Something i noticed

So over the last few weeks ive been messing with my timing as some of you know but have noticed that the timing seems to go from perfect to slightly off 5 degrees or more after i drive it. Yet sometimes nothing changes at all. Ive been confused.

I checked for vacuum leaks and everything else and came up empty until just now.

Ive been meaning to swap over to the smaller dist cap and rotor but havent yet because of work and lack of time, and have kept using the oversized adapter cap and big button because of the wrong plug wires recieved weeks ago.

Today i wondered if the lose feeling oversized cap was moving enough to cause timing changes. With the engine running, i barely twisted the cap just enough to move the back and forth play it had and the engine died. Iit wouldnt crank again until i took it apart and reset the rotor button. Apparently this small movement caused just enough slop to mess with my timing. I put it back together and tapped it down.... Cranked it and reset timing. It runs perfect now when the play is limited. Tomorrow ill switch over to the small cap and button as intended. Ive been racking my brain thinking i had worse problems i couldnt find.

Anyone else ever have this problem or knew about this?

Pic included of the bigger cap.

 

I have no idea, but that engine sure looks good .

 

Thanks. The valve covers is what does it for me.

 

Beware those valve covers scratch easily, even the plastic wire looms will scratch them . And yes it looks great glad it has all came together and you have learned a lot, well maybe we all learned something

 

In the real world, the cap has zero to do with timing, to alter timing the dist housing has to move. Moving the cap will effect rotor indexing, meaning the rotor may be misaligned to point the spark has to jump from rotor to dist terminal. In a severe case, spark may jump to two adjacent terminals.

 

Just to be safe, send my your carb and you can get another.

 

Nice motor! Make sure your lower hose doesnt collapse when you rev up. I had an issue with one shaped like yours.

 

They sell a spring that you can put in it to stop that. Just look for a mustang one.

 

Parts stores around me didnt stock the molded hose with a spring....so I used a ribbed hose. I never thought about trying to buy just a spring.

 

Yep thats it. I drove it 180 miles today and its the biggest test yet and it ran perfect the entire way. I checked timing eevery 50 miles and it was dead on. The small cap is solid and doesnt move at all. No slop.

 

Ill def check that tomorrow.

 

I've made my own "spring" by winding up a piece of metal coat hanger and stuffing it in there. Just make sure it's tight so it doesn't work it's way up into the water pump.

 

So if it starts again does that mean the distributor may be bad?

 

I doubt you have a dist problem, to alter timing the gear would have to slip.

I have seen badly worn dist cause erratic timing but OK at idle, jumped around at higher RPM.