Topic: Ugly CB750K4 Rat Resto

[newday777]

Well I read back through your posts in this thread to try to figure out 1st how you cleaned the carbs as that was my 1st thought being dirty carbs. Did you fully strip the carbs before you ultrasonic cleaned them? What solution did you use in the cleaner and how long of time(I also have the hf ultrasonic cleaner and know it only goes @ 7 minutes and shuts off), did you use preheated distilled water?
Did you derust the tank? Even surface rust in the tank can put particles in the carbs causing problems.
Also, you used the keyster float valves? The aftermarket brass is known to give tuning problems, includingthe float height settings. Highly recommended that you only use Honda brass including the float valves. I think Mark(Hondaman) posted the other day on float heights in another thread.

Yes vacuum syncing the carbs is necessary, bench sync is just to get it ready to use vac gauges to dial them in to the motor.

The whitish smoke.... I read you put in standard pistons and rings in your first post??, should have bored it to bigger pistons and rings as the cylinders are probably tapered bigger from wear at the bottom of the stroke (per Hondaman's book).

Derusting tanks by electrolysis

I go a couple steps further than this guy went, after the electrolysis cleaning and water rinsing, using 5 gallons of Evaporust for 2 days, followed up immediately by rinsing with diesel fuel several times, wiping the inside with rags on the graber tool, heat the inside of the tank, then coating with the tank 2 stroke oil. The diesel fuel has oil in it which helps grab moisture from the tank and helps to protect from flash rusting that water rinsing causes.

[Jake88]

Well I read back through your posts in this thread to try to figure out 1st how you cleaned the carbs as that was my 1st thought being dirty carbs. Did you fully strip the carbs before you ultrasonic cleaned them? What solution did you use in the cleaner and how long of time(I also have the hf ultrasonic cleaner and know it only goes @ 7 minutes and shuts off), did you use preheated distilled water?
Did you derust the tank? Even surface rust in the tank can put particles in the carbs causing problems.
Also, you used the keyster float valves? The aftermarket brass is known to give tuning problems, includingthe float height settings. Highly recommended that you only use Honda brass including the float valves. I think Mark(Hondaman) posted the other day on float heights in another thread.

Yes vacuum syncing the carbs is necessary, bench sync is just to get it ready to use vac gauges to dial them in to the motor.

The whitish smoke.... I read you put in standard pistons and rings in your first post??, should have bored it to bigger pistons and rings as the cylinders are probably tapered bigger from wear at the bottom of the stroke (per Hondaman's book).

Derusting tanks by electrolysis

I go a couple steps further than this guy went, after the electrolysis cleaning and water rinsing, using 5 gallons of Evaporust for 2 days, followed up immediately by rinsing with diesel fuel several times, wiping the inside with rags on the graber tool, heat the inside of the tank, then coating with the tank 2 stroke oil. The diesel fuel has oil in it which helps grab moisture from the tank and helps to protect from flash rusting that water rinsing causes.

Thanks for the reply. I did fully strip the carbs before putting them through the ultrasonic cleaner. I used half pinesol half water.  The mix was preheated. Each carb got run for several cycles or until I felt they were clean. 

The temporary fuel tank I'm using is clean. It's also got a screen inside and I've got a inline filter.  I've used vinegar and evaporust on different occasions for tanks. Never tried electrolysis. 

Yes, the keyster float valves were the only brass part I used out of the rebuild kits. The old float valve needles had wear marks on the tip. My thought was that The new ones would be better even if they were not Honda. If I test them, and they shut fuel off, is there any reason to replace them with Honda parts? Just seeing what the thought is on the matter.

I will vacuum sync the carbs, but I haven't looked into where to start. I don't have that equipment on hand. 

Correct, I put standard rings and pistons back into it.  As accurately as I could measure with what I was using, cylinders seemed in spec And the ring gaps with the new rings checked out.  Going back, I probably would have had them bored, but it's all back together now.  The smoke is pretty minimal. I've also got good compression in all cylinders.  Could the smoke clear up after the rings have a chance to seat in?

[RAFster122s]

Keyster needles can be a bit longer and this can cause the float height set by distance to not have the correct fuel levels in the carb. If I recall the discussion about this correctly...

[newday777]

Keyster needles can be a bit longer and this can cause the float height set by distance to not have the correct fuel levels in the carb. If I recall the discussion about this correctly...

That's about what I remember reading too.

[Jake88]

I could see that being the case. I've still got the old ones, so I guess I could stack them up against each other and see the difference. Is there some kind of adapter I can buy to screw into the float bowl drains and connect some clear tube to check the actual fuel level in the carb? Seems like I've heard of people doing this but not sure what equipment I need to get the clear tube on the carb. 

Another thought.  Does any of this sound like it could be caused by a vacuum leak? Besides the carb boots, where are other common sources of a vacuum leak? The little rubber grommets that go around the throttle slide rod Don't appear to be making a great seal.  Could that be an issue? 

I ordered a four dial carb sink tool last night.

Thank you for the thought-provoking ideas and help. 

[Jake88]

Update. 

I took an aftermarket float valve out to compare to the stock float valves. The needles on the keysters were longer than the Honda needles, but The hole in the seat that the needle rides in is deeper on the keysters. When they were stacked up side by side, the height to the tip of the spring from The surface of the seat that goes against the smash washer/carb body was the same.  But there was a difference in the stiffness of the spring on the needle. Aftermarket was stiffer. It seems that it's possible that this would not allow the float to float as high in the bowl and a 26 mm measurement with the aftermarket float valves would result in a lower fuel level in the bowl.  That is assuming that the spring is actually depressed by the force of the float. I don't know that to be the case.  But even so, maybe a millimeter or two?

I adjusted The float on the outside number one carburetor to 25 mm instead of 26 to see if raising the level of fuel would do anything. Before this I used a clear tube and it looked like the level was about 5 mm below the top of the bowl. 

I also got my vacuum meter set in the mail. I warmed the bike and got everything hooked up. The difference in vacuum between the cylinders was not great, but cylinders 3 and 4 were higher than 1 and 2. I got everything synced up as best as I could. It will idle under 1000, but I have it set to about 1100.   

Seemed like a good time too see if the transmission worked, so I wired my janky fuel tank up to the left handlebar and put a rug over the battery for a seat. I'm running on old rubber and with only a back brake so did not get too carried away and just went up and down my street a few times.  It seems to shift well. Power delivery seems smooth, though I did not get on it much. Seems that the white smoke I had noticed before has cleared. Maybe having to do with getting the bike hotter than I have previously.   Cylinders one and two are still running cooler than three and four. Maybe running Richer?  I've got the air mixture screws turned out 1 and 1/2 on those cylinders compared to one turn on three and four. My understanding is that turning out is supposed to lean things down. I will have to fiddle with stuff more.   Pretty pumped that she moves and shifts!

[Jake88]

Pics

[Jake88]

I've created a monster... Seat. I've used black duct tape to patch vinyl, but I've never taken it this far.  I hated the look of that king and queen seat, so I cut it as close to the shape of a CB750 seat as I could and upholstered it with gorilla tape. I'm on the hunt for a real seat, but this will give me something to sit on in the meantime.  The tank has a few pinholes in the top. I think the tank is beyond saving as it looks like someone beat the piss out of it at some point. I think I'm just going to leave it bare And fill the pinholes with JB weld.  My goal is to find a tank with some original paint on it.

[SOHC4 Cafe Racer Fan]

The tank is saveable, but you'd likely need to braze-weld the pinholes, and then line it with Caswell expoxy (and have it pressure tested to make sure you got everything plugged).  It will also require a fair degree of bodywork and paint.  Yes, much cheaper to find a replacement with paint.

[Jake88]

A little update.

I got the tank patched up with JB tank weld.  That stuff is kind of fun to use.  It's a putty that you cut from a stick and kneed together. It sets up rock hard.   

I've taken it out on a few short spins, but I'm waiting till I get my new tires on in the next few days to really give it a go.  It seems to be running okay, and pulls hard when you get on it. The throttle is very stiff, I think due to a very stiff throttle return spring down at the carbs. Might try to remedy that. Cylinders one and two still seem a little weird at idle.  The little bit of smoke from the exhaust seems to be getting better. 

I had an oil leak that ultimately made it to the floor at the left foot of my center stand. Turns out it was coming from the chain oiler. Something I did not even know these bikes had, though I was wondering what that slotted screw was in the middle of the drive shaft. I tightened it all the way, we'll see if that stops it.

I put some inline filters in the fuel line. I think the tank is pretty clean after my efforts but wanted some insurance. I'm not crazy about the route I took with the fuel lines coming in from the bottom. Does anyone think that the screen in the petcock is good enough and I can remove the inline filters?

I took the front wheel off last night and removed the tire. What a b****!  I've got new bearings coming shortly so I drilled out the punch marks on the retainer and used a punch to get it loose before switching to a pair of needle nose as a spanner wrench.  Worked like a charm. Bearings came out with out too much fuss.  I can't for the life of me find my set of tire irons anywhere. I'm going to try the zip tie method. I'll let you know how it goes. 

[Jake88]

Pics

[Jake88]

Today I replaced both tires with Dunlop k70.   The rear hub was a bit of an adventure. Did not realize there was another retainer underneath the drive plate. Figured it out before I caused any damage trying to pound the bearings out from the other side. All in all everything went pretty smooth. The new bearings went in easy enough and the zip tie method worked pretty darn good for getting the new tires on. I was able to fire it up and cruise up and down the street a few times before dark. With new rubber and bearings under me, I might try to get out tomorrow and explore the throttle a little more. 

[Jake88]

Pics

[Jake88]

I wanted to share this picture of a photo that my dad sent me. He was visiting his home area and saw this at the historical building. It's a photo of four guys getting ready to leave on a long trip. They all have cb750's.  You can see the one license plate is from 73. Look how high those things are piled!
Just thought it was cool and wanted to share.

[newday777]

Yes that is cool Jake.

[Jake88]

I was out messing around with a cracked side cover last night. I used a crack stabilization technique that I've used on my three-wheeler. Thought I would post it up in case it could help someone.

I cut little half inch pieces out of a paper clip. Lay one across the crack and then used an old wood burning tool I've got to heat it up. Put the tip of your wood burner or soldering iron right on the center of the wire and once it gets hot enough, the wire will start sinking into the plastic. Sink it about halfway into the thickness of the side cover and then use the hot tip of your tool to pull molten plastic over top of the wire. When it cools, the wire reinforcements are locked inside.  Better than duct tape!

[Jake88]

So it's looking like I need a new valve cover.  If anyone out there has one we could do business on, please let me know.

I have a spare

Awesome! I sent you a message. 

Replied

I think this build thread has run its course for the time being. The bike is together and running. I'd like to think everyone that lent their knowledge and helped me through this project. A special thanks to stev-o for hooking me up with that valve cover and a sweet SOHC t-shirt!

I plan on sprucing the old girl up over the course of the winter.  I"ll throw up some picture updates from time to time. 

Take it easy!

[Stev-o]

Is this the bike you are looking for a rear wheel for?

[Jake88]

Is this the bike you are looking for a rear wheel for?

Steve.  Nope, I've got a good rear wheel on this old girl! You must be thinking of some other project.   The only thing on my list for now is a new seat. And maybe some factory paint someday!

[newday777]

Is this the bike you are looking for a rear wheel for?

I saw a wanted post for the rear wheel by another Jake(jakec) that you replied to Stev-o

[Stev-o]

Is this the bike you are looking for a rear wheel for?

I saw a wanted post for the rear wheel by another Jake(jakec) that you replied to Stev-o

Oh yeah, wrong Jake....sorry.

[PeWe]

Bike look good and almost there....
There are good looking stock seat replica seats for not that much.
Repaint tank and side covers too stock style and correct color will lift the status several notches.
A bike people will comment with their old memories from the days when you have stopped at a cafe, restaurant or gas station.

[Jake88]

Bike look good and almost there....
There are good looking stock seat replica seats for not that much.
Repaint tank and side covers too stock style and correct color will lift the status several notches.
A bike people will comment with their old memories from the days when you have stopped at a cafe, restaurant or gas station.

Thanks. I actually just ordered a seat from David Silver a few days ago. Along with a whole slew of parts for a CB175 I'm working on! 

[Jake88]

Wanted to give an update on my project.  My 750 is now sporting a new aftermarket seat and some faded 70s paint! I think it looks a lot better.

I found the tank sitting in the far back corner of a little old-school motorcycle shop in Western IL. $100.  The side shown here is much better than the other side of the tank, which is very sun faded. It must have sat outside for a long time. It is however indecent enough shape and only has one small dent. The old guy that owns the shop cleaned it out with muriatic acid and lined it with red kote.  The lining appears to be in good shape And the tank does not leak.  I repainted the badges, but I kind of like the patinaed tank and plan to just run with it as is for now.

The saddle is from David silver. The cheaper of the two options. For the price, it seems to be pretty good quality. Metal seat pan complete with a compartment to store papers. I bought a stencil and painted Honda on the back.

Also included a picture of my freshly painted 71 CB175K5.  With all the black pieces painted, I feel like I'm on the downhill slide with that project. Hope to have it together and going by July

I hope everyone had a good winter!. 

[newday777]

That's a good price for the tank you found. 👌