Weird Problem and I have No Clue

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Mopar85

Mopar85

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I just assembled and installed my motor and i was turning it over with ignition off to check for any issues and after a few rotations air/fuel flew out of the carburetor like a pop back! there was no fire like normal because the ignition but that's why I am confused. why would it do that? If there is no explosion why would air explode out of the carb with enough force to pop off vacuum caps? The timing chain is brand new and yes its set right.
 
Are you sure its timed correctly? Pull the plugs and do a compression test. It does sound like the cam timing COULD be off
 
i have an msd ignition that gets power from my painless switch box so there was no power to the coil. the timing chain is a brand new comp cam pre stretched running on the 0 degree with a offset crank key.
 
just had the heads rebuilt and the valve guides are new with comp cam springs to match the cam.
 
all power from the ignition goes through the msd box. coil gets power from the box. crank trigger is wired to the box. so if the box is off there will be no spark. my car has a complete painless wiring system. Not to mention the coil wire wasn't even hooked up. it was still on the spark tester
 
OK, Painless DOES NOT wire the resistor bypass the way Mopar did, so HOW are you getting "cranking" ignition power?

IF you are using the original Mopar ignition switch, you had to

A add a second wire from the original ignition switch "ign2" terminal to the ignition

B add a diode from the "start" wire at the start relay to the ignition

C add a second relay in parallel with the start relay to ignition

B use the later multi-terminal start relay like this thing:

StarterRelay.jpg
 
If you think the coil is the problem just pull the wire off it and see what happens. Also, if you hold the throttle plates open it will not be able to generate that kind of back pressure in the intake manifold. Maybe then you can get on with diagnosing it. With the info you gave it will be hard to diagnose. Could be someone put potatoes in the exhaust pipes. I can tell you this, when I build a new engine I set it up so it will fire and run instantly, and continue to run without overheating or anything till the cam and rings and bearings are broke in somewhat. Especially the cam. Turning it over like that will just wipe the assembly lube off everything.
 
Has to be a mechanical problem. Crank/cam relation wrong, exhaust valves not opening, blocked exhaust, or intake valves not closing.
 
As I read your original post, there was no fire as the ignition was off.
How were you turning it over, with a socket on the crank?
My vote is also timing. Check that you don't have it 180* off.
C
 
RedFish said:
Has to be a mechanical problem. Crank/cam relation wrong, exhaust valves not opening, blocked exhaust, or intake valves not closing.
Click to expand...

Gotta agree here , on all four mechanical points.
Addendum...(based on the assumption all the guide work/ assembled height
is correct),
A bit more info Please. I.e., solid or hydraulic lifters?
 
I am starting to think a exhaust valve is not opening. or there is something in one of my header tubes. it has to be mechanical. I do appreciate the help with the ignition but I know for a fact that it is not sparking because i removed the coil from the car and it still did it. it has done it maybe four times now for testing. pulling the valve covers and carb to do more tests and observe the rockers.
 
I'm def with timing. If you got your compression stroke going while the valve is behaving as if it's an intake stroke...

Basically the valve is open and instead of the piston going down, its going up -- forcing air OUT of the carb. Your timing is off :|
 
wow i figured it out. the magnetic pick-up was wired backwards! somehow it was causing a plug to have a weak spark i guess in one of the cylinders but it wasn't enough to cause flames out of the carb. the new pick-up had a reverse connector than the one i had installed. iI am gonna call msd about it and find out if they switched it for a reason or if mine was a fluke.

Thank you for all the help and sorry for being stubborn
 
Mopar85 said:
wow i figured it out. the magnetic pick-up was wired backwards! somehow it was causing a plug to have a weak spark i guess in one of the cylinders but it wasn't enough to cause flames out of the carb. the new pick-up had a reverse connector than the one i had installed. iI am gonna call msd about it and find out if they switched it for a reason or if mine was a fluke.

Thank you for all the help and sorry for being stubborn
Click to expand...

What this causes is known as "rotor phasing" or in this case NOT in phase.

The pulse that the pickup generates is like an AC wave, it goes first one way, then the other. If you reverse the pickup, it effectively moves the timing, but the rotor is in the same place

If you google this, there are all kinds of people CLAIMING that this is a "huge problem." Drilling holes in dist. caps, etc etc to test for spark timing.

Glad ya got 'er figggggered out.
 
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