1981 CB750K - Repair/Tune-up

[cdaiscool]

Thoughts on making a carb sync tool like this?

http://www.kzrider.com/forum/3-carburetor/360538-carb-sync-vacuum-toolgauge#360824

I understand that it doesn't show WHAT the vacuum is that's being pulled, but... it still should do the job, yes?

Or is there multiple reasons to go the more expensive 4-gauge way? I can't find 'em online now, only 1 site and they're asking $90 for a carb adjustment tool and gauge set.

[shinyribs]

Dang,they have gotten expensive! I tried to get you the link off ebay where I got mine. They WERE $50,now they are $80. You can do it with one $20 vacuum gauge from an auto parts store,it'll just take alot of fiddling and probably piss you off in the process.

The fluid balance will get them perfectly balanced,you just won't know if you are pulling the recommended amount of vacuum.

You could get a single $20 from Advance,establish a mark on the fluid tubes to show that particular reading and go from there.

[cdaiscool]

What I will plan to do then is just the fluid way, then hook up the vacuum gauge to see what the number is.

Not fond of doing it this way, but when you have no choice...

On May 1, 2012 12:38 AM, "shinyribs [via Honda CB750'S]" <[hidden email]> wrote:

Dang,they have gotten expensive! I tried to get you the link off ebay where I got mine. They WERE $50,now they are $80. You can do it with one $20 vacuum gauge from an auto parts store,it'll just take alot of fiddling and probably piss you off in the process.

The fluid balance will get them perfectly balanced,you just won't know if you are pulling the recommended amount of vacuum.

You could get a single $20 from Advance,establish a mark on the fluid tubes to show that particular reading and go from there.

Montvale,Virginia
 Piute said it best:  "wheres my 10mm?"
Hellbilly-"that is a great way to tell if you have come to your senses, when you start drilling random holes in things... "

Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato

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[cdaiscool]

Arghh, my e-mail replies aren't coming through...

So, I'm wondering if I've got 2 things happening. 1, the tach is off. 2, either the carbs are dirty or the advancer isn't advancing the motor, causing it to stumble at the higher rpms.

To check, and since I kind of need 'em anyways, I am getting a timing light and dwell/tachometer/voltage meter tonight. I won't have any time to work on the bike, as I'm going to the MSF today, but this will allow me to start doing more diagnosing.

I've also decided on my gearing. 18/45. This will allow me to, at 80 mph, be at 5890 rpm. I'm thinking the bike will cruise nicely at that RPM. It's hopefully not too much lagging on the motor, causing it to be screwed.

Per that site, using a 630 chain (stock chain) and my gearing, and my tire, I'm within about 400 rpm of the real-life tests. So the 530 chain, the 18/45 sprockets will get me much closer to my goal. And the carb cleaning and new spark plug wires will get me much better usability I believe.

I'm going to use the hose trick, and once it's done check the vacuum then. I can't adjust #2 anyways, so it doesn't matter too much what it is at.

Anyone know where to get just the adapter tubes to go into the carbs, so I can put the hose on those? I've already got a great idea for how to do everything else. Just need to get the adapters for the carbs.

Thanks guys!

[bosco39]

Here's a link to the directions I followed to make my carb sync tool : http://www.xs11.com/forum/showthread.php?t=986

Works real good. After I dialed in my carbs with it, I took it to a local mechanic who put the mercury carb sticks on it, and it only needed one carb tweaked a little to bring them all into line. For the price, you can't beat it.

[cdaiscool]

That's awesome. But how do you close off one at a time? The fish valve? 

Also, where did you get the carb nozzles? From Lowes/Home Depot? 

On Tue, May 1, 2012 at 3:37 PM, bosco39 [via Honda CB750'S] <[hidden email]> wrote:

Here's a link to the directions I followed to make my carb sync tool : http://www.xs11.com/forum/showthread.php?t=986

Works real good. After I dialed in my carbs with it, I took it to a local mechanic who put the mercury carb sticks on it, and it only needed one carb tweaked a little to bring them all into line. For the price, you can't beat it.

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[cdaiscool]

Thanks man!

I have to figure out why my e-mail responses have 100% stopped. This is the 3rd one in a row it didn't update...

Anyways, so I think I've bought the last piece for the bike for a while. Just put in an order for Sunstar 18/45 steel sprockets, and a DID non-o-ring chain. I kind of doubt I'm putting down enough power - especially right now - to screw this chain up bad.

http://www.motorcycle-superstore.com/1/4/61/5565/ITEM/DID-530-Standard-Roller-Chain.aspx

So let's recap:
-Sissy Bar to replace the back... thing.
-New to me left switch (old one's cracked and has exposed wires)
-Randakk carb rebuild kit
-Spark plug wires, boots, caps
-Chain
-Front and rear sprockets selected based on Gearingcommander recommendation for what I want.
-Mechanical RPM reader to verify tachometer
-Picking up timing light to verify timing

Did I mention all this has to be done by Thursday, Friday next week? Oh, AND I want to get a lot more done on my car? Pulled the head tonight, didn't look too bad.

[cdaiscool]

Geez! I may have figured out at least part of the reason she was stumbling. If not the entire reason. Note to self: Never trust a dealer to do a full tune-up when they say they will. Otherwise you'll get this:





I forgot to check it when I was doing my tune-up initially. I put a trouble light up to it, can't see ANYTHING on the inside. So she's good and blocked.

I think the previous owner got his money out of this. As did the other dozen owners.

[slownugly007]

GOOD GRIEF CHARLIE BROWN!!!!!  That thing will probably run like new now!

[cdaiscool]

Not quite. Found evidence of someone's prior attempt to do carb work. Certain places where there should be an o-ring... no o-ring. None were on the Pilot jet, though my teardown guide said there would be. Stripped out screws that were put back in (wonder how he tightened 'em...) and other miscellaneous things.

Unfortunately, I had to drill out 2 screws, in the choke bar for carbs 3/4. Anyone have an extra? Otherwise I'm going to have to re-tap what I've got. It's the bar the butterflies attach to for the choke. Stripped out 2, but were in the same chamber.

I figured out real quick how to prevent that from now on. I've got a perfect-tipped bit for my power drill/driver. Anytime I come across one I can't get out, she gets 'em out right away. Wish I'd known that for those screws.

Carbs are completely disassembled except for 1 jet from each carb. Now to get a good screwdriver for that, and some Pinesol! Hopefully carbs will be completely reassembled by Sunday. Going to put Pinesol over everything tomorrow, and let it sit until Saturday. Then it'll be on to assembly.

[TOOLS1]

I might have that choke bar. I will check tomorrow. If I don't post back, remind me. I tend to forget things.
TOOLS

[cdaiscool]

So my petcock leaks, even when in the off position. And I'm betting my vacuum-assist jobey-doo is leaking too, which leads to the smell of fuel whenever around the bike.

What's cheaper - replacing the petcock, or the spawn of satan deal?

I found a petcock for my bike for $50 or $60 depending on the auction. Might pick up the $62 just so I can get it right away, vs waiting for the auction to end.

Also, Tools, were you able to find a carb bar like the one I had to drill out?

Dealer's getting me an Emgo air filter for $11, and Emgo inline fuel filter for $3. So that will be taken care of by Wednesday for sure. He said he can get it in a day or 2.

Now off to the guitar store for some high-E guitar string (hope they've got some broken there) and back to the dealer to order my air filter.

[TOOLS1]

Good thing, you reminded me. I forgot all about it.
TOOLS

[cdaiscool]

Okay. Current at-the-moment plan.

I'm going to keep cleaning my parts. I'm about 1/4 maybe finished, but I found out earlier that I accidentally mixed oil in with my Pinesol. I didn't realize the oil pan still was oily - I'd cleaned it with brake clean; guess it wasn't completely cleaned yet.

As a result, it didn't clean NEARLY as awesome as it could have. So I'm getting the easy dirt off, and then going to soak everything again overnight. With new Pinesol. I'll do another cleaning tomorrow, inspect my boots tonight yet, and look at what I've got to do with those.

Ordering a petcock from these guys http://www.ebay.com/itm/220987091088?item=220987091088&frommaketrack=true&viewitem=&vxp=mtr#ht_520wt_1037 since I just got confirmation that they have the right part. After the last debacle, I decided I better first make sure. Sucks they're in NY though; won't have until Wednesday. Oh well, I can put the tank back on, then when it comes in just swap it quick.

I'm going to remove the vacuum-assist petcock, since I know it's leaking. I'm wondering if it's bad as well, and possibly putting fuel into the vacuum a bit, possibly affecting the carbs.

I'm going to remove it, and block off the vacuum port. That SHOULD get me a more simpler operation, HOPEFULLY then making it easier to find out wtf is causing my above 6500 rpm break-up. I kind of want to keep it, but figure a simpler way of doing everything is like this. Perhaps I'll put it back on later after I've got time to mess with it some more.

Ordered my air filter and picked up my in-line today as well. And got some High-E Acoustic guitar string today. So I'm ready to start building my carbs. Just once they're cleaned, of course.

Completely unrelated note: Took the first of 2 days of MSF range riding today. Was fun! Got to do some swerving, high-speed cornering, etc. Tomorrow's the final day. So next week, I'll be legal to go riding alone!

Now to just get my bike in the same condition...

[cdaiscool]

Okay. Hope I didn't fudge myself up pretty good.

I got around 3 hours of sleep last night. Maybe less. Was up at 5:30 this morning, and it's 10:39 pm right now.  I may not be coherent...

http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revD.pdf this is the guide I'm using to clean my carbs. On page 12, at the bottom, it mentions getting the Primary main jet out. Unfortunately, I think I may have stripped the flathead in the carb. I didn't have a screwdriver that fit in there, so I made one. I ground down the side of a slightly larger screw driver. I put that down the hole, and it stripped the head. On 2 of 'em. I'm hoping I didn't screw it up.  

Found out today that I had some oil mixed in with the Pinesol. Apparently this combo causes Pinesol to gum up. So today, after my MSF class, I spent the rest of the day - and night - cleaning out the carbs to get the gunk out. Now the carbs are soaking in pure Pinesol to get any gunk built up out of 'em. I'll clean 'em out again tomorrow. Then start putting everything together tomorrow or Monday.

I should probably not work on carbs when I'm this tired. I don't quite know if I did everything correct.

Tools, any luck with the choke bar?

[Piute]

  I didn't get to sleep till 4am,woke at5;30 back to sleep at 10am ,didn't wont to work on my carbs or any fumes,bad day fo sho. But tomorrow early start and that Ole CB is moving not just starting,had water in the the oil on the truck,blown head

[cdaiscool]

Yuck!  That sucks.

Graduated from the MSF class today! I apparently lost 10 points, out of 15 - I decel'd in the corner, and took too long. But did everything else perfect.

Then hit a going away party a friend of mine was doing for me. mashed/baked potato (don't ask, but tasted AWESOME), grilled steak and corn-on-the-cob, and an ice cream cake that said, "We'll miss you... maybe.". She's mean to me. :( Then we played Apples to Apples and a few other games until just recently.

Needless to say, I didn't have time to get my stuff out of the Pinesol and cleaned. Is it okay if it's in there until around 5, 6 pm tomorrow? Or do I need to get it out asap? I put everything in around 10, 11 pm last night. If I need to get it out, then I need to get out there soon. Because I'm going to pass out soon since I'm tired.

Other news - Tools, any luck finding that choke bar? For carbs 3/4?

[cdaiscool]

Sorry, no pictures since I was in a hurry, but...

Got everything out of the Pinesol, then did the guide to clean the stuff as I went through the rebuild process. Man, that guide was THOROUGH.

All individual carbs are put together, just need to start attaching the tubes and such. And going to plug the vacuum port for the vacuum-assist auto-fuel valve since I'm removing it. Then off to install the in-line filter and remove sprockets/chain tomorrow. Let's see what my remaining to-do list is:

-Spark plug wires assemble and install
-Sprocket/chain removal; new sprockets and chain install (arrive Wednesday)
-Sync/adjust carbs on bike (Sync tool arrives Thursday)
-Petcock install (Arrives Thursday)
-If time: install new left-side switch (Arrived last week iirc)
-Re-set up mirrors (They came loose)
-Install in-line fuel filter (Already here)
-Remove vacuum-assist auto fuel valve
-Install air filter; clean air filter box and put side cover back on (Should be in tomorrow)
-Install sissy bar (Still didn't get M&M's)
-Anything else I may have forgotten... (Because I always do)

Some time this week, I will get to ride it. I hope. We will see. Goal is to ride by Thursday evening, put a couple hundred miles on it Friday, including on the highway at 80 mph, to make sure she's running tip-top shape. I need this thing running well before I move this weekend, and Saturday's probably best used to wash and pack before moving Sunday.

Welp, I'm off to bed. Adios people!

[bosco39]

Man, sorry - I didn't see your questions about the carb sync last week until just now.

That 4 - 1 fish tank valve has an on/off control on each of the ports. Basically turn it 90 degrees and it doesn't let anything through. Keep 3 off while you get the reading on the other one. Turn that off, and another one on, and you get the reading for that one. Adjust until they all read the same.

Hmm, carb nozzles... I don't remember carb nozzles. There were ports on the carb intake boots on my XS. Is that what you mean by nozzles? I haven't synched my CB with the tool, so it may not work?? If they're Constant Velocity carbs, they ought to have a vacuum port nipple to hook the tubing to.

Or was it the brass plenum fitting? If that's the one you mean, I think I got mine at either a plumbing shop or hardware store. Either way, Lowe's & Home Depot would probably have what you need.

Hope this helps, & it's not too late. I don't know how I didn't see your reply before. Also, congrats on the MSF class! That cornering test is the toughest one, IMO, but also pretty important. Judging entry speed for a given curve/corner is sort of a big deal... going outside the lines means oncoming traffic.

[cdaiscool]

I was talking about the nipples, as the carbs have a screw that blocks off the vacuum port, and you need brass nipples to go in there. I ended up ordering the Carb sync tool from Cycle X. Ultimately, seeing what all of 'em are running at should help me diagnose 'er if needed anyways. So I bit the bullet.

Thanks for the congrats! I didn't go outside the line, I think it was my entry - how I entered the corner. I went the correct way, but I think I was just too nervous and came out of my lean too early.

I rode a 1980's GS250 w/ forward controls - man what a blast it was! I didn't think it would be, but boy was I wrong. Now I just need to get my bike going so I can fully enjoy my newfound skills!