1981 CB750K - Repair/Tune-up

[cdaiscool]

This is actually the 2nd video. Bike is warming up right now.

I think its pushing so much gas through it that it is keeping the exhaust cool to the touch. It's mildly warm, but NOT hot whatsoever. Time to go tune it out.

[Half-Caf]

Won't let me view it

[cdaiscool]

Try 'er now!

Here's the first one, after I fixed the carb issue.



Now, the battery is dead and she doesn't want to fire. WHY CAN'T I JUST HAVE A BREAK??

I burned my hand trying to get to #2's pilot jet, and said fuck it, someone suggested doing a carb sync, then doing the pilot jets, then doing a vacuum sync again. So I hooked up everything, went to start 'er again... and she's dead.

I don't have the patience for this.

[cdaiscool]

I'm done. I'm sick and tired of dealing with this fucking bike.

Went to jump it off the Integra's battery. It is out anyways. No change.

Went to jump it off the truck's battery (truck not running). No change. She is a dead battery, and probably bad given how old it is. Just like everything else on this bike.

No idea how I'm going to get it running at this point. I've poured WAY too much money into it, it STILL isn't bringing me any joy, nor saving me money, and I guarantee that if I get this done, the pilot screws adjusted, the vacuum done, and everything else? Something else will still go wrong.

Any hints or tricks for how I can jump this damn battery, without having something blow when I do it? Even though the handles are painted and the frame's painted, I'm avoiding touching the positive to the frame so I don't fry anything.

[cdaiscool]

Well, pulled the battery, and went to Auto Zone to have them charge it for me.

After waiting 15 minutes for them to literally help 2 customers, I put my battery on their counter. "Need a new battery?" Glad to know they prefer selling 'em.

"Nope, just want this one charged. But I just noticed she's a tad low on fluid. Would you mind throwing some water in 'er before you charge it?"

"Ummm.... *looks at boss* Can we do that?" "Nope."

"Okay... mind giving me a bottle of water and a screwdriver?"

"Can't do that either. Can't let you fill it, even outside. If it blows up, I'll get fired."

"I'll go off the property. It's not going to explode. I'm not a smoker, I'm not around sparks."

"I don't care."

I was not happy. Usually they go outta their way to help me. These guys just didn't want to be there, 'twas obvious by how they were helping their customers etc.

Went and grabbed some Taco Bell, went and got some distilled water, threw it in the battery and hooked up the battery.



And then she died a bit later. Now she's dead again. So it still needs a charge. Drats. And since she won't run until charged, I think I'm out of ideas guys. I think I'm out of ways to keep working on 'er.

Also, apologies for my outburst earlier. Was quite frustrated. I've worked all week on this thing, and keep getting pulled down. Have to live with the fact that I don't think I can bring the bike with me to Ann Arbor. Not this week, at least. I hate the idea, too.

[cdaiscool]

Also, as she warmed up, Carb 2 kept dipping down to -7 on the gauges. And that's what she's supposed to be at, per the dealer.

I think my motor's healthy.


Now if only I could get this battery charged tonight. :/

[cdaiscool]

Question: if I get it running, can I just keep the idle at 3k rpm and tune it there? I'm guessing no...

Otherwise, can I just leave it at 3k rpm for like 20 minutes and expect it to charge the battery so I can run it for a while at idle without killing the battery?

Or do I need to charge it for a few hours on a battery tender or other suitable device so I can get the pilot screws adjusted proper?

I need to find a way to get the bike to run @ idle without dying due to no spark from battery...

[Piute]

I use a car battery and jumper cables ,not wonting my new bike bat. to go dead to many times(not good)It's not A marina bat.(thats made for that)Gave it (bike bat.)a good tender charge(2.5hr's before light went green) Ready for morning carb install myself.

[TOOLS1]

I would recommend charging the battery, and taking a break. I am guessing your pilot circuits are still dirty. Did, you remove the pilot jets to clean them?
TOOLS

[cdaiscool]

Exactly what I was thinking as well.

So I looked closer at the terminals on the battery. They were good and rusted. So I took a brush to the screws that hold the battery terminals to the leads for the bike. Now she'll spin good n fast when trying from the Integra battery.

Figuring that I wanted the battery charged for when I get back to messing tomorrow, I decided to go to Wal-Mart and get a charger. $25 later...



 and



So then I thought... while that's charging, what else can I get done? Well, my dad earlier commented that if I cut the excess out of the spark plug wires, I'd get a hotter, more direct spark. I said less wire on a hot valve cover probably ain't  bad, so...



Then I remembered I still wanted to officially finish up the chain/sprocket portion.





And been working on a surprise project for this. You'll see it when the bike's together.


I'm officially excited again. Now to get this beast finished!

[cdaiscool]

I've considered changing the battery, but I want to see if this one's got life yet. The charger's a trickle charger with a microprocessor, so it's good for winter storage use as well.

As for the pilot set-up, I removed each one and sprayed cleaner in there when they were apart. I got a nice clear spray per the instructions.

Bottom of page 18:

http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revD.pdf wrote

Cleaning the Slow Speed Jets
There’s nothing more important for proper carb operation than having clean slow-speed jets, so I’m going to dedicate several pix to help you.

If the jets were removable, you’re golden - just blow them out with some carb cleaner before reinstalling, but if the slow-speed jets were the pressed-in variety, and you could not remove them in the carb breakdown section, you need to prep them for spray-down: Take that E-string we had you get, and push it through the center hole down in the center tube – don’t force it; you may need to twist it as you go, but you want to be able to push down about 1-1/2” of the E-string down the hole to be sure you’ve cleared the slow-speed jet. They gunk up easily and will cause no end of grief if you don’t get them cleared. Don’t short-change this step – it’s critical.

Once cleared with the E-string, here is where you want to modify the straw. Take enough electrical tape and wrap it around the end so that it will fit fairly snug in the slow-speed jet tube. Hold a thumb over the primary main-jet hole and your index finger over the lower air cutoff hole and spray. If the slow-speed jet is truly clear, you’ll get a bubbling (or stream) of carb spray out the pilot screw hole. Don’t consider the carb cleaned until you can do that!

So I'm guessing it's clean? I could obviously be wrong, especially if these instructions are incorrect.

[shinyribs]

Buddy,you just cant get a break.But you just keep pushing and getting it done! It takes time and outburst are just part of the fun

Put those lil valves in your vacuum tubes to restrict the pulses out of the needles.You will be glad you did.

[cdaiscool]

... What little valves? I thought the brass tubes were supposed to. Obviously they don't, but I thought that was the original intended purpose...

[shinyribs]

Some of the kits have little valves that go inline with the vacuum lines. Mine are 90 degrees and have a little thumb screw that you turn. The needles jump around so much they are basically unusable without them IMO. You can kink the hose and get the same effect.

[cdaiscool]

I found 'em after you said that! I just went out to put the rear sprocket cover on. Now I just gotta find those dang bolts...

I really should figure out a way to keep myself organized. Or just get new bolts...

[cdaiscool]

Another day, a solved issue.

The battery is fully charged, and WOW does it spin the motor fast. It definitely was low on juice for some time.

Another issue solved, another new one.

It doesn't want to start. It acts like it does. But doesn't. I pulled all 4 spark plugs, and they all have spark. I just verified each one is on the correct coil.

Coil 1 - Cylinder 1
Coil 2 - Cylinder 4
Coil 3 - Cylinder 2
Coil 4 - Cylinder 3

I smell fuel coming out. Plugs 2, 3 were wet but 1, 4 smelled like fuel. I can't see the bike randomly losing compression overnight, while sitting.

When I took the battery out last night the first time, I did accidentally touch the positive to the body and sparked a little. However, it DID run for app. 10 minutes after that. That was when I finally got the vacuum gauges to show what was going on. So I don't THINK I messed up any electronics...

[cdaiscool]

 I feel like a moron.

I just remembered - I had not gotten gas in a while, some leaked out while she sat, and I've been running it on 'ON' versus 'Reserve'.

I wonder if I'm out of gas. Gotta get food and run to the bank, but then will throw 'er over to 'RES' and see if she fires.

[shinyribs]

Sounds like it tried to take off. Couldnt see in the video,did you give it some air? You know,work the throttle just a little ? Whether you have the choke and carbs tuned perfectly or not,a carburetor still needs a little finessing at times. Very rarely can you start any carbureted engine without touching the throttle or something.

[cdaiscool]

Oh I worked the throttle like Congress is working America....


It was out of gas. I checked the tank as I left, she was pretty empty. Just got back, put the petcock in a different spot, set it to reserve, and she finally started after about 15 seconds.

I'm betting that's why she died last night, too, instead of the battery just dying and being unable to provide spark...




My kitty is being cute right now, so I'll run out in 30 or so to get more go-go juice, then start working to adjust the pilot screws then vacuum sync. Also need to find my shifter and the sprocket cover's bolts yet. Then it'll be bolt up and go.

[cdaiscool]

Turned all 4 pilot screws OUT per FSM, and she dropped idle! SO FUCKING EXCITED.

However, I think there's an issue with the FSM. It says to now start turning the screws IN, until she drops idle. But in = increased idle. Or will it indeed drop idle as I go in, aka clockwise, on the pilot screw?

Also, 1, 3, 4 exhaust pipe are burning hot. 2 is still warmish-cool. I hope this will rectify that. There may be something wrong with that cylinder after all.

Also, I pulled the plug on that cylinder. No change whatsoever. Of course, I did this while she was at 3k rpm. I did NOT do it at idle rpm. As it warmed up, I had to adjust the idle screw out to drop 'er down.

Once she's properly tuned, I'll make a video of her. I just hope I'm doing this right. So scared that I'm not...

If the pilot screws are too rich or too lean, will that mess up the higher rpm range, say 3k and above?