Qaxe
CB750 Addict
Had I known I was going to blather on and on here about my bike, I'd have made one thread to rule them all. Oops. Since the bike is running more normally now, I've made a quick video to get some of your thoughts on the various sounds. To quote ol' Bill Shakespere down at the bar, "Friends, Romans, Countrymen, lend me your ears."
Thought I'd better post some facts here, to save a couple questions.
Thought I'd better post some facts here, to save a couple questions.
My CB750 is primarily K6 on a K7 frame. Sat still for 10 years at least. Based on light scratches or dents on the dynamo cover, fuel tank and points cover, it must have been lightly dropped on both sides. Obviously wasn't wrecked outright. There doesn't appear to be any reason to believe that the engine has been modified.
All that's left of the K7 which is listed on my registration is as follows: Frame, swing arm, triple clamps, rear wheel, sprocket carrier, axle, wiring harness, ignition switch, handlebar switches, and the electrical components behind the right side cover.
Odometer that came with the K6 reads 11k miles. The gauges are in good shape, with a healthy green color, and almost definitely a paired set. Nobody knows if they are original or if the gauges were replaced at some point. In comparison, the condition of the paint on the tank was much more faded and flat. The gauges are at least correct for the year: 1976 CB750K gauges had green faces and the odometer knob is on the side (which began with K6). So they aren't K5 or K7.
The engine itself doesn't run like an 11,000 mile engine, nor did the tank look like it. On the other hand, this is the Rainy State, so if it sat outside uncovered for even a few years, it's possible that tank could look that bad.
All that's left of the K7 which is listed on my registration is as follows: Frame, swing arm, triple clamps, rear wheel, sprocket carrier, axle, wiring harness, ignition switch, handlebar switches, and the electrical components behind the right side cover.
Odometer that came with the K6 reads 11k miles. The gauges are in good shape, with a healthy green color, and almost definitely a paired set. Nobody knows if they are original or if the gauges were replaced at some point. In comparison, the condition of the paint on the tank was much more faded and flat. The gauges are at least correct for the year: 1976 CB750K gauges had green faces and the odometer knob is on the side (which began with K6). So they aren't K5 or K7.
The engine itself doesn't run like an 11,000 mile engine, nor did the tank look like it. On the other hand, this is the Rainy State, so if it sat outside uncovered for even a few years, it's possible that tank could look that bad.
- Compression as of 6/2023 (psi): #1 = 125, #2 = 120, #3 = 120, #4 = 125
- Valve clearances: Set to K6 spec. .05 intake, .08 exhaust.
- Oil & filter change: 50 miles since last change. Non-synthetic 10W40.
- Gas: Fresh. No old gas from last season.
- Fuel filter: 40 miles.
- Air filter: Standard airbox with 200 miles on filter. No dust, clear in front, dry and dark in the back near the middle.
- Exhaust setup: 4-into-4, OEM K6 pipes
- Throttle cables are brand new, stock K6 length.
- Handlebars are stock K6 size.
Carburetor: Keihin 086A
- Jet size unknown. Have not replaced them.
- Carbs cleaned 50 miles ago (August): Carb bodies soaked in Berryman's Chem-Dip, all ports cleared with carb-cleaner & compressed air. All jets clear and clean, all holes appear free of obstructions under magnifying glass. New idle screw springs. New O-rings. New rubber lines between carbs. Rubber top seals and float bowl seals are supple and re-sealed with silicone grease.
- Vacuum synced to 200mm (spec. is between 16-20cmHg)
- Idle screws out 1 turn across the board.
- Float level at 26mm. (Measured with carbs at angle, so floats not depressing needles)
ELECTRICAL
- Points and condensers have 200 miles on them. Contact surface clean.
- Ignition timing: Spark advance “F” is aligned with timing mark.
- Point gap: .35mm (Spec: .3 – .4mm)
- Ignition advance angle: Unknown. How can I measure the angle? (Spec. 35°)
- Point dwell? (I don't own such a testing device.)
- Spark-plugs: NGK, D8EA. New, just used 30 miles.
Plug gap: Spec. .6 to .7mm Unchanged from factory, measure @ .65mm.
- Plug caps: Brand new NGK caps as of Sept. 2023
- Ignition Coils: Stock TEC brand FL703
- High tension lead for cyl. #2 missing a 3/8" of the hard plastic insulation at tip.
- Trimmed leads back 1/8".
- Primary Winding, cyl. 1&4: 5.8 k ohms (Initial reading 6.2k minus .4 internal resistance)
(Initial reading 6.2 ohms, minus .4 internal resistance)
- Secondary Winding, cyl. 1&4: 14.6-14.8 k ohms
- Primary Winding, cyl. 2&3: 5.6 k ohms (Initial reading 6.0k minus .4 internal resistance)
- Secondary Winding, cyl. 2&3: 14.15 k ohms
- Valve clearances: Set to K6 spec. .05 intake, .08 exhaust.
- Oil & filter change: 50 miles since last change. Non-synthetic 10W40.
- Gas: Fresh. No old gas from last season.
- Fuel filter: 40 miles.
- Air filter: Standard airbox with 200 miles on filter. No dust, clear in front, dry and dark in the back near the middle.
- Exhaust setup: 4-into-4, OEM K6 pipes
- Throttle cables are brand new, stock K6 length.
- Handlebars are stock K6 size.
Carburetor: Keihin 086A
- Jet size unknown. Have not replaced them.
- Carbs cleaned 50 miles ago (August): Carb bodies soaked in Berryman's Chem-Dip, all ports cleared with carb-cleaner & compressed air. All jets clear and clean, all holes appear free of obstructions under magnifying glass. New idle screw springs. New O-rings. New rubber lines between carbs. Rubber top seals and float bowl seals are supple and re-sealed with silicone grease.
- Vacuum synced to 200mm (spec. is between 16-20cmHg)
- Idle screws out 1 turn across the board.
- Float level at 26mm. (Measured with carbs at angle, so floats not depressing needles)
ELECTRICAL
- Points and condensers have 200 miles on them. Contact surface clean.
- Ignition timing: Spark advance “F” is aligned with timing mark.
- Point gap: .35mm (Spec: .3 – .4mm)
- Ignition advance angle: Unknown. How can I measure the angle? (Spec. 35°)
- Point dwell? (I don't own such a testing device.)
- Spark-plugs: NGK, D8EA. New, just used 30 miles.
Plug gap: Spec. .6 to .7mm Unchanged from factory, measure @ .65mm.
- Plug caps: Brand new NGK caps as of Sept. 2023
- Ignition Coils: Stock TEC brand FL703
- High tension lead for cyl. #2 missing a 3/8" of the hard plastic insulation at tip.
- Trimmed leads back 1/8".
- Primary Winding, cyl. 1&4: 5.8 k ohms (Initial reading 6.2k minus .4 internal resistance)
(Initial reading 6.2 ohms, minus .4 internal resistance)
- Secondary Winding, cyl. 1&4: 14.6-14.8 k ohms
- Primary Winding, cyl. 2&3: 5.6 k ohms (Initial reading 6.0k minus .4 internal resistance)
- Secondary Winding, cyl. 2&3: 14.15 k ohms
– New battery and spark-plugs installed, gas and oil changed.
– Discovered that neither project nor parts bike ran. Began cleanup.
– Inspected and cleaned wire harness, replaced old light bulbs, fuses, and cleaned connections.
– Replaced one very crusty "Weather-pack" connector on wiring harness
– Fuse box replaced as one contact was damaged.
– Cleaned and mounted up K6 carburetors (Keihin 086A) since K7's were in pieces.
– Damaged gauge chrome replaced, gauge bracket repainted
– Removed paint from the aluminum switch housings, front brake master cylinder, and handlebar mounts and polished them.
– Was able to get K7 to run on all 4 cylinders briefly, but metallic sound in engine sounds like bad rings or valves.
– Buffed aluminum engine covers: Alternator, clutch, sprocket covers
– Buffed aluminum on rear wheel hub, and front fork lowers
– Rear brake pads checked (Minimum spec. is 2mm, these are 4mm as of Aug. 2023)
– Cleaned exterior of air-box with peanut oil. Filter is clean.
– Re-painted metal air-box mounts.
– Removed K7 engine (Compression test: 120, 85, 95, 110, and there was a loud metallic clinking sound)
– Stripped bike and touched up frame.
– Battery box removed and painted
– Cleaned and greased the swing arm (K7's has a grease-fitting on left side)
– Replaced the rear brake rod with a straight one.
– Greased both front and rear axles and related spacers and mounted up wheels.
– Replaced engine with K6 engine.
Compression: #1 125psi; #2 120psi;#3 120psi;#4 125psi. (Not 170, but results are within 10% of each other)
– Valves adjusted, timing set, cam chain tensioner set.
Replaced front and rear tires (new)
– Rear sprocket replaced (new 48T x 530)
– Chain replaced (new 530 x 100)
– All external engine cover bolts replaced with brand new hex type bolts.
– Swapped out the 77' rear fender with a 76' with longer taillight bracket.
– Replaced broken taillight lens with a brand new part.
– Replaced rusted exhaust system with OEM, K6, 4-into-4 system (CB750 SL HM341)
– Exhaust gaskets replaced
– Replaced fork seals (2023)
– Fork dust-covers replaced with K1-K6 style gaiters (new part)
– Front brake caliper rebuilt (new parts)
– Front brake master cylinder rebuilt (new internal parts)
– Throttle cables both replaced a second time in 2023.
– Speedometer and tachometer cables replaced (new parts)
– Speedometer drive unit bolt replaced with a hex head type (M5 x 16)
– Mirrors replaced (after-market)
– Handle-grips replaced
– Winkers replaced (originals badly damaged)
– Coils, points, and condensers replaced (new parts) and timing reset
– Spark plugs (replaced again after all the engine testing and drama)
– Buffed out rear shocks (did not replace)
– Air-box rubber boots replaced with brand new parts (all 4)
– Kickstand cleaned, greased and painted
– Rider pegs rust removed and re-painted (replaced missing left rider peg)
– Seat foam and cover replaced (used)
– Side covers bought (New repro.)
– Tank damage filled before painting (Small dent on left side, near seat).
– Re-drilled K7 rear fender to retro-fit 76' taillight. Unused holes filled.
(K6 fenders don't align well with K7 frame and inner fender)
– Painted: Tank, headlight, side covers and both fenders with Wesco PPG, #5857 white, single-stage paint.
2023
– New battery installed
– Gas-cap rubber seal replaced
– Fuel filter replaced
– Disassembled carburetors completely, and all parts cleaned thoroughly. O-rings and idle screw springs replaced.
– Retested timing: no change.
– Retested valves just to be sure. Still spec.
– Tested ignition coils: Within spec.
– Spark plug caps failed resistance tests, replaced with new NGK caps.
– OEM brake lines switched to braided steel lines. (Bleeder screw cleaned with brass wire brush, new rubber cap added.)
– In-line brake switch swapped out to K7, as it matches the frame better.
– FAILED: Ignition switch steering lock worked on, but still frozen inside. (Must replace to gain locking function)
– Reattached the winker horn to its proper location, and fixed wire leads. Is NOT connected (Super noisy)
– Discovered that neither project nor parts bike ran. Began cleanup.
– Inspected and cleaned wire harness, replaced old light bulbs, fuses, and cleaned connections.
– Replaced one very crusty "Weather-pack" connector on wiring harness
– Fuse box replaced as one contact was damaged.
– Cleaned and mounted up K6 carburetors (Keihin 086A) since K7's were in pieces.
– Damaged gauge chrome replaced, gauge bracket repainted
– Removed paint from the aluminum switch housings, front brake master cylinder, and handlebar mounts and polished them.
– Was able to get K7 to run on all 4 cylinders briefly, but metallic sound in engine sounds like bad rings or valves.
– Buffed aluminum engine covers: Alternator, clutch, sprocket covers
– Buffed aluminum on rear wheel hub, and front fork lowers
– Rear brake pads checked (Minimum spec. is 2mm, these are 4mm as of Aug. 2023)
– Cleaned exterior of air-box with peanut oil. Filter is clean.
– Re-painted metal air-box mounts.
– Removed K7 engine (Compression test: 120, 85, 95, 110, and there was a loud metallic clinking sound)
– Stripped bike and touched up frame.
– Battery box removed and painted
– Cleaned and greased the swing arm (K7's has a grease-fitting on left side)
– Replaced the rear brake rod with a straight one.
– Greased both front and rear axles and related spacers and mounted up wheels.
– Replaced engine with K6 engine.
Compression: #1 125psi; #2 120psi;#3 120psi;#4 125psi. (Not 170, but results are within 10% of each other)
– Valves adjusted, timing set, cam chain tensioner set.
Replaced front and rear tires (new)
– Rear sprocket replaced (new 48T x 530)
– Chain replaced (new 530 x 100)
– All external engine cover bolts replaced with brand new hex type bolts.
– Swapped out the 77' rear fender with a 76' with longer taillight bracket.
– Replaced broken taillight lens with a brand new part.
– Replaced rusted exhaust system with OEM, K6, 4-into-4 system (CB750 SL HM341)
– Exhaust gaskets replaced
– Replaced fork seals (2023)
– Fork dust-covers replaced with K1-K6 style gaiters (new part)
– Front brake caliper rebuilt (new parts)
– Front brake master cylinder rebuilt (new internal parts)
– Throttle cables both replaced a second time in 2023.
– Speedometer and tachometer cables replaced (new parts)
– Speedometer drive unit bolt replaced with a hex head type (M5 x 16)
– Mirrors replaced (after-market)
– Handle-grips replaced
– Winkers replaced (originals badly damaged)
– Coils, points, and condensers replaced (new parts) and timing reset
– Spark plugs (replaced again after all the engine testing and drama)
– Buffed out rear shocks (did not replace)
– Air-box rubber boots replaced with brand new parts (all 4)
– Kickstand cleaned, greased and painted
– Rider pegs rust removed and re-painted (replaced missing left rider peg)
– Seat foam and cover replaced (used)
– Side covers bought (New repro.)
– Tank damage filled before painting (Small dent on left side, near seat).
– Re-drilled K7 rear fender to retro-fit 76' taillight. Unused holes filled.
(K6 fenders don't align well with K7 frame and inner fender)
– Painted: Tank, headlight, side covers and both fenders with Wesco PPG, #5857 white, single-stage paint.
2023
– New battery installed
– Gas-cap rubber seal replaced
– Fuel filter replaced
– Disassembled carburetors completely, and all parts cleaned thoroughly. O-rings and idle screw springs replaced.
– Retested timing: no change.
– Retested valves just to be sure. Still spec.
– Tested ignition coils: Within spec.
– Spark plug caps failed resistance tests, replaced with new NGK caps.
– OEM brake lines switched to braided steel lines. (Bleeder screw cleaned with brass wire brush, new rubber cap added.)
– In-line brake switch swapped out to K7, as it matches the frame better.
– FAILED: Ignition switch steering lock worked on, but still frozen inside. (Must replace to gain locking function)
– Reattached the winker horn to its proper location, and fixed wire leads. Is NOT connected (Super noisy)
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