pidjones rat bike project - '79 CB750F

[pidjones]

Bought it about a month ago for a winter project. My last was a '78 GL1000 frame with '75 engine done in a cafe style.  The 750 had set in the weather for a couple decades - last tagged in '99! Looks awful, and will stay that way as I'm doing a rat bike out of it. Has KZ750H forks (unknown reason) that I've already rebuilt. Carb rack is off, and beginning to go through it. Luckily, I think it was last fueled before the ethanol mandate, so a little rust debris and a lot of varnish are the main battle. Not seeing any aluminum oxide bloom where the castings are degraded. So far most all screws (on the carbs) are coming loose with assistance of vice grips and PBBlaster. Had to drill out heads for a few on the timing cover, though. Running into a lot of PO issues, but saw the same on the GoldWing.

I'll be watching and reading for hints, tips, and cautions plus adding anything I've picked up.

BTW, I'm retired this last year from 39 years working on various particle accelerators (cyclotrons and Van de Graffs). But, I was a gearhead in school and have maintained my own vehicles. Present ride is an '06 GL1800 that I've put about 113k miles on. Next weekend the wife and I do Barber's for vintage weekend!

[TOOLS1]

I love the patina on the tank. Cannot wait to see more of this build.
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[pidjones]

Patina? Flaking 1/4" or more of poor Bondo, black paint over original silver, you name it! I think the green mold on the aluminum cases is primo. Strongly dislike "rat rods" that have fake aging and fading. Nothing fake about this! Only setting in the East Tennessee environment can cause original aging like this.

Today I was able to get started on the carbs.  One at a time pulled the float bowl off each (no ruined screws!) and sprayed the bowls with carb cleaner, pulled the drain valves and opened overflow and drain on each, cleaned the valves. Pulled secondary main jet on each (each one plugged solid with lacquer) and softened the lacquer with carb cleaner then was able to work a .008" guitar string through and finally shoot cleaner through them. Loosened the needles with carb cleaner and gently, padded with rag and tongue depressor, pried each piston up to free the needles fully. Pretty gummy, but still a LOT easier than working through the damage caused by ethanol gas.

Looks like the accelerator pump diaphragm will need replaced, however. Just so stiff that it hangs up when pressed. I'm sure all rubber will need replaced also, and already have bowl o-rings and rubber plugs on order. Should have the other o-rings in my supplies.

[TOOLS1]

I know what you mean about the "fake" aging patina. Original patina is priceless. I am at the moment trying to save a 1938 Excelsior survivor with 80 years of perfect patina from an owner that thinks everything should be shiny red and chrome.
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[pidjones]

I really have no problem with a good restoration. It is the fake rust, sanded and waxed or clear coated fake sun damage. Still, the real patina of a survivor is irreplaceable. Maybe one of the few issues that I have with Wheels Through Time is that Dale and crew have, on occasion, artificially "aged" machinery. I see it as showmanship for the museum's sake, but it damages some limited remaining historical specimens.

BTW, I will have to replace the front end on the bike. A PO had replaced the front forks with KZ750H leading axle forks that cause the trail to be only ~ 3.2". I have a set of GL1000 forks that only need new seals (which I have) and fluid plus cleanup. I will have to pick up a triple for them (37mm), but GL1000 triples are readily available on eBay and have the same stem as the CB750F triples. The brake calipers should bolt right up (they are '78 forks which use the same calipers). The other good thing about these forks is that they are really rough looking - so will match the rat rod motif of the rest of the bike.

[TOOLS1]

I like the Gold Wing forks, wish I could come across a few sets of them.
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[pidjones]

Build him a nice, shiny, black red and chrome fake Excelsior.

[TOOLS1]

I need a "LIKE" button. I have told him that he is the AntiElvis.
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[pidjones]

Getting the forks together finally. Had to turn a cap for one because the original has disappeared. They are cleaned and assembled with new seals, new dust seals came in today so they should soon be for filling and installation.

The carbs are now broken down individually and #1 is fully cleaned, new o-rings installed, and reassembled. The floats on all of them were way off - probably trying to fix leaky float valves - I'm relapping the seats with jewelers rouge.

The tank is flopping around all over with about 1.5 gallons of Evapo-rust in it. I think it will be fine, as this is all that my paint filter caught after draining a gallon of acetone that had been left in it for a couple weeks to get the varnish out.
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[pidjones]

Finished cleaning, assembling, adjusting and testing all carbs. Had to change out the acetone that I run the jets and such through in the US tank twice because it was getting too contaminated with varnish! First, just pressure testing the float seats to see if they will hold ~2 psi for hours. Had to make a tool for lapping the seats as some were pretty dinged. Easy to pressure check while cleaning the next carb. Then after ganging them up I checked them all. Had to make the little washers on the pilot screw o-ring as they were all missing. Also bypassed all of the air cuts. Set the pilots 1/2 turn more open to accommodate. New accelerator pump is on order. This one is too stiff and often hangs up.

One thing the pressure test doesn't tell you is if your overflow tubes are cracked! Dooo. #2 and #4 both cracked. So, solder? JBWeld? How about - is heat shrink tubing gasoline proof? Let's find out! At least all of my float valves are seating well. But, I had to make a drain screw for #4 because it was too far corroded to clean up. Made one out of a bolt. Didn't worry about a screwdriver slot or an o-ring groove. This IS a rat bike!

All that remains before re-mounting is a new accelerator pump. I just know that if I order one from a USA source, the China pump will show up!

[TOOLS1]

I find the washers missing from probably half the carbs I work on. I now buy them in bulk form. Heat shrink will not work on the overflow tubes, however both JB Weld and solder will. I do not know about "pressure testing" carbs, I always hook them up to my IV bottle and put gas to them for testing before installing them on the bike. While the bottle is hooked up I will turn them and shake them to make sure that they are not going to leak.
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[pidjones]

Pressure testing works pretty well for seat integrity testing. Guess I'll be scraping the heat shrink off and getting the crack cleaned of so I can throw some melted metal in it (that sounds wrong). I have a pretty powerful butane - powered iron.

I can only liquid test with isopropyl alcohol as I have a basement garage. It worked great for the GL1000 set.

[TOOLS1]

Using alcohol sounds like a good idea, I am getting sick of the gasoline smell in my house from the attached garage.
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[pidjones]

Cleaned the heat shrink off today (had already softened in the remaining isopropyl) and soldered the cracks. Butane iron had plenty of power, and it looks like the fix will hold up.

All that remains on the carbs is the accelerator pump repair kit to get here on a slow boat from Taiwan. The fuel tank is flushed (pressure washer) dried and coated with spray fogging oil. Knocked a chunk of Bondo off of it about 1/2" thick. Might try the inner tube trick to try and get some of that dent out. I also ground a large socket I had for removing the flywheel nut from a boat I no longer had into a tool to remove the locking nut for the front wheel bearing. The bearings are rusted solid, so I hope they will not be too bad to tap out. Took the chain off today also - threw it straight in the trash as it is rusted badly and I don't want it eating sprockets. Will probably go with a lower priced o-ring chain. Chain and tires will wait until the engine is running. Kind of a deal with the wife. I can get the higher cost items on a project after I get it running. I don't think she has any faith in my abilities.

[TOOLS1]

Good job.
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[pidjones]

I hate brakes!

Well, they are pretty necessary when you are riding, but I hate working on them. Was able to pump one of the pistons from these GL1000 front calipers out with a front master. The other wouldn't budge. Had to put an 8mm grease fitting in the bleeder hole and pump it out with the grease gun. All cleaned now and pistons dressed, awaiting seals and reassembly. Will have to get a Chinabay special for the rear master because after two hours to get it off, the rear is trash.


Got the CB750F dash mounted with a little mountain engineering and the G1000 headlight ears installed. Also installed new bearings in the front wheel.

This week is paint the G1000 week because the weather is forecast to finally be right.

[TOOLS1]

I would rather work on brakes then fight a front wheel bearing retaining nut.
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[pidjones]

Ground an old 3/4" drive socket that I had used to remove the flywheel nut on a 115 HP Evinrude outboard into a spanner for the bearing retainer nut. Initial grinding on the bench grinder, finish with the Dremel.

Slow boat from Taiwan arrived with my accelerator pump. Carbs mounted to intake horns but haven't connected the airbox boots yet. Assembled and installed the front calipers and hooked up the lines. Still not bled, though. Afraid I'll have to jump-start this master cylinder again. Turned out I bought the wrong piston for the rear (75 - 77 front vs 78 rear in GoldWing numbers). This one is too tall. Correct one on order. I hate brakes!

[pidjones]

I hate brakes.

BOTH front calipers are leaking. Guess new pistons are the only way to fix it. On order. I HATE brakes! At least the rear piston came in a day early and I was able to get the rear brakes working, but not until after having brake fluid leaking out of the new master and finding that the hole for the screw that holds the plastic inlet adapter in was drilled ~2mm off - causing the o-ring to have no compression on one side. Whittled out the hole on that side and the rear brake system seems to be in good shape, now.

Also connected airbox and throttle/choke cables (why didn't I do that first? I thought about it but didn't do it!) Compression tested and right around 150 across all four now.

I hate brakes.

[pidjones]

New front caliper pistons in, brakes bled. Waiting for used coils and caps to come in. If the ignition all checks out then, I'll probably put some fuel in the tank, mount it, and try to fire it  up. Rear wheel is off right now and of course the oil around the bearings is brown with rust, so they will need replaced. Don't mind the work as much as the continuing mounting expense.