Topic: '71 CB750 shifting problems, timing problems, ignition problems

[Cataldo]

When i ride the bike and shift lazily it shifts just fine, when i am giving it any kind f decent throttle it will miss shift, and will grind trying to go into gear. Also when the clutch is disengaged i get a knocking sound. When you pull the clutch in though it goes away. I have only had the bike on the road for a short while and it has done this ever since i got it running.

When i go to time the thing, i can not see the timing mark, no matter which wire i put it on, i can go through the entire adjustment and not see the timing mark, i can however see the advanced mark. The bike does idle kind of high, about 1,000rpm and maybe a little over. I have tried rotating the engine 180* and putting the points back on, no change. Also on my timing light i have a tach and it is all over the place, and not near what the tach on the bike is reading.

She is only really running on 3 cylinders there is a week spark on #4. (So a new coil).

[Alan F.]

When i go to time the thing, i can not see the timing mark, no matter which wire i put it on, i can go through the entire adjustment and not see the timing mark, i can however see the advanced mark.

This could be because your timing advancer is stuck in the 'advanced' position and the springs are not pulling the advance weights in at lower rpms, Take the advancer out (it's behind your points plate) and clean it up with some penetrating oil and make sure it moves freely from one position to the other.
Good luck dude.

[Gordon]

1000 rpm is a good idle for your bike, not too high at all.  The tach reading on your timing light is off because these bikes have a very different ignition system than the cars it was made to be used on (two sets of breaker points instead of one, and a wasted spark system).  And a weak spark on #4 doesn't indicate the need for a new coil.  One coil fires two cylinders, so if the coil were bad you would have trouble with both those cylinders. 

[Cataldo]

Thanks.

I should have noted that i can't get to the Advanced mark, but i can start to see it. I'll go pull the thing apart clean and lube it. As for the spark problems, i guess i should start at a new plug cap (One from a SBC should work, right?) and then work on a new wire, i was reading the tech article on running an accel wire, i guess that'd be step two.

it likes to idle at about 1,500 much better. anything under a grand, and it will stall.

Any thoughts on the clutch/shifting issues?

Upon further reading in the FAQ, i found this
http://forums.sohc4.net/index.php?topic=260.0
Looks like syncing the carbs should help this.

[Alan F.]

a new plug cap (One from a SBC should work, right?)

it's possible, but NGK caps with the 5K resistor inside are available over the counter at any decent bike shop for about $5-7  and you'll probably get a choice of a few different angled boots.  The resistance inside the boot will rise over time with corrosion, causing a weaker spark.  My original plug caps varied widely from 7K to almost 20K, they should read 5K.

[Cataldo]

I guess i should just replace all of the plug caps.