Topic: Cannot retard timing enough on a CB750K4

[jwalters]

Hello, I  am helping a friend out with his bike.  The bikes doesn't like to idle very well, although it does run and he can ride it.  It's been carb synced, cleaned the carbs, descent compression, all the basics and everything is pretty much stock.  However, I hooked up a timing light to his bike, and I noticed that even at idle <1000rpm the timing mark for his 1st and 4th cylinder is almost at the " advanced mark. 

We cannot adjust his dial enough to get the timing to the proper F1.4 mark (it physically won't turn any farther b/c of the screw hitting the plate).  Any thoughts on this problem?  Unfortunately, I know nothing about the history of this bike, just trying to help a fellow CB 750er.  I am hoping someone else has had this problem and can tell me if it's a worn condensor (possibly cannot recharge fast enough), point or something else. 

 --Oh ya, the points look to be in good shape, no sparking across extranious contacts or anything.
Thanks
Jesse

[LeoLegendATL]

usually thats a problem with the point gap, check that according to the manual, at it's maximum distance apart.

[Bob Wessner]

Also see this item in our FAQ section


http://www.sohc4.us/forums/index.php?topic=261.0

[jwalters]

Thanks Leo and Bob.  Bob, honest I read the FAQ first but I didn't see that.... honest.

Sounds like points gap will be my next item to check off the list.  Thanks guys.
jesse

[Sam Green Racing]

Jesse,

I think this has cropped up before and it turned out to be the positioning of the main back plate.
Although the points on the main back plate look to be fine, they are not.
It would seem that when you slacken the screws that hold the plate, not only can you rotate it you can move it up down and side to side.
although this is only fractional, if the plate is not dead central to the crank it will not allow you to time the second pair of cylinders.
I had the same problem once, it was a Honda but not a 4.
I know you will have to retime the first pair of cylinders but just slacken the three screws an see how much play you have in the back plate.

Sam.

[dpen]

Had the same problem with my K7.
Fixed it ok, the question & the answers I got are around page 42 of this forum under the heading of "new timing question".

[bryanj]

DO NOT use a strobe at tickover, Use an ordinary bulb as in the manual to set static timing and then strobe at 3,000 to check the advance. Points gap 0.35mm or 14 thou, NO 15 wont do. First time you do this expect to spend 1-2 hours just getting the gap and timing right. Dont forget to remove any "pips" before setting the gap

[Gordon]

DO NOT use a strobe at tickover,

Why do you say this?

[bryanj]

Gordon, Honda used to say specifically NOT to use a strobe at tickover as the advance can start to move early and this makes it unreliable

[carl550k]

had the same prob with my 76 550k. even though the points looked fine, they were badly worn.put in new ones and ones and gained major adjustabilty at the points plate.