Tag: CB750F

Tonight was mostly Q&A along with cleaning; I won’t be able to rebuild the carbs before class ends tomorrow.
May I leave the trickle charger on? Yes. Does the kickstand or center stand need new rubber? No and maybe. Ratio of water to simple green for the ultrasonic carb clean? 2/1. May I leave parts here over break? Yes. Do I need to replace the gas in the tank? No, it is already OK. Should I get a new air cleaner? Yes. Does carb cleaner damage the seals? Yes, that is why we took them out. How do I measure the petcock line? Inner diameter. Are digital torque wrenches any good? Maybe, but they are generally fragile.
Took the exhaust, muffler, and chain guard home. It took a while but I cleaned most of the 3cm of gunk accumulated in the chain guard off.
Continue reading “CB750F: Day 08”

Today I was well enough to even think of working on the bike, at all. Got back to researching a carb rebuild kit. It has been interesting searching for one, Pat helped me find one that probably works and then I searched for more and got these results:
denniskirk.com: no
knfilters.com: no
outwestmotorcycles.com: no
randakks.com: no
vintagecb750.com: Probably part # 48-1963
mrcycle.com: no
ebay.com: no, or rather found the kit fro Kaizen without jets
dimecitycycles.com: yes
partsnmore.com:no
mrcycles.com: individual parts
bikebandit.com: individual parts but no microfiche!
cheapcycleparts.com: individual parts
In summary, there are not a lot of kits.
Only one, and two if you count vintagecb750 with a big “maybe” since it doesn’t specifically support the model I need. They do have one model specific kit, but it doesn’t have new jets, and that is the plan. I will go with dimecitycycles.
It has been interesting learning about how well this model is supported. My original idea was to go with a Honda CB750 because there is such good support for it out there. From what I am seeing, this model was not as prevalent as the touring style bike, so there isn’t as-good support. Also choosing first year of the model was a mistake. With persistence and patience though it should go fine.
Although I did purchase the original service manual along with the Haynes, resources like mrcycles.com that have the microfiche for the OEM parts online are extremely helpful for managing the replacement of parts.
The paint store had Simple Green for sale, so I bought some. I figured since the bike is mostly stripped down I can clean off the gunk that has accrued everywhere, and that it is less inexpensive in time and money to completely disassemble the bike and refinish it.
Addendum: 01/18/13
power-barn.com doesn’t have kits, either.
jetsrus.com, no.

Need to order a new fuel line, it is pretty neat because although it is now totally inflexible, it had still worked correctly. There is probably a painful metaphor hiding in there.
Took the jets out and put them in order. The idle jet has “98” written on it, the one on top (T). Before taking the idle jets out turned them to all the way in and wrote that down so I install the new ones at the correct setting. There is oxidation in the float bowls, I’m going to buy an ultrasonic cleaner and use true green on them, and put the whole rack in the dip tank next week. Used a socket for the topmost jet. The pin holding the 4th carb float didn’t want to come up but was coerced eventually.

Sprayed carb cleaner in each of the jets and on the parts a little bit. Pat found the kit I need on http://vintagecb750.com/, the key was to select “Series 2”!
The right-hand grip is all rotten, pulled the tape off.

Need to order parts and an ultrasonic cleaner, too.

Tonight I pulled the carburetor rack out. Visually it appears that they won’t come out. Just starting at it you see that it has to be lifted up from the air box side, but when you try it, it barely moves. Left the two choke and one throttle cable hooked up, and tried to stand over the bike and it was still not enough. The start of it is just lifting it up to give it some space.

Finally I just focused all of my pulling on the right side and then it popped right out of the manifold side. In the future, I would slide the metal retainer on the air-box side shrouds all the way back, I think that they were holding the carbs in, and made it difficult to get out. Also when I did pop them out, the retaining clips were sort of mangled out of shape, but not damaaged though, I just bent them back into shape.

Then I pulled out the left side.

In the process, the rings on the air box side got kind of twisted out of shape so I squeezed the back right. That left the row of carbs just sitting in there. It didn’t want to slid out because the throttle cable was blocking it from coming out, so I removed that. It didn’t resist, I should check if that is a problem. I couldn’t figure out how to disconnected the choke and my teacher, Pat, showed me there is a slot where the wire-and-ball sit inside of to secure to the assembly.

Although I had vacuumed the area, after pulling out the carbs a ton of carbon looking junk appeared all over the bench, the engine block, and even sitting on the edge of the manifold gaskets.

Next time I would loosen the rings on the air box side almost all the way, I think that would have helped.
This can not have been good for the running of the engine. I vaccumed all of that up and put the battery back in and took the compression measurements again.
Just kept turning it over and over watching the pressure go up, and the teacher and entire room stopped and stared at me, I learned my lesson, just test it out 4 and 6 cranks. Basically just watch the PSI needle pop-up and that is one crank. The measurements were PSI at 4x: 100, 92, 75, 100 and 6x: 110, 110, 100, 125. Pat said ok, cylinder 3 is less. Why? I said bad rings, or valves are not sealed. Pat what else, and why? I forgot the head gasket seal, and that running lean will cause overheating that will seize the cylinder. The spark plug said it was lean, I think because it was not worn out and blackish like the other ones. Pat said to put a half cap of oil in the cylinder and test it again, this time 100 and 125, perfect! The rings are bad. We will leave it for now and once we get it running check how good the rings are operating.
Took the top, the slides, and the float bowls off tonight and left it for tomorrow. Ther was years of crud stuck on the outside of the carbs so I scrubbed in off in the solvent station. Most of the screws holding the covers and float bowls on were stripped so Pat showed me what is an impact-driver and how to use it. Awesome. Laid everything out to make it easier to know when something disappears!

Took the exhaust and muffler off, muffler first. There was a bolt missing from the thing that attaches them. There was one missing stem and one stem that came out from the parts that hold on the muffler. Teacher said that I can go to U-Spray to media-blast it and paint the exhaust, it is in decent enough shape. Maybe this is a POR-15 candidate.

That bolt that was misaligned in the frame, I used a jack to lift up the frame. It was specifically for stuff like this, I was surprised to see that you can turn it and lift it just with your hand.

Teacher brought the compression tester adapter, it was 114 and 110 on 1 and 2 but in the process the battery wore out. 4 turnovers wasn’t enough to test it, so Teacher said turn it over until the gauge doesn’t go up any further. I set up the battery charger and 12V on medium for 40 minutes, I will test the other two tonight.
Followed the direction in the service manual to get the carbs out. Set up a drain pain under the carb drain hoses, loosened the air cleaner bands, loosened the airbox top bolt, and slid the air cleaner back. Loosened the manifold bands, drained fuel out of the carbs, and disconnected the drain cables. Still figuring out how to get the shrouds off the carbs on the manifold side, they are solid and stuck on there. I will finish tomorrow.

Once we look at the carbs we will look at what parts to order.

The night before I had spent an hour trying to get out that bolt holding on the tip over bars. I griped to Teacher about it. He said “Grant… most of mechanics is about patience.” and walked away. It was very memorable. Tonight I spent another 45m on that bolt, this time with a small flat head screwdriver and a hammer. Great progress, got it out. On to the other side, same problem with a twist, the bolt had the top half of its threads stripped, so there were 8 washers between the bolt and the frame. Same trick with the screwdriver to get it out. This one doesn’t get a photo though, I refuse to give publicity to such bad practices.
It really got me thinking though. In software, things are very malleable and flexible and poorly defined so you can screw up a lot easily. Motorcycles on the other hand are not, they are well-defined, you buy a manual and then you use the correct parts and tools and torque. What a waste to take such a beautifully designed system and screw it up with crap like this? That last bolt I took out was ground almost to a circular-octagon shape before I got it out.
Tonight I wore plastic gloves. That helped a lot in the really dirty areas underneath the bike. Nitrile gloves don’t cost much.
Teacher reminded me that I can use a lift, and I did, it was just too hard to work on the floor anymore. Teacher showed me how to use it, the safety, and so on.
One note, any errors expressed here are a product of myself, not of Teacher. This is really a journal for me more than anything else.
Tonight I talked to Teacher about POR-15’ing the tank, he said if it ain’t broke…. Good point. He said just drain it out and put some fresh gas in there. I had this idea that it would be time that would be the big cost since I’m a newbie… well that is true, but 2H to remove a bolt! Geez I didn’t expect that. Now I’m a lot more interested in reducing work (without cutting corners of course).
Looked into replacing the 4-into-1 exhaust pipe, looks expensive, 200-300, ouch. Maybe I can just POR-15 them. Next time I will take them off and Teacher will check them out. I will also check whether I can do an oil change without removing the current pipes, that would be a nice to have.
Left the bike with the right side frame needed to bolt on, it sagged a bit. Teacher showed me a lift specifically to lift up motorcycle frames… brilliant, I would never have this stuff at home or even know it existed. Compression check and carb removal are still on the agenda, once we look at the latter we will order the rebuild kit. Will also remove the pipes next week. Teacher said since a sporty 4-1 pipe is on there, the carbs have probably been modified, too. Teacher said that both of those engine mount points are probably stripped out, so we should fix it at some point. It makes me curious about what kind of life this machine has had until my ownership.
Once again I forgot my dirty clothes to work in. It might be a lot easier just to buy some overalls and leave them there.
I bought a 35G plastic container to store the gas tank in, that way nobody will easily walk into it or something. Ordered a battery charger last night, SEM-1562, should get it next Wednesday. I also bough large and small ziplock bags, a notepad, sharpie, pen, and painter’s tape to label things, along with a little first-aid kit in case of anything.
To wrap up the night I got the tip over bars off. Teacher said it is OK to clean them in solvent, then soap and water, then air dry. Look much better, though still might make sense to blast them and paint them as most of the chrome is off.

We couldn’t check the engine compression today, we need an adapter for the checker. Removed the spark plug from cylinder 2, Teacher said it is running lean (there is too much air in the air/fuel ratio of the mixture). Put fingertip on top of plug opening and tried starting it and it pushed my finger off and sucked it in, so the rings are allowing *some* compression. We need to remove the carburetors. Before class I did grab the service manual with the compression levels, and ordered printed copies, too from Helminc.com.

After pulling the plug out I realized there was crud all over in there, so I put the plug back in and shop-vac’d the top out first.
I wanted to remove the crash bars, they are not sporty. 3 bolts hold them on, all through the frame and one through the engine. The 2 on the top frame loosened easily, the one in the engine did not want to come out. Looked underneath to find that there were two bolts on the end. This was surprising. Teacher said the bolt was probably stripped, and that we might fix it later.
This makes it really difficult to get out. Jammed a screwdriver in there and turned it bit by bit for 1.5 hours and headed home. Teacher said mechanics is mostly about patience. I will print out directions for carb removal after talking to teacher about POR-15’ing the tank.

Working on the floor was really dirty, might have to dig out a lift and put it up there instead.

The bike was set up as a cruiser. That is too bad because it is a 1979 Honda CB750F which is a “supersport”. I removed the windshield and bagged the bolts.

Only 32K miles, that is nice. Supposedly the speedometer should go up to 160MPH, but only 150MPH is listed on this one.
I took the bike to school. Here is the “as is” profile:

I took the side panels off, they are black, not purple like the tank. The left side panel had the top most mount broken off and a large bolt glued in it’s place instead, which came off at some point. I wonder how I’ll fix that. I took off the license plate and bagged the bolts. It was interesting to learn that the set is bolted on, I bagged those bolts. Finally I removed the backrest, it was easy after removing the seat first, and bagged those bolts, which incidentally did not fit the rear mounts.
I removed the tail light assembly and labeled the wires first and found that there is a wire-harness. Teacher said to just replace the busted stalks.



The bike starts, runs, and stops, but Teacher checked and the 2nd cylinder is not firing (left to right looking forward sitting on bike, 1 to 4). Took the gas tank off. First turned the petcock to OFF. The fuel line was hard as a rock so teacher said just cut it, also there were heavy metal clamps on both the petcock and the distributor, so he said to be careful to protect the plastic part on the distributor, so I just cut the line in half and covered it up with a paper towel. The tank came right off, it was interesting to see how simple it was removed:

Tomorrow we’ll check the engine compression.

Here is the new patient:

She is a patient because she will be patient as I learn how not to be scared to work on a bike and make all of the stupid mistakes that are to be expected.
It is a 1979 Honda CB750F.
A nice young man named Mitch sold it to me. It was the first time I had towed a trailer, that was interesting. Make sure you budget for tie downs, a hitch, and a trailer.