I decided to try and keep track of some of the relevant parts of the revival of this bike that hadn't been running for 14 years, yet seemed to be in good shape. Hopefully I can get some feedback on a list of questions that will arise during the project and at the same time return the favour! Like I said, I made some pictures but when I started I didn't yet had in mind to document the project, so it might look a bit incomplete.
Let's start at the beginning:
The bike was stored for 14 years in a nice place where it was waiting for the owner to restore it. However, he passed away and we ran into a friend of his selling it. It looked in pretty good shape, as far as I could tell. Hooking it up to a battery showed life in the electrical system! Running the starter motor indicated that the pistons were still able to move, but the starter motor seemed to spin in overdrive after a few seconds of trying to get it starting. Starter clutch broken?
We bought the bike, shipped it to a place closeby and figured we'd start by cleaning the carbs.
Those float chambers look like they used to contain some petrol...
Hmm... torn air cut-off valves!
Most float needles were stuck or the spring inside didn't move any more. It also looked like some were a bit worn so I wanted to replace them.
This is where I got the first surprise. Judging by the pressed idle jet, idle jet screws, black floaters and float needles with springs, these are '79 carbs and not post '80 carbs. Correct? Is it likely that these are carbs which did not belong to this bike, or was there a small overlap with '79 carbs being used for '80 bikes?
This idle jet screw looks a bit bent as well
At least it came out, which cannot be said from its neighbour which required drilling... Probably need to re-tap this. Anybody who knows what type of thread it is? M6x0.75?
Another surprise... someone before me tried removing the emulsion tube and destroyed the top of this one. No way I can remove it with a normal flat-head any more. Guess it will just have to stay in there...
Bit of cleaning before going into the ultrasonic bath! Already looking nice and shiny.
Ah, some new parts. I must be honest though, I'm on a tight budget and am trying to balance cost and effectiveness in a sensible way. Afterall, I am Dutch
This set however also contained one large O-ring which I couldn't place. But the set is also supposed to fit other bikes, so maybe it's just not used in these carbs?
Reassembly!
Fresh jets and adjusting of the floats
Good old Haynes to help me out as well. And who needs a garage when you have a living room!
Nice and shiny...
And that's where the images run out. Although I wanted to fully reassemble the carbs, I noticed that I lacked two 010 o-rings for the fuel rail, so I'll need to order that.
Some questions that I have and couldn't yet find an answer to although I used the well known MacGregor pdf for a large part:
- Is it a problem if I replace all the old (pre 1980) idle mixture screws with newer (post 1980) versions? Do the same number of outward rotations still apply? If I remember correctly it's 1 and 3/4 rotation.
- When removing the choke rail, I noticed 6 cotton like rings that started to fall out on the inside of the carbs where the rail would go through. These all came out after the ultrasonic bath and looked quite worn and non-reusable. When I look into the side of the carbs there's room for a small ring, but I had no O-rings that would fit into it. I looked at CB750 parts sites but couldn't find any indication of these rings being sold. Can I just leave them out? I can post another picture if it isn't clear.
- I tried cleaning the pressed idle jets with a .010 E-string but wasn't sure if I got through them. I'll probably use the trick of spraying in some (Brake/Carb) cleaner to see whether it comes out at the idle mixture screw. But I'd like to know if the E-string should in theory be able to go right through or get stuck after going in a few centimeters?
That's it for now. Hope to fully reassemble the carbs soon, but most likely I will check if I can get a spark from the 4 spark plugs this Friday. I am afraid both CDI/Spark Units might be dead (black tar running out) and perhaps a dead pulse generator as well, as I only measured resistance on one of them and it was a bit low (390 Ohm instead of 510?)
Keep you updated and would love to hear some comments on my project!
Hey I think the starter going into over drive is definitely the starter clutch. There's a few pictures explaining how to fix it on my build thread. It's usually worn out springs. Does it make a terrible clanking sound? Kind of whirls?
1981 SS with Kerker 4-1 exhaust and extremely attractive rider.
Hi, not sure if it was a clanking sound (which I would see as metal hitting metal) but it did sound like a whirl or just simply an electric engine without resistance making lots of RPM.
What I also noted was that the starter motor cover had only 1 screw as one of the holes didn't seem to align with any thread, as if the starter motor cover didn't match. Normally you screw the cover to the starter motor, do you not?
Those large circular of-rings are likely for your float bowls. Almost useless as far as I am concerned. You really need the formed ones. Did you buy a cheap carb rebuild kit? I'm Canadian, and the lesson that you get what you pay for is something that I seem to need to learn multiple times....
Welcome to the forum Ruben. You have a sweet bike; especially for it sitting 14 years. It looks to have minimal rust and complete; defiantly a plus. Your idle mixture screws should be 3 complete turns out from the bottom of the carburetor throat. There should be no problem with your new pilot screws (idle mixture screws), just make sure you removed both the old flat washer and rubber o-ring, replacing them both.
I’m not 100% sure if those felt o-rings are necessary. I wouldn’t replace them with a rubber washer; that may cause friction and binding. If you can replace them with another felt o-ring, I would, but looking at mine, there is always going to be some escaping air, that washer doesn’t seal it completely, it just eases movement I believe. Make sure your choke plates close completely, and I wouldn’t worry too much about it, the hole on the inside of the carburetor body is fairly tight to the choke rail.
Your E- string should stop at about 3.81 cm, or 1 ½ inches from the top of the tube. You will want to wrap tape around your carburetor and throttle spray straw to make a tight fit into the slow speed tube (middle tube). Hold a thumb over the primary main jet hole (tall tube), a finger over the low air cut off hole, and spray. If the hole is clear you should get a spray out of the pilot hole. I had one carburetor I had to repeat the pin sol dunk until this passage came clean. I would get a spray out of the secondary main air jet, and primary main air jet, but nothing out of the pilot screw hole (idle mixture).
Before checking the electrical system, make sure you have a charged motorcycle battery, to get a good reading. There are a few steps in the factory service manual that trouble shoots the ignition system for our DOHC bikes. Your spark units should read 12V with a fully charged battery. I will attach the trouble shooting method with pictures.
They are made in Japan (TourMax), but not that expensive. I ordered it at the garage I am working at on Saturdays, as they can get it a bit cheaper. I think it's this set
The big O-ring is still smaller than the pre-shaped rings for the vacuum piston, if that's what you're referring to?
@myTUNES
Thanks for all the information! Will replace the o-rings and washer for the idle mixture screws.
About the felt (that was the word I was looking for) o-rings: I agree that it probably wouldn't prevent air leakage and will most likely function to keep out dirt etc. Although I will try to think of a possible way of creating these rings myself.
Also bought a new battery and fully charged it. The link to creativeconceptcomputers.com isn't working for me though?
Today me and a friend checked the ignition circuit, which appeared to be somewhat different from the Haynes manual. It had no 6-pin red connector but two separate connectors. One 4-pin for the Pulse generators and a 2-pin for the engine oil and neutral lights:
To our joy hooking up a new battery resulted in 4 sparks! A little bit of a surprise as I saw the black tar that had leaked out of the CDI/Spark Units. We measured both of them and the current was either 11.4V or 1.4V (when grounding) for both spark units. The Haynes manual says it should fluctuate between 0 and 12V so I'm not sure whether this is acceptable enough?
We also measured the pulse generators at 475Ohms and 490Ohms. the 475 is a bit low but probably acceptable.
Didn't check the ignition coils, but I suspect them to be fine considering we have 4 sparks?
The starter engine was giving some issues though. It would either not start and you would hear a *clack* from probably within the starter relay, or it would turn but not always grab the crankshaft. It appears the starter engine is not original either as there was no thread for one of the screws (as I said before) and part of the housing seemed to be filed:
I took of the left crankshaft casing to have a peak:
Can I remove the starter clutch with a big spanner for the nut while holding the centre with an allen wrench?
Finally, I checked the frame number with the engine number using the Haynes and we discovered it can't be a '80 CB750! It's one of the first engine numbers: RC01E-2000008 of the US models. So I am guessing even the 8th engine produced?! It would mean the bike was introduced September '78 which also fits the pre '80 carbs. And am I correct in thinking that the engine and frame number don't necessarily need to be the same? I believe the frame No. is something like 2015377.
All in all a good day and came home with a smile. Can't wait to get those carbs finished and give it a try!
huh, weird. No idea what those round ones are for. The only place I think you could use them is where the cap interfaces with the body of the carb, but there is a stock hard plastic piece there that doesn't wear out.
My starter clutch also had a bolt not an allen. interesting. The link that sees sent is also what I used to fix my starter clutch. Theres a little bit that he leaves out at the end though. Basically you need to put the gear back on the starter clutch assembly BEFORE you put the rollers back in and seal it back up. I think he just says don't let this happen and its a picture of the assembly and you're left scratching your head...
1981 SS with Kerker 4-1 exhaust and extremely attractive rider.
The reason the link probably isn’t working for you is because you don’t have adobe flash player. Don’t install chrome if you don’t want to, but to get the most out of these forums, the FSM (Factory Service Manual), and other posted manuals, you will need the adobe flash player.
I had the same issues when I would first try starting my bike. When it doesn’t turn over at all, it is usually the starter solenoid (relay) that is going bad. Next time it won’t turn over at all you could try tapping the solenoid (relay) with a screwdriver. The whining sound you hear is probably those three screws on your starter clutch being loose, or your springs behind the starter clutch being worn out. If you can replace those springs with new ones, that is always a good idea regardless. Just get some loctite, dap a few drops on the three screws, and tighten back. The starter solenoid (relay), if you do need one, is a 16 dollar part on e-bay. You’re doing great so far dude; it will be no time now.
Join this forum too. I’m sure they will love to see your bike as much as we have. They are very knowledgeable about our DOHC bikes.
www.cb750c.com
I have attached a link to one of their write ups about the OKI spark units leaking the potting goo, and how to fix it without replacing, save a $100 bucks just because you know what you’re looking at.
Also, it will be the allen head bolt that will come off of the advancer I believe, but yes hold the nut and turn the allen head to remove, or vise versa. Lol This 78 has me wondering myself, factory differences are cool commodities.
Finally, an update! Sorry for the long silence, but I was waiting for one carb to return from a guy doing a free repair on the tube holding the idle mixture screw. As I reported on earlier, one of the idle mixture screws had to be drilled out, leaving a damaged thread and not enough room to use something like a heli-coil. Not wanting to do a half decent job, I sent it out to a professional (the guy was making imitation Ferrari engine blocks). Since it was a free job, I didn't wanna rush him. Besides, I also received a CB1 that suffered fire (and water) damage. Got it running again, but the bike needs some love.
In the meanwhile, I tried to repair the starter motor (originally belonging to a Kawasaki, I think) which had badly connected brushes. Did a half decent finish, but the starter motor seemed to be working ok.
So the actual update with some pictures and videos!:
2nd carb from the left has a new idle mixture screw seating (also put in mixture screws from a newer CB750)
A better view:
Assembled and all! Some new screws where needed. Assembling the choke rods and springs was quite a tedious job, but eventually they were working as intended. Smooth operating:
Not attending to win any beauty contest. First want to know if this baby will be the effort by getting it running:
Then came the assembly on the bike. I had reassembled the carbs before on a 750 Nighthawk, and remembered that the air box rubbers were giving me some trouble, but this time.... *#&@!!1 What a pain! Took over an hour and still they don't align up. It was as if the airbox was pulling the rubbers of the carb intakes. I think they still aren't properly seated, but it had to do for a first try. Maybe they are just old and dried out, but still.... I noticed the center two rubbers had a L and R stamped on their sides. Tried to align them in such a fashion that L pointed to the left drivers side (makes sense right?). However, the rubbers were almost always pulled of the lower side of the carb intakes. Anyway, just continued after a while.
Everything connected to give her a first go!:
So, battery check, fuel check, choke check, let's see what happens (let me know if the video isn't working):
Hmm, there seems to be some ignition of fuel, which is promising. However, the starter motor stopped working. Not sure whether it was the battery, or the starter motor. The starter relais clicked, but nothing else happened. After switching to another battery, still just the starter relais clicking, so I suspect my starter motor fix wasn't much good. However, the (supposedly new) battery I first used only gave 12.2V output, which is quite low?
So, only way to get it starting now is by roll starting the motor. So that's what we did. And behold, it started within a few meters! (Sorry for the shaky video)
However, there's a nasty rattle coming from the middle of the cylinder blocks. Disappears when revving higher. My guess would be the camshaft chain being too slack?
Other than that, it ran quite ok and responded nicely to the throttle. Some popping when closing the throttle, but still need to adjust the idle mixture screws (currently 2 turns out). Haynes says 1,5 or 1,75 turns out for VB42A or C carbs, but mine are VB52's.... Any ideas on how many turns out they should be?
Very glad to have it running after 14! years of standing still, and hope the rattle can be fixed! Happy to hear your input on it.
The cam chain guide missed one bolt and the other two mounts had broken off! It was basically jumping up and down the connecting cam chain all the time.
So, the previous owner had either forgotten one bolt and this caused the chain guide to vibrate and eventually break, or the bolt wasn't tightened enough and came loose. In the last case, my question would be, where could the bolt have gone? Since the engine turns, it's not stuck between any gears. Could it have fallen between the camshaft chains into the oil pan?
Some more pics showing the broken hinges of the cam chain and a time-sert on one of the camshaft guides. I'm still a beginner at this, but it looks to me like the previous owner also put on quite a lot of sealant:
Picture of the other side. Sorry for the fuzzy quality. The red arrow indicates where a bolt was missing, causing the chain guide to vibrate and break.
Shortly ran the bike afterwards (with the valve covers on of course) without the camchain guide. Sounded much better:
So my major question is, where can I expect to find the missing bolt? And secondary, is the guide needed to safely run the engine? To me it looks like it's mainly to keep the chain from wobbling too much if it is loose. We adjusted the tensioner, and the chain seems pretty tight, so I wondered what the function of it is.
Pull the oil pan. I really hope you find it there.
Also check the condition of your b chain tensioner. It may have failed.
Sent from my BlackBerry device
From: Ruben [via Honda CB750'S]
Sent: Friday, May 31, 2013 4:03 AM
To: seestheday
Subject: Re: Reviving a CB750K(Z) '78 - 1st bike project
Another update:
So I found what was causing the loud rattle....
The cam chain guide missed one bolt and the other two mounts had broken off! It was basically jumping up and down the connecting cam chain all the time.
So, the previous owner had either forgotten one bolt and this caused the chain guide to vibrate and eventually break, or the bolt wasn't tightened enough and came loose. In the last case, my question would be, where could the bolt have gone? Since the engine turns, it's not stuck between any gears. Could it have fallen between the camshaft chains into the oil pan?
Some more pics showing the broken hinges of the cam chain and a time-sert on one of the camshaft guides. I'm still a beginner at this, but it looks to me like the previous owner also put on quite a lot of sealant:
Picture of the other side. Sorry for the fuzzy quality. The red arrow indicates where a bolt was missing, causing the chain guide to vibrate and break.
Shortly ran the bike afterwards (with the valve covers on of course) without the camchain guide. Sounded much better: http://youtu.be/bxMBLAMU6uE
So my major question is, where can I expect to find the missing bolt? And secondary, is the guide needed to safely run the engine? To me it looks like it's mainly to keep the chain from wobbling too much if it is loose. We adjust the tensioner, and it seems pretty tight, so I wondered what the function of it is.
- CB750K(z) '80
- BMW K100RT '88
If you reply to this email, your message will be added to the discussion below:
You should really pull cams and cam chain off to get a good look at it.
In a pinch though, you should be able just see if the chain running between the cams (cam chain b) is tight. If there is slop in it then you either need to tighten it or the tensioner has failed. The tensioner is below the B cam chain and presses on it from the bottom.
Also - this is likely a bigger problem that you need to pay attention to: it looks like someone used a lot of blue silicone sealer to seal your valve cover gasket.
There are a lot of threads over on the C forum about how this stuff is a recipe for a blown engine. The silicone dissolves in the oil, breaks off in boogers, and clogs oil passageways.
Clean it all off, pull your oil pan, and clean the oil screen. You will likely find silicone boogers in the oil pan. Change the oil, filter, get a new valve cover gasket and then run some seafoam through it.
If your valve cover gasket is leaking, first get all new valve cover bolt grommets, and if it's still leaking use a little bit of hondabond or yammabond (not the HT stuff, but the kind that doesn't say "silicone" anywhere on it).
WOW!!!
I agree with Seestheday, you need to pull the oil pan and see what carnage lays within.
I have a feeling you are going to find bits of metal, ground up rubber, along with the blue silicone laying in the bottom of the pan and in the pick-up screen.
Do not run your engine without the tensioner, no matter how "tight" you chain feels. It is there to support and guide the chain along the span between the cams. If it wasn't needed it wouldn't be there. The Factory Engineers don't design in extra parts.
81 Honda CB750C - Current Project
67 BSA Spitfire MkIII - Next Up (Full Resto)
81 Honda GL1100 - Bob / Cafe´
80 Suzuki GS750L - Bratstyle
72 Honda CB450K5 - Basket Case
73 Honda CB350F Cafe' (Gone but not forgotten)
Don't wait for opportunity to knock... kick the door down and drag the old harlot in!
Well, I opened up the oil pan. The 4 in 1 exhaust was sort of in the way but after removing it, the pan came off easily after a whack with the rubber hammer. So what did I find?
A bolt! Let's hope it's the one fron the cam chain guide :D
The oil screen didn't look too bad in my opinion. Not as clogged as I was fearing.
The oil pan itself had a bit of sludge in it but cleaned out nicely.
Will order a new cam chain guide of course and oil filter and oil pan gasket (broke as I removed the pan)
Pfhew, glad I found the bolt though. Would it be useful to use some Loctite on it during reassembly?
Locked
