Why This Matters
Classic bikes like the CB750 are iconic — powerful, beautiful, timeless. But because they’re old and often modified over decades, not every listing that says “CB750” is a good buy. If you don’t check carefully, you might end up with a project that costs more than it’s worth — or even a bike that’s chronically unreliable.
Here’s what to look out for before you drop serious cash.
What to Inspect Before You Buy
✅ 1. Inside the Fuel Tank – Beware of Rust & Varnish
-
Shine a flashlight into the tank — check for rust, pitting, or dark varnish. Surface rust can sometimes be cleaned, but deep corrosion or holes may mean tank replacement (expensive and sometimes hard to source).
-
If you smell stale fuel or find residue when opening fuel caps, that’s a warning sign. Sometimes old bikes—especially ones that sat for years—develop internal fuel/gas issues that lead to carb and engine problems.
What this means: A tank full of rust or varnish can lead to clogged fuel lines, carburetor troubles, or fuel leaks. Fixing or replacing a tank is often expensive and sometimes tricky — worth seriously factoring in before buying.
2. Carburetors, Airbox & Intake Setup – Modifications = Extra Work
-
Original bikes often ran with stock airbox + carburetors tuned for it. If carburetors have been swapped or aftermarket pods fitted — check carefully. Owners often warn that if the stock airbox is removed or carbs mismatched, the bike may “run poorly across the entire RPM range.”
-
When possible, ask to see float bowl condition, and overall carb cleanliness. Dirty/mis‑tuned carbs can mean frequent headaches (hard starts, rough idle, poor throttle response).
What this means: Modified intake/exhaust setups may look cool — but if done without care, they can lead to constant tuning struggles. This is especially true for a project bike where original parts are missing.
3. Electrical & Charging System — Often a Silent Killer
According to classic‑bike buying guides, the charging system (stator, rotor, regulator) is a particularly fragile area on later CB750s — especially DOHC or upgraded bikes.
Before you buy:
-
Test the charging system — battery voltage at idle and running should be within reasonable range (if possible, monitor or ask for evidence). On bikes that have sat or been poorly maintained, stator wiring or rotor windings may be faulty.
-
Check all electrics: lights, horn, ignition, wiring integrity. If you spot modifications like random crimp connectors or messy wiring — that suggests a “quick fix” rather than quality work.
What this means: Electrical issues often show up after purchase — once you’re already committed. A faulty charging or ignition system can leave you stranded or force you into costly rewiring or part replacement.
4. Chassis, Frame & Suspension — Rust, Leaks & Wear
When dealing with a decades-old bike, frame, suspension, brakes, and tires are just as important as the engine. Key checks:
-
Frame & Welds: Look for cracked welds, visible rust or heavy corrosion, especially around the steering head, swingarm, rear suspension mounts.
-
Fork Seals & Suspension: If there’s old oil around the fork legs (oil residue, leaking), buckle — that means seals are shot. Replacing fork seals and bushings is common but it’s time + money.
-
Chain, Sprockets & Wheels: Check chain slack, sprocket tooth wear, wheel alignment, rim/chrome condition. A worn or misaligned chain/sprocket set can lead to horrible riding behavior or failure.
-
Brakes & Tires: Brake pads, lines, and tires must be in usable condition — don’t trust old or unknown rubber/hoses.
What this means: A worn frame or suspension could turn a “project bike” into a “money pit.” Sometimes the fixes are easy and cheap, other times they require big work — tread carefully.
5. Engine Health: Compression, Leak, and History Checks
Beyond cosmetics and accessories, you want to ensure the engine itself has a decent shot at being roadworthy:
-
Compression & Valve Health: Low or uneven cylinder compression can mean worn valves, rings, or worse (camshaft/cam chain problems). If possible, ask the seller for compression readings, or at least inspect spark plug conditions (for signs of oil burning or rich/lean mixtures). Some old‑bike‑owners point out that replacing valves or doing a top‑end rebuild can be inevitable if things are ignored too long.
-
Leaks & Oil Condition: Look under the bike for oil puddles, signs of oil leaks around engine cases or gaskets — black, gummy gaskets or seepage suggest neglect. Old oil and dark sludge in engine compartments or under crankcases is a bad sign.
-
Service History & Maintenance Records: A CB750 that had regular maintenance, carb cleaning, valve checks, and fresh fluids is far more trustworthy than one with an unknown or missing history. Many classic‑bike‑buyers caution against “low‑mileage” bikes that sat for decades, because long idle periods can be just as detrimental as heavy use.
What this means: A bike that “runs now, but hasn’t had care” may still bite you down the road. Engine internals wear out, gaskets get brittle, and carb/ignition/electrical issues accumulate. Always expect some love — or be prepared for budget surprises.
6. Exhaust System — Damage, Rot & Costly Replacements
The original CB750 exhaust system — especially the iconic 4-into-4 setup on K models — is a huge part of the bike’s identity. But over time, many have rusted out, been replaced with aftermarket pipes, or were modified in ways that are tough to reverse.
Here’s what to look for:
-
Check the headers for rust bubbles, dents, and cracks — especially on the underside, where road salt and moisture collect.
-
Inspect the mufflers (if present) for rattling internals or rusted seams. Tap lightly — a dull thud or loose sound inside may mean baffles are gone or rusted through.
-
Many bikes have had the original system swapped for 4-into-1 pipes or generic mufflers. If the seller says “original exhaust,” confirm the part numbers or look for OEM stampings under the mufflers.
-
Replacement cost: Finding a new mint set is like finding gold - expect to pay $1,000+$3000 for reproductions, or more for OEM originals in good shape.
What this means: A clean, intact OEM exhaust adds major value. If it’s rusty, hacked up, or missing altogether, factor in a big chunk of budget — or be okay running used aftermarket. For collectors or purists, a missing exhaust may be a deal-breaker.
What to Walk Away From — When the Red Flags Add Up
Before you buy, treat these signs seriously. If you see multiple of these warnings:
-
Rusted or leaking fuel tank
-
Carburetors missing/modified with unknown history
-
Dodgy or sloppy wiring / charging issues
-
Frame/suspension/structural wear or damage
-
Engine leaks or very questionable compression/plug/wear history
-
No documentation, unclear maintenance records, or vague seller’s description
- It needs a new exhaust system
Then — unless the price is very, very low, or you’re looking for a full-blown project bike with time, patience, and budget — walk away. The money you think you save upfront will often be eaten up by parts, labor, and frustration.
If You Still Want to Buy — What to Bring on a Viewing
If you decide to check a CB750 in person, bring these:
-
A flashlight — great to inspect inside the tank, under engine, and inside frame areas for rust or leaks.
-
Basic tools — to check spark plugs, maybe pop a float bowl to inspect the carb internals, look under the engine or open valve covers if possible.
-
A multimeter — to test battery health, charging voltage (if seller allows running the bike), and basic electrical integrity (wiring, lights, stator output if possible).
-
Your eyes and skepticism — don’t be afraid to look closely at welds, wiring, frame work, and ask blunt questions. If something feels dodgy or poorly maintained — it probably is.
Final Thoughts — Buy Smart, Not Impulsively
The CB750 Four is legendary — and when it’s sorted, it’s one of the best vintage bikes you can own. But the age, modifications over decades, and sometimes careless owners make it easy to pick a bike that’s more headache than joy.
Use this checklist. Bring common sense. Treat every “good” deal as suspicious until proven honest. Because when you do find a clean, well-kept CB750 — it still hits like magic.
Whether you’re buying to restore, ride, or just enjoy the nostalgia — stay sharp, demand transparency, and don’t let emotion override your judgment.