78 351M dies after the truck warms up. When I drive it, the truck will start up fine, but in a couple of minutes, it warms up and tries to choke down. Or so I thought. I am afraid the vacuum advance is kicking in and it just feels like it is choking down. I get alot of black smoke when this happens. I ran it at idle in the driveway this weekend. A couple of minutes after I felt the t-stat open the engine dies and I was unable to get it started again. Any suggestions?

I have read several threads about the timing - which I have yet to check - and I think the timing may need adjusted, but should it advance to the point that it will not run? or even start? should the dura-spark controller retart timing 10degree for start up?

 

Sounds like your choke pull-off may be malfunctioning. Black smoke is an indication of the fuel ratio being too rich.

 

Next time it dies after you warm it up pull off your air cleaner and see if the top set off butterflys in your carb are all the way open. If they are not your choke is set to rich are is malfuctioing.

 

Just like another user at the moment. A blown power valve will also choke the engine with fuel.

 

what is the power valve? where is it located?? What do I look for to see if mine is blown???

 

but I got the truck running last night. I fiddled with the ECM wires. Found several splices which are questionable. I plan to re-work some of the engine electrical over the next week. I do not want the electrical to be questionable. I have a wiring diagram in my Hayes repair manual.

 

I found a Painless wiring harness for the ECM. $132 from Advance Auto. I will try to clean up the wiring myself.

I found more of the problem(s). I got the truck started and watched it idle as it warmed up. The choke never open up. I remember, now, the previous owner had the choke wired open, guess I found out why.

The choke is not moving at all. It must not be set up correctly, or may not be working at all. Also, the choke pulldown is not working. I think the pulldown will open the choke as vacuum is applied. Two problems here. The pulldown rod is not connected to the choke mechanism all the time. There is a connecting rod which falls out of the hole in the pull down rod. 2nd, the pull down rod does not seem to move as the the engine is throttled. If I understand correctly, more throttle means more vaccum which should mean the choke is pulled off by the choke pulldown. Please let me know if I am understanding this wrong.

So.... I will at least have to replace/ fix the choke and the pulldown accuator. I need to rebuilt the carb. or... I could just wire open the choke like the last guy.

 

Yes, as throttle is applied the choke pulloff should open the choke. I would try replacing the pulloff. I haven't wired a choke open, and would try to get everything working properly without resorting to that. A carb rebuild is probably a good idea.

 

Is it possible to replace one piece of the carb at time? Like... start with the pulldown, then the choke, then the rebuild?

I agree. I would like to get it working correctly and not just wire the choke open.

 

Yes, you can purchase individual parts. I know the choke (I have a climatic choke) actuator housing as well as pulloff are available at NAPA. I don't know what type of choke you have so I can only relate my experience. A rebuild could expose/remedy any other issues which may not be corrected by replacing the other items.

 

I have the climatic choke. Good to know I can replace as needed, or as I have time to work on it. I have not verified the idle solinoid is working correctly. I found another problem. It seems that the choke mechanism is getting stuck with the choke fully closed. I can open the choke by hand, but it feels like it is catching on something. Need to work through the choke setup proceedure in my Hayes manual. Thanks for the comments above.

 

What ECM, and $132 for what? There are only a few wires to the ignition module and they are easy to find at any salvage yard in good condition. They can be found on many period vehicles, not just trucks.

 

ECM=DuraSparkII in my mind. Not really looking to replace 30 year old parts with 25 year old parts. I found the new wiring harness on the Painlesswiring.com site. Had no idea it would cost so much.

 

I have a 351M that will hold oil presure at 60 lbs for 20 or so minintes then dropes to 0 and starts to over heat,it has blown several head gasgets.I thought it was not getting oil up top so I though it was the camberrings, so I changed them and put a high presure oil pump and water pump and radior and it still does it.I would aperacate some help, if someone could, thank you

 

You would probably be better served by starting a new thread entitled something like "351M Oil Pressure/Overheating Problems." A separate thread will probably generate considerably more responses/assistance as this thread had little relating to oil pressure problems or overheating problems.