Author Topic: Tuned a 71 CB750 today and have some advice (Read 12010 times)

chewbacca5000 · « **Reply #25 on:** May 10, 2015, 06:05:32 PM »

Got me a fancy dwell meter for $5 clams at the flee market today. Thanks for posting this up. Will be trying it out soon.

PeWe · « **Reply #26 on:** May 11, 2015, 02:04:48 PM »

This is how to do it, much easier and much much better result! Both points will easy be equal. Impossible with feeler gauges.
I think I'll make a video when the engine is warmed up and has a nice bubbling idle. 4-1 exhaust.

BobbyR · « **Reply #27 on:** May 11, 2015, 02:28:43 PM »

Dammit. I have a nice high end tach and dwell meter. Now I have to take out the PAMCO and put the points back in so it does not go to waste. What was I thinking?

brandEn · « **Reply #28 on:** May 11, 2015, 05:44:16 PM »

good info, subscribed

PeWe · « **Reply #29 on:** May 11, 2015, 11:21:07 PM »

Quote from: BobbyR on May 11, 2015, 02:28:43 PM

Dammit. I have a nice high end tach and dwell meter. Now I have to take out the PAMCO and put the points back in so it does not go to waste. What was I thinking?

Yes, points are nice! Time for a transparent ign cover to show the technical marvel!!!
I told the guys at last dyno run that the bike has points too, as in the old days....

Hondaman ign module might help too.

chewbacca5000 · « **Reply #30 on:** June 09, 2015, 10:05:56 AM »

So I got my dwell meter busted out, and figured out how to use the darn thing. It helps if you set it to dwell! Duh! O well got 1,4 at 24.5 degrees and 2,3 at 25 degrees.

So both are pretty close, but not at the magic number of 23 degrees.

Any tips to more easily move the points for adjustment? Seems like you need to subtract degrees to compensate for the tightening. I let it fall to 20 then tightened.

Any tips here would be appreciated.

DH · « **Reply #31 on:** June 09, 2015, 03:07:46 PM »

I dunno why, but the manual tells to set points statically first, then use the meter to verify correct dwell.
I always cheat and just adjust/fine tune with the engine idling. It always works out. May be a bit fiddly, but
the readings end good. Don't forget to check/adj. timing afterwards. I always use Genuine Honda parts. easier to dial in.

Restoration Fan · « **Reply #32 on:** June 09, 2015, 05:11:35 PM »

I assume this only applies to the manual points type systems and not for an electronic system like the PAMCO, correct?

BobbyR · « **Reply #33 on:** June 09, 2015, 05:35:37 PM »

Quote from: Restoration Fan on June 09, 2015, 05:11:35 PM

I assume this only applies to the manual points type systems and not for an electronic system like the PAMCO, correct?

Correct

RAFster122s · « **Reply #34 on:** October 02, 2017, 01:25:44 PM »

Quote from: MRieck on May 04, 2015, 05:25:25 PM

Quote from: chewbacca5000 on May 04, 2015, 05:06:47 PM
Hey Mike,

Can you post us up a pic of your dwell meter and show us where to look for the 23 degrees. Reading that you have to double the 8 cylinder reading for a four cylinder?
Here you go Chewy. Very simple. I have an big,older Craftsman unit that is analytical too but this unit is small and simple. Reasonable price too.
http://www.amazon.com/Actron-CP7605-Tachometer-Voltmeter-Analyzer/dp/B00062YUUS

Too bad this is no longer available for all the newbies starting to get into CB bikes...
now you have the digital CP7677 to choose from...
Try and find a new analog gauge dwell meter. I dare you.

David

flybox1 · « **Reply #35 on:** October 02, 2017, 02:51:49 PM »

I bought one of those Actron Dwell units. It was a POS. $:-\$
The closer my points dwell got to 24deg, the worse the bike ran.
Switched to to volts, and it read completely different than my two DMMs. The unit was bad, so reverted to the shop manual procedure, and have had no issues.

No way to calibrate it unless your point dwell is already set and you can check it, or, ship it back to Actron, for a fee.
If the unit is dropped, by you or during shipping, its gone out of spec.

Dwell function on a DMM is the way to go.

mrbreeze · « **Reply #36 on:** October 02, 2017, 04:58:50 PM »

Here's a pic of my Craftsman dwell meter I bought at Sears back in the 80's. The day I bought it paid for itself. A buddy paid me to do a tune up on his old Chevy pick up and I used it to set his dwell and adjust his idle. When I set dwell on my old Kawi LTD it made it run like never before. Feeler gauges will get you into the ball park but the dwell meter don't lie. My 750 has Dyna 2000 but the dwell meter is right in my tool box when for when the occasional old school ride shows up.

markreimer · « **Reply #37 on:** October 03, 2017, 10:30:37 AM »

This has got me thinking now. I did a vacuum sync on my K4 after verifying cam chain tension, valve clearances, timing (Pamco), clean carbs and no vacuum leaks. I have some really noisy clutch rattle when the lever isn't pulled in. I thought dialing the sync in PERFECT would help with that. It did help, but still sounds like it's falling apart a bit.

Do the mercury gauges really work that much better than vacuum gauges? I checked at idle and at 3K on the tach, blipping the throttle after each adjustment. The bike can idle lower than ever before, right down to 900 if I wanted (but I usually keep it at about 1050), but I still have that cacophony from the clutch basket.

Yamahawk · « **Reply #38 on:** March 10, 2018, 02:35:49 PM »

Checked my Dwell today, and it was at 27deg on both cylinders at 1100rpm, and using my Actron Dwell/Tach meter, and also my auto test digital multimeter, also 27.1 deg dwell on both cylinders. Does this mean my gap is too wide, and I need to adjust each side to 24deg dwell? Also, when I rev the engine, the dwell doesn't change much at all. Should the advance mechanism also advance the dwell? If so, would my springs be the culprit and being weak, allow the advance to already make the dwell higher...?
Questions, questions lol...
Charlie

BobbyR · « **Reply #39 on:** March 10, 2018, 07:32:39 PM »

Thanks for the nice tutorial Mike. I am struggling with removing the head to replace a leaky gasket. I have stock pipes and i agree the sound of them is special. Kind of like a turbine whine.

HondaMan · « **Reply #40 on:** March 10, 2018, 07:42:33 PM »

Quote from: Yamahawk on March 10, 2018, 02:35:49 PM

Checked my Dwell today, and it was at 27deg on both cylinders at 1100rpm, and using my Actron Dwell/Tach meter, and also my auto test digital multimeter, also 27.1 deg dwell on both cylinders. Does this mean my gap is too wide, and I need to adjust each side to 24deg dwell? Also, when I rev the engine, the dwell doesn't change much at all. Should the advance mechanism also advance the dwell? If so, would my springs be the culprit and being weak, allow the advance to already make the dwell higher...?
Questions, questions lol...
Charlie

The dwell should not change with RPM. If it does, the points cam is wobbling and needs to be shimmed.

Yamahawk · « **Reply #41 on:** March 11, 2018, 04:39:31 AM »

Quote from: HondaMan on March 10, 2018, 07:42:33 PM

Quote from: Yamahawk on March 10, 2018, 02:35:49 PM
Checked my Dwell today, and it was at 27deg on both cylinders at 1100rpm, and using my Actron Dwell/Tach meter, and also my auto test digital multimeter, also 27.1 deg dwell on both cylinders. Does this mean my gap is too wide, and I need to adjust each side to 24deg dwell? Also, when I rev the engine, the dwell doesn't change much at all. Should the advance mechanism also advance the dwell? If so, would my springs be the culprit and being weak, allow the advance to already make the dwell higher...?
Questions, questions lol...
Charlie
The dwell should not change with RPM. If it does, the points cam is wobbling and needs to be shimmed.

Ok, I do see the nut spinning slightly off center, or so it seems... the dwell is at 27.1 on the DMM and the Actron, but raises to 28 when throttle is applied and RPM increase to 3-4k rpm. I will look into the shimming, I believe it is covered under your 'Thoughts of Hondaman" in FAQ, correct? Now, should I also close up the point gap to get closer to 24 deg dwell, or am I good at 27 deg? And thanks, Mark!
Charlie

Keith · « **Reply #42 on:** March 11, 2018, 02:29:35 PM »

Old timers? As a mechanic in the 70's a dwell meter and timing light were mandatory items. I once watched a guy attempt to time a 427 Chevy with a vacuum gauge...he wouldn't listen to any of that timing light nonsense. He was a bit stunned when my GTO cleaned his clock. 😀

Yamahawk · « **Reply #43 on:** March 31, 2018, 03:46:38 AM »

After following advice to set the dwell to around 24 deg. my bike actually seemed less responsive and perhaps even 'passive' in contrast as to how it ran with the dwell at 27deg. Then I re-read this article, and figured out why...
http://www.motorcycleproject.com/text/sohcign.html

I am going to set the dwell back up a little, and check performance again, this means the gaps should be more towards the minimum setting, for more coil saturation. Now, I have the yellow Accel coils, which came on my bike, so perhaps they like the smaller gap, for more saturation time, vs the stock coils. I am not sure about that... but, one thing I am sure of, is the engine was more responsive, and had more balls with the higher dwell (less gap). I had originally set up the points gap to the lower side of the spec with static timing, and it seemed to run ok, set the dwell with my Actron and the DMM I have with dwell function, and it seemed like the point gap was really a bit more than I thought the adjustment would be. So, back to setting the timing first, then dwell, and see if I can get the performance tuned back in!
Charlie

PeWe · « **Reply #44 on:** March 31, 2018, 05:31:25 AM »

That is good reading! Optimizing the Standard SOHC4 Ignition System
I could finally get my point plate to stop wiggle around when open the 3 bolts when follow the hints written there.

Check the final ignition 1:4 + 2-3 with strobe lamp to verify proper setting at idle (around 1200 rpm) + full advance kick in after 2500 rpm.
When this is OK, the future maintenance will be a quick check with the dwell meter (with same setting) since it's the points bakelite that will grind off a little. They need to have lubrication.
Fun to use the old tech.
EDIT:
My bike has TEC points + Hondaman ignition + Dyna 5 ohm coils. Dwell of 23.0-23.5/V8 setting work fine. It might differ with another dwell meter.
The final point gap after adjustment change the ignition, smaller and smaller gap (higher dwell in degrees) by wear will advance the ignition.

I ran it without capacitors for a while since the points only work as triggers, very low current. Hondaman recommended to use condensers.
I noticed some intermittent single misfires at higher rpm's, condensers back in fixed that. Easy to hear when standing beside the Dyno.

Phoenix · « **Reply #45 on:** March 31, 2018, 12:43:05 PM »

Great start from Mike and the other notes. It seems there is now an agreed method of doing this. Could someone make a list of the steps required to set points and do timing using the dwell and timing light. My confusion is adjusting points to correct the dwell. I used to do this on my Vette monthly but that was in the dark ages. Thanks.

DV Red Herring · « **Reply #46 on:** April 01, 2018, 06:18:16 PM »

I have old 70's timing light and dwell meter by Sears. I got these after reading this thread a few months ago. My bike runs as good as I could ever hope for. These tools are invaluable for tuning these old bikes.

Charlie, I have the yellow Accel coils too. I never liked how it ran with D8ea plugs. Switched to DR8ES-L and it is way better.

Don R · « **Reply #47 on:** April 02, 2018, 08:48:18 PM »

I've been known to slightly loosen the points screws and bump them a LITTLE with a straight screwdriver and a small plastic hammer to fine tune the dwell/point gap. Just what works for me, your results may vary.
I also make a reference mark on case and points plate with a sharp snap punch. It gives you a good starting place when tuning it up, especially if you remove the plate.

BobbyR · « **Reply #48 on:** April 03, 2018, 06:38:33 AM »

Quote from: MRieck on May 10, 2015, 06:00:23 PM

Timing under actual running conditions rules....period.

+1

Yamahawk · « **Reply #49 on:** April 03, 2018, 08:34:04 AM »

Quote from: DV 750 Red Herring on April 01, 2018, 06:18:16 PM

I have old 70's timing light and dwell meter by Sears. I got these after reading this thread a few months ago. My bike runs as good as I could ever hope for. These tools are invaluable for tuning these old bikes.

Charlie, I have the yellow Accel coils too. I never liked how it ran with D8ea plugs. Switched to DR8ES-L and it is way better.

I think I am using the D8EA plugs, and will try to find the DR8ES-L plugs. Will let you know how the Accel coils like them! Couldn't find the D8ES plugs, as they are an older plug, but the D8EA's are more current... unless my memory has flipped the numbers lol.
Charlie

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Author Topic: Tuned a 71 CB750 today and have some advice (Read 12010 times)

DH