I have checked the timing it's a 8° before tdc. But it also jumps around.

 

so somethings wrong timing wise then... whats your cap and rotor look like?

 

They look to be in good shape.

 

ok so rule that out then... umm... yours got that spark control computer in the driver side fender? sometimes if they get excess moisture in there then they can go bad.... could be a vacuum advance problem on the distributor too

 

Mine does have the scc. I replaced it about 3 years ago. No vacuum advance on the distributor.

 

is it an aftermarket distributor? mines an original 87 distributor and ive got the scc AND vacuum advance.... if you think you have broken valve springs then pull the covers and check!... could be an intake gasket leak too take some starter fluid or carb cleaner and spray around the gasket and if it revs up on its own wll there ya go its leakin

 

The distributor is stock.

 

do the other thing with the intake gasket if you can and get back to me

 

You say you rebuilt the carb? Did the truck run fine for X amount of time after you rebuilt it? Or has it not run correctly since the rebuild?

 

You can read on this link how to check for timing chain deflection:

http://www.crankshaftcoalition.com/w...ing_chain_wear