Tag: CB750

Ran out of time last week so here is a picture of the reassembled rack of carburetors. For the heck of it, re-checked the previously 1-finger-tightened float bowl screws, and they were not as tight as I had left them. Re-tightened them. Decided that I had better replace the air filter so as not to gross-up these immaculate carbs. Found out that it is reusable, great. Why are there insect remains in the air cleaner box? They and the grime and crap need to be removed, so out came the brake cleaner, even cleaned up the shifter lever. Decided to re-check the carb holder (shrouds that hold the carbs on the engine manifold) and they were somehow even harder than last year. They are rock hard and must be replaced.

The carburetor bodies are back together and 1&2 and 3&4 have been paired together. It isn’t obvious but reading ahead reveals that the choke tab spring attaches on one end to the 1&2 body and the other on the 3&4 body. The build guide recommended hanging the parallel end on the tab as you join the pairs, and that worked fine. After testing the operation, the choke tab spring wasn’t wound tightly enough, so an additional one round was all it took. The helper picks were my best friend here; though a paper-clip probably would have been fine. The operation cycled fine for 9 times, so it seemed OK. The top and bottom rail went in fine… checking the choke operation every single time after each torquing according to the order. Learned about a tiny thing, the difference between two 4mm allen key drivers, the notched makes it easy slip! With everything aligned, I red loc-tited the choke plate screws checking them off along the way. Learned on the first one that if you torque to half-way between the min and max of the service manual spec, that you will strip out the bolt…grrrrr.

Stopped at Tom’s house and bought a side cover, but the back end pin was missing. Between the two of them I should be able to fabricate one. John from The Shop happened to be sitting there, so I talked to them for a while. Stopped at The Shop the next day but they didn’t have the float valves, so they ordered them for Tuesday.
At class I install the air cuts, slowly, and cleaned the air cut covers for 1 and 4 again, they were filthy for some reason. Tightened up the pucks to the required tightness. Cleaned the air cut passages themselves with carb cleaner and guitar string and finally they were clear. Those were all sealed to a two-finger tightness. Installed all of them. On carb 2 Pat said that something non-metal could hold the throttle plate open fine.
Replaced the gaskets in the float bowl drain screws. Started removing the gaskets from the connecting hardware between the carbs. It was rotten hard in place and required a pick to get it off. The locking grip was my new best friend.
The hex key buttonhead screws are nice. Replaced the keychain with a much nicer one, too.
Continue reading “CB750F: Day 15”

Scott the parking attendant said hi. Tonight I cleaned the float seals. I should have attached a q-tip to a drill like Tim said, it took forever, but was worth it, and the Brasso helped. You could even read little symbols on the brass float passage itself. The puck covers all had this tacky material on them; not sure whether it was oxidation or what. Installed the pilot screws according to the original measurements: 2.5, 2.39, 2.62, 2.5 (turns back out). Did the float bowl leak test, and blew them out with compressed air including the drain screw afterwards. Next time it will be the float valves and bowl installation. After staring at the float values for while, I wondered if they should be replaced after one of them got stuck recessed. The ultrasonic cleaner continues to serve diligently; but doesn’t need any more photos at this point.
Continue reading “CB750F: Day 14”

Normally 13 is unlucky, but never for me (don’t worry it comes in other ways). Tonight was the end of the ultrasonic cleaning and the wrap up of the carburetor cleaner manual cleanup; I did bring some along because I didn’t want to use up an entire can at class. The brass bristle brushes were invaluable; as were MacGregor’s directions, really, really great. One high point was trying to put the silver jet in backwards, and only after measuring it with a micrometer (remember it is dollars, quarters, cents…) did I realize that although silver jet has a .089″ gap, which is probably to big, it doesn’t matter when you try to insert it in the wrong end of the port. Ah well, Pat said I should ask him about stuff sooner, but that just isn’t my way I guess.
This bike was not well loved. The horns are even worn out and ought to be replaced. Tail lights busted. Headlight attached with a twig. Front fender wrong. What happened to this machine? Well, we will fix it up.
Started reassembly tonight. Finally, but it was worth the wait to really clean these things up. The button head Allen screws look great, and hoping that they provide some relief for future maintainers who need to rebuild these carburetors. The ceramic cleaner did good on the float seals, but I will bring in some brasso to see how much cleaner they can be. The workstation was a little too involved to tidy up tonight; can’t wait to get back.
Continue reading “CB750F: Day 13”

Tonight was ostensibly the least exciting of any, but I got a ton of work done. Every carburetor and all of their supporting parts got a bath in the ultrasonic cleaner with 55/45 SimpleGreen/H20 tonight. Afterwards they got a solvent rinse and a thorough carburetor cleaner clean-down. It was so impressive how dirty they were outside; and to a lesser degree inside.
MacGregor Carb Cleaning Services guide has turned out to be stellar; the notes are brief and can be no briefer, everything is included there for a reason and failure to follow the instructions will result in unhappiness.
The light brass bristle brushes were really helpful for cleaning the carbs where the q-tips just didn’t do enough, but was still gentle no tearing up the metal anywhere. One mistake I mad was not to use an exacto, I used a bench-grinder instead. The tip got a little hot and melted, so again, do what the MacGregor guide says, it is really optimized! The tip about wrapping up the end of the cleaner tube was just great; the thing was though that you really have to blast the cleaner in there to even get a drizzle out of the pilot screw as expected. You can see the crud coming out of those carbs… geez!
Had one inspired though while the solution in the ultrasonic cleaner heated up to boiling and cooked my fingers… if we designed an ultrasonic cleaner that also worked as a deep-fryer, then after using the fryer, the machine could clean itself. It might just work.
Continue reading “CB750F: Day 12”

Tonight I hooked up the Harbor Freight ultrasonic cleaner (that is now property of the class) which everyone seems to own and use to clean carburetors. For a solution I used about 55/45 SimpleGreen to water because the carbs were just filthy.
For each I ran a cycle of 8 minutes, 4 times with the air intake valve side down. The basket was crammed full of the rest of the carb and parts. In retrospect, someone pointed out to me that will make the clean a little less effective and instead I should hang the carb itself by a clothing hanger directly above the ultrasonic emitter. Good point. The heater heats up quickly and although there is an over-heating cutoff built in, it will get hot enough to boil before that happens to pay attention here. This took most of the evening; I will get the other side that was sitting out of the water later.
After their final bath, I rinsed all of the big parts in solvent because the gunk just didn’t want to let go. The cleaning solution was completely filthy; light would not penetrate it. The next step is to clean everything with carb cleaner. The problem is that there is a layer of gunk that just does not want to let go of the surface, so I’ll come back with brushes and q-tips and a guitar string next week.
The pictures show how much a carb fits into the cleaner, along with how many parts you can cram in there but probably should not. At the end of the night, I try to keep my work-space in decent order.
Continue reading “CB750F: Day 11”

Back to class again. This time it is only twice a week but for 4.5 hours. The majority of the evening was spent taking the rack of carbs apart. Not much to screw up here, but I always find a way. Most of the screws were stuck and/or stripped out, so Brian helped me with the last one using just a pliers. Arriving late to class, that is all I got done.
Most of these photos are for my reference later. In particular the spring locations are important.
For directions I’m using the Honda service manual, Mike Nixon’s guide, MacGregor Carb Cleaning Services guide, and Randakk’s rebuild kit.
Continue reading “CB750F: Day 10”

Tonight was preparation for break. Hooked up the adapter cable to the battery for the trickle charger and learned about what it means to ground a circuit (fireworks in face) along with a trick of wrapping the screwdriver in a layer of electric tape to insulate it.
It was real hassle getting the bolts into the nut on the battery posts, so I stuck some paper tape underneath to jack it up and pulled it out once it was gripped.
Finding a carb kit is still a work in progress, I suspect that I will buy individual jets.
Debating buying an ultrasonic cleaner; though it is certainly easier than building one. One interesting item I found though was a drop-in transducer, which could turn any container into an ultrasonic cleaner!
The cheapo nitrile gloves aren’t cutting it, they break too much, got a recommendation for the Microflex MidKnight Nitrile gloves instead.
Brandon shared his carb gaskets with me, they look like they will fit (thanks!). I might break apart that rack so I can replace/clean all of the diaphragms.
The rest of the night I just cleaned off the bike; she is in rough shape and deserves to be clean.
Continue reading “CB750F: Day 09”