Engine - Checks and Adjustments

MOTORCYCLE  CHECKING AND ADJUSTING

As the motorcycle had been adjusted and tested before delivery, there is no need to make any initial adjustment. However as mileage increases, it will be necessary to carry out minor adjustments to maintain peak operating condition.

Spark Plug Gap Adjustment

After the first 1000 km, check the spark plug gap. If necessary adjust the gap to 0.6 - 0.8mm.

Valve clearance adjustment.

Inadequate valve operating clearance will affect engine power, ease of starting, idle stability and fuel consumption. It is normal for the valves to recede slightly into the valve seats during the running in period and it is therefore important to check the valve clearance at the specified intervals. Valve clearance is set to 0.10mm cold at the factory. It is necessary to check and re-adjust the valve clearances to the correct clearance of 0.10mm after the first 1000 km.

NB: VALVE CLEARANCE IS ALWAYS SET WITH COLD ENGINE

 Ignition system

The "distributor" is the FDQ-6 type, which incorporates an automatic centrifugal ignition advance unit. It is installed on top left of front crankcase. The CJ750 does not distribute spark to each cylinder individually, but fires both sparkplugs at the same time that a piston nears Top Dead Center (TDC) . This "lost spark" system is common on  horizontally apposed engines. It is important to keep the points housing clean and dry. The platinum tipped contact breakers should be free from dust and lube (oil) contamination. The contact area of the breaker points should not be less than 80%, and the centers of upper and lower contacts should align with each other.

When the points open and close a voltage of 200v - 300v is induced across the points. The purpose of the condensor is to absorb this voltage and reduce sparking across the points. If excessive excessive arcing of the points is noticed replace the condensor. The specification of the condensor is 2 - 2.5 microfarads

The ignition coil model is DQ107, which has dual high voltage output. The primary winding of the coil should have a resistance of 2.4ohms, and the secondary winding a resistance of 13.5k ohm

. NOTE:

Although the CJ750 sidevalve and OHV engine distributors are fully interchangeable from a fitment point of view, there are differences in the spark advance curves between the two distributors.

 




 

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4.4 Ignition Timing Checking and Adjusting

 CJ750 engine ignition angle adjusting (see Figs 9 and 10):

a. Remove the rubber block from observation hole in crankcase. Gently apply the kick-starter to align the “6" mark on the flywheel with the center of the observation hole (see Fig. 10). Loosen distributor nut (Item 1 in Fig.9) and turn the installation plate so that the scale aligns with the center scale on the crankcase and then tighten the lock nut.


 

 

 

 

b. Remove distributor-cover and connect in parallel an indicating light across the distributor capacitor. Loosen securing bolt (Item1 in Fig.9), turn on ignition switch, rotate distributor till the indicating light just comes on (at this moment the platinum contacts are moving apart to the extent of a paper-thick clearance). Tighten the securing bolt and operate the crankshaft for 360 degrees. Check to see if the mark "6" on flywheel is in the center of observation hole when the indicating light just comes on. Otherwise, it should be readjusted. The ignition angle of the two cylinders should not exceed +/-2 degrees.

NOTE: If it is felt by road test that the ignition is too advanced, loosen the distributor and rotate the distributor counter clockwise to move installation plate scale against front crankcase scale (moving one graduation varies 2 of ignition angle). If it is felt in operation that ignition is too retarded rotate the distributor clockwise, and tighten the distributor nut after adjustment.

For best accuracy recheck the ignition timing using a timing light. Set the timing by aligning the “6” mark on the flywheel with the mark in the center of the crankcase hole at idle.

To adjust points (see Fig.9).

Remove distributor cover. Rotate ignition camshaft by applying the kick-starter to open the contact points fully. Using a feeler gauge check the gap between upper and lower platinum contacts. The correct gap is 0.35mm to 0.45mm.f the gap needs adjustment; loosen the securing screw and adjust the gap by turning the platinum contact adjusting screw. Retighten the securing screw

Distributor Type

CJ750 Model

Points gap

Initial timing

Max advance  degrees

FDQ-5

CJ750 sidevalve

0.35mm – 0.45mm

6 BTDC

24 BTDC   +- 2

FDQ-6

CJ750 OHV

0.35mm – 0.45mm

6 BTDC

30 BTDC   +- 3

Note:: When checking maximum spark advance with a stroboscope the maximum engine advance at 2200 RPM is the maximum engine degree advance PLUS the initial 6 degree BTDC value.

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