Incorrect poins gap side effects

surein

surein

My Cougar
hi - I have a 73' cb750 that I placed new points due to pitting. Even though I thought I did this according to the book, idle is a bit rattling and it kept stalling every time I went to first. I reduced the gaps and no more stalling but idle still doesn't sound the smoothest. I adjusted the idle screw to smooth it out but still no love.


I was wondering if someone can enlighten me with the ramifications of incorrect gaps? What's affected by gaps?
Plus I have a Hondaman transistor on the bike - doubt that's an issue


Thanks
 
Reducing the points gap will retard the timing as it opens later.


Your carbs will benefit from a balance too if the idle is rough.
 
It was smooth before I replaced the points - well running a bit rich but smooth idle.
Do I have to time the bike after I replace the points?
 
Make sure they are fully open and gap to 0.014"
Then adjust timing so it fires at F 1.4, check F 2.3
Re-check points gap as the plate rotation can cause gap to change
 
You don't need a timing light. Just a test light is all that is required. When the points open, the light will come on.

I won't give the whole process of setting the points in this post. If you don't have a manual, then do a little research on YouTube, and no doubt you will find a complete tutorial on setting up the points and timing.

As was mentioned, changing the point gap changes the timing. On a lot of single cylinder engines, changing the point gap is how the timing is adjusted. Also, having too small of a point gap increases point "dwell" and can cause the points and coils to overheat. Too wide of a point gap can lead to a weak spark.

The procedure, in a nutshell, is you set point gaps between 0.014" and 0.16". Then you set the timing to the first timing mark. The timing of the second timing mark is fine tuned by making minor adjustment to the other set of points.

Now, another point to consider...Pitted points are often caused by bad or out of tolerance condensers. You should change them, too.
 
thanks Alpha. I'll search for a test light. Do I hand rotate the crank?
If the timing was good before I placed the new points, do I have to time it with new points?
 
Setting the timing when installing new point is mandatory. No way can you install a set of points without affecting the timing.

I haven't done a points installation/timing on your particular engine, so I am not going to get into the nuances of technique. Yes, you rotate the crank by hand, forward only. Use a breaker bar with a socket on the end of the crankshaft. I am assuming that it is about the same as setting up the points on a CB350 from that period, (which I did recently.) Like I suggested, to to YouTube and do a search. I am certain you will find a video tutorial on exactly how to do it.

A test light will cost <$5.00, or you can use a voltmeter to read that instant that the points open.
 
Thanks Alpha - do you know if a circuit tester is the same as a tester light?
Will this work?


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What you don't want is a "continuity tester." Those have a battery in them, and the light illuminates when there is a complete circuit between the probe and the clip. A test light illuminates when it detects power. You connect the test light across the points. When the points open, the light will light. (With ignition turned on.) Remove spark plug wires. You don't want the engine to fire!

I couldn't find a video for setting the timing on the cb750, but there is this excellent one for the cb350. I presume the procedure is about the same.
setting ignition timing on a honda cb350 part 2
 
350 and 750 are totally different
350 points cam runs at 'half speed as its on the cam, 750 runs at crank speed qas it's on the crank
You have to watch for the timing marks through the points plate 'window' on 350f/400f/500f/550f/750f (they all use same points plate)
It's still pretty easy.
If your using a multi-meter, it may be easier to disconnect the blue and yellow wires from the points and connect meter lead to (I think?) yellow for 1.4, the other meter lead to ground (disconnect at bullet connectors into harness, jst follow the wires under clutch cover)
Should have very close to zero resistance with points closed (check meter resistance by touching leads together on Ohms scale)
When points open meter will read infinity OR resistance of condensers
Either way, you will see a difference in reading
 
Basically here's the to do list.


1) set valve clearance as per this: http://www.salocal.com/sohc/tech/vlvadj/vlv.htm
2) set points gaps to .014 at around 90deg of the 1.4 and at 90deg from the 2.3 marks.
3) Making sure the spark plugs are off line and the engine on, use tester light to check for voltage at the f mark.
3a) if not, loosen the back plate and rotate till the light comes on
4) Pray I don't have to take my bike to the mechanic come tomorrow


let me know if I'm missing a step


Thanks!
 
That works.
You set valve clearances though, not valve timing ;)
Watch the intake valves fro 1.4, the intake that goes down then comes up is approaching TDCC
 
to set points gap, rotate the motor until points are fully pen and set the gap. where valves and pistons are, is of no consequence to the gap setting. It's important for timing but not for the gap. Points are open for a long time, so they are really easy to check.

If the points are replaced, there is no way that the timing is right (well there's an extremely low probability at least).

Set gap
Set timing on one set (1.4)
Check timing on second pair and adjust points on the backing plate to get that second pair spot on too. You will notice that one pair of points is fixed on the backing plate and the other set sits on its own small plate which allows timing to be adjusted.
 
Doesn't really sound all that different. I think those cb350 video instructions, while differing on a couple of key points, (like where the marks are,) is still a pretty good tutorial on how to set up an ignition system with two sets of points.
 
So I adjusted the points but didn't get to the valve lash. I opened the caps and my knees trembled. I need to read up on that more.
Getting back to the points (pun intended), I wasn't able to time for the light to come on at the F mark. I ran out of plate rotation. It's firing before the 1.4 mark so well advance. Is that due to improper valve lash?


Changed all the plugs - the middle two was a biatch but got it done. Rode the bike to work even with the advance timing and it felt great, idled great and throttle response was great too. knock on wood cause I still have to ride it back home.


another question: I read the feet of the points have to be greased - any particular grease?


Thanks for all the help
 
Valve lash does not affect timing. It's just part of a routine tune up.

If the timing is advanced out of adjustment range, your point gap might be too large.

I use a dab of hi-temp moly grease. It's the same stuff that I use for brake caliper sliders.
 
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