Explosions under acceleration

[COKE]

Hi,
My car doesn,t run fine,it is makes exhaust  explosions under load or acceleration.
Sometimes it makes an explosion and stalls...
It has new spark plugs,new plug wires,new cap rotor and plug ,new orange box...
The firing order is correct.
The carb is a Holley 750 with vac.secondaries,i cleaned the carb and put new  gaskets and diaphragms.



Could be from  the carb or the distributor?
Thanks.

[RT DAVE]

My best guess is you have a timing issue.  I have a thread started about this and there have been a few others under ignition timing.  Here's a link to my current thread which includes a link to another good thread on the 1970 charger registry board.   

Mine:


http://www.dodgecharger.com/forum/index.php/topic,16780.0.html

70 board:


http://1970chargerregistry.com/70messageboard/viewtopic.php?t=1207

[COKE]

Hi Dave,
Today i have removed the air filter and it also makes backfiring.
Even at idle, it makes a "pop" noise each five seconds or so.
I have tried turning the distributor in several positions,but the trouble persists.

Did you fix the troubles on your car?
Thanks.

[whitehatspecial]

Exhaust popping through the carb can be the result of a broken rocker arm or a bad exhaust valve spring.

[firefighter3931]

Check for vacuum leaks....it sounds like the carb is lean.


Ron

[Chryco Psycho]

I argee , probably lean , increase the squirter size & check flaot levels

[COKE]

I did adjust the floats when i rebuild the carb.
I have removed the plug from the bowls  at idle, and it is just under the hole,you can see the fuel through the hole.
If i open a vacuum port, if i remove the hose from the booster or from the distributor,for example,the RPMs goes up(A little opening a small port like the distributor one,a lot with the booster hose port)
Other detail is if i rev the engine to 2500 rpm for example and leave the pedal, it keeps them for  several seconds and then itself back  to the 600 rpm idle .

Now i,m going to remove the head covers to check the rocker arms like whitehat says.

[Chryco Psycho]

check for a vacuum leak through the brake booster too

[COKE]

I have found that the #8 cilinder spark plug was cut.Somedays ago i found the #5 cilinder plug cut too.
This is a trouble,cause the plugs are news.I just have crancked the engine  5 or 6 times in the garage since i installed them,so i don,t know what is the cause to cut them.
I have replaced the plug and checked the others.
The plugs are black with coal.They are NGK V power .

Also have found the culprit of the engine don,t return to the idle after an acceleration was the vacuum avance,so i have disconcted it.
The engine  holds the rpms until you disconect the hose from the avance so i suppouse it is hooking or maybe it has a bad spring in anyplace.
i really belive that  those Mopar orange or Chrome boxes and electronic ignition distributors sucks..

At least now the car is "Driveable",but it does not accept  striping, it continues backfing-stalling under heavy aceleration.
I have been able to drive it 5 miles and back to home without troubles, except a "Pop" that it made arriving to home.

Chryco, if i disconect the hose from the booster the RPMs goes up a lot(Should it to go down or stall?),so i think a vacuum leak is not the trouble.
The plugs are black so i suppouse it is working rich.
However i have sprayed with fuel around the carb and the intake without notice.


I,ll  continue fighting....

[Chryco Psycho]

sounds like thebrake booster is Ok
you are definatly rich & NGK plugs foul & quit firing very easily compared to most brands start trying to fix that first , float level could be wrong in the carb or the jets are too big

[COKE]

Float levels seems to be ok,the level is just under the hole when the engine is at idle.
Both jests are 70 size.
What size could i try?

My doubt continues with the vacuum leak.
Why the engine increase the  RPMs  when the booster hose is open?
I  belive it should to stall ..

[dodge freak]

It depends, mine motor does the samething with the brake hose open, if its very lean to start with or has very low vacuum then it might stall. A good way to check the brake booster is to push the brake pedal down after the motor has been off for a few hours, maybe even days. If the pedal goes down easy the first time, the booster is not leaking vacuum. I never had your problem so I have not a clue what it could be.

[Chryco Psycho]

try 67 jets , see if the plugs clean up

[COKE]

Hi thanks,
I will try with a 67 jets and a new air filter
However i  still only have drive this car on the road a couple of times so  almost all the time it is working at idle cause i cranked it just  to move it into  the garage .
Maybe this can be the cause of the premature damage on the spark plugs.

About the backfiring,i tuned the distributor with a timming light and now it goes a bit  better.
Yesterday it didn,t want to starts(Engine was cold),and this was because it was not making spark.
I wait few minutes an i tried again and it starts with a touch of key.
So i,m doubting if the distributor is ok,so i think that i,m going to change the entire ignition sistem for a MSD 6AL with his distributor.
I,m doubting  if  i should to get a distributor with vacuum adavance or without it.

[Chryco Psycho]

I would go without vacuum advance

[rt green]

just a thought, but if the plugs are black, and backfires, check and see if the power valve is blown. you are running a holley, right?

[Chryco Psycho]

definatly worth checking

[COKE]

Yes, i put a new one when i rebuilt the carb  ,but i don,t know if the backfirng have destroyed them.
How can i now if it works?
Thanks for the help.

[Chryco Psycho]

see fi ti is wet on the vacuum side & you can suck on it & see if it holds vacuum

[myk]

What are your guys' ideas on a motor that "pops" once before it takes off when the pedal is mashed from a standing idle?  I'm not talking about a detonation like sound, rather a sound like popcorn popping...

[Chryco Psycho]

not enough accelerator pump shot & it is going lean as the throttle is opened , you need a bigger squirter

[myk]

Damn these edelbrock 'carbs.  I don't think you can get a bigger squirter.  As for being lean, I'm going to try to jet up, but I only have one more size up to go to...

[dodge freak]

If you have the room you can use a hand held wire drill to open the squirter just be very careful you don't over do it. If you have a mic you can see what size it is and open it up  .002 -.004 and drive it and see if it helps. Should not have to go more than .010 max I would think.

PS. This is how I adjust the idle bleeds on my holley hp 750, use the mains and open them up to .055-.070 and buy a 10 pack of air bleeds from holley ,the .028 size. Cost like $12 for 10 -sure beats paying $175 for a full air bleed set from holley.

The pin drill cost me $10 and the drills are like 50 cents each-the high dollar item is the mic but they do make cheap ones. Really don't needs it , just don't mess up the drills.

[Chryco Psycho]

I do the same with a pin vice & numbered drill set