Help me find my miss

[Don G 1947]

Tim,

I'm working on a Job Rated Truck ('47) and the manual for that truck is short on technical details. Only advice it gives on the step up piston is "...don't distort the spring!"

At any rate, I think I am going down the wrong path with the fuel system, although I will check those things out. The reason I feel it is not a carb issue is because of the "fluttering" of the timing light. At idle (450-500) it will go from nice clean pulses to fluttering with no clear delineation of the the plug firing. Just slightly weaker (less bright), extremely rapid pulses of the light. So during the time that there would normally be 2 bright pulses I get maybe 3,4 or 5 weak rapid pulses. A carb problem is not going to cause a disruption of the signal to plugs. Just changed the wires and all the connectors along with the points and the problem is still there, but slightly improved. I guess the only thing left is the condenser and the coil.

Don

[Greenbomb]

Well, dang! Ya stole my thunder. The coil and/or condenser is my guess.

[Alshere59]

Something else you may want to look at is your valves. Have you set them hot yet or what was your cold setting?

Al

Edited August 7, 2011 by Alshere59

[randroid]

Folks,

Seems as though no system or sub-system has been left untouched in this thread and all of them have been ruled out except for inductive firing. I'm not trying to beat a dead horse with this but all of the symptoms point directly to it and it would be cheap and easy to test.

I'll get off that soapbox now.

-Randy

[Rodney Bullock]

How do you test it Randy?

[randroid]

Rodney,

It occurs when electricity from one wire goes through the insulation and sinks into the adjacent wire (I gave a little more detailed account in post #6). It will happen when the wires run along side each other, like when they're in the wire tubes. The test is to remove the plug wires from the tubes and separate them with those plastic wire holding thingies, making certain they're not close to each other and crossing at 90 degrees if they must cross. Shouldn't take more than ten minutes to do.

-Randy

[Don G 1947]

Randy,

I was listening. I changed the wires and got some improvement. I no longer have a "fluttering" in the timing light instead of nice clean pulses. Also changed the coil which also helped. Still some stumbling of the engine so I am going to switch out the carb and check the valves.

You have ALL been incredibly helpful and I certainly appreciate it.

Don

[randroid]

Don,

Glad we could be of help because that's why this forum is here. I'll be anxious to hear what eventually clears it because with your enthusiasm it will get fixed.

If I may suggest, in the future please post your results as you get them, be they good or bad, because that's what will give us better direction to assist your farther should you need it.

-Randy

[190bearplace]

Don,

You said the vacuum drops when it misses. Does the needle flutter? If so you have mechanical issues, most likely sticking valves

[Rodney Bullock]

  randroid said:

Rodney,

It occurs when electricity from one wire goes through the insulation and sinks into the adjacent wire (I gave a little more detailed account in post #6). It will happen when the wires run along side each other, like when they're in the wire tubes. The test is to remove the plug wires from the tubes and separate them with those plastic wire holding thingies, making certain they're not close to each other and crossing at 90 degrees if they must cross. Shouldn't take more than ten minutes to do.

-Randy

The reason I ask is I had this problem awhile back. When I touch my wires I would get a shock. I separated them better as they came out of the "wireloom" and they stopped shocking me. The car ran alot better as well.

[Don G 1947]

  190bearplace said:

Don,

You said the vacuum drops when it misses. Does the needle flutter? If so you have mechanical issues, most likely sticking valves

The needle holds pretty steady at 18 in., but drops noticeably when the miss occurs. Valve issue? Am going to adjust them in the next couple of days.

Don

[Don Coatney]

Did you do the rebuild yourself? Are the piston rods installed correctly with the squirt hole facing the valve train?

[Don G 1947]

Yep Don, all assembled correctly.

The miss is mostly gone now. I think it was a combination of carb adjustment and ignition problems. Replaced wires (which I think were the main culprit), points, coil and condenser. Also found that the screw holding the condenser wire and points spring was a bit too long and the metal part of the movable arm made contact with the screw every time it reached its maximum gap (could this have been the cause of the flutter?).

The distributor must be a bit worn because to maintain a dwell of 38* I need to have a gap of about .023". Should I set the points based on maintaining optimum dwell angle or based on proper gap .020"? Of course the real answer is to fix the distributor, but that will have to wait.

Don