Bomber electrics problem

[royhall]

Hi. Got a weird problem that I haven't encountered before. Using the starter on the Bomber, the engine turns slowly and you get just 3 to 4 presses on the button before the battery goes dead. The engine does not start. This problem came on suddenly rather than getting progressively worse. The battery is pulled down immediately to about 5 volts. I guessed the battery was done so I replaced it with a standard lead acid type but it does exactly the same. I have taken the starter motor off and tried it on the bench but it seems to spin okay. I have a rebuild kit for the motor so I will rebuild it before it goes back on.  Other than checking all the earths I am at a loss, any ideas out there. Thanks.

[Deano400]

Hi Roy. Never worked on a Bomber before but I guess starter circuit can’t be much different to a 400/4. Battery connection to starter solenoid, solenoid connection to starter motor. So, if all the connections are ok and you have good earth to me that only leaves the starter solenoid. You could disconnect the battery and starter leads from the solenoid and use a meter on ohms setting to check the solenoid contacts. Will be open circuit until you press the starter button then should go to 0 (short circuit). If there is a high resistance, then that could be your issue.

[royhall]

Thanks Deano. To be honest most of the components in the starter circuit are 57 years old so I am thinking of rebuilding the starter motor, replacing the solenoid, checking all the leads and cleaning the contacts so everything is new. Don't know why I didn't do that at the rebuild as I replaced virtually everything else.

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[McCabe-Thiele (Ted)]

In my experience albeit mainly automotive of almost 60 years the order of decline has been as follows.
1. Poor earths.
2. Solenoids.
3. Main leads.
4. Starter motors.

[royhall]

Whatever it is it's serious. It pulls a new fully charged battery down to 5 volts in about 4 goes. That's a huge drain comparable to a full short circuit, maybe a chafed lead earthing on the engine. It must be between the solenoid and and (or) the motor as the battery stays fully charged until the button is pressed. And as I say it started suddenly, one day fine next day doing this.

[Nurse Julie]

Could it be the main earth cable Roy.
I had very similar symptoms on Kittie when Graham 1st built her, he used the original earth cable but this is what we found that was causing the problem.

https://www.sohc.co.uk/index.php/topic,15937.msg133703.html#msg133703

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[royhall]

Looks like I may be replacing the cables as well. Do we know a place that can make up new cables.

[Nurse Julie]

Looks like I may be replacing the cables as well. Do we know a place that can make up new cables.

Graham mades his own by unsoldering the attachments on the knackered ones and re soldering them on a new length of cable.

[royhall]

Sounds like a plan will check it out. But thinking about it I may have replaced the earth cable when I built it, or that could have been another bike. I defo got a cable from Vehicle Electrical Supplies at some point. Cheers.

[royhall]

Have found this site for custom cables. Not too expensive so I may strip out all the cables and replace it all.

Build your Battery Cable : Speeding AB (speedingparts.co.uk)

[K2-K6]

If you've an "amp  clamp" try a measurement of feed pre and post solenoid to at least see what you've got there.

Also try it off the engine (the starter motor) to see if there's significant drop as you'd expect.

Would give good comparison too, if you rebuild it.

A double check though .... pull plugs and turn engine over to see if there's significant resistance there that may be causing it. Unlikely, but not completely out of the question. Was helping someone recently with a starter motor "problem" which had been replaced, only then to let all the smoke out of the new one  ultimately he'd got a significant problem with crankshaft much to our consternation.

[royhall]

At the risk of looking stupid, what's an amp clamp?

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[K2-K6]

One of those multi meters that have something of a "lobster claw" sticking out the front, that to open and then close around the lead .... then it measures load going through that cable while you operate the circuit.

Essentially reading  resistance load on that circuit while it's fully cranked up.

[royhall]

I think I have that attachment on my meter, never used it. Will have a look.

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[K2-K6]

I hadn't previously used in automotive diagnostic.

Recently someone showed me on a suspect failed fuel pump (located inside diesel tank) by jumping across the pump relay loom contacts, so the pump line was permanently on, then checking with clamp on that jumper wire to see load through that supply point. It should have been drawing 4.7 ohm but was at 12.7 ohm and had in fact partially siezed to such extent it wasn't pumping much at all.  Certainly a good illustration.

Relevant info clip but on ac volts in this case https://youtu.be/z-KfZvbjyBY?si=vyNvatTYpJx9RwZ3 which may be of use.