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This is a brief "how to" guide for tuning your 2.25 petrol Land Rover. I hope it is not to vague.

It is best to tune an engine when warm. Try to combine the tune-up with an oil change. After a lot of winter starts with the cold start (choke) on, a certain amount of gasoline blows by the piston rings into the crankcase, affecting the oil pressure, lubrication and the way the engine runs in general.

So warm it up, change the oil, and then start with the valves. I know the valve cover plate says " Hot or Cold" but always try to adjust them hot (read warm). Follow this sequence:

  • 1 open adjust 8,
  • 2 open adjust 7,
  • 3 open adjust 6,
  • 4 open adjust 5 or visa/versa.
Continue until all eight valves are adjusted. Open is when the valve spring appears as compressed as it is going to be. Remember, don't slacken off all the locknuts at once. and only adjust the valves (tappets) that require attention. Tight is, tight enough, on the locknuts. A good trick for the right adjustment is to go tight with the next larger size feeler gauge (0.011 inches). Then run the correct size through. It should feel just right, not loose, but not pinching or sticking. When you have adjusted all the valves then check the valves once again, maybe twice. This is a critical step in tuning your engine so take care and do it properly!!!

Another guide: When the o valve is open, adjust the a valve. This is numbered front to back. The clearance should be .010. Use a .009 and a .011 gauge. .009 should go, the .011 should not. Do not tighten the adjustment screw with the feeler in place. It will deform (flatten it). After you finish, check it again to be sure. When in doubt, adjust on the loose side, especially with exhaust valves.

This does not show the order in which they open, but is a guide for which valve should be adjusted when it's opposite is open. Have fun.

a = adjust
o = open

	1 2 3 4 5 6 7 8
	o             a

	1 2 3 4 5 6 7 8
	  o         a

	1 2 3 4 5 6 7 8
	    o     a

	1 2 3 4 5 6 7 8
	      o a

	1 2 3 4 5 6 7 8
	      a o

	1 2 3 4 5 6 7 8
	    a     o

	1 2 3 4 5 6 7 8
	  a         o

	1 2 3 4 5 6 7 8
	a             o

[Bill Maloney]

Next, do a compression check, try to use a screw in type gauge. Disconnect the wire from the switch (SW side of the coil). Record the compression readings as you measure each cylinder. If you get exactly the same readings from each cylinder, great, but unlikely. Usually there will be some variation e.g.: 147, 150, 142 and 151 lbs. However if three readings are close and one is 100 lbs lower than the other three, a tune-up is not going to help.

Moving to the sparking plugs, (spark plugs). Plugs are relatively cheap, and vital to the performance of your engine. Throw away the old plugs and buy a set of new plugs. (not Crappy Tire's own brand). Use a spark plug gauge with an electrode adjuster and use it to adjust the spark plug gap. Do not assume the gap is correct straight out of the box and do not bang them on the bench or valve cover until you think they look right. Adjust for a 0.030 inch gap. Put a little anti-seize on the threads. and once again, tight is, tight enough.

Now have a look at your distributor cap, rotor, spark plug and coil wires. If they don't look perfect, throw them under the front seat and fit new parts. Fit genuine Land Rover parts if you can not purchase good qualify aftermarket parts for the 25D4 or 45D4 distributor. There can be a significant difference in quality between original Land Rover and after market parts. (For spark plug wires, Genuine Land Rover Series III wires are the best. The Genuine Series IIA wires are made by Noma in Toronto. Noma also makes cheap Christmas tree lights that sell at Cajun Tire. Experience with these blue wires has not been good) Make sure the base plate to which the parts attach rotates freely. If it does not move, do not force it. You might remove it completely from the distributor and make sure the centrifugal weights are not seized and the springs to the distributor cam are intact and attached. The distributor cam should rotate slightly as well. Apply suction or vacuum to the pipe or hose on your vacuum advance to remove any debris.

If your points are burned or damaged, don't attempt to file or repair them. Fit new points and set them to 0.015 inches. At the same time change the condenser. Make sure the "pigtail"(the low tension lead and block) is in good condition.

If you have a fuel filter (highly recommended) replace it. Clean the sediment bowl on you fuel pump. Make sure it comes off easily enough so you can reassemble it.

Do not ignore the air filter. Take it apart and clean . Refill with 20W50 oil to the level mark.

Set your timing next, 7:1 engines 6 deg. BTDC, 8:1 engines 0 deg. TDC and 8:1 (emission controlled) 6 deg. ATDC.

The best advice I can give you for your carburetor is, if it is not broken don't fix it. Most of us have one of three carburetors fitted, but they all have two main adjustments, idle and mixture. So as long as the throttle shaft is not too warn, proceed. Turn your idle down as low as it will go, 700 to 800 RPM is good. Find the highest, smoothest idle speed with the mixture screw, then readjust the idle with the idle screw to about 800 RPM or until it sounds right, not too fast, remember you have to be able to shift gears. Give the throttle a couple of snaps, if it stalls, increase the idle speed a bit, and you are done.

Copyright Dixon Kenner, 1995-2011. Last modified March 15, 2005.
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