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Hey there, I recently got into riding and my first bike owned by me is a lovely 1974 Honda CB750, done up in nice bright orange on the side panels and tank. I learn fast, but I'll admit I'm pretty new and there is a LOT I don't know, which brings me to tonight. I have run into a problem. First, one of my points actual little contact "discs" broke right off the body of the points. So I acquired a new set of points, put em in, and set the gaps, double checked them and still had a problem..... I cant get a single bloody engine turn over, no pops, putts, purrs or vrooms ( all of which it did before), now it just spins the engine until the cows came home. Could the changing of the points have thrown the timing off SO badly that not one cylinder or spark plug will ignite whatsoever? I need help, winters coming and I'm worried I'll hardly get any riding time in before the snow flies.
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Administrator
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Assuming the bike was running on all 4 cylinders before, the points you didn't change should be working fine. You should be able to get it close with the static adjustments. When the points rub block is on the highest point of the timing cam, that should be the gap specified in the manual. On my son's CB550, I think it was .022" or somesuch. If there's still no spark in there, either the points may be grounded somewhere (the little bolt that holds the wires for the points and the condensor), or there's a problem with the wiring or the coils.
I'd suggest pulling one of the spark plugs from the head, and placing it on the outside of the head somewhere. Turn over the engine and see if either pair (1 and 4, 2 and 3) delivers a spark.
You checked the IGN fuse?
Just a few things to check. Good luck, and keep us informed.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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Administrator
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I will assume you replaced both points correct? Setting timing on points is almost art.
I suggest you download the manual here and read it over. Once you look at it, it is pretty simple and yet hard to do at first.
Ultimately, you are setting the points gap at its widest opening to something about the thickness of a business card. so about .012 - .016 if I remember right. Been a while since I tossed on a dyna s.
That is the widest point gap BUT that should be right about at the "T" position for each particular point set in regards to 1-4 and 2-3. Shortly after the "T", the points should close and start the charge process for the coils. When it comes back around and hits the "F" mark, that is when the points should JUST start opening.
You can make a static timing light out of a 12V bulb and wire with 2 clips. When this bulb is connected, the light will be on(I think) when the points are closed and then goes out as soon as you hit the F.
I will see if I can dig up the contact points but get the manual here and look it over.
The ride IS the adventure. The destination is just to get gas!
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Well this certainly is frustrating...
I checked the fuses, all three were still good and conducted power, I've double checked my points gaps, they're good, I built a timing light out of a 12v light bulb, a block of wood, 2 wires and a pair of gator clamps, and they light, lights up, and the points open just as they pass the F tic, also, I have pulled and cleaned the plugs from 1-4 and 2-3. They all get spark and gas (came out wet but not gunky), although they seem to spark better when held away from the engine block or chassis, as opposed to pressed up against it. At any rate, there is still zero ignition and I'm stumped.
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Administrator
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Well that seems to be about right so lets try a couple things.
First off, pull the wires off the plugs and unscrew the plug caps.
Snip about 1/4 inch of wire off each lead.
Before putting the caps back on, test the ohm ratings. Set meter to ohms, stick one probe in one side and the other of course on the opposite end. Your ohm reading should be about 5K or so. If you get nothing, try again just to verify. If the ohms hit 10K or more, then replace the caps.
once you have the caps checked out. Screw them back on snugly.
Now how old are your plugs? Also, what brand and what number?
The sohc stock plug has been superseded with the NGK D8EA with a gap of .028
If the plugs were in the bike when you got it, you may want to replace them as you don't know how old they are.
The ride IS the adventure. The destination is just to get gas!
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Hazaa hazaa! signs of life. After some more tinkering, an evening with the ohm meter, some new plugs (the old ones sparked but apparently not enough any more, despite not being too too old), some gurgling and sputtering, the bike woke up and rumbled to life. Once I got it going it smoked and stank something fierce for a few minuets but I feel that it probably needed to clean itself out. I shut it off for a while and came back a few hours later, It didn't start right away, but the fuel level was a little iffy so I flipped it to reserve and away it went. I still don't think its quite perfectly tuned, it has a bit of a whirr to it and every 5-10 seconds it "coughs" or sputters once but doesn't seem to interrupt the engine function too badly. However it is not smoking any more, which is something it did only out of its left hand exhaust. After a few moments of idling, it did however jump in RPM from about 1000 to 2000 and remain there for a few minuets until I shut it off. Could this be an issue or the engine trying to heat up and shake things back into place after being dormant?
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Administrator
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Well it could be that the engine warmed up enough and when that happens, rpm will go up.
You should be able to turn that nut down to compensate. Some people turn the nut back and forth as they first start the engine and it warms up.
The ride IS the adventure. The destination is just to get gas!
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My friend who is rather handy with motors suggested I try running some seafoam through the engine to try and clean out the carbs and fuel lines and jets. Its helped a little but its still revving much to high. Before I changed up the points and spark plugs, it started and idled around 800-1000 RPM. Since the new points and plugs, it starts with one little tap of the starter button finally, but right away it idles up to 3000-3500 rpm right off the bat, and that's with the throttle cable nut adjusted to be the most slack it can be at the handle bars. (I tried adjusting the nut on the cable back and forth in both directions, and there was never more than a 100-200 RPM adjustment) Any idea what might cause such an increase in idling rpm? Cuz I don't believe that I could safely drop the bike into gear (with regards to my own safety, and jarring on the engine and transmission) with an idle that high at all. I'm thinking I'm going to have to pull a bit more of the bike apart to find out whats causing this. :(
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Administrator
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Have you adjusted the idle knob on the carb bank?
The ride IS the adventure. The destination is just to get gas!
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