Assembly manual
Richard Taylor wrote this manual.
This section is a practical guide to fault finding, although it is not fully comprehensive it does cover the majority of problems that we have encountered over the years. This section offers no warranties and makes no guarantees, if your engine still does not start or run properly seek additional help from your Lambretta workshop manual or a competent Lambretta dealer.
Symptom | Possible problem | Check or perform the following |
Engine does not start or stops after short time |
No fuel getting through | Check tap, check filter, check float valve is screwed home, check float is free. Smother carb with hand and prime by kicking over |
Engine does not start, is hard to start or misfires |
No Spark, intermittent or weak spark | Look for short in loom, Check ignition and replace parts accordingly. Faults in new ignition components are not uncommon, test as you go. |
Engine does not start No Compression but crank turns over |
Compression problems, from loss of rings, seals, petals or hole in piston |
Check reed valve and petals are closing properly. Check for holed piston, damaged rings/piston. Check timing and jetting if piston holed. |
Engine runs erratically has intermittent misfires |
Possible carb or ignition problems | Check ignition & loom for correct operation, check carb for air leaks, loose jets & needle valves. |
Engine starts and idles but misfires when ridden |
Carb, fuel & compression is OK but timing mysteriously seems to move |
Possible broken crank, loose timing/pickup, loose flywheel or flywheel boss, damaged woodruff key |
Back firing & ignition problems | Reed petal broken and pushed inside reed block |
Re-time ignition, or replace ignition. Replace broken petals and clean out petal debris from crank case & barrel |
Light heat seizure, caught before wheel locks |
Barrel over heating and tight ring gap tolerances. Possible weak mixture, air leaks or no oil. Engine not “run in” long enough |
Light hone of barrel to remove marks, replace piston and rings if damaged and re-gap |
Medium heat seizure, wheel locks up. Barrel scored, rings bent and light damage to piston. |
Barrel over heating and tight ring gap tolerances. Possible weak mixture, air leaks or no oil. Engine not “run in” long enough |
Hone/re-bore barrel to remove marks, replace piston (possible next over size dependant on damage) and rings generously re-gap |
Heavy heat seizure, sharp screeching noise, wheel locks up, possible bang & rattle followed by no compression. Barrel heavily scored, rings shattered and blown into exhaust, piston is history & looks like Ben Hurr’s helmet. |
Barrel badly overheating and tight ring gap tolerances. Possible weak mixture, air leaks, catastrophic failure of rod & bearings, barrel stud loose or pulled out or no oil. Engine not “run in” long enough and running flat out. |
Re-bore barrel to next oversize. Replace piston & rings with next oversize. Clean out debris from exhaust, and crank case. Inspect for damage to crank, crankcase and cylinder head. |
In winter engines runs sluggish and does not achieve peak power, but runs well in the wet. |
Possible carburettor restriction, related to weather conditions. |
Check to see if your over-trousers stuffed under the seat are blocking the air scoop before getting the spanners out. |
Spark plug colours | Colour indication | Action |
Spark plug insulator & electrode is very dark or black and oily |
Fuel mixture is rich and or oily. This is expected during “running in”. |
Keep spare plug, brush, clean and rotate use during “running in”. If not running in reduce jetting. Check your oil / fuel ratios. Possible drive side oil seal failure. |
Spark plug is white, light grey or very light brown and slightly shiny around the insulator |
Fuel mixture is lean, weak and or fuel starvation. Warning, Prolonged running like this will cause damage. |
Check for air leaks, correct oil mixture and or increase jetting. Possible mag side oil seal failure |
Spark plug insulator is a dark dusty coffee brown colour (coffee with a bit of milk) |
Mixture is correct (some say a lighter brown colour is better but best to stay on the richer mixture side we think) |
All is well in the world, pat yourself on the back and go down the pub (do not drink and drive / ride) |
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