Topic: 1971 honda cb 750 project / Update problem changing oil

[MRieck]

It says 1200 on the tach but being mechanical and old as hell who knows what it actually is. Do you have a tach/dwell meter to get an accurate reading?

[Garystratos201]

It says 1200 on the tach but being mechanical and old as hell who knows what it actually is. Do you have a tach/dwell meter to get an accurate reading?

No I dont. I dont think its the idle setting. I`m concerned about the old coils, wires and spark plug caps and the ponts and condensers.........Gary

[iron_worker]

It definitely sounds like the miss is phasing in and out.

Measure the resistance of your plug caps and plugs. I believe they should both be around 5k ohms each. You could also check that you're not getting an arc anyway. In a somewhat dark area you can mist water around the plug wires and see if any arcing occurs.

Have you replaced your points and/or condensors? Did you set the gap and timing? What did you set the gap to?

Have you checked for vacuum leaks? I don't think that's it but worth a check.

From what I can tell, coils rarely fail so I wouldn't be suspect of the coils right away.

IW

[Garystratos201]

New carb boots both intake and breather so I dont think its a vacuum leak. I havent replaced the points and condensers, points setting range is .012-.016 inch I set to mid range at .014. I set the timing with a test light I know thats not the best way but I dont have a timing lite. I dont have a way to test the spark plug caps but the plugs are new NGK D8EA. When I cut the ends off the plug wires I did notice that they still had some corrsion showing but I couldnt cut off anymore or they would be too short.  Thanks for the help IW.............Gary

[Johnie]

Had the same issue with my K3 and only had 5,300 miles on it when I bought it a year ago. I figured points are OK with so few miles...wrong...new points, condensors and plug caps she runs like a new bike. As a general rule I will always change these on any of my acquired bikes now. I should have known better...those items were 40 years old...what was I thinking.

[Tews19]

I always have a spare spark plug and will pop it in to see if each wire making the same size spark or even a spark.

[Tews19]

Another thing I do is feel each head pipe. Maybe if one pipe isn't as hot as the rest you can start with that.

[iron_worker]

Since it seems like the issue is "on and off" I wouldn't suspect a spark plug. I think they are more of a work or don't work item. Unless the porcelain is cracked and it's arcing some of the time? Seems unlikely.

Static timing it should get you very close to properly timed so I wouldn't think that is your problem either.

Since condensors are cheap I would start with new condensors.

Also, are you points new? Check the surface of the points for pitting or uneven wear.

You could also measure the voltage to the coils while running. Check voltage at the battery as well. Is it charging? Is your battery good?

IW

[Tews19]

When I mentioned spare spark plug that was to see if the coils are producing spark. The you can see if it is intermittent.

Looking forward to the resolution. Keep plugging away

[Johnie]

It is all process of elimination...try one thing and then move on to the next. Just keep at it. For sure change out the condensors if you can not afford to do those and the points. After all those years those will go bad. Some get worse as they heat up and act erratic.

[Garystratos201]

Thanks guys for all the advice. I`m going to start with points, condensers, and plug caps. Has anyone had experience with aftermarket points and condensers or would I be better off going with OEM ?.............Gary

[iron_worker]

Condensers ... dont' think it matters to much either way.

Points... definitely go OEM. The cheap repros are slightly different geometry and can make it really tough to get it timed up right.

Plug caps ... I'm not sure. I think I'm running NGK repros now and they seem to be fine. Well ... last year before I tore it all apart. lol

IW

[Garystratos201]

Thanks IW I`m just going all OEM What the heck I`m in this deep.lol If this doesnt correct it I`ll move to the plug wires. There are several good threads on how to replace the wires only..........Gary

[Stev-o]

Gary - these coils rarely go out. +1, get good points and caps are cheap, about $3 ea.

[Garystratos201]

Gary - these coils rarely go out. +1, get good points and caps are cheap, about $3 ea.

I`m not so concerned about the coils as much as I am the plug wires being corroded. Does that matter ?................Gary

[Kevin D]

Old spark plug caps are bad news.
Fouled spark plugs are bad news. I took hondamans advice and got the Densos.
Anything but clean gas is bad news.

C'mon GS you're almost there!!! 

[Garystratos201]

Old spark plug caps are bad news.
Fouled spark plugs are bad news. I took hondamans advice and got the Densos.
Anything but clean gas is bad news.

C'mon GS you're almost there!!! 

ok  so what about the wires ?..............Gary

[Kevin D]

Some change the wires.
Most everybody clips the ends a bit to get to fresh copper.
On mine, the outer jacket was as stiff as could be.
The inner, insulating part was soft and supple.
The copper strands will likely be OK.

15000? ohms from plug wire to plug wire.
5000 ohms across the plug cap or
25000? ohms from plug cap to plug cap.
5 ohms across small wires.

[Garystratos201]

Simple question........Corroded wires,  could they cause the condition I described earlier ?..........Gary

[Kevin D]

sorry I'm not more help. I have only the experience of one bike.
tired, long day today, court tomorrow.
The plug cap has a screw thread intended to cut through surface crud.
The resistance test should help you find bad connections caused by corroded wire.

And yeah I guess corroded wire could cause rough running.
Can you see copper color with the caps off?
have you snipped the ends?
Got an ohmmeter?

KD (pooped) out.
 

[Garystratos201]

Can you see copper color with the caps off?
have you snipped the ends?
Got an ohmmeter?

Lets see Kevin; No, Yes, No.  New points and condenser plate assy and caps wshould be here early next week. If that doesnt cure the problem then I`ll move to the plug wires. If that doesnt work I`ll seek psychiatric help.lol.........Gary

[Kevin D]

If that doesnt work I`ll seek psychiatric help.lol

Can I have the appointment after yours?
Its been said here that you will never see motorcycle parked in front of a psychiatrists office. Its late April and I havent yet had a ride/my therapy session this season.

Better idea: get your bike going, get mine going, skip the shrink.

[Garystratos201]

Thats works for me Kevin..........Gary

[Kevin D]

IIRC, the wires are plated/tinned, and you only see the copper at the very tip of the strand.

[Garystratos201]

At long last she is street legal. I got the tag today and the title transferred. Waiting impatiently for my new points, comdensers and spark plug caps. There on the UPS truck out for delivery as we speak. Have two softball games tonite so probably wont get them in until tomorow. Hopefully that will cure the problem and I will be ready to ride...........Gary