Author Topic: 1973 CB750 Need Help Last Run 1984 (Read 3519 times)

chewbacca5000 · « **on:** August 02, 2011, 06:05:51 PM »

Last Winter I came across what looks like a very nice 1973 with all original exhaust, seat, tank, and side covers too! None of the electrical stuff is working at all lights, horn etc.

I noticed that the original owner hacked up the ignition switch to make it longer. I replaced it with another still same problem. I have verified the ground and tried probing with a test light and with the ignition key in the on position I am only getting power to the main 15 AMP fuse. The other fuses have no power to them. Since it's a 1973 all the wires for the handlebar switches run through the handlebars.

I am thinking that my problem is in those switches or the headlight bucket. If anyone has any idea on how to test these switches out I would love to hear it!

Much Thanks!

fergie · « **Reply #1 on:** August 02, 2011, 06:10:47 PM »

If the po has cut up the harness I would just replace the whole thing with a un altered one.

chewbacca5000 · « **Reply #2 on:** August 02, 2011, 06:35:48 PM »

The PO did cut the wiring harness just extended the ignition switch kinda a homemade relocation kit. It didn't look like he cut into the wiring anywhere. It looked light he opened the right handle bar switch with start button, kill switch, and an ON / Off switch.

Does anybody know what this ON / Off switch is? It's not present on my 72 or 76, just my 73? Could this be part of my problem?

Stev-o · « **Reply #3 on:** August 02, 2011, 08:03:23 PM »

The on/off switch is for you headlight. I think it's a good thing, I keep it off when first starting the bike to keep battery draw lower.

Sounds like your going to have to o through the whole harness to fond your issue. Download a good wiring diagram from this site and do you have a multimeter?

Good Luck.

chewbacca5000 · « **Reply #4 on:** August 03, 2011, 05:00:57 AM »

I have a multimeter and a test light. Now what am I supposed to do with the multimeter?

magnum56 · « **Reply #5 on:** August 03, 2011, 05:23:24 AM »

Quote from: chewbacca5000 on August 03, 2011, 05:00:57 AM

I have a multimeter and a test light. Now what am I supposed to do with the multimeter?

The multimeter will provide a wider range of "accurate" information. Voltage, resistance, etc.
A test light is a quick check, but can "light" even with less than acceptable voltage levels.

Use the multimeter to determine battery voltage available, (i.e. is the battery fully charged), and provide feedback regarding voltage drop offs, which could help track bad connections.

Much of the individual testing related to your bikes electrical system components are tested using the various multimeter settings. Check out the link below for a starting point.

As the previous poster indicated, get a good wiring diagram, and take your time researching your connections.

http://www.wikihow.com/Use-a-Multimeter

chewbacca5000 · « **Reply #6 on:** August 03, 2011, 06:32:04 AM »

Ok, will do.

chewbacca5000 · « **Reply #7 on:** August 03, 2011, 07:20:31 AM »

Thanks for the wiki some good info. I have a wiring diagram and am going to test for continuity to make sure I have no breaks in the wiring harness. Seems pretty simple green is ground, black is hot, and everything else I'd imagine is switched hot through the handlebar swithes ie. lights, horn, start button etc..

My plan is to first test all the black wires then green / black to make sure no wires are touching inside the harness then move onto the handle bar switches. Does this sound like a reasonable plan of attack?

magnum56 · « **Reply #8 on:** August 03, 2011, 09:25:39 AM »

Not a bad idea, but it seems kinda tedious, and may get pretty confusing. You may want to try and tackle one piece of the puzzle at a time. For instance, you don't need working turn signals to have the bike start and run.

Here is another link I personally found quite handy. It allows you to "filter" out the various electrical components and subsystems, allowing you to easily focus on your immediate concerns. While it will not exactly match your 73, the basics are there, and when used in conjunction with your bikes actual wiring diagram, it may help you isolate the important parts related to your own troubleshooting.

http://oldmanhonda.com/MC/wiring750K1.html

Hope it helps, and good luck.

greenjeans · « **Reply #9 on:** August 03, 2011, 12:07:45 PM »

On my current bike, all the handlebar switches had creepy-crawlies in there. You can loosen them with out taking them off. Spray some electrical cleaner in there and blow them out with some compressed air. Repeat. There is not much to those switches. I'd do the same , 1 at a time to keep things in order, to every other connector that you can find - mainly in the headlamp. If the harness hasn't been hacked into, it's probably still good. Take a good long look at the ignition switch.

chewbacca5000 · « **Reply #10 on:** August 03, 2011, 06:23:51 PM »

I ran some test and it looks like the handle bar switch is good. I think I might take a couple days off from it then give it another try. Thanks everyone for the suggestions.

chewbacca5000 · « **Reply #11 on:** August 05, 2011, 04:35:00 PM »

I made a little progress if you can call taking the wiring harness from a parts bike and putting it on my project progress. At least I know the major components work ie. starter, directions, tail light. No headlight though.

The electric contact cleaner spray and compressed air seemed to work ok though. Compression on 1 is 165 and 4 is 175. kinda hard to get a good reading with the old style push in gauge. Should have enough compression to run ok. Could use a valve cover gasket. It has a little seepage at the outer head where the oil dowels go. Don't think I will worry about this now though.

chewbacca5000 · « **Reply #12 on:** August 09, 2011, 07:04:08 PM »

Turned out the problem was the wrong wire harness and missing ground pins in the handlebar controls. It looked like someone took them apart at some point and the pins fell out. My guess it was parked after that.

I looked at the VIN today and it does not match the engine. I have heard honda would randomly pull engines on the assembly line for quality control. Is there any way to tell if this is the original engine?

Thanks!

chewbacca5000 · « **Reply #13 on:** August 14, 2011, 03:55:18 PM »

We'll after much cleaning of everything I fired here up today on the 2nd start. I adjusted the timing and am not sure I got it 100% correct. It's on the F mark at idle and the first mark of the two marks for full advance. I know I am supposed to be between both marks.

The problem I am having is that it bogs down when I hit the gas. I am slightly retarded on the advance and my airbox is pretty leaky. I just want to get it down the road to test the clutch / transmission without spending $150 bucks on air intake / box boots. Choke does not help either.

Any ideas would be appreciated.

chewbacca5000 · « **Reply #14 on:** August 18, 2011, 06:21:45 PM »

I finally got though a bunch of junk with overflowing carbs, and oil mess today and had the final hurdle of airbox. The airbox isolators were so rock hard they would not go the carbs at all. I could get the bike to run right like that.

Out of frustration I took the air horns / velocity stacks out of the airbox and put them in the microwave with a wash cloth for 30 seconds to 2 minutes. Got the first one on other hardened up so I had to repeat individually. To my amazement I was able to get the bike to idle.

The carbs are 1 clip down from middle or second to last, 120 mains, stock exhaust with no baffles. To my amazement I was able to get the bike to idle and run good enough to get up to highway speeds!! I did get a little pop pop pop on decel and one big pop as well. 95% of the time it was fine. Didn't want to go too far as I didn't want to suck up too many bugs.

I am not going to keep it like this just felt good to know she is a runner. Another Thoroughbred added to the stable!! Can't believe the stock rubber velocity stacks will work without an airbox. Compare this to the woes of the pod people and velocity stacks sound like a good deal.

The only reason I can tell that they work is that they are not in the direct airstream like a pods are. I am wondering if cheap $20 dollar pods in the airbox will work as good?

chewbacca5000 · « **Reply #15 on:** January 07, 2012, 05:38:02 PM »

We'll things didn't go quite as good as I had hoped. After getting her all polished up she started leaking oil At first it was from the pucks and now I am not 100% sure where the oil came from so it's top end rebuild time. Pics to follow.

putnaja1 · « **Reply #16 on:** January 08, 2012, 07:02:08 AM »

Quote from: chewbacca5000 on January 07, 2012, 05:38:02 PM

We'll things didn't go quite as good as I had hoped. After getting her all polished up she started leaking oil At first it was from the pucks and now I am not 100% sure where the oil came from so it's top end rebuild time. Pics to follow.

I'm trying to follow your thread.. First you had a no-start condition from electrical issues and it looked like the previous onwer had hacked up parts of your wiring. Sounds like you have that resolved. Then you said you cleaned a lot of things, and it sounds like you've been through the carbs because you talk about what the mains are and needle positions- but I didn't read if you'd cleaned the carbs thoroughly, got the floats right, etc. Also you mention timing isn't quite right, and the exhaust is non-stock (baffles removed), and now you're changing up the airbox..

No offense is meant with this- but, it sounds like you are changing an awful lot of things all at once- which makes it hard to measure what improves things and what tuning of carbs is right for the rest of the bike, etc. Also, you said there is oil leaking from the "pucks" (Caliper pistons?) and you're not sure, so it is top end rebuild time?! You already mentioned it leaked from the valve cover gasket- could that be your leak issue?

Maybe you've got a ton of experience with these bikes, and you're well within your comfort zone, but if not- you might be making change after change after change, frustrated at the bike for not running like a swiss watch, and then diving into motor work- which may end up being really expensive, and then upon re-assembly the best case scenario may be that the bike would run the same as it does now with all the unresolved changes you've just made..

If it were me, I'd just stop, and take a second to re-assess. Do you know if this bike ran before it was put away? If it did, then fixing the wiring problem, then cleaning the carbs and resolving any age-induced issue should get it back to running.. I haven't priced the air-intake boots in years, but that would be my next attack- fixing stuff that is obviously broken. Unless you're looking to make this a custom cycle without stock airbox?

Hope this doesn't offend in any way- I'd just hate to see you blow a bunch of money, or have this bike end up in 20 milk-crates when it sounds like you are close to having a runner now.

Jason

chewbacca5000 · « **Reply #17 on:** January 08, 2012, 08:52:09 AM »

Hi Jason,

No offense taken. I am not an expert, but hope to be one day with help from guys like yourself and Hondaman I am sure I will get there eventually. I am still working up a learning curve, but am improving with each new challenge. I am good on the wiring and the carbs. The carbs initial issue was the float level adjustment which caused an overflow condition. I got that fixed by still had leaks, and this time it was the overflow tubes cracked on 2,3.

The bike was not running as strong as I would have liked that combined with the oil leak prompted the tear down. The current state is the engine is out and the top end apart. Got really bad leaky valves and am going to recut seat and have the valves re ground.

Now I am trying to decide what to do with the pistons, bores, and rings. All look really good so I am thinking of sticking them back in with new gaskets, and calling it good. Hondaman seems to think re boring is the why to go and brings back 10% of the power lost due to out of round bores.

All told I got about $700 into this bike original exhaust, seat, tank side covers etc. I am thinking of getting the cycle x piton kit and rebore to .5 over which would put me at $1000 and I will essentially have a bike that runs like brand new. Seems easy enough, but money is tight.

putnaja1 · « **Reply #18 on:** January 08, 2012, 01:32:42 PM »

Right-on man.. I'm not an expert either- and I think we all continue to learn. Sounds like you're doing awesome and making good choices for the money you've got invested. I shoulda never doubted you! :-) Now if only I can make the same headway with my BSA project!

chewbacca5000 · « **Reply #19 on:** January 08, 2012, 06:48:50 PM »

Quote from: putnaja1 on January 08, 2012, 01:32:42 PM

Right-on man.. I'm not an expert either- and I think we all continue to learn. Sounds like you're doing awesome and making good choices for the money you've got invested. I shoulda never doubted you! :-) Now if only I can make the same headway with my BSA project!

Good luck on that BSA project I had an XS650 what a PITA that bike was! Was one heck of a rush after you get it started. Kinda like driving a 2 wheeled jack hammer. I'd have to do a re-torque after every other ride.

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Author Topic: 1973 CB750 Need Help Last Run 1984 (Read 3519 times)