Topic: Knocking Sounds

[chucktrumpetsounding]

I just purchased a 1977 Honda cb750A Hondamatic, and I am having a few issues with it.  I am traditionally a scooter rider, but I just purchased this bike as my first.  It has all the attachments to make it look like a Goldwing.

1.  My ignition switch is screwy...which I know I need to replace.
2.  The cold startup makes strange whirling sounds...not sure if the starter is going out.
3.  My rear tire just went flat on me after riding it for 30 miles.  Not sure if its tubeless or tubed.
4.  ****There is this strange knocking sound that seems louder on the right side.

Any advice would be greatly appreciate.

Please see the video below:
1977 Honda CB750A (Hondamatic) Knocking Sounds From Engine while Idling

Sincerely,
Charles

[raymond10078]

Items:

1.  Yes - that switch is acting funky - replace it.
2.  Sounds like your starter clutch needs some help.  If you haven't done so, download the shop manual.  The starter clutch parts aren't expensive, but you do have to remove the left engine covers and the alternator to get to it.  You'll need a special tool (to remove the rotor off of the crank). 
3.  The rear tire is a tube tire.
4.  The knocking sound appears to be the primary chain - but is most likely still fine.  It sounded like the idle speed is too low, and a good carb sync will really smooth out the bike.  I noted that as your bike warmed up, the knocking went away - and the idle speed increased, too.  The fact that the sound goes away as the bike is revved up points to the idle/carb sync, too.  Since this bike doesn't have a tach, you can connect a electrical meter to the points to get engine speed.  I own/use a very old meter like this:  http://www.sears.com/actron-dwell-tach-volt-meter/p-00902165000P?prdNo=3&blockNo=3&blockType=G3.

[mrbreeze]

Has this bike been sitting? It sounds to me like it could use some carb work/cleaning.Do the 3K tune up before going through carbs. Carb sync comes last. The first time you started revving ......it sounded sluggish.

[Jerry Rxman Griffin aka MuthaF'er]

A GOOD tune up by someone that knows how to tune 750's is sorely needed for starters. It will cover a number of issues.

The starter clutch is definitely going out. As stated it's not a hard job and the parts are not expensive. And you will need a rotor removal tool which is not expensive either.

Download a manual and study up. You should be able to do the starter clutch yourself. Ask questions when you begin.

Are you talking ignition switch or starter switch?

 

[chucktrumpetsounding]

Has this bike been sitting?

The previous owner said its been sitting in his shed for 4 months.  I just rode it for about ten miles three days ago, and then I rode it yesterday for 30 miles.

[chucktrumpetsounding]

Are you talking ignition switch or starter switch?

Jerry, I was referring to the ignition switch.  The switch will turn on and off the electricity, but when the engine is on, it will not turn the engine off so I have to use the kill switch to turn the engine off.

The starter button works fine, but I was concern about the whirling sound...which is the starter clutch going bad.

[chucktrumpetsounding]

Do the 3K tune up before going through carbs. Carb sync comes last. The first time you started revving ......it sounded sluggish.

What exactly needs to be done on a 3K tune up?

[Jerry Rxman Griffin aka MuthaF'er]

Plugs, points, timing, carbs, cam chain adjust, valve adjust, ?? etc

[chucktrumpetsounding]

Where can I download the shop manual for the 1977 honda cb750a?

[raymond10078]

http://forums.sohc4.net/index.php?board=154.0

[chucktrumpetsounding]

I found this website with free downloads.

http://www.classiccycles.org/1852/3701.html

I am going to need help with this. 

I saw a lot of parts on Motorcycle Superstore.

Ignition Switch:  They have two listed...

Which one should I go with?

1.  Emgo for $24.95
http://www.motorcycle-superstore.com/37338/i/emgo-ignition-switch

2.  Emgo Universal for $10.99
http://www.motorcycle-superstore.com/30345/i/emgo-universal-ignition-switch

Starter Clutch:

I have no idea which one works with the 1977 Honda CB750A...
http://www.motorcycle-superstore.com/search/go#w=starter%20clutch

[raymond10078]

The link I provided also had the Shop Manual available - glad you found another source.

Ignition Switch:  The universal one is the WRONG one - the other one you listed is identified as a 750A switch.

Starter Clutch:  it appears that these parts remain available through Honda (items 8, 9, and 19).  I didn't find the parts on the web-site you linked.  Support your local Honda shop.  I'm out in the boonies somewhat, and I typically go to westernhillshondayamaha.com or partzilla.com - and often go to ebay with part numbers.  You may want to open up your bike and just order what you need (unless you just want to buy 3 sets of each part).

[mrbreeze]

From what I've heard here on the forum you don't want either of those switches (Emgo). They supposedly aren't up to the task and melt down leaving you stranded (unless you hot wire).

[raymond10078]

mrbreeze - you beat me to it.  was looking for the link:

http://forums.sohc4.net/index.php?topic=97034.25

[chucktrumpetsounding]

Can anyone provide a link to which ignition switch I need to get?

[raymond10078]

Here's the deal - as far as I know: EMGO is the only non-OEM source.  NOT TRUE - SEE POST BELOW FOR UPDATE!

Have you tried ordering a switch from Honda?  This site periodically reports success - even though some shops show the part as discontinued.

The problem appears to be that the EMGO switch contacts aren't made to handle the higher currents associated with CB750 loads.  Some people install relays to handle the headlight loads - to remove this load from the switch.  Your bike has been modified with the fairing, etc - who knows how it is really wired up.  The other possibility for you - take apart the switch you have - maybe you'll get lucky.

I see that there is a used one on ebay right now - but that is hit/miss.

[raymond10078]

I just received an e-mail from PartsNMore, and they tell me that thier ignition switch is NOT an EMGO.

So, based on the desire to avoid EMGO, if Honda lets you down, I'd order a switch from them.

http://www.partsnmore.com/parts/honda/cb750a/

[chucktrumpetsounding]

The ignition switch is actually working in shutting the engine off, but I think the wiring is backwards on it since I have to turn the key to the Parking position in order to turn off the engine.

I finally fixed the knocking sounds.  The carburetor was already sync'd, but the issue was very cold start ups with the idle throttle set too low.  I simply increased the throttle speed, and the knocking went away.

Now I need to change the oil and the rear tire.