1981 CB750K - Repair/Tune-up

[shinyribs]

DANG! That thing sounds A W E S O M E !    Glad you got it going.




                                  How can I make your exhaust note my ringtone???

[cdaiscool]

2 ways that I know of.

1, come over, I'll start 'er up, you record the sound, then press 'make ringtone'.

2, do this http://www.vidtomp3.com/

Then take mp3 and make it into ringtone.

But #1 sounds better.

[shinyribs]

I was just kidding,but you can do that?! Coooool.

Oh,btw...race on a closed course...yeah right     Integra?

[cdaiscool]

You can do anything you want!

And no. I was filming, so not the Integra. It was only in a couple races last year, my clutch gave way quite early. So I'm looking forward to getting it out there this season. I've got a couple people waiting for rematches. They don't know what they're in for.

I'm kind of thinking about running it some more. Perhaps even working on 'er a bit more yet tonight. It's only 1:14 am. Not like it's LATE or anything...

Do you think I'll get in trouble if kids walking to school see me working on it?

[cdaiscool]

Okay people. So because my bike is idling at around 900 rpms, does that mean that its essentially fine and just needs a carb sync? Or do I need to still adjust the pilot jet some?

How exactly do I do that? I know I have to run the bike as-is for like 20 minutes so she gets warmed up, and open the choke, and that's all after the airbox is set up properly. But after all that...

Please. School/teach me, o wise Nabble!

[shinyribs]

I'm far from wise,but I just set my idle mixture screw by ear. Like I would on a Holley.If you are adjusting the screw in the direction that gives it more fuel,and idle speed increases,that means it needed that extra fuel. If there is no change in idle speed then it is just extra,wasted fuel. Kinda gotta fiddle with it and get them all set evenly in the end,but thats how I do it. Quarter turn at a time on each carb til it reaches a max idle speed( without changing the actual idle speed screw) and call it a day. Just my way...could be wrong...wouldn't surprise me if it was.

[cdaiscool]

From the FSM:



From the guide I used:

Pilot Screws
Slide the spring on the pilot screw, followed by the flat washer then a new O-ring. Screw the whole assembly into the body of the carb. Screw it all the way in until you feel resistance – DON’T force it, or the little neck below the threads will give way, and you’ll be getting out the drill and EZ-Outs®. Once the flat section below the thin neck is even with the bottom of the pilot screw hole, you’ll be bottomed out. On the 900, 1000, and 1100 carbs, you will see a bit of the pilot screw tip sticking up through the bottom of the
24 © 2010 – MacGregor Carb Cleaning Service
carb throat; you won’t be able to see that on the 750’s. Now back the pilot screw out the following amount:
• 750’s – 3 turns
• 900’s – 2-1/2 turns
• 1000’s and 1100’s – 3-1/2 turns



Yep, I'm pretty certain I've discovered why she's running rich.

Now to just get them mixed properly. And I hope I've got a screw driver that'll work on these bad boys.

[cdaiscool]

Oh, and the reason why I ask though I have the FSM is simply because, well, I have no idea what I'm doing. This doesn't make sense. Wouldn't 2, 3, 4 be messed up if 1 is adjusted?

Anyways, I'm off to clean up my mess outside, then bed. I am going to try waking up by 8 am and getting the air box taken care of. Then start messing with the tuning of the carbs.

I have a date with mileage tomorrow. I hear she's getting some use.

[cdaiscool]

so I think I understand now how the pilot screws work.

I have also come to the conclusion that #4 is not firing. Its exhaust is cold. The others burned me. Time to go do more troubleshooting.

At this rate, I don't think I'll have the bike done today.

[cdaiscool]

@#$r%jkq#4R5L;J34L5J345K34;JLT54

That's how I feel.

Apparently, when I put my airbox boots on, the carbs ripped out from the motor boots. THAT'S why she isn't firing in that cylinder, I'm sure. There's an 1/8" gap from the damn carb to the boot! So all fuel is going away from that cylinder.

In other news, the compression tester I bought, all the threads - 3 of 'em - are too big for the spark plug hole. So I can't even check that. ARGGHHHHH.

If it can go wrong on this thing, it has.

Off to fix that now. THEN maybe I can get the pilot screws to work properly. When I was trying them initially, I couldn't get the rpms to change. Even after 1 full turn. Probably is masked by another idle screw. And the piss-poor idle from running on 3 cylinders.

[cdaiscool]

That didn't fix it.

The spark plug for #4 is tan; #1 is sooty black. I went to drain the fuel bowl. SURPRISE! No fuel.

So mad right now. Words cannot express what is coursing through my veins right now.

What would cause #4 carb to not have gas? What could possibly be plugged? Everything sprayed proper when I was doing everything. All 4 carbs acted the exact same.

Welp, time to pull the carb again.

[rrgunslinger]

When you take the float out of the carb you get no gas???

On Fri, May 11, 2012 at 1:46 PM, cdaiscool [via Honda CB750'S] <[hidden email]> wrote:

That didn't fix it.

The spark plug for #4 is tan; #1 is sooty black. I went to drain the fuel bowl. SURPRISE! No fuel.

So mad right now. Words cannot express what is coursing through my veins right now.

What would cause #4 carb to not have gas? What could possibly be plugged? Everything sprayed proper when I was doing everything. All 4 carbs acted the exact same.

Welp, time to pull the carb again.

Turbos, Hondas, 4-bangers, what could go wrong?

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NAML

[cdaiscool]

I didn't think to remove the float on the bike. But the float is out right now; carbs are on my bench. I put seafoam into the gas line, and never got anything - not a drop - out of the 4th bowl. Float and needle are out.

Something's GOTTA be plugging it. I think I'm going to go get some canned air, drill a tiny hole through a rubber plug, and see if I can force it clear. It's GOT to be in the 3/4 line between the carbs. I can't think of anything else that'd be causing it to be plugged. Then again, I'm not a carb guy. But 1-3 had PLENTY of gas when I drained the bowls. 4 was empty. But there was gas residue on the floats when I removed the bowl. Which tells me its getting some, but not NEARLY enough. Aka, something's plugged.

Otherwise, am I able to get to the line from #3? Can I remove #3's bowl and run some brake clean between the 2 passageways? Where does #4 get its gas supply from immediately? I get that it comes from the gas line ultimately, but the gas line is obviously clear as its feeding 1-3. And it's brand-new.

[rrgunslinger]

Take a look at this digram. Maybe it will help.  Bikebandit has helped me alot.

http://www.bikebandit.com/houseofmotorcycles/1981-honda-cb750k-carburetor-assy-link/o/m2003sch44059

[TOOLS1]

Do, you have the 3, and 4 carbs switched? If, you did that there would not be any gas getting to the end carb.
TOOLS

[cdaiscool]

Thanks guys! I figured it out, I think.

In carb 3, there was so much pinesol jelly that when I was cleaning everything, it looked like a brass insert. So I cleaned each side of it. But not the damn thing itself.

I figured this out when I rammed a pick through 1/2, and it went to the end with ease. And then through the old 3/4 carbs TOOLS sent me. Again, with ease. On mine? Blocked. I had to work the pick through it, and it got stuck itself!

Finally got it cleaned up, and my dad came over to see how progress was going so he helped me with blocking certain holes so we could make sure there was a good stream. Well, by the time we were done, there was a waterfall coming from the hole in #4 carb to where 2/3 meet up. It was beautiful.

It was weird, in that I could shoot brake clean from #3, and it would shoot out of #4. So I think the actual blockage was on the #2 side of the 3 carb. And just enough fuel was getting to the #3 bowl that it was able to run. But that was it. Given as much as came out from that bowl vs. #1 and 2, it was low, but had 'enough'.

Now I'm anxious to start 'er up and see how she does now.

[Half-Caf]

Nice! That means you're gonna put up a new video, right?

[rrgunslinger]

Outstanding.

Harvey

On May 11, 2012 5:07 PM, "cdaiscool [via Honda CB750'S]" <[hidden email]> wrote:

Thanks guys! I figured it out, I think.

In carb 3, there was so much pinesol jelly that when I was cleaning everything, it looked like a brass insert. So I cleaned each side of it. But not the damn thing itself.

I figured this out when I rammed a pick through 1/2, and it went to the end with ease. And then through the old 3/4 carbs TOOLS sent me. Again, with ease. On mine? Blocked. I had to work the pick through it, and it got stuck itself!

Finally got it cleaned up, and my dad came over to see how progress was going so he helped me with blocking certain holes so we could make sure there was a good stream. Well, by the time we were done, there was a waterfall coming from the hole in #4 carb to where 2/3 meet up. It was beautiful.

It was weird, in that I could shoot brake clean from #3, and it would shoot out of #4. So I think the actual blockage was on the #2 side of the 3 carb. And just enough fuel was getting to the #3 bowl that it was able to run. But that was it. Given as much as came out from that bowl vs. #1 and 2, it was low, but had 'enough'.

Now I'm anxious to start 'er up and see how she does now.

Turbos, Hondas, 4-bangers, what could go wrong?

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NAML

[cdaiscool]

Yay! Cylinder 4 is firing, it burnt me!

Boo, now cylinder 2 is out. But I'm not 100% on that. I pulled the spark plug wire once, no change. Pulled it again, and it dipped. I don't know if it was luck or not. But then after that, the couple times I pulled it, no change again.

I'm working on video, it sounds good. But cylinder 2, WHY YOU NO WORK. Changing out the spark plug with an old one, see if that helps.

[cdaiscool]

Disregard that last message. Apparently, she's running so damn rich, that when pulled it only dips slightly. But once hooked up, she runs. But she's so full of fuel that its keeping the exhaust cooler. That can be tuned, once the airbox is hooked up.

I might make my deadline yet... Doubtful, but just might...

Have to reboot my phone, as its refusing to upload either video to Youtube. So I will get these to you guys in a second.