Topic: Ignition timing/spark advancer

[dgedinyte]

Hey guys hope everyone is well. I've got a 75 cb750K. I am trying to set the ignition timing(for the first time). I set it according to the manual using a continuity light. Then I strapped on the timing light. Even though it seemed to be firing right at the F mark using the manual's procedure, it was way off when I checked it with the timing light. So I adjusted it according to the timing light. I've got it timed at idol on all cylinders. But as I get just over 2500RPM's 2 and 3 are advancing properly but 1 and 4 is way late. I took everything apart at that point and cleaned and lubed the spark advancer. Rebuilt everything and same result. seems good at idol, but when advanced 2 and 3 are good, 1 and 4 is way late. Anybody got any suggestions? the summer is disappearing on me!

[Tews19]

I switched to a dyna electronic ignition. I made sure it fired on F when advance for both 1-4 and 2-3.  I didn't worry about idle due to Dyna customer support telling me not to.

[dgedinyte]

Thanks TEWS. I am really hoping for a solution that doesn't break the bank. I've looked into an electronic ignition, but I'd rather get the points working correctly.

[Tews19]

Try setting in advance.

[PeWe]

It is rather easy to do it properly.1:4 , 2:3 at idle and full advance at after 2500rpm.
The reason why Dyna recommend people to skip idle is most likely due to sloppy advancer springs that can be fixed. Result will be proper ignition at idle and full advance after 2500rpm.

Follow this description. (There are several descriptions on this forum.)
http://www.hondachopper.com/garage/carb_info/timing/Static_and_Strobe_Timing.pdf

If you have adjusted static setting correct, but yoiu will see full advance too early when running the engine and check ignition with timing lamp. Tighten the adv springs.

I got full advance before1500 rpm which ended up in spitting carbs. I found a description here by Hondaman to tighten the springs which I did.
After that I have F at idle or full advance at about 2600-2800rpm.
Here my case when I cut the springs. You can try to cut one spring only to start with. 1/2 turn off + reshape it with a plier
http://forums.sohc4.net/index.php?topic=131339.0

[HondaMan]

Hey guys hope everyone is well. I've got a 75 cb750K. I am trying to set the ignition timing(for the first time). I set it according to the manual using a continuity light. Then I strapped on the timing light. Even though it seemed to be firing right at the F mark using the manual's procedure, it was way off when I checked it with the timing light. So I adjusted it according to the timing light. I've got it timed at idol on all cylinders. But as I get just over 2500RPM's 2 and 3 are advancing properly but 1 and 4 is way late. I took everything apart at that point and cleaned and lubed the spark advancer. Rebuilt everything and same result. seems good at idol, but when advanced 2 and 3 are good, 1 and 4 is way late. Anybody got any suggestions? the summer is disappearing on me!

The shaft that holds the advancer on it probably bent a little. This happens when the big nut is pulled backward (CCW) with the sparkplugs in the engine.

On page Appendix G-3 in my book, I show pictures and step-by-step how to fix it again.

[dgedinyte]

Thanks for the advice guys. I'll look into both solutions tonight. I appreciate your time and consideration.

[evanphi]

Mine are opposite of yours... 2/3 not reaching advance, but OK at idle. Likely a bent shaft. Going to set 2/3 to the advance mark. I don't have the time or patience right now to fix the shaft.

[dgedinyte]

When you say your going to set it at the advance mark. Do you mean line up the advance mark with the timing mark and move the two and three plate until the points are at their widest position? Again this is my first time.

[evanphi]

When dynamically timing with an inductive timing light, set your rpm to where the index marks won't advance anymore (usually around 2500 rpm). In your case, you would then move the 1/4 points plate until that timing mark is between the full advance marks.

Don't forget: You'll have to re-adjust your 2/3 after you do the 1/4 because 2/3 is attached to the main plate.

[dgedinyte]

Alright thanks man. You just planned my evening.

[dgedinyte]

Ok, so I went back to the beginning.reset the gaps, and then timed with the static light @ the 'F' mark. Then I cranked it to about 26-2700 RPMs. Adjusted 1 and 4 and then 2 and 3 at the advance mark. But when I get back down to idle, (1000-1100 RPMs) it's firing late on 1 and 4 but 2 and 3 is good. I'm thinking about trying to clip the spring for 1 and 4 on the spark advancer. SOOOO nervous though. Advancer itself is in really good shape. It is rust free. well greased and moves well. Should I dive in and clip the spring?

[evanphi]

You spend more of your time riding at full advance. Don't worry about it.

[PeWe]

...... But when I get back down to idle, (1000-1100 RPMs) it's firing late on 1 and 4 but 2 and 3 is good.good shape. It is rust free. well greased and moves well. Should I dive in and clip the spring? I'm thinking about trying to clip the spring for 1 and 4 on the spark advancer. SOOOO nervous though. Advancer itself is in really

Check Hondaman's advice. The 6mm stud that is attached to the crank keeping the adv unit in place might be bent.
Check if it moves sideways when running the engine. Maybe easier with electric starter only, kill switch off.

When you need to tighten the springs by cutting them is when you will see full advance too early (low rpm as 2000 rpm or less) with timing light despite F is OK with static timing. Probably not possible to turn the baseplate enough either.

[dgedinyte]

You spend more of your time riding at full advance. Don't worry about it.

She's got no go. she sounds good, I can ride her out of the driveway, but If I try to do more than 10-15 mph, she just falls on her face. No acceleration.

[Tews19]

DGE, can you make a video and post? This is becoming a personal challenge to help you get this bike running.

[Vinhead1957]

Try swapping the springs to see if it moves to 2/3

[dgedinyte]

...... But when I get back down to idle, (1000-1100 RPMs) it's firing late on 1 and 4 but 2 and 3 is good.good shape. It is rust free. well greased and moves well. Should I dive in and clip the spring? I'm thinking about trying to clip the spring for 1 and 4 on the spark advancer. SOOOO nervous though. Advancer itself is in really

Check Hondaman's advice. The 6mm stud that is attached to the crank keeping the adv unit in place might be bent.
Check if it moves sideways when running the engine. Maybe easier with electric starter only, kill switch off.

When you need to tighten the springs by cutting them is when you will see full advance too early (low rpm as 2000 rpm or less) with timing light despite F is OK with static timing. Probably not possible to turn the baseplate enough either.

The disparity doesn't change. It's the same amount off in the same direction. If I dynamically time it using the strobe light so that it fires on the F mark it won't reach full advance. If I do the same at high RPMs so that it fires directly at the full advance, it fires late at idle. I did check the stud but didn't detect a bend. Maybe it's too subtle for the naked untrained eye.

[dgedinyte]

DGE, can you make a video and post? This is becoming a personal challenge to help you get this bike running.

I am at the daily grind right just now. I'll crank it up when I get home. I'll post pictures both at idle and at full advance, and then a video of an attempted test ride. Oh and Vinhead1957, great idea I'll try that. I'm attaching pics of the springs for now.

[HondaMan]

The springs are symmetric: if you simply remove one of them, the advance happens twice as fast. Left-right makes no difference.

Check for a bent stud that holds the advancer to the crankshaft. If it is more than .010" out of alignment, one set of points will advance differently from the other. These get bent when the big nut gets pulled CCW, with the sparkplugs in the engine, in an attempt to "static time" the points. The engine must ALWAYS be pulled CW only by the big nut, preferably with the sparkplugs removed, or the shaft will bend.

[PeWe]

...... But when I get back down to idle, (1000-1100 RPMs) it's firing late on 1 and 4 but 2 and 3 is good.good shape. It is rust free. well greased and moves well. Should I dive in and clip the spring? I'm thinking about trying to clip the spring for 1 and 4 on the spark advancer. SOOOO nervous though. Advancer itself is in really

Check Hondaman's advice. The 6mm stud that is attached to the crank keeping the adv unit in place might be bent.
Check if it moves sideways when running the engine. Maybe easier with electric starter only, kill switch off.

When you need to tighten the springs by cutting them is when you will see full advance too early (low rpm as 2000 rpm or less) with timing light despite F is OK with static timing. Probably not possible to turn the baseplate enough either.

The disparity doesn't change. It's the same amount off in the same direction. If I dynamically time it using the strobe light so that it fires on the F mark it won't reach full advance. If I do the same at high RPMs so that it fires directly at the full advance, it fires late at idle. I did check the stud but didn't detect a bend. Maybe it's too subtle for the naked untrained eye.

Can the advancer unit rotate freely by hand and snap back by its spring force?  Your description is opposite when springs need to be adjusted. Sloppy springs will alllow full advance too early at low rpm. Springs hold the advance back.
Is it the correct advancer and correctly assembled?

[dgedinyte]

The advancer has the number 300 on it. It's a 1975 cb750K. I think that's right. But I've ridden this bike for three seasons since I bought it. So I know it was working at the end of last season. HondaMan I didn't know it could be off by that little and cause a problem. I only turn the motor with the kick start lever, so only ever forward. But maybe I bent that stud some other way. .010 is not a whole lot. As I said I might just have overlooked it. Thanks so much to everyone for taking the time to reply.

[flybox1]

You spend more of your time riding at full advance. Don't worry about it.

She's got no go. she sounds good, I can ride her out of the driveway, but If I try to do more than 10-15 mph, she just falls on her face. No acceleration.

sounds more like an air/fuel mixture imbalance (jetting or dirty carbs) to me....

[Vinhead1957]

I did want to mention the fuel filter in the petcock too!

[HondaMan]

I did want to mention the fuel filter in the petcock too!

+1 here: if the bike sat a long time (more than a month) with ethanol-laced gas in it, the gas is now "wet" and won't burn for beams, either. The ethanol strips any grit from the gas tank, and makes a paste with it to seal the above-mentioned screen in the petcock.