CB750KZ Project / Conversion

Here is my new project that I got yesterday. This is how it was when I got it:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-09174632.jpg

This is the sort of thing I want to turn it in to (in my head at least):

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/HondaCB750flattracker.jpg

Bikes Background:

It is a 1978 Honda CB750KZ with the DOHC. Bought it off a guy in Stoke-On-Trent who had owned it since 1987, but he had just had it stuck in the back of his garage for the last 20 years and not had it on the road or ridden it in that time. Supposedly before he bought it the guy who had it before him had removed the engine and fully rebuilt it ready to put in a custom chopper but then changed his mind and put it back in this and sold it to the last owner who ran it for 3 or 4 years before putting it away for 20 years.

Guy I bought it from said he had turned the engine over with the wife's car battery and it did turn over but it leaked some fuel out of the overflow of the carbs and he thought the float(s) may have been sticking so he didn't try harder to get it to fire. Will just have to see if it starts later on in the process. He may have just lied and it might be completely seized.

Not too sure on the KZ bit of the model as I am struggling to find info on it. I know the bike was previously registered overseas and was brought in to the UK in 1987, but I cant find out where it was originally registered (yet). If anybody has any insight on this then that would be great. Or if anyone knows of bike specific forums or places where it could help me find the history of the bike then that would be a great help and much appreciated.

Day 1

When I got the bike home yesterday all I did was give it a good spray over with some ACF-50, trying to get it on to as many bolts and fixings as I could see so that it had 24 hours at least to soak in before I tried to undo a single bolt.

Then in the evening it was finding the first few parts that I need / want to start the recommissioning of the engine. So I ordered; plugs, oil, oil filter, battery, and a full gasket set (biggest expense). They should hopefully be here Tuesday with a bit of look, so then hopefully later this week I can start fitting / renewing stuff.

Day 2

Tonight I had a couple of hours on the bike with the intention of stripping off all the bodywork, removing the spark plugs, and sticking some ACF-50 down the plug holes so that it can try soak in around the piston rings and when I then try turn it over by hand later in the week, this should help.

Started at the back end of the bike. Removed the seat, the grab rail, rear fairing, rear light, disconnected the rear light wiring, removed the rear mudguard, and then the inner rear mudguard / undertray thingy. I then had a look at the battery which seemed to be a little old (there's a surprise on a bike that's stood for 20 years) and seemed to be weeping a little so I removed it and thought it wasn't worth trying to salvage. This was the result at this stage:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10195004.jpg

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10195012.jpg

Then off came the front mudguard:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10194943.jpg

Just left with the tank to remove. Unfortunately the tank had a fair bit of fuel in it, which I was told was unleaded with lead additive put in it, although I don't know how old the fuel is. I lifted the tank up and located the fuel pipe. When I tried to pull it off I undid the clip and pulled but it was really stuck on. Tried to get my nail under it and it started breaking up so decided it was clear it needed replacing so easiest thing to do was to just cut it off for now. Snip! Off the tank came. I then stood there with the fuel tap open letting it SLOWLY drain in to a fuel can, although it got full to the top and there was still a little left in the tank, but decided it was probably best just to leave a little in the bottom for now anyway.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10202137.jpg

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10203757.jpg

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10204126.jpg

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10204136.jpg

So all the bodywork was now removed, and not one seized or broken bolt, or stripped screwhead :thumbsu:

So then it was time to get the plugs out. Disconnected the HT leads and put a little masking tape around each one as I removed it and wrote on the cylinder number so hopefully no mistakes when I go to put them back on.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10203746.jpg

The plugs came out real easy. A lot easier to get to and work on the top of the engine compared to the more modern bikes like my ZZR1400. The plugs came out real easy and they didn't look too bad. A little sooty but not bad at all considering. Also they all looked pretty even in appearance so no one carb having a major difference from the others.

Cylinder 1 to 4 left to right

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-10203905.jpg

I then sprayed a good dose of ACF-50 down each of the plug holes and covered them over with some clean rags.

The plan now is to let the ACF-50 soak through and then maybe spray a little more down tomorrow, and then on Wednesday or maybe at the weekend, take the engine side covers off (or whichever panels I need to) and put a socket on the crank / flywheel / whatever you call it, and gentle turn it over (hopefully).

I bought one of these brand new when they were first released in the UK. It's Honda's first 750 with DOHC the previous models being the SOHC Kseries then the F1 and F2. The KZ had a 4 into 4 exhaust system and was aimed at replacing the K series bike rather than the sportier F series. The CB900F was also released the same time with a similar style engine sportier looks and aimed more at the sports market.

One major flaw of the KZ is the frame, they used a thinner wall to the tubeing than on the fine handling CB900 giving the KZ absolute shite handling in corners if you were having fun! They later replaced the KZ with the CB750F which used the same frame as the CB900.

It's amazing what crap you can remember lol

I lost control and came off mine when it went into a weave on a high speed corner doing around 80, it flipped and cartwheeled down the road in front of me while I was sliding down the tarmac, like me it had scrapes and scratches and dents everywhere!

I learnt a lot from that bike

Already liking this thread, keep it up.

UPDATE:

The battery, spark plugs, oil, and filter arrived today so I filled up the battery with aceeeeeeeed and have put it on charge. I then checked on the power cables ready for fitting the battery in the next couple of days and found that the spade connector on the end of the power cable coming off the positive terminal of the battery was missing. In fact it was still attached to the old battery. Tried to prise it open so I could re-fit it, but it is just too tough, so I have removed the cable and will take it to a suitable car / bike parts shop tomorrow and get a new one made up.

I must say that the battery was a right sh1tty job. It was one of those where you have to fill it up with the acid yourself. What a sh1t way of doing it. For a start you can hardly see through the case of the battery to see how far up you have filled it. Then secondly, when I had finished filling it up I was left with about 15% of the acid in the bottle left, but because of the design of the bottle you have to chop the top of the spout off to open it up, but this then means that there is no real way of sealing it up safely to dispose of it or store it until you can dispose of it properly. Crap crap crappy crap system!!

Also today I put another squirt of ACF-50 down the plug holes.

Questions I now have for you fine people are;

• Will I need to drain the oil before taking side covers off so that I can turn the engine over by hand?
  
• The oil in the engine looks VERY clean when you take out the dipstick and look at whats on it. Do you think it is best to just leave this in for the first attempts at properly firing it up, let it run a few minutes to get it all round the engine, and then change the oil and filter? Or should I just empty it out now, put fresh in, run it for ten minutes, and then chage it again? (just dont want to waste £20-30 on another batch of oil if not needed)
  
• Anybody got any advice or words of wisdom on cleaning carbs and unsticking floats?
  
• Is anybody on here good at welding and willing to weld me a hoop on to the back of the frame?

Drain the oil, leave it overnight in a white container to settle,check drain plug for metal or dirt. Skim off the top 1/2 inch. Look for water on top . Pour oil back into engine using a white muslin sieve/rag. Check bottom of container for bits of metal.

You can turn engine over by hand with no oil in sump.

Clean carbs with carb or brake cleaner, remove any rubber items first if using carb cleaner

Can weld but a bit far from you.

If you fancy putting 4 or 2 megaphones on it and a new stainless collector box, gimme a shout?

If you fancy putting 4 or 2 megaphones on it and a new stainless collector box, gimme a shout?

I am liking the sound of that

also check the carbs vaccum rubbers in the tops of the carbs as they are well known for tearing and perishing and the bike will not run right if they have any damage also the spark amplifiers that are bolted to the side of the battery tray or the frame near the battery cradle as they can melt the back out of them and then stop working

UPDATE

Today I had a spare couple of hours this afternoon so got myself working on the bike. First job was to get a new battery to bike power cable made up as the existing one has a fixing eyelet missing on one end so thought it best to replace it. The cable is so short that it isn't a standard length that you could just buy over the counter pre-made. So a trip to a local auto electrician and £1.36 later and I had a new piece of cable with new eylets on either end. Bargain!! The cable is slightly fatter, and slightly longer than the original but only just so shouldn't hopefully be a problem. Then it was off home to crack on.

Checked that the new battery had fully charged on a slow 2 Amp charge and it seemed good. So I slid the battery in and offered up the new cable and at first it seemed a little long, and as it is such a fat cable, being the main power cable from the battery, and as it is very very short (only about 4-5 inch - bring on the jokes)it is very difficult to manipulate. Bit of jiggery-pokery and it seems to be ok.

Then on to putting the new plugs in. A quick squirt down the holes again with some ACF-50 and the new NGK plugs went in.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12154936.jpg

HT leads all look pretty good, so checking the numbers I wrote on tape around each lead, I ensured I plugged them all up to the correct cylinders (always a good start - pun intended).

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12155638.jpg

Then what I wanted to do was try turn the engine over by hand. From what Whizzy on here said, the cover I needed to take off to turn the engine by hand was this one:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12155643.jpg

I went round all the bolts on the outside at first and when I took the cover off I was greeted by this sight:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12160445.jpg

Looks immaculate inside. No broken teeth on the cogs and no signs of any damage either. Looks very tidy. I then realised though that I didnt need the whole cover off, I could have just took the inner round cover off to get to the crank bolt to turn it over. Put the big cover on and then removed the smaller inner cover to reveal this:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12155643.jpg

Looks good too. Put the wrench on the dark grey bolt right in the middle and gentle turned and round it went. Some slight resistance but that is what you would expect I think as no oil up there without the engine running and moving it about. Definitely wasn't stuck or anything though. As I turned it I could also here it make a noise like it was sucking air in when it turned to a certain point, then went quiet, then sucked air, then quiet etc. Perhaps someone could explain the technicalities of this :pardon: So we have a moving engine which is a relief :good:

I then got the dipstick out (no not Trippo, the one that read the oil level) and had a look at the colour of the oil. I wiped some on my finger and this is what it looked like, very clear and very light golden colour as you would expect clean oil to look.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12155705.jpg

I then turned the ignition on and tried it with the starter button and it turned over very strongly, but did not fire. I didn't worry though as I was only trying to fire it on the sh1tty petrol still in the carbs.

I thought that it may be a good idea to remove the airbox so that I could spray some Quick Start stuff in to the carbs perhaps if it needed a little enticing to start. But the airbox is totally wedged in. I also wanted to have a look at the air filter and see what condition that is in. The only way to remove it is to take the carbs of, which are sandwiched between the engine and the airbox. So first off I thought I would just remove the filter from the airbox and see what it was like. I looks brand new! In fact if I wasn't telling you this, I would suspect you would think it was a new one.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12163542.jpg

So then job now was to try remove the carbs so that the airbox could be removed. I wanted to remove the carbs to give them a good clean, but wanted to try fire it up first, but nevermind, will just remove them now. Firstly I undid the clamps around the rubber boots that connect the carbs to the airbox, and then loosened the clamps at the carb side of the boots that connect the carbs to the engine. Room in there is so tight it makes it very difficult as the airbox only moves back a tiny tiny bit when you unbolt it and you basically have to wriggle the carbs out. I just couldn't get the carbs off the carb to engine boots though. I then tried undoing the boots ont he engine side of them and with a long flat screwdriver and some manipulation I managed to get them free. You can see in this photo how the carbs squeeze in between the engine and airbox. The carbs go where there is now a gap.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12165853.jpg

Disconnected the choke cable and throttle cables then from the carbs, pissed remaining fuel in the carbs all down my leg and over the outside of the engine, and then put the carbs down. I then got a rag and cleaned the spilt petrol of the top of the lower engine block and when I did so it removed the black paint and grease that was on there, so I reckon I am going to repaint the engine in black at some point of this project.

So here are the carbs

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12170112.jpg

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12170203.jpg

I checked the butterfly valves and they all opened and closed smoothly by hand. I then put my finger inside each carb to just try lift up the block bit inside (dont know official name of the part) and 2 moved very freely. One then was just a tiny bit stiff, and then the last one was pretty stuck. I eventually got it to move up but it was a bit stiff to then come back down again. I guess this may be why the previous owner said he thought one of the floats was sticking (is that what that bit is called, the float? Or is it the piston?). This shows the bit I am talking about, right at the back.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12170137.jpg

I took the carbs out in to the garden then and gave then a really good spraying with carb cleaner for a initial quick clean, and will then try strip them down and clean them properly another day.

I then finished off by removing the air box and here we are.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12170754.jpg

Stuck some tissue paper then in to the 4 holes where the carbs attach to keep out any sh1t and left it at that for the day.

A question I was left pondering though was what this hole is??? It is the dark hole just above the oil filler cap in the picture below. I know on the photo it only looks like a black hole, but in fact it appears to have an open ended metal pipe inside it sticking upwards, but it has had nothing connected to it when I have been taking stuff off the bike. Anyone know what it is?

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-12165853.jpg

cant see the pipe very well in the pics but i would imagine it is the engine breather it would of had a pipe on it going into the airbox if thats what i think you mean

UPDATE

Bit more work on the bike tonight. Firstly I wanted to give the carbs a bit more of a clean up. I set about taking the bottoms off the carbs to expose the floats. All the screws came out fine apart from one where the head had been a little mashed. Managed to get a flat blade screwdriver in there though and got it of.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-13180909.jpg

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-13180915.jpg

Gave the insides of the bottoms I took off a good clean out with carb cleaner and a rag to get rid of the brown staining / marking on the insides, and then gave the floats and pins inside a good blast with carb cleaner. The floats seemed to move up and down freely when you moved the carbs about, so then put them back together and didn't do anything more with them.

Do you think there is something else I should do with them?

Then I decided to take the plunge and do an oil change. Trying to find the right socket for the sump plug and when I offered it up to see if it would fit I couldn't get it in as there is a clamp on the exhaust that clamps the 4-1 part to the individual downpipes. I wanted to take the exhaust off at some point so this then seemed like the ideal time.

Got the first few exhaust header stud nuts undone and then the next one unscrewed the actual stud when the nut got a little bot off. I guess the nut just couldn't get through a certain part of the thread and that then just started to unscrew the stud itself as it must have been the point of least resistance. Then another stud did the same thing. Going to have to get those off before reinstalling. Other than that though the exhaust came off no probs and that got me the access to the sump.

Dropped the sump plug out and the oil flowed out nicely and was still looking pretty clear. After that drain off I then removed the sump plate and that revealed the oil strainer and it looked like this:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/IMG00808-20111013-1937.jpg

The picture doesn't show it too great but there was a fair bit on gunk stuck to the gauze. So a quick clean off and a blast with some carb cleaner and it was looking much better. The inside of the sump plate looked pretty dark with all the dirt / silt that had settle down on to it so I also then gave this a good clean out and blast with carb cleaner. Came up much better.

From this:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/IMG00811-20111013-1937.jpg

To this:

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-13194726.jpg

Then fitted a new sump gasket and put the sump plate, and sump plug with a new washer, back on the bike. After this it was time to replace the oil filter. Out came the bolt nice and easy and so did the filter. I replaced the filter and the big and small rubber o-rings too, so all nice and new and clean in the oil department now :thumbsu:

Last job was to put the new exhaust header gaskets in and re-attach the exhaust. Got the old gaskets out and offered up the new ones, but didnt have time to put the exhaust back on so put the gaskets away and will fit when I put the exhaust back.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-13191020.jpg

Shoulda removed all the jets, emulsion tubes and float valves and blasted BRAKE cleaner through them and all fuel and air ways. Check diaphragms for splits and holes as well.

Shoulda removed all the jets, emulsion tubes and float valves and blasted BRAKE cleaner through them and all fuel and air ways. Check diaphragms for splits and holes as well.

I still can do that as the carbs are still sat off the bike. How do I do all that though lol

UPDATE

Finished work and got a couple more hours on the bike.

I picked up some new cylinder / exhaust header fixing studs from the local bike shop today, so the 3 that came out yesterday when when undoing the bolts have been replaced. The new exhaust gaskets then went in and then went on the exhaust no problem.

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-14171512.jpg

Then I decided to give the carbs a bit more of a clean up (on the advice of Megawatt), so took the tops of and the spring and slides out and gave them all a good blasting with carb cleaner (is this what you meant?).

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-14171026.jpg

http://i268.photobucket.com/albums/jj12/jonabonospen/1978%20Honda%20CB750KZ/2011-10-14171038.jpg

I bobbed the carbs back on with a bit of a struggle to get them to seat properly but got there in the end. Tightened up the clamps around the rubber connectors between the carbs and engine and it was time to give it a bash (once I had hooked up some fuel).

Effort No. 1

Hmmm.... that didnt go too well. Realised that I couldnt get to the throttle or choke mechanisms on the carbs very well manually so thought it was best if I took the carbs back off and attached the throttle cables and then refit the carbs to the bike. Also petrol was starting to pish out of all of the carb overflows all over the floor.

So carbs removed and throttle cables fitted, carbs back on, lets try again!

Effort No. 2

Hmmm..... In the video, when it does fire, I am actually spraying Kwik Start in to the carbs (no airbox on) and with that spray it fires up, but then it wont actually run, it just instantly dies, even though I had the throttle cranked back. I tried and tried and tried thinking that it just needed the first few little efforts until it freed up a little, but still wasn't getting it to stay running.

I put my hand on the exhaust headers and number 1 was a little warm, 2 and 3 were burning hot, and number 4 was only mildly warm at best. This worried me. Does this mean that perhaps only cylinders 2 and 3 are firing or am I just trying to read to much in to things?

Anyone got any suggestion on the most logical way forward now? All advice greatly received

Looking good

1 and 4 will be a little cooler then 2 and 3 but you shouldn't be able to tell that easily to be honest!

Did you check the float hight? Make sure fuel is getting to the carbs

Looking good

1 and 4 will be a little cooler then 2 and 3 but you shouldn't be able to tell that easily to be honest!

Did you check the float hight? Make sure fuel is getting to the carbs

I checked that the floats were moving freely on their pivot pins, but didn't check the height of them. I don't honestly know too much about carbs and all the components and how to get to them and what to clean so it is a learning experience.

Another friend has suggested taking out the jets and emulsion tubes and giving them a good clean too so think I am going to dismantle them again tomorrow but more than previously done, and give them a better clean up. Then see what happens.

Great thread and oh so familiar,much better seeing someone else doing all the hard work though

Looking forward to seeing more

Well done so far but you do need to clean the carbs properly, remove all the jets one carb at a time and clean and blow through the jets also if you have an air line blow through all the holes and tubes in the carb body do each carb in turn so you do not mix up bits from one to the other,

did you check the diaphragms for cracks splits etc, if there are any you will need to replace them, I would replace all of them as they are old, also while the float bowls are off hold the carbs upside down with the floats in place and blow by mouth through the fuel supply tube of each in turn and lift and drop the float you should not be able to blow through the fuel supply tube with the float down if you can you will need to replace the needle valves, again it might be wise to replace all of them,

I assume the needle valves are the type with a rubber tip and this may well be no good now (hard), if they are the type that are metal, check the seats are not grooved (around the point) if they are they are scrap as is the female bit screwed in to the carb body they slide in too.

Hope this helps, and I also hope I am not telling you how to suck eggs

Keith

Just veering off topic, I think you've been a bad influence on my dad! (also called Fozzie)

Just got sent a link to a Honda CB750 for pennies and he's thinking of getting it as a cafe racer project. Have you two been talking?

Ive told him its definately a good idea. However how long he would survive the wrath of my mother is an unknown.