Topic: Pamco ignition always at full advance

[Greenducky55]

So I recently rebuilt my entire bike. I had previously installed the pamco ignition with no problems. Saturday night I fire up the bike for the first time runs a bit rough get the carbs closely synced. Borrow a buddies timing light and the light flashes at the advance marks not at the F mark. I remove triple check and reinstall still no luck. So next I read up on weak springs so I cut out 1 coil and reinstalled. Much stiffer also lubes the unit up with some belray greese. but still remains at full advance at idle.  I am quite stumped at this time. Here's some info on the bike.

1975 cb750f originally had a f2 motor when I aquired it. But cam and bearing where shot but it ran.
Swapped in a k1 motor that I rebuilt with an 836 eBay kit lapped the valves and everything else is stock.
Uni pods and a motogpwerks stainless yosh exhaust. Can't get my carbs dialed in until I get this timing figured out.

[dave500]

does it advance past those full advance marks when you increase the rpm?

[Greenducky55]

When I last tried it remained the same. But I was not the man behind the timing gun at the time. I'll double check it tonight. When I install the pamco magnet rotor there isn't much room left for the advance to open. I can take a few pictures to explain.

[scottly]

Welcome Ducky. Is there room in the slots on the ignition plate to rotate it clockwise?

[Greenducky55]

There is but not sure if it's too little. I have my stock piece that attaches to the weights it and should see what the difference is.

[scottly]

Pic might help...

[brandEn]

Make sure the advance mechanism can twist to full advance and then snap back closed smoothly. If its binding up and not closing it would cause issues.

[Greenducky55]

Problem found. It's the actual pamco rotor it itself dose not let the advance mechanism relax  here's some pics

Advance by itself


Advance with stock cam mechanism thing lol you can see the space between the stoppers and the weights


And the advance with the pamco rotor installed


Huge difference in the gap available. So I figure I can just file out some more space in the rotor where it
Meets the pin seen in this pic


And I believe this should solve the problem as the diameter of both pieces are identical it should just be in the stops

[scottly]

Whoa!!! Don't take a file to it just yet. If it was machined wrong, give Pete the chance to make it right. In the last pic, it looks like the rotor hasn't been assembled properly with regards to the weights?

[dave500]

your rotor is assembled incorrectly,on the very end of the cams edge is a tiny index mark,on the hitachi unit you have it should point to the brand logo on the main plate,if you had a tec unit the index mark points to a tiny hole on the main plate.

[dave500]

try the pamco rotor 180 around?you have to move the weights to one side and let the pamco rotor drop down fully,the heel of the weight has to go into that slot in the pamco rotor,or it wont advance.

[Greenducky55]

Actually found what I believe the actuall issue may be. On the stock cam the pin actually dose not stop I from turning it has a machined gap in it to allow it to spin freely. Where my pamco dose not

[Greenducky55]

Turned the pamco rotor every which way no change

[Greenducky55]

And I sent Pete a message earlier I'll send him one showing him the problem so he can fix it.

[dave500]

you havent got the pamco rotor hooked into the weights correctly.

[scottly]

Actually found what I believe the actuall issue may be. On the stock cam the pin actually dose not stop I from turning it has a machined gap in it to allow it to spin freely. Where my pamco dose not

OK, I think I figured out what is going on: the K1 point cam has a groove inside where the pin goes when the rotor cam is fully seated. This locates the cam laterally on the rotor. Later rotor cams have a very thin flange on the bottom to locate the cam laterally, with no pin!!!

[Greenducky55]

Ex

Actually found what I believe the actuall issue may be. On the stock cam the pin actually dose not stop I from turning it has a machined gap in it to allow it to spin freely. Where my pamco dose not

OK, I think I figured out what is going on: the K1 point cam has a groove inside where the pin goes when the rotor cam is fully seated. This locates the cam laterally on the rotor. Later rotor cams have a very thin flange on the bottom to locate the cam laterally, with no pin!!!

Exactly as you are saying. And for reference in the pic of the pin and rotor from the side I know the weights are not installed. The pic was just to show the pin in the notch. Pete has been messaged

[scottly]

The change in the cam was very subtle; I only found out about it myself recently, and I've owned my K1 for over 30 years. I searched, but I couldn't find the thread. The simple solution would be to grind the pin down, or remove it, if possible.
Edit* Do you still have the F motor? If so, use the rotor from it!

[Greenducky55]

Have the f motor but couldn't find the rotor for some reason. Filed the pin down works perfect now.

[dave500]

well done,i just dug out some rotors and cams,the hitachi one on the right has the groove for the pin,the tec one on the left wont work with it,thats the problem you had with the pamco rotor.

heres a tec one on the hitachi rotor,it locks up and wont advance.

your weights will go into the pamco rotor like this and the expanding action will advance it with that pin gone.

maybe something for the tech tips section?

[KC_Northstar]

Does the K0 advancer have the same issue??  I have a Pamco, but haven't installed it yet.

[AJK]

Dear Gents,
I'm a long time reader, first time submitter. I have a CB750 K2. I purchased the PAMCO just yesterday and completed the install today. In the end, i got the bike running just fine after purchasing the 'ULTIMATE' kit from CB750supply.com

I ran into the same advance problem as described earlier. I.e. The advance mechanism being caught, thus not advancing due to the pin/slot problem. I'm in Australia so i decided to fix it myself. What i found was I had to drill a small 3mm hole (2mm would have worked as well) to make way for the pin. Its important to note which lug opening to drill as only one side needs doing. I.e. If you look at the 2nd and 3rd pictures, make note of the magnet position as this will tell you which side you need to drill. If you do this, you will get full travel with your advancer.
 I also found that I had to file a little off the grooves on the rotor, but don't do this unless you find you have too as your mileage may vary.
 Also, the last picture shows the PAMCO plate installed. I ended up drilling a small hole (bottom red arrow) so I could neatly insert a cable tie from the rear and hold back the cable from getting snagged on the rotor. I also found that the rotors face must be flush, so you might need to do some slight clean up with a sharp razor. i found I had to as my advance was a bit 'sticky' until i did this and also put a smear of grease on the face.

Apart from the above, the bike seems to be running quite well with plenty of bite.

One more note, I found that the timing was a bit jumpy (not much) at idle using the strobe light. Instead, I timed it at full advance at ~ 4000 rpms which seemed to be steadier and more consistent, then re-checked that it was in the ballpark at idle, which it was.

Hope this helps
cheers
Alex

[pamcopete]

That pin is there on a lot of the advancers, but the simplest thing to do is just file it off.  It serves no purpose with the PAMCO rotor.

That was specifically mentioned in the installation instructions:

http://www.cb750ignition.com/installation3.htm

I see the problem in the picture above with the stake mark used to secure the magnet. Will correct that. Thanks for the tip.

[AJK]

Hi Pamcopete,

I didn't realise you had an update of the instructions, hence did not know about the pin. The reason is because when you go to
 http://www.cb750supply.com/products/5/electrical
 as I did, then follow the link, it takes you to a previous version of your instructions which doesn't include the detail about the pin. I.e. It takes you to this link instead
http://www.cb750ignition.com/installation2.htm
which is what i worked from.

You might have to get onto them about it so they can update their link to your latest instructions.

That aside, I actually prefer to leave the dowl in there (not filing it away) and drill it anyway. Most wont care but i like to keep 40 year old parts intact if possible as they might be useful to someone else who has a 750/4 as a spare.

I rechecked the timing at idle and watched the advance again tonight. All is working fine as expected. The bike also started straight up from cold, although it did this before on the points. As an aside, my main reason for the upgrade to your system was that I was confronted with 40 yr old coils and leads that were botched up by a previous owner. Not forgetting to mention that my plug caps were gone. They were actaully leaking spark and I could only tell this at night with the engine running, seeing the spark arcing on 40 yr old plug caps. Your suggestion on the site to upgrade the plug caps is a good one.

I've just installed new spark plugs tonight and experimenting with 0.88mm gap. The 17-6903 coils in the pack should handle that ok i think. Unless i see problems, i'll keep it at that.

Overall, seems to be a good kit for the money.

cheers

[70CB750]

You gonna love it.  I installed Pamco and same coils as you in 2011 and did not touch it since.  Makes it 9000 miles so far.

My reasons were to avoid points and also - as you - cables from original coils were shot.