So I got my truck all back together after rebuilding the heads, and I'm having some issues with the timing. It runs reasonably well, and I've played with the distributer, but for the life of me I can't get it to run well at WOT, it backfires some through the throttle body when the tranny shifts into high gear. Also, sometimes it wants to stall out after WOT sitting still. I'm unsure what the manufacturer spec on advance or retarding is and at the moment I don't own a timing light. It's a 1990 W250 with a 360.

 

it sounds like you have the distributor in 180 degrees off. does it also fire throught the throtlebody when you start it?

 

If it was 180 out it would not be running.

 

yes it would run. i put a new distributor in my truck. it was off 180. it would cough thru the throttlebody then fire up. it would not run perfect but it would still run.

 

the manufacturer spec on advance or retarding is usually on a sticker under the hood covered in dirt. alldata says 10°±2°.

 

If it fires back through the intake, it it is advanced too much or your wires are mixed up. When you do put a light on it, don't bet your life that the marks are where they should be. If you look at that front pulley you'll see a rubber insert in there (or what used to be) and the outside "Spins" on the central core (hub). That is, the TDC mark on the pulley is not at TDC any longer. Correct me if I'm wrong, but I believe that when new, the TDC pulley mark lines up with the keyway on the collar (Hub). Here is how I set my timing. Find a hill in a residential area and set your timing retarded enough just to prevent pinging. Mine run on propane and are ultra sensitive to any excess spark advance. They fire back through the intake upon any amount of acceleration if advanced too much.

 

you have to rememeber that the crank spins twice for one rotation of your cam so it is really easy to to have your timing off by 180

 

Charlie is correct. An engine will not run properly if the distributor is installed 180 out. The distributor is indirectly timed to the crank and is directly timed to the camshaft. There is a good reason for this design. If it is 180 out from the camshaft the valves will not be open or closed at the proper time. The only way to get an engine to run if the distributor is installed 180 out is to correct the installation problem or change the plug wires on the cap to compensate for the improper installation .

 

I'm thinking it will have difficulty even running with the dist. turned 180. That would now mean it would fire at the beginning of the intake stroke and nothing would happen there with the cyl. just exhausted. Draw yourself a little diagram, I did.

There is only so much you can compensate with the adjusted timing. Example, many years back I had a 1974 W100 (318) and had to continually adjust the timing for it to run properly. Did this a couple of times over the next 6 months until the pistons started hitting the valves. Then it finally occured to me what was happening. The timing chain was apparently jumping one tooth at a time. But, there was enough room to compensate with the timing. Don't remember now whether I had to advance or retard the timing...........time for another little diagram.

 

I think I've got it good now, it is amazing how small of a turn of the distributor it takes to screw up the timing altogether.