Topic: CB750 K1 Project

[Justin]

Bought it back in January '14 with the intention of making a cool daily rider out of it. I didn't know much about the K1 and it wasn't immediately obvious that the bike is a 71 until you look at the frame and engine number. I'm not sure how much is original to it either..

Someone had "updated" it to 77-78 supersport comstar wheels with double discs up front and made a few mods to other stuff as well... Perhaps some of you can turn me on to some of the more unique 71 attributes.

I got it running and it runs well enough, I've ridden it a few hundred miles but there are several things that need attention:
The rear brake was stuck on, when I pulled the caliper off the brake pads fell apart and the piston wouldn't go back in.
The front brakes were in need of attention, too
There were no mirrors
The gauges aren't accurate at all and have nothing to mount to.. the triple tree that was on it when I got was cracked at the fork holes, and the new one that I replaced it with doesn't have proper gauge mounts..
The petcock leaked
The shocks were totally shot
There is no center stand 
The side stand is bent so it leans way too far over when it's parked.
The key lock for the forks is still frozen..
The tires were easily almost 30 years old, I promise they're at least 20 years old.

[Justin]

I'm not too sure about where the stock mounting for the ignition switch is, but it's mounted on the riser right now..
I bought a new petcock for the bike to stop the leaking.. but it doesn't seem to work on reserve hardly at all. I ran new fuel line from the petcock to the carbs, but I routed it under the carbs to fuel filters and then back up to the carbs, so the lines sit above the starter cover. only one is pictured because I had taken the other one out. I found another discussion regarding the factory routing for the lines through the carb plate but 1) my fuel lines are a little too thick to fit through the holes in the carbs 2) I wanted to use in line filters (the petcock does have the screen filter, but I'm not convinced of how well it does it's job, despite being brand new) on the lines.

My problem is this. Sometimes my 3 & 4 carbs stop getting fuel and my bike becomes a CB375 with only cylinders 1 & 2 doing any real work and a fancy air pump on the right side of the engine where I should have cylinder 3 & 4. Does anybody know if it's because of the filters?
Where is the factory mounting location for a k1 ignition switch?
How do I get the key lock unfrozen, or removed for that matter, from under the tree?

[calj737]

You've got quite a list of things to address there...

First, have you pulled down a manual? Lots of these questions can be answered that way. Another great resource, is "Hondaman's Book". It's for sale, well worth having as it discusses many design intricacies, flaws, and modifications to improve the stock bike.

The cracked trees at the forks is likely due to a missing "D" washer in between the ear clamps, that the pinch bolt passes through. This is a common occurrence, and a guaranteed result. Either buy or make your own, but put them back in once you repair/replace the tree.

Fuel starvation on 2 cylinders could be many, many things. Could be improperly setup carbs, gunk and residue from sitting, need for a rebuild. Pick one. The moral is: time to pull them, carefully disassemble them, and clean them. TONS of threads on here about this process, step-by-step with pictures, Do's and Dont's to get you through it.

Refer to the manual for removing the steering lock. It's a bit tricky, and you'll need to see a picture to get it off.

Route your fuel lines per factory, it provides the best flow. Rebuild/clean your petcock and filter. Also, examine carefully the inside of the tank for rust or sediment. If it's in there, get it out. You do NOT want that debris heading to your carbs...

Fom the manual, perform the 3,000 Mile Service. It will provide you the best insight to the condition of your new beauty, and enable you to identify any areas in disrepair, restore the safe, proper operation of your bike, and generally get very acquainted with it. It will also be the second question from anyone's mouth, the first being: "Got a manual?"

Take and post as many pictures as you can imagine. Document everything, and do your best to supply some pics when you post up a problem. It does really help those with helping you-

The side stand may have been modified to suit a smaller rider. Center stands are about, re-install is not difficult. If your tires and brakes are that neglected, then so too are your swing arm bushings, steering head bearings, wheel bearings and cables. Lubricate, replace, and service ALL these parts.

[SOHC4 Cafe Racer Fan]

All good advice from Cal above.

The stock ignition switch location is the left side frame rail (the bottom left if the three linked top rails) toward the front of the frame close to where it joins the steering stem.

[Justin]

I do have a manual, a couple different ones, only one hard copy that I'm trying not to soil too much while I'm working on the bike Definitely going to get my hands on a copy of the Hondaman book.

The cracked tree has already been replaced with one from a later 750K It was the only one that I could find that wasn't a Dime City Cycles aftermarket aluminium style. I wasn't going to ride it with the tree cracked like that but it's exactly as you said. I'm going to check the triple tree that's on there now to see if there are D washers, I don't remember them when I installed the new tree.

The carbs have been rebuilt already, I didn't use a kit but I usually don't need one. The bike sat for a long time before I got it but now it's up and running and most of the time it rides great... but once in a while (every 200 miles or so) I run into issues with getting fuel to carbs 3 & 4.

I couldn't find anything in my manual regarding the steering lock, but I didn't go page by page. Maybe I'll have a second look.

The petcock is brand new as of January, and I just got through disassembling it and putting it back together yesterday. Reserve barely trickles any gas out and it seems to flow out of only the front tube exit on the petcock until you plug it, then it runs from the rear one. I read about how the fuel is supposed to arrive at the carbs and it works most of the time but it's very possible that my fuel line routing is what's causing the carbs not to get gas sometimes.

Solid advice on replacing the rest of likely neglected parts. I'll be doing that when I take the wheels off.

Cal (or other helpful folks),
do you think that I should be running a filter over the top of the stem of the petcock inside the tank, http://www.cruisercustomizing.com/replacement-petcock-filter-screen-long-harley-davidson-sportster-big-twin-81-05/part/BC-49-2858?utm_source=adwordsfroogle&utm_medium=cse&utm_campaign=adwordsfroogle&utm_content=62249&gclid=CKa5kM2Qh74CFaNj7AodzyUALg
or should I only run the one filter screen that's in the petcock?
I wanted to be able to use fuel filters in the lines that go to the carbs... but that may be what's causing my fuel issue for carbs 3 & 4

[calj737]

I don't think the inline filter is the problem, but I'd remove it anyway to verify a few things.

How is the condition of the tank inside? If the tank is full, switch the petcock to Reserve and measure the flow of fuel. It should be equal to the Run position. If not, possibly, there's debris obstructing on the inside of the tank. The 2 fuel lines "should" deliver fuel simultaneously. The fact that #3 and 4 suffer indicate a non-electrical issue, so fuel-centric troubleshooting it is...

Can you snap some better pics of the fuel line routing? Does the line feeding 3/4 take an "upturn" along its path? If so, you could be getting an air bubble between the tanks and carbs interfering with volume or flow?

Of course, a confident carb vacuum synch is in order after a rebuild- Float height measure, all those pesky things-

[Justin]

Cal, thanks a bunch for your help.. I'm trying to figure this out..

Here's a picture of the current routing along with photos of what happens when I turn the petcock on and then to reserve

As you can see, only the one side of the petcock flows, while the adjacent side sort of dribbles a bit of fuel out. Then the whole operation comes to a trickle when you set it to reserve. Perhaps I just need a new petcock as this one is knackered?

My fingers are over the two lines where the petcock connects, and one line goes down to the 1 & 2 carb set and the other to the 3 & 4 carb set. It's funny because they both make upturns but I never have issues (that I can tell) with the 1 2 carb set. Also, the carbs have been synched by bench with the slides and then synched on the bike with a tachometer. I should probably go back and check the floats. I think #2 is sticking...

[calj737]

Have you noticed any air trapped in the inline filter for the 3/4 line when you encounter the starvation issue?

The petcock also concerns me as both ports should feed fuel constantly. One serves 1/2, the other 3/4. Can you remove and double-check the internals and the rear port for any obstructions? Again, anything about the internals of the tank? It could be debris in the petcock having been sucked up from the bottom of the tank, especially if you've run the bike on the "Reserve" setting of the petcock.

[Justin]

The tank internals are pretty clean, not bare metal clean but the inside has been coated. Each time I've taken the petcock off (I just got done cleaning and reassembling it yesterday) there's nothing in the bowl, filter, or passageways... there really shouldn't be anything in the petcock since it's new, unless the inside tank lining is shedding, but I never find debris in the petcock when I take it apart. The only thing I could think to do is to modify the actual petcock body by drilling a hole to the bowl from the other tube.

[Justin]

For some reason it won't let me post any pictures but I'll get some up soon. I've been really busy with wedding planning lately.

[calj737]

Justin - how'd you make out with the petcock/fuel flow? You mentioned a tank liner inside, is it possible when that was installed, it may have obstructed the reserve side of the outlet? I know you say that every time you remove the petcock there's no debris in the petcock or bowl, but wondering if actually at the tank there's a problem.


Looking at your posted picture of the tank, quite a few knobbies in that blue tank? Hopefully thise occurred prior to buying it and you haven't suffered a fall on the bike 

Tip: get a photobucket account (they're free) and post your pictures there, then link to them from here. It's faster, the pictures come up clearer, and you can post unlimited shots all day long! Also makes for a good "image library" for documentation for yourself as you go along.

[Justin]

Cal,
the main dents in the tank were there when I got the tank. When I first got the bike it had a fiberglass tank on it, my buddy that I bought it from found an original tank for it. The tank he bought for me had an existing petcock that was leaky at the bowl (as well as a couple dents), so I bought a petcock online (the one I was complaining about) and it turned out to be lousy, so I bought another petcock but haven't installed it yet. I started going to service/replace stuff and I decided to rebuild the bike.

The ripples in the most recent photo of the tank appeared because I was working on the gas tank and had it on a box in the garage, and when I came in to the garage the next day it had fallen somehow. 

I don't know what about the tank would cause an issue because it's just a hole in the bottom of the tank, but I guess I can't rule out an issue with the tank. I'm going to have the inside restored/coated and then restore and paint the tank.

[calj737]

I'd reverse the tank repair sequence: fix the metal then line it (if a liner is needed). Metal repairs might need heat, studs to pull the metal, pushing from inside with rods, etc...  Best to do this with no liner inside.

[Justin]

Well, to be more accurate, I've already fixed the metal, as good as it's going to get anyway
I don't have Internet at the house, I just moved, but when I do I'll post the pictures of what I've managed to do in the last several weeks

[Justin]

Update since I've been away. It's been a crazy year: Got married, we moved, got new jobs, went across the world and halfway across the US, now we're finally a bit settled.

I had a running and riding bike that needed a lot of help. I had some "upgrades" for it that I wanted to install but the more I inspected, the most dissatisfied I became with the condition of the bike overall. It had been sitting for a looooong while, so there was a lot that needed attention.

I went to convert my headlight to HID so I could actually see something while riding, maybe because I'm just used to the newer vehicles with more than adequate lighting. I had an HID lying around that actually fit the tri-bar headlight I had bought for the CB so I decided to give it a whirl.
Then I decided I should really do something about the tires before they cause me and the bike some damage. So I took the wheels off to get the tires going, with the plans to install stainless steel brake lines while I'm in there.
The calipers were disgusting and the rear one was hardly moving at all. The wheel bearings were 30 years old and the comstar wheels were actually a little rusty under all the dust, mostly on the inside behind the spokes where they're hard to clean. Oddly, the tires had tubes in them, presumably because they were equipped that way from factory??
I began to clean up the spokes on the outside, after I got all the brakes off. They looked okay after some cleaning but I still have a really long way to go with those...
I took the exhaust off and started trying to clean off all the pitting and nastyness.
Then I started on getting some dents out of the tank.

then it turned into "why don't I just restore everything while I'm in here... "
and now my garage is an organized smattering of CB750 parts.

[SOHC4 Cafe Racer Fan]

Does your particular HID have a ballast?  If so, where are you planning to hide/mount it?

[Justin]

It does have a ballast, I was under the impression that the only way you could have a true HID bulb is by use of a ballast? I could be wrong..  I'm planning on fitting it into the headlight bucket, I believe that it is small enough to get in there, off to one side or the other. I'm planning to clean up the wiring spaghetti mess now that I've torn it all apart to make everything a little easier/friendly/streamlined.

[Justin]

It's been a little while since I've been able to make any progress on the CB, the holidays and all have a tendency to do that. And it gets cold up here in the mountains of California, I don't like the cold much so I haven't been in the garage all that often.
At any rate, I've been able to make a little progress on a sunny day here and there.

I took the frame to my brother's place where it's resting for the moment until I can media blast it. It will get powder coated after I weld on the bracket for the rear master cylinder, the steering dampener, and a couple other little changes I want to make. I'm going to clean up the factory welds a little more and I'm considering adding a gusset at the steering head where the top tube and sides come together, if it will add any strength or reduce flex I'm not sure.

I've begun some work on the engine, disassembling the top end and examining what I have here. The engine appears completely factory, the pistons measured 60.61mm across (roughly, they were each ever so slightly different each). The top end looks unadultered.

I did most of the engine work in the front yard because it's much warmer than in the garage during the winter, and there's much better light. I also don't have a ton of work space left on the work benches, so it seemed to make sense at the time. I took the head and cylinders to work and put them in the parts washer so I didn't have to clean off so much crud. They're going to get painted anyway but it's nice to work on it when they're not so coated in 40 years of road grime.

[Justin]

I was able to get some time in on Saturday working on the bike a little between bursts of rain. The valves are going to get replaced for sure after looking at them..

I media blasted the frame using coal slag and walnuts, and I was able to do the front brake calipers as well before I ran out of blast media. Next is some welding for the frame and powder coating.





On a side note: we've started on my wife's motorcycle - 1974 CB360 ruination (it was a crazy steal..  )

[Justin]

Got some parts back from the powder coater. The whole frame will be done like this after I finish cleaning up the factory welds and welding on the steering dampener bracket and the rear brake reservoir mount. These are just a sample of a couple parts my friend did. The pictures don't really do them justice, they're beautiful.

[Justin]

These were just media blasted and powder coated, gloss black with a tiny bit of copper and a blue metal flake look

[Justin]

I also soaked the engine cases in hot water mixed with Simple Green Xtreme and then scrubbed all the gunk off. I'm going to paint them after I finish the prep.

A bunch of parts are getting prepped to get sent out: rocker arms are probably going to Megacycle to get hard welded, head is going to JMR for porting/polishing , crank and trans going to APE for some talented work. Can't wait to flip the direction on all the wrenches and start putting things back together!!

I still have a bunch of internals that I was going to glass bead blast when I get some free time in the shop.

Is there any place else I should be considering for sending the rocker arms to be hard welded? Megacycle is here in California and they're hard welding the cam so I figured that it couldn't hurt to have them done at the same time at the same place. 

[calj737]

+1 MegaCycle

[Justin]

WOO!!! Got some goodies in the mail today, long awaited! Still waiting on quite a bit of it.. Shouldn't be too much longer to come in. I've love to start making some real progress. The valve train arrived and the cam chain are here, still waiting on the rest of the engine bits.

[Justin]

The photos didn't work from my computer but here it is from my phone, probably not that great of quality