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Restoration
Technical
Mechanical
Electrical
Other
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This
is a guide to help you identify and resolve problems. But first a few
tips.
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| Symptoms | Possible Cause | Resolution |
| Engine Fails to Start | Fuel Shortage. | Check there is fuel in the tank. |
| Blockage in Carburetor jet or fuel line. | Check fuel is flowing from the tank to the carb, remove pipe is necessary or use tickler. | |
| No Fuel in Carburetor | Check float is not stuck or jet blocked. | |
| Carburetor flooded. |
Wet spark-plug insulator is
obvious sign Kick over the engine with the throttle wide open and the fuel off to clear excess fuel. Remove spark-plug, clean and dry in the sunshine or warm place. |
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| Spark Failure | Remove spark plug from cylinder head, lodge on metal fins and kick over engine. If you do not get a spark, change the plug. | |
| If still no spark check: Points & condenser, you should get a spark across the points as you open them with a screw driver blade. If not check battery an wires. | ||
| Change coil. | ||
| Fouled or 'Wiskered' Plug | Clean or replace plug. Two strokes suffer from wiskering were a deposit bridges the plug gap, a remedy is a cooler plug or larger gap. | |
| No electrical power. | Battery may be dead, on battery
ignition models is evident by no lights or horn. Check the fuse if fitted. Charge battery if dead. Check, clean and tighten battery terminals. Bump start is possible on some models, disconnect battery earth lead and reconnect when started. |
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| Slipped ignition Timing | If there is a spark, check that it
comes just before top-dead-centre. Check timing marks if present. |
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| Engine Fails to start after Rain or washing. | Wet HT leads, plug covers, ignition coil or distributor. | Dry off these component (You can
spray with Duck Oil - Water Repellant). Dry off spark plugs or turn over engine with throttle open. |
| Engine hard to start, idles poorly or runs erratically. | Breaker points dirty or out of adjustment | Clean and adjust points. |
| HT pickup and slip ring dirty (Mag ignition) | Remove pickup wire, wipe clean, wipe collector ring while rotating engine. | |
| Magneto or Ignition Coil Fault | Remove spark-plug and check spark will jump gap (1/8" for Magneto and 1/4" for Coil) when engine is turned over. Check again when everything is warmed up to determine whether there is any deterioration. | |
| Condenser Fault | Usually indicated by rapid pitting of the contact-breaker points and steady intense blue spark across the contacts, whereas a small white spark is normal. | |
| Ignition coil or condenser terminals loose | Check and tighten. | |
| Water in Carburetor | Drain carburetor bowl, blow out jets and passage ways. | |
| Carburettor out of adjustment or requires cleaning. | Adjust mixture and clean carb with suitable aerosol cleanser. | |
| Fuel flow restricted | Check vent hole in filler cap is not blocked. | |
| Engine misfires when accelerating | Dirty Plugs | Clean Plugs or replace |
| Weak Spark | Check ignition system | |
| Magneto pick-up brush missing | Replace | |
| Dirty pick-up or collector ring | Clean | |
| Plug cap or HT cable faulty | Replace | |
| Poor Idle | Air leakage at Carburetor flange | Tighten (do not
over tighten as you will distort flange) Replace gasket or rubber seal. |
| Air leakage in manifold balance pipe | Seal joint or replace pipe. | |
| Worn carburetor slide and body | Replace carburetor. | |
| Engine cuts out and misfires on load. Pronounced when climbing hills. | Dirty spark plug | Clean or replace spark plug |
| Plug gap to large | Adjust to correct size. | |
| Weak Spark or Ignition trouble | Battery ignition:- Check coil and condenser. | |
| Magneto ignition:- clean and set points, check armature and condenser. | ||
| Engine hesitates or dies when full throttle is applied | Blocked carburettor main jet | Remove main jet and blow through. Avoid using a pin to clear. |
| Water in carburettor | Drain and clean carb bowl, jets and passages. | |
| Mixture too weak | Raise needle position, increase main jet or adjust as per manufacturer instruction. | |
| Engine runs poorly after period of storage | Stale Fuel | Drain the fuel from the tank and refill with new fuel. |
| Gum deposits in carburettor | Clean carb with suitable aerosol carb cleanser or mentholated spirit. | |
| Medium speed misfire | Mixture too rich | Lower needle position, reduce main jet or adjust as per manufacturer instruction. |
| Magneto fault | Check magneto for fault and repair. | |
| Coil fault | Replace coil. | |
| Poor Top speed performance | Retarded ignition | Check and set correct ignition advance. |
| Faulty ignition auto-advance | Oil advance spindle, check advance springs and establish functionality. | |
| Dirty or blocked air filter | Clean filer or replace cartridge. | |
| Loss of performance due to poor compression | No valve clearance | Adjust tappets correctly. |
| Burnt valve seats | Replace valve and re-cut seat. | |
| Sticking valve | Clean valve stems and remove gum. | |
| Worn piston rings or bore | Replace rings, re-bore if bore is badly worn. | |
| Piston failure | Usually a holed piston, accompanied by large amount of smoke from the exhaust, cause by weak mixture. | |
| Engine seizes or becomes tight after prolonged high speed | Plug pre-ignition | Fit a cooler plug |
| Piston seizure caused by incorrect piston clearance, weak mixture or incorrect timing | Resolve problem, may require new piston or careful smoothing of surfaces. | |
| Mixture weak | Raise needle position, increase main jet or adjust as per manufacturer instruction. | |
| Oil pressure failure caused by lack of oil, oil pump failure | Resolve problem, may require new piston, bore and cams or careful smoothing of surfaces. | |
| Knock when accelerating | Piston Slap | Check clearances on piston and bore. May need new piston or rebore as well as piston |
| Small end bearing | Check. Tolerance no more than 3 thou. | |
| Engine overheating | Weak mixture | Raise needle position, increase main jet or adjust as per manufacturer instruction. |
| Ignition timing out | Retime ignition to manufacturers settings. | |
| Spark plug wrong grade | Replace with manufacturers recommended grade or equivalent. | |
| Engine knocking when accelerating from low revs. (Pinking) | Ignition too advanced | Retard ignition by a degree or two. |
| Automatic advance/retard mechanism springs too weak | Replace springs. | |
| Engine needs decoke | Strip top end down and remove carbon from cylinder head and piston. | |
| Back-firing & Kicking back. | Ignition too advanced | Retard ignition by a degree or two. |
| Auto-advance unit stuck or broken spring | Strip unit and replace any broken parts. | |
| Blue smoke from exhaust when changing gear | Worn valve guides or valve stems | Replace valves if the stem is worn or replace both guide and valve if excessive play in the guide. |
| Clicking noise from engine at higher revs | Tappet clearance to great | Adjust tappets to correct clearance. |
| Misfire in wet weather | Short circuit of HT system | Check plug cap, coil and cable. Use duck oil (Water repellant). |
| Contact breaker points burning | Faulty condenser | Replace condenser. |
| Loose condenser terminal | Tighten terminal screw. | |
| Dirty battery terminals | Clean and tighten terminals. | |
| Engine revs up but speed does not increase or kick-start slips, fails to turn engine over. | Clutch slipping | Adjust clutch pressure plate springs. |
| Replace clutch driving plates if friction material worn. | ||
| Add extra driven plate to increase pressure. | ||
| Excessive vibration | Loose or worn engine mountings | Tighten bolts or bush mounting holes to remove play. |
| Loose head stabiliser | Tighten bolts. | |
| Worn piston and crankshaft bearings. | Engine overhaul. | |
| Worn gearbox main shaft bearings | Gearbox overhaul. | |
| Crankshaft unbalanced | Balance crankshaft. | |
| Blue
smoke from exhaust when cold starting and when gear changing.
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| Worn valve stems | Replace valve and re-cut seat. | |
| Worn valve guides | Replace valve and re-cut seat. | |
| Blue smoke from exhaust when cold starting. | Wet Sumping caused by leaking oil-pump valves. Oil settles in the sump, pushes past the piston into the cylinder and burns off as blue smoke. | After standing a few days, check the oil level before you start up the engine, if it has dropped or low. Re-check after running for a couple of minutes and it should have risen back to normal. Not a major problem, after periods of standing, turn the engine carefully over on the kick-start about ten times before you switch on the fuel and ignition. This will allow the oil pump to return some of the oil out of the sump before starting. Alternatively fix or replace oil-pump non-return valves. |
| Blue smoke from exhaust when engine is warmed up. | Worn bore or piston rings. | Replace
piston rings. Re-bore, fit new piston and rings. |
Trouble Shooting