110k Mile Z24 running issues.

[Madness]

My 720 has had issues since I bought it and I'm starting to realize that the previous owners took care of the appearances but not much was done maintenance wise.

 

So far I have set timing back to the 3-5 degree advance as recommended.

Replaced plugs with the proper part numbers per side.

Checked firing order and confirmed wire placement.

I have experimented with the air fuel mixture on the carb by ear and with a vacuum gauge.

Cooling system flush with new t-stat and cap.

 

Issues:

I've had backfire and hard start issues when hot and cold, choke open and closed.

Backfiring through the exhaust between shifts and when quickly letting off the throttle.

Strong full throttle pulls to redline in first and second but it will fall on its face and misfire horribly when shifting into third. Extremely light throttle is required to recover.

Random missfire at idle.

Lagging and sluggish during easy driving but will randomly recover and run strong.

Free revving while not under load seems fine.

Choke operates flawlessly.

 

I am hearing tapping from the top end so I think it's safe to assume it's time for a valve adjustment and head bolt re torque and I am at 5200 ft in altitude but this truck is originally from Texas so I'm not sure if jetting could be the issue.

 

Myself and the lead tech have gone over this truck and can't seem to find the smoking gun. Any of you guys could venture a guess?

[Doctor510]

Might be that the upper chain tensioner is bad.

[datzenmike]

Not in any order...

 

Runs string through one or more gears and falls flat on it's face, cured by letting off the gas is classic carb running dry. This can be when the carb uses fuel faster that it can be supplied. The most common cause would be a dirty/plugged fuel filter. The carb begins full but full throttle use uses it up and the pump can't push fuel through the filter and it runs out. Letting off the throttle decreases the demand and the carb slowly fills up again. Usually the filter just needs replacing but the carb float may also be set too low. Try the filter first. Note also that on the stock electric fuel pump there is also a replaceable fuel filter accessed by unscrewing the bottom off.

 

The mixture adjustment on the carb is the IDLE mixture adjustment screw and only affects idle speed and not an other.

 

 

Might be that the upper chain tensioner is bad.

 

Well the KA24E engines have a chain tensioner that is at the top edge of the block but the tensioner on the Z and L series is much closer to the crank shaft timing chain sprocket. They tension the chain as it may stretch with wear. At 110K I'm going to suspect the valve lash is loose first. Set lash to 0.013" on both sides.

 

 

Cylinder head bolt re-torque....

 

Do this only on a COLD engine. Fully loosen only ONE bolt at a time and tighten to 60 ft lbs with a torque wrench. Only then move to the next bolt. You can do in any order you like.

 

 

Starting...

 

If used to EFI engines you will need to pump the throttle at least once to set the choke on a carburetor engine. It should immediately start and rev up (1,800-2,200rpm) is normal to speed the warm up.