have multiple issues from what you've informed me about how the points operate. My "test light" which is just your basic hardware store continuity tester, the ones with a little light bulb inbedded in the see through handle and a pointed probe on one end and a spring clip on the other.

If im seeing no change in continuity, Im thinking I either have bad points that arent allowing the coils to store energy (which I dont think is the case, due to the fact that the bike does run, although extremely rough. OR I have a bad condenser or one that isnt functioning properly 100% of the time.

Im posting a video of the points with the engine running and the test light hooked up.  It looks like there is a big difference between points 1-4 and 2-3. Im not sure exactly what it should look like but I know something is off.

Let me know what yall think


https://youtube.com/shorts/y8_JX3qRfV8?feature=share

[newday777]

A continuity tester is different than a voltage test light.  That is your problem if you actually are using a continuity tester as you say.

[TimboTec]

I believe you are correct. I made a little DIY "test light" with a small incandescent bulb and some wires. Seemed to show proper circuitry with the points.

However I still believe my problem is Timing related. Here is a video of the points with the engine running.

https://youtube.com/shorts/y8_JX3qRfV8?feature=share

I don't think Im supposed to see arching on points 2-3. Bad condenser? Thats what Im hoping for. whatya think?

[bryanj]

A small amount of tiny arcing is normalish as you are breaking a power circuit, large amounts of heavy blue sparking would suggest a bad condenser

[HondaMan]

You say the bike has 'sat far too long' 

Did you drain the tank and carbs of all the gas before you let it set? Or did you leave the gas in as if you were going to get back to it right away?

My 1st impression is dirty carbs from gas being left in them far too long(seen this far too many times over the years)

Here is a video on setting the points and timing.

Very  typical of Common Motor BS.
The #1 PROBLEM WITH THIS VIDEO is shown at 2:09 into it!

With the 750 in particular, you must NEVER TURN THE CRANKSHAFT WITH THE NUT SHOWN IN THIS VIDEO. If you turn it CCW even a fraction of a rotation, you WILL bend the shaft that mounts the spark advancer. This WILL leave you with serious 'timing jitter', where the spark timing jumps back-and-forth, as seen under a timing strobe light.

The only cure is then to remove the points plate and spark advancer, re-straighten the shaft with a dial indicator to less than 0.002".

For those interested, here is the PROPER way to set points on the CB750:
1. Remove the sparkplugs.
2. Mount the points and wiring.
3. Using the kickstarter or via bumping with the electric starter, turn the engine 180 degrees past the 1-4 "T" mark. Set the 1-4 points to 0.014" gap here.
4. Using the kickstarter or via bumping with the electric starter, turn the engine 180 degrees past the 2-3 "T" mark. Set the 2-3 points to 0.014" gap here.
5. Using a strobe timing light, start the engine and find out where the 1-4 timing marks are located. Turning the baseplate adjusts this set of points: do that to make it fire on the "F" mark for the 1-4 points.
6. Repeat Step 5 for the 2-3 points, adjusting the smaller baseplate in its slots to reach the 2-3 "F" mark.

Now, this said...if your points plate is a genuine Honda TEC or older ND, TEC or Hitachi plate, it will go as described above.
If your points plate is a recent TEC plate, you may find that the slots in the 2 lower screw hole mounts must be widened to reach the timing marks, or the gap may be adjusted slightly, within the range of 0.012"-0.016", to reach the marks.

If you have a Daiichi points plate set, search these forums for "Daiichi" for my many, many other counsels on the issues with those plates.

If you have a CB500/550/400F/350F/250F: Honda realized this mistake of design and corrected the spark advancer mount situation in those later designs. In those bikes, you can simply remove the sparkplugs and then you can follow the Common Motor Collective video to your heart's content, but Honda never intended the SOHC4 points tobe set this way, ever. It was commonly done on the older Honda Twins, so many unknowing folks just thought the Mighty Four was the same. No, it isn't...

I'd give Common Motor Collective a piece of my mind, if I could spare it.

...end of rant... 

[Ellz10]

You say the bike has 'sat far too long' 

Did you drain the tank and carbs of all the gas before you let it set? Or did you leave the gas in as if you were going to get back to it right away?

My 1st impression is dirty carbs from gas being left in them far too long(seen this far too many times over the years)

Here is a video on setting the points and timing.

Very  typical of Common Motor BS.
The #1 PROBLEM WITH THIS VIDEO is shown at 2:09 into it!

With the 750 in particular, you must NEVER TURN THE CRANKSHAFT WITH THE NUT SHOWN IN THIS VIDEO. If you turn it CCW even a fraction of a rotation, you WILL bend the shaft that mounts the spark advancer. This WILL leave you with serious 'timing jitter', where the spark timing jumps back-and-forth, as seen under a timing strobe light.

The only cure is then to remove the points plate and spark advancer, re-straighten the shaft with a dial indicator to less than 0.002".

For those interested, here is the PROPER way to set points on the CB750:
1. Remove the sparkplugs.
2. Mount the points and wiring.
3. Using the kickstarter or via bumping with the electric starter, turn the engine 180 degrees past the 1-4 "T" mark. Set the 1-4 points to 0.014" gap here.
4. Using the kickstarter or via bumping with the electric starter, turn the engine 180 degrees past the 2-3 "T" mark. Set the 2-3 points to 0.014" gap here.
5. Using a strobe timing light, start the engine and find out where the 1-4 timing marks are located. Turning the baseplate adjusts this set of points: do that to make it fire on the "F" mark for the 1-4 points.
6. Repeat Step 5 for the 2-3 points, adjusting the smaller baseplate in its slots to reach the 2-3 "F" mark.

Now, this said...if your points plate is a genuine Honda TEC or older ND, TEC or Hitachi plate, it will go as described above.
If your points plate is a recent TEC plate, you may find that the slots in the 2 lower screw hole mounts must be widened to reach the timing marks, or the gap may be adjusted slightly, within the range of 0.012"-0.016", to reach the marks.

If you have a Daiichi points plate set, search these forums for "Daiichi" for my many, many other counsels on the issues with those plates.

If you have a CB500/550/400F/350F/250F: Honda realized this mistake of design and corrected the spark advancer mount situation in those later designs. In those bikes, you can simply remove the sparkplugs and then you can follow the Common Motor Collective video to your heart's content, but Honda never intended the SOHC4 points tobe set this way, ever. It was commonly done on the older Honda Twins, so many unknowing folks just thought the Mighty Four was the same. No, it isn't...

I'd give Common Motor Collective a piece of my mind, if I could spare it.

...end of rant... 

Learned this the hard way when I rebuilt my motor. Not a good time lol