Compression; Ignition; Carburation - Tecumseh SPECTRA 37 Service And Repair Manual

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b)

COMPRESSION

If compression is poor, check for:
- Flywheel slipping on crankshaft.
- Loose spark plug.
- Loose cylinder head bolts.
- Damaged cylinder head.
- Warped cylinder head.
- Insufficient tappet clearance (4-stroke engines).
- Broken connecting rod.
- Loose or worn crankshaft seals (2-stroke).
If engine is fitted with compression release, it is necessary
to remove cylinder head and check components visually
if a leak tester is not available.
NOTE - With the compression leak tester faults can be
found easily within minutes (Fig 4).
c)

IGNITION

Remove spark plug and connect a new one to the HT
lead, earth plug body to cylinder head, turn the engine
and check that a strong spark occurs between the plug
electrodes. If no spark occurs see chapter E for service
and repair instructions.
If spark occurs, fit new spark plug and attempt to start
engine. Remember that spark failure can also be due to
such faults as:
- Broken flywheel key.
- Crankshaft bearing worn, thus preventing cam from
opening (breaker point ignition).
- Incorrect air gap setting (electronic ignition).
NOTE - When using the compression leak tester
( Fig 4) and the ignition tester (Fig 5), faults may quickly
be located. If no fault can be found, the defect must be
within the carburation system or the equipment.
Fig. 4
Compression Leak Tester. Tests for leakage of valves,
rings and cylinder head in situ.
Fig. 5
Tests standard ignition system in situ. Solid state units
must be removed for test.
d) CARBURATION
After having drained and cleaned fuel tank, refill with fresh
fuel and check (float carburettors) that fuel flows from the
bowl when the drain valve is pressed.
On diaphragm carburettors without primer, remove high
speed jet and operate diaphragm. Fuel should then flow
from jet seat.
If fuel does not flow, check fuel line and filters, re-set
carburettor as in chapter G and carry out starting
procedure.
If engine still fails to start, remove sparking plug and pour
a small quantity of fuel into the cylinder, replace sparking
plug and attempt to start. If engine fires a few times it
may be assumed that the carburettor is at fault. Check
completely the carburettor as in chapter G.
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Fig. 4
Fig. 5
6