Author Topic: Trixie - 1977 CB750K - Project  (Read 29143 times)

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BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #25 on: January 18, 2012, 07:02:25 AM »
Thanks!  Was my first attempt at cleaning up any metal. 

A brass brush attachment for the drill.  Was < $5 at Lowes.  Then I went over them with fine sandpaper and some generic aluminum polish (do not remember the name).  Then cleaned everything up with WD40. 

I am starting to rethink taking the polish route... given that its so painful pulling out the carbs on a 750.  It might have made more sense to paint some of the parts but I will report back with how long the polish lasts.

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #26 on: January 18, 2012, 10:25:45 AM »
Finally!  Found the answer to my question here:

http://forums.sohc4.net/index.php?topic=74061.0

Everything I needed to know about how those rubbers should fit.

Offline lucky

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Re: 1977 CB750K Cafe - Project
« Reply #27 on: January 18, 2012, 11:30:38 AM »
For those interested or if you were face palming after seeing another Pod question I have finished going through the forums and I came to a decision.  No matter what those Pods are going to have to go.  TwoTired really laid down the facts and science behind why removing the air box and replacing with pod filters will just be a headache for me in the long run.  If you see this TwoTired, thank you very much!  I did like the look of the pod filters, oh well.

I also have been able to get a general idea of what the accelerator pumps actually do.  From what I understand is that it improves throttle response that was lost because of the leaning out of the A/F ratio in the 77-78 engines. 

So right now I think the best route to take is keep the Mikuni carbs and fit them to the original air box.  It is making me wonder that if the "carb cleaning" that was needed was actually a conclusion he came to because of symptoms of using the pod filters. 

I am going to pull the carbs off the bike later this week and take them apart to get a good idea of the condition they are in.  I will take a lot of pictures.

Question:
Anyone know of a reason that I should go with the original Keihin carbs over the Mikuni?

A lot of confusion here.

The link given did have a lot of useful information especially about how to take things apart without breaking them.
Yes you needed to take apart the carbs and clean them.
BTW in the link given some of the parts were very very old style.
If you do come across a all metal float needle replace the needle and the seat with the modern version that has a rubber tipped needle.
If you replace the all metal float needle and do not replace the seat it will probably leak.
The all metal float needles would get a groove worn in them from engine vibration and would leak. Look at the needle with a magnifying glass.
That air pilot screw with the hole in it must be retained. But is was less fragile than the modern ones. The modern pilot air screw has a spring and "O" ring down in that hole. Look to see.
The old slide needles shown in the link were problamatic because they would get worn on one side and it was not something you could measure with your eyes.
It would idle poorly as a result of the needles on the slide being worn on one side. The modern needles are allowed to float and find the center so they do not just rub on one side of the hole.

About the POD filters.
If you go to pod filters you will have to make adjustments to get the engine to run right. But if you are willing to do the work you could gain about 8 HP.

The mid range will be lean and will require shims under the needles if the slide needles have no adjustment grooves with clips. With clips it will be easier.

So if you have a performance exhaust and pod filters the engine will need more fuel. But make one adjustment at a time and see how it runs on the road.
Do not expect to get the carbs dialed in, in one day.


Most carbs do not have that style of needle anymore.

Offline lucky

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Re: 1977 CB750K Cafe - Project
« Reply #28 on: January 18, 2012, 11:32:45 AM »
Thanks!  Yeah I actually had that exact page open.  I was thinking of taking a bike to a local shop to get their opinion but I feel like I would regret doing that.

Many motorcycle shops do not know anything about motorcycle carbs.
They just want to plug a lap top computer into the bike to tune it up.
Ask first if they know about carbs and have experience.

Offline lucky

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Re: 1977 CB750K Cafe - Project
« Reply #29 on: January 18, 2012, 11:39:54 AM »
Ok I need help.  I am a bit confused about float bowl height and measuring it.  I have searched and searched and blah blah blah and I got conflicting wording on how to properly measure. 

**NOTE** I am using a tape measure that has centimeters on it.  This not by any means accurate, I am still waiting for the more accurate measuring tool to come into the mail.

In the first picture you can see how I am measuring the float.  It is perfectly parallel to the carb.  Also this is where separation from seating on that valve begins to occur.  Right where the red arrow is pointing.  This is how I **think** I am supposed to measure this.  I am supposed to be at 14.5mm and it looks like I will be right on once I have the correct tool... at least in the ball park.

The second picture is me measuring with the float bowl pushed down.  I read somewhere that this is how you are supposed to measure and from the lowest point.  Not only does this not make sense it does not seem to line up with the actuation of the valve.  Also, its damn near impossible to take a picture of with two hands. haha.

Am I doing it right in the first picture?  Also, how do I adjust.  I can not figure out what the hell would adjust that.

Thanks!
You cannot use a carpenters tape measure because of the sliding metal tab.
You will get poor results. Use a good metal ruler.
Also the measurement is taken from the edge of the lip of the casting that the float bowl sits on.
« Last Edit: January 18, 2012, 11:47:57 AM by lucky »

Offline lucky

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Re: 1977 CB750K Cafe - Project
« Reply #30 on: January 18, 2012, 11:45:11 AM »
That bottom photo of the float measurement being taken with the carpenters tape is incorrect.
Motorcycles do not generally give the float drop measurement like cars.

Just do the measurement like you are doing in the top photo, but use a metal ruler,not a carpenters tape.
Hold the carb sideways so the weight of the floats is not pushing down on the float needle pin. It should be just touching.

Some floats are brass and some are plastic filled with foam.
A long time ago floats were cork sealed with shellac.
The brass floats did not get soaked with fuel like cork ones did but the heavy brass floats would bounce up and down when the bike was on the road. The modern plastic ones do not bounce as much.
« Last Edit: January 18, 2012, 11:51:02 AM by lucky »

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #31 on: January 19, 2012, 07:22:04 AM »
Lucky, thanks for taking a time to look at all my questions and providing input:

Before I knew all of the headaches with tuning with pod filters I figured I would just pay for a professional to get the bike running consistently.  After some thought I realized that would be a terrible idea because I still would be clueless.  It was a really shortsighted knee jerk reaction because there were a few really good days to ride recently and I was dying to get on the bike.  I decided to go with working on the bike myself completely. 

So since making that decision as you can see I took the carbs apart and made sure everything appeared to be in order.  As far as the pictures with the crappy measuring tape... I was using that just to go through the procedure of measuring the floats and posting it here as verification that I was doing it correctly.  I have since picked up a digital caliber that is very accurate for that type of measurement. 

Also, just some background on the PD carbs... they came with the bike when I bought it.  After recommendations here and extensive reading I decided to recondition the airbox and PD carbs.  I opened up the carbs and it was apparent that they had been cleaned and rebuilt with new gaskets.  The main jets and pilot jets were also spotless and even had tool marks from when they were pulled and cleaned.  The Accelerator pump had a new diaphragm and even the plastic retainer for that little ball appeared to be replaced.  I am moderately confident that they are good to go.  I will find out this Saturday when I replace the Mikuni carbs with these. 

I will be posting up pictures of the condition of the Mikuni carbs (PO told me it wouldn't be pretty) probably Sunday or Monday.  I am also sure Saturday I will come across something that I can't figure out and will make some frantic post for help.  I am a little worried about what will need to be changed (shorter/longer throttle cable?) when swapping back in the PD carbs.  I will also try to take a ton of pictures as I am doing the work. 

Thanks again for those that have provided input or pointed me in the right direction for information.

Offline lucky

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Re: 1977 CB750K Cafe - Project
« Reply #32 on: January 20, 2012, 11:53:29 AM »
It sounds like you are on the right path.
IF it was me, once I got the throttle cable hooked up at least the pull cable,I would turn on the gas (ENGINE OFF) and look into the intakes of the carbs and make sure that when you turn the throttle that fuel squirts out of the brass accelerator nozzles in the venturi. One twist of the throttle -one squirt.

Then you know it is working.

Another thing...If the floats have not been tampered with and mistreated the float should be in adjustment.
The worst case is when someone adjusts the float because the carb was leaking from overflowing. If they just replace the float needle then you do not need to adjust the floats.
« Last Edit: January 20, 2012, 12:00:55 PM by lucky »

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #33 on: January 23, 2012, 04:26:04 PM »
I can not figure out how to get the throttle cable back on the carbs.  It seems as you turn the throttle it actually closes the valves... should it not be opposite of that?  I am trying to find instructions here for the PD41A carb to throttle assembly and how it should be attached...

Edit:

Well I figured out everything.  I have one throttle cable.  It is pull only.  It is long enough only for the Mikuni carbs I just pulled off.  Looks like the PO took out the pull cable.  Opened up the throttle assembly and this was confirmed. 

Also, the Mikuni carbs have a choke built into the side of them.  So it looks like the PO removed whatever choke functionality existed on the bike previously. 

So now I need to at the very least get the choke assembly and cable and also at least get a new pull cable... I should probably get the push cable too... would rather not have the throttle get stuck open...

This is an annoying problem but one I should have expected from the start.  Also, to just further push my buttons I received my antique plates for the bike and they are MASSIVE.  The are as big if not slightly bigger than my car's plates and they are super thick with razor sharp edges.  What the @#$@ is with that?  I can't put this on my bike!

Does anyone know how I can identify these Mikuni carbs?  I am seeing no model/serial numbers.  Included are a bunch of pictures.  There is the number "29" assuming this represents 29mm.
« Last Edit: January 23, 2012, 06:55:32 PM by BrockSamson »

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #34 on: January 23, 2012, 07:01:59 PM »
My best guess are Mikuni 29mm Smoothbore?

Edit:
Using this reference there is a picture that shows the markings just about identical to mine.  I feel like I can definitively say they are Mikuni 29mm Smoothbores!  Looks like they will be going back on the bike after all.

http://www.z1enterprises.com/reference/z1-carb-guide.aspx
« Last Edit: January 23, 2012, 07:47:58 PM by BrockSamson »

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #35 on: January 24, 2012, 07:18:02 AM »
Bump.  I am getting ready to order dynoman "intake manifolds" or the rubbers that go from the mikuni VM29 carbs to the CB750 engine.  Waiting to get a reply from them to insure that they will fit on my 77.  They are very expensive, but I want a correct fit.

Does anyone have enough experience to confirm that these are VM29?  The markings next to the 29 are too faint to read.  I am also under the impression that the only Mikuni carbs marked 29 were the smoothbores. 

Any help would be much appreciated.  Thanks!

Edit:
I have found a couple threads here asking for identification.  I will take a picture of the bore tonight.  Hopefully showing the insert and a completely "smoothbore" when its wide open.
« Last Edit: January 24, 2012, 07:34:40 AM by BrockSamson »

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #36 on: January 24, 2012, 09:09:59 AM »
Someone emailed me back.  Their boots do not fit the 1977 CB750s....

Now I need to figure out a way to fit them...

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #37 on: January 24, 2012, 04:03:24 PM »
Smoothbore (I think) pictures:

Offline seanbarney41

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Re: 1977 CB750K Cafe - Project
« Reply #38 on: January 24, 2012, 07:09:37 PM »
...those carbs are probably off Kawasaki kz1000, I believe I have a couple sets of 'em for myKwaka  basket case, hard to tell from your photos...do they have an accelerator pump?...mine do which makes them non-smoothebore vm29sand, I was thinking the smoothe bore Mikuni vm only came in 28mm but I am no expert.  Might try logging on and posting at KZRider.com...those guys are experts will id those carbs for ya in a flash, try not to mention Honda's though, unless you are ready for some ribbing :P
If it works good, it looks good...

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #39 on: January 24, 2012, 08:09:58 PM »
I think you might be correct on where they came from. 

After scrubbing more grime off I found a couple more letters next to the "29"  an "A7". 

There is not an accelerator pump.

http://www.postdiluvian.org/~mason/moto/jetting.html
Kawasaki KZ 650, 900, 1000   Mikuni VM29 A7

I searched up and down the intertubes and "29 A7" seems to only refer to the VM29-A7 smoothbores.  The carbs look identical to them also.  I think the last thing that makes me think these are certainly smoothbores is that there is no obstruction in the last couple pictures I posted.

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #40 on: January 24, 2012, 08:21:57 PM »
Seanbarney41, I made a post at that Kawi website like you suggested.  I will report back what info they give me.  Ha, also took your advice and left out any mention of owning a Honda  :-X.

http://kzrider.com/forum/3-carburetor/499956-need-help-identifyingvm29-a7-smoothbores

Edit:
A really friendly group over there.  They got my questions answered  8).
« Last Edit: January 25, 2012, 05:42:05 AM by BrockSamson »

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #41 on: January 25, 2012, 11:39:14 AM »
Anyone have experience with the Sudco Motion Pro Push/Pull Throttle assembly for the Mikuni Smoothbores? 

I am confused what kind of fit these will be... do I even need to worry about length?  They just need to open and close the carb throttle correctly... right?  What about the throttle assembly on the handle bars?

Ugh so much to think about.   ???

Offline lucky

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Re: 1977 CB750K Cafe - Project
« Reply #42 on: January 25, 2012, 02:30:49 PM »
When you looked into the float bowls of the PD carbs and said it all looked good and parts were clean is not good enough.

IF the idle jets are clogged it will never run right.
I would make sure those idle jets are clear.
If they are the push in style try putting a .010 thousandths guitar string through them. If they are stock #35's that is .013 thousandths.

You have to know for sure that they are clear.

The mains almost never get clogged up. They are very large holes.

"I purchased Mark Paris' My CB750 Book which deals mostly with the pre-77 CB750, but the differences are so small from what I understand that I saw no reason to not have this book on hand.  I read the carb section of the book in its entirety.  I have also done a bit of research here on the forums.  I kept coming across threads about people putting pod filters on their carbs and for a few reasons produced inconsistencies in A/F ratios across different throttle positions.  Generally it seemed jetting the carbs to 130s fixed the problem but not always.  I also noticed that this occurred mostly on pre-77 CB750s.  "

Most people are too lazy to put shims on the slide needles and that is why they run poorly with pods. Midrange is way too lean. Instead they blame it on the pods themselves. Also with pods and stock idle jets it is too lean and that is why you hear of people opening the mixture screw so many turns. Three turns is too much.
« Last Edit: January 25, 2012, 02:38:11 PM by lucky »

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #43 on: January 25, 2012, 02:41:32 PM »
I actually ran copper wire through the holes/passages to make sure they were clear. 

I actually have not been able to get the bike running with the carbs.  Not even a throttle pull cable that will reach.  Looks like a different length throttle cable was put on the bike for the VM29 carbs.  the Push cable was removed entirely ???.  Not to mention there is no longer a choke assembly or cable (choke built onto the side of the VM29s).  So I am having to order a few parts before I can safely get the bike running with the PDs.

Offline lucky

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Re: 1977 CB750K Cafe - Project
« Reply #44 on: January 27, 2012, 02:55:48 PM »
I actually ran copper wire through the holes/passages to make sure they were clear. 

I actually have not been able to get the bike running with the carbs.  Not even a throttle pull cable that will reach.  Looks like a different length throttle cable was put on the bike for the VM29 carbs.  the Push cable was removed entirely ???.  Not to mention there is no longer a choke assembly or cable (choke built onto the side of the VM29s).  So I am having to order a few parts before I can safely get the bike running with the PDs.

I would not have used a soft copper wire.
But as long as you are 100% sure those jets are clear is what matters.
You now they will pull out with pliers. You have to remove the float first so you do not damage the float.
A soft copper wire would bend or could get stuck easily and break off.
That i what would worry me.
A steel guitar string is not going to break.

As far as the cables  go you are just straightening out a mess someone else made.
Just order the OEM cables and be done with it. Worth every penny.

None of this is your fault. You are on the right track.

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #45 on: February 08, 2012, 05:39:15 PM »
Alright thanks to the guys over in the KZ forum I got the VM29 carbs taken apart and put back together.  New jets, gaskets, etc.  Going to bolt them back up tomorrow and see how it runs. 

I also picked up a new push/pull throttle cable. 

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #46 on: February 10, 2012, 08:06:45 AM »
Update!  No pictures or video because I left my cellular telephone at home :/.  Will get some very soon.

So first the really good, then the really bad.

I slapped on the rebuilt VM29s and the bike started up after 3 or 4 kicks.  This was without the filters on.  It was a bit wonky for a few seconds but stabilized and the idle is rock solid.  That is the end of running we did for the night.  So other than it starting and running at idle I don't know about the rest of the performance.  That was because something horrible happened.

Now, let me preface this with that what I did made sense to be at the time and now I see why it was a really dumb idea.  To facilitate easier access to the engine and carbs for removal and installation I took of the seat and the tank.  The tank had very little gas in it.  So I close the valve and the logic was that the valve would be the location most likely to leak gas so I store the tank upside down on a shelf.  It sat there for about two weeks.  Fast forward to last night we get the carbs on and the pull throttle hooked up and I am ready to put the tank on.  I grab the tank and something catches my eye.  There are wrinkles... ALL OVER.  I lift the gas lid and the paint completely ripped apart soaked in gas.  The tank paint is ruined.  There was some good that came of this.  First I learned that my gas cap has a leak and I probably need a new rubber gasket.  Second, I learned that the bike has been painted at least 4 times.  It was once blue, then red, then bondo/primer, back to blue, and finally the flat black rattle can paint.  The paint has never been stripped off the bike. 

Now, I always knew I wanted to repaint the tank and was even thinking about getting knee dents in the tank but that was planned for a year down the road.  I really wanted to ride the bike this season and worry about that next year.  So now I need to strip all the #$%* that is on it and prep and paint it.  Honestly I am just going to rattle can flat black it.  Which might get some hate here, but I am a VERY inexperienced rider.  There is a very high chance I will drop the bike or do something stupid and would rather do stupid stuff on a rattle can flat black paint job.  So I think I am going to buy some paint stripper and try my hand at prep and paint.

What do you guys think?  Any advice? 

Whats next:
Install push throttle
New sparkplugs
Tune carbs
Doing something with this tank disaster
Getting the seat and tank back on the bike
Riding

I want to say thank you to everyone who has given me advice and gotten me to this point.  I also want to thank any of the KZ guys that come over to check out my build thread... they were invaluable to the rebuild of the VM29 carbs.

Offline seanbarney41

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Re: 1977 CB750K Cafe - Project
« Reply #47 on: February 10, 2012, 02:07:32 PM »
...geez...your running 29 smoothies and your worried about some black primer... ;)
If it works good, it looks good...

Offline lucky

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Re: 1977 CB750K Cafe - Project
« Reply #48 on: February 10, 2012, 02:42:14 PM »
The older motorcycle tanks with bayonet style caps were vented caps.
When you turned the tank upside down gas was coming out of the cap from the air vent OR a old rubber seal.


You could have burned your house down if the hot water heater has a flame and was in the general vicinity. You are very lucky!!!

The paint job? Just be glad there was no fire, and no one got hurt or burned to death. You could be in jail for manslaughter right now.

Basically a motorcycle gas tank will leak if it is turned upside down AND it will not be able to vent properly. Never leave a motorcycle gas tank upside down with gas in it.

BrockSamson

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Re: 1977 CB750K Cafe - Project
« Reply #49 on: February 11, 2012, 10:29:14 AM »
I am having a problem with the bike.  It was idling fine and now all of a sudden the RPMs are running out of control.  As soon as I kick it shoots straight to 4k RPM and I have to cut it off.

The idle is all the way out, so that is not the problem.  I am very confused how it could go from a stable idle at about 1400 RPM and now its acting all goofy.  Anyone know whats going on?

Another question, why can't I get one of the spark plugs out?  Is there something I am missing?  I was able to pull the outside two and one of the middle ones... its not rounded... the problem is that I can't get the socket deep enough to get around it.  Its weird.