Author Topic: CB750 Ignition Help (Read 6119 times)

surein · « **on:** September 19, 2011, 07:52:54 AM »

Hey guys,

Need some thoughts on what is causing my ignition to malfunction. I got the bike at the beginning of summer and no issues starting. Recently though I now have to randomly turn the key on/off several times, have to neutral it a few times and switch the kill engine toggle back and forth (not sure if I really even have to do this) before the bikes even turns. Doubt it's the battery since I can't even kick start it. This doesn't happen every time but it does happen frequent enough. Starts strong once it finds a turn

I'm sure someone out there has experienced this before

Thank you

cameron · « **Reply #1 on:** September 19, 2011, 07:57:37 AM »

question:

when it is giving problems, is the problem solved by pulling in the clutch?

surein · « **Reply #2 on:** September 19, 2011, 08:45:13 AM »

nope - clutch doesn't help. It acts up whenever and quite randomly. It eventually starts but I'm afraid one day it might strand me

surein · « **Reply #3 on:** September 19, 2011, 10:23:27 AM »

okay so I guess it's the battery. I just tried to start and same issue. Kicked and it started. Will get a meter

Steve_K · « **Reply #4 on:** September 19, 2011, 02:36:01 PM »

Does your lights come on? High beam neutal, oil light up? No horn, brake lights, ect? If not, key switch going wonky?
Steve

surein · « **Reply #5 on:** September 19, 2011, 04:01:02 PM »

all the lights are working properly - so you think it's the ignition switch?

cameron · « **Reply #6 on:** September 19, 2011, 05:03:54 PM »

The 'have to neutral it a few times' thing is getting to me.

Isn't there a circuit that senses neutral.. and disallows starting if not in neutral?

I keep thinking that is it.

surein · « **Reply #7 on:** September 19, 2011, 05:12:11 PM »

I neutral hoping that's the cause, but it definitely not the case since I am able to kick it over now. It must be electric ignition related. No idea where to even start - no pun intended

TwoTired · « **Reply #8 on:** September 19, 2011, 05:28:11 PM »

You could tell us what year and model you have. ...and what's been changed to the electrical since the showroom floor.

Do you have a wire diagram for your bike?

A multimeter? Knowledge to use it?

surein · « **Reply #9 on:** September 19, 2011, 06:44:04 PM »

it's a 73 CB750. The only electrical upgrade is the Hondaman ignition I just installed two days ago. The malfunction started about a month ago so I did install the transistor correctly.

I can get the wiring diagram from the forum - no issues.

I haven't used a multimeter before. Is the idea to use the meter along the path of current until it tells me where the short is?

TwoTired · « **Reply #10 on:** September 19, 2011, 08:34:44 PM »

Start with the basics. Tells us which make and model meter you have. Some are operated differently than others.
If you know how to set the instrument to measure voltage, then apply the probes to the battery terminals and note the reading.

Next, I suppose is to determine if the same voltage you measured at the battery is getting to the Blk/Wht wire going to each coil. The Red probe will go on that wire and the Black probe will go on the engine case where there is no paint coating (or any convenient solid green wire).

Cheers,

MrGardman · « **Reply #11 on:** September 20, 2011, 04:52:00 AM »

Since you mentioned about the engine not actually turning over with the starter, I would start looking at the battery, solenoid and starter connections. I am thinking solenoid issues to begin with.

surein · « **Reply #12 on:** September 20, 2011, 07:18:15 AM »

I have to say kick starting the bike is invigorating.. but sometimes it's nice to feel like I'm driving a ferrari with a push button start.
Will get me a mulitimeter and learn how to read it - Thanks

surein · « **Reply #13 on:** September 26, 2011, 07:09:22 AM »

So I got a multimeter and checked the battery. Voltage was at 12.4 when the bike was off and went to 11.6 when I turned it on. The solenoid read the same 11.6. I tried to start with the button and it started. But no luck two hours after when I went for a ride. I guess I should check the voltage when it didn't turn over with the starter button.

Johnny5 · « **Reply #14 on:** September 26, 2011, 10:16:33 AM »

Quote from: surein on September 26, 2011, 07:09:22 AM

So I got a multimeter and checked the battery. Voltage was at 12.4 when the bike was off and went to 11.6 when I turned it on. The solenoid read the same 11.6. I tried to start with the button and it started. But no luck two hours after when I went for a ride. I guess I should check the voltage when it didn't turn over with the starter button.

That sounds about normal. What does the voltage jump to when you rev it up? Should go to around 14v. If so, I would say your battery and charging system is good. Are you sure you dont have a loose wire/connection at the kill switch going into the headlight bucket? Possible loose ignition wire?

Rgconner · « **Reply #15 on:** September 26, 2011, 10:35:28 AM »

Quote from: Johnny5 on September 26, 2011, 10:16:33 AM

Quote from: surein on September 26, 2011, 07:09:22 AM
So I got a multimeter and checked the battery. Voltage was at 12.4 when the bike was off and went to 11.6 when I turned it on. The solenoid read the same 11.6. I tried to start with the button and it started. But no luck two hours after when I went for a ride. I guess I should check the voltage when it didn't turn over with the starter button.

That sounds about normal. What does the voltage jump to when you rev it up? Should go to around 14v. If so, I would say your battery and charging system is good. Are you sure you dont have a loose wire/connection at the kill switch going into the headlight bucket? Possible loose ignition wire?

+1 on loose wires.

IF you start checking connections, get some contact cleaner/water barrier spray and hit them up as you check them.

This will help reduce power loss in what is a "Just enough power" system.

surein · « **Reply #16 on:** September 26, 2011, 11:13:21 AM »

loose wires?!? I have a feeling this is going to get ugly..

Johnny5 · « **Reply #17 on:** September 26, 2011, 11:48:58 AM »

Quote from: surein on September 26, 2011, 11:13:21 AM

loose wires?!? I have a feeling this is going to get ugly..

Consider yourself lucky if it's just loose connections. Check each connection, one at a time. Clean and reconnect. That's to be sure nothing gets messed up. Always good to do at least once anyway. These are old bikes with old wiring.

surein · « **Reply #18 on:** September 26, 2011, 01:42:21 PM »

true - just that there's a good chance I might mess this up more LOL!
What's contact cleaner/water barrier?

surein · « **Reply #19 on:** September 26, 2011, 01:53:57 PM »

Love google. So clean it first and then apply some dielectric grease?

Johnny5 · « **Reply #20 on:** September 26, 2011, 05:19:52 PM »

Quote from: surein on September 26, 2011, 01:53:57 PM

Love google. So clean it first and then apply some dielectric grease?

Radioshack sells contact cleaner. Comes in a can and has a brush on the end to clean the contacts. Works well.

octagon · « **Reply #21 on:** September 26, 2011, 07:32:30 PM »

doesn't hurt to find all your ground connections and clean them well

cameron · « **Reply #22 on:** September 27, 2011, 07:53:55 AM »

Except your sanity. Might hurt that a little

surein · « **Reply #23 on:** September 28, 2011, 06:47:59 AM »

So I cleaned and greased all contacts (except for my ground connections), even the non black/white wires and the bike started on the first push. I took it our for a ride beaming with pride and confidence. Even thought I will tackle the apparent oil leaking into my combustion. Head gasket issues - nothing to fear.

This morning.. alas. No love. I kept pushing for a few minutes till it finally made contact.

Could it be the starter itself? I notice all the wires go through the brake lever. Are there connectors inside?

Patrick · « **Reply #24 on:** September 28, 2011, 07:17:52 AM »

It probably wouldn't hurt to clean the contact on the starter button itself, inside the right hand switch. It sounds like your starter safety module is acting up, but I don't think a '73 has a starter safety module - if you have the stock harness. Do you have a red electrical component down near your fusebox?

Patrick

News:

Author Topic: CB750 Ignition Help (Read 6119 times)