72 115 ignition problems

[birdnbuck]

checked switchbox and rectifier all checked out, was running great now has spark at plugs and fuel but will not fire. when you switch the ignition off it will fire but not when you crank it. any ideas.

 

[Clams Canino]

Re: 72 115 ignition problems

Will it spark at the plugs while cranking it - at all? If not suspect the trigger (distributor body) 1st. But do "the switchbox test" to be sure.

Also FIRST check all connections and VERIFY you have +12 at the red AND white terminals of the switchbox while cranking. A bad connection can cause a voltage drop when running the starter motor.

-W

 

[Clams Canino]

Re: 72 115 ignition problems

MERCURY BATTERY POWERED SWITCHBOX TEST
FOR DISTRIBUTOR THUNDERBOLT MODELS


This test is for the 332-2986 switchbox used from 1967-1978 on all the
inlines.

This test assumes your coil is good (most all are).

DISCONNECT BATTERY

1. Turn off ignion
2. Disconnect all 3 wires on the distributor side of the switchbox.
3. Remove the HV lead from the coil to the center cap (remember it unscrews
from cap)
4. Reconnect that HV center lead to the COIL side only.
5. Position that HV lead about about 3/8" from ground (block, shrouds etc)
and find a way to hold it there.
6. Jumper the brown and white terminals on the dist. side of the switchbox
together.

RECONNECT BATTERRY

7. Check that you have +12 V at red terminal.
8. Turn on ignition and verify +12V at white terminal (on red terminal side)
9. Touch the black terminal to ground - unit should cause spark each time
you touch ground.

If this passes and it still won't fire at all, suspect the trigger (distributor).

To test replacement trigger if/when switchbox passes test: Remove jumper wire and hook up the 3 wires from the new distributor to the switchbox, turn on key and manually spin the distributor, spark should jump from coil wire just like in the switchbox test.

 

[birdnbuck]

Re: 72 115 ignition problems

Clams, I have a aftermarket cdi switchbox and only have a brown, black, white and white with red stripe wire coming out of it so i do not have a red and white terminal, where do i check one of these for 12v while cranking. I did check switchbox and got good spark and i do get fire at the plugs, but it will not fire when cranked but when you let off the key it will fire.

 

[Clams Canino]

Re: 72 115 ignition problems

I'd assume brown,black, white are headed to the distributor and white with red stripe is the +12 feed. (never used one)

-W

 

[thibauja]

Re: 72 115 ignition problems

let see if i got this right... you tested the switchbox and you get a good spark from the coil to the distrib ... but you have no fire while its turning on the starter and you get one spark when you let go the key ...
is that it ? well it may not be much help but i have THE SAME prob
many times tests and advices would bring me back to .."MAKE SURE you do have the 12v WHILE its turning " not only befor and after.. the switchbox will not do its job properly with less than 12 V
but then again its my 10 cents comment...i m still stuck with the same prob even i HAVE the 12V so guys feel fre to correct me but it would be one of the first thing to check i think..
if i finaly get mine working ill let you know what was the issue ..im changing the whole distrib assembly whithin the next few days i was lucky anough to find a used one COMPLETE.
Jack

 

[CharlieB]

Re: 72 115 ignition problems

You haven't mentioned if the distributor belt is intact and the distributor is turning?