L20b tune up guide?

[frank88]

Hi guys,

 

Is there a simple tune up guide somewhere for the l20b engine. Just basic starting and idling, hot and cold starts. 

 

I have a haynes manual but it's suggests a big over hall and my truck starts with a squirt of fuel in the intake and does idles when hot so just needs some tweaks. Cheers.

[datzenmike]

The accelerator pump on the carb should squirt fuel for you. One or two pumps (depending on the temps outside) this will also set the automatic choke and the fast idle to speed the warm up. Set up properly you should be able to start, put in gear and drive away. Take top off air filter, hold the choke plate open and pump the throttle. You should see a strong squirt of raw fuel into the primary barrel. If not, a rebuild kit (a good  one) will have a replacement for it. Most rebuilds are a thorough cleaning and setting factory adjustments such as the float level and choke.

 

 

Set the valve clearances on a hot engine. 0.010' intake and 0.012" exhaust. Set engine to TDC compression stroke adjust both valves #1,  Intake on #2, Exhaust #3 turn engine ONE complete turn back to TDC exhaust stroke, set exhaust on #2, intake on #3 and both valves on number 4. Done this way there is minimal time lost turning the engine over and it's completed before the engine cool down.

 

Set timing to 12 degrees before TDC on #1.

 

Check, clean or replace plugs, wiring, distributor cap/rotor and  points if you have them. Points should be set to about 0.022"

 

Idle adjustment (after valves and timing are set ... warm thoroughly, turn idle down as low as possible. Turn idle mix screw in or out slowly, looking for fastest smooth running engine. Usually there is a plateau of about one turn where it runs beat and falls off on either side... just set in the middle. Turn engine idle down with the idle speed screw and repeat the mixture adjustment looking for the best strong smooth and fastest idle. Keep repeating this back and forth until you cannot improve the idle quality and the idle speed is around 750.

 

This should get you well on your way.

 

[DanielC]

I would suggest that 750 RPM idle is a little fast.   I recently put a 1980 720 engine in my 521, and it tended to run on after key was shut off.  I reset the idle to 600, and that problem went away.

[datzenmike]

Mine will idle at 600 but it shakes more.

[DanielC]

I have found that every engine and carb combo has a little different "personality"  If you engine likes a 750 RPM idle, and that does not cause other problems, go with that.  I would.  After putting the L-20-B engine in my 521, at first it had a tendency to run on, when the key was shut off.  Of course, I could stall the engine with the clutch when parked, but I sometimes coast the truck in neutral down long hills.

[frank88]

Thanks guys that's great I'll write the list up in the garage and crack on.