New TQ backfires a lot- lots and more lots

[billschroeder5842]

I swapped out my old, leaky but well running TQ for a brand new rebuilt model.

I can get the car to idle very smooth and it will rev nicely in the garage. When driving, it will bog, the die when cold and back fire very early upon acceleration.

After it "gets over the hump" of the backfire, the car runs great and accelerates nicely.

I have nbot touched anything other than adjusting the rich lean (who knows if I'm doing it right) and it ideals smoothly at 750 pulling 17 hg. I left the timing alone at 10BTC.

Oh, on the side note, the hi idle does not seem to work either.

Any ideas? Thanks!

[John_Kunkel]

Have you checked the accelerator pump shot? If it's OK could be the metering rod adjustment.

https://www.youtube.com/watch?v=Dwh6SQ7kV6E

[billschroeder5842]

Thanks, I just watched the video and I'll go and mess with the metering rod.

I did get it a bit better---- backed out the rich/lean screws and bumped the timing to 12-14. That seemed to make it more drivable. The HG is about 20 now.... huh?

I seem to have this "hump" about 1100 rpms-- that is where it seems that everything goes haywire.

Also, if I give the gas a bit up a bump while taking off, it seem to do better (no back fire) than if I press slowly.

[billschroeder5842]

I gave the metering rod two full turns counter clockwise--it made no difference....

On to the accelerator pump...

[billschroeder5842]

I adjusted the accelerator pump so that it took the "full" shot; the factory adjustment had pressure on the plunger that kept it about 25% of the way down. No real difference.

I'm stumped.

So....

Timing from 8-10 to 12-14
Rich/lean screws backed way out
Accelerator pump with "full stroke"
Metering rods "two full turns" clockwise from factory
Pulls steady (rock steady" 19-20hg at idle
Smooth at idle and smooth at speed.

But...

Back fires and/or stalls at 1000-1200 rpms.

I wish I had my old leaky carb.

Any thoughts?

[cdr]

might have the wrong spring for the metering rods

[gtx6970]

If it backfires , it's running lean

question is,,why

[Steve P.]

CORRECT.... ^^^^^ Pull a plug an see your proof.

[billschroeder5842]

I pulled all the plugs and they were all a bit black and oily. 120k on a non rebuilt motor.

I gave up on the TQ and put on a Demon.

Car runs great and feels like it has more power. I bumped up the timing and the carb works as advertised.

I DO get a back fire when I stab the gas at about 1000 rpms, but above 1500 it takes everything and feels great.

I'm chalking it up to mean that the low compression car needs some revs to get going.

[polywideblock]

backfiring like that no matter what carb, sounds like a sticking intake valve 

[billschroeder5842]

Ok, what is the best way to unstick a valve? Does this require a rebuild or is this something I can fix by messing with the valve cover off?

It is a 75 so I'm not all that thrilled to put ALOT of money in it. I really runs pretty good for "normal" driving and I'm under no illusion about
it's performance capabilities.

Someday I'll go back to a Charger and it will have a fire breathing 440. In the mean time I'll just drive a curiosity.

[ACUDANUT]

 

[BSB67]

backfiring like that no matter what carb, sounds like a sticking intake valve 

Probably seen 50 different backfires through carb.....none caused by a sticking valve.

[polywideblock]

only had one car that backfired every now  and again thought it was the carb ,new carb still backfiring . then they thought it was dizzy , new one didn't fix it lucky that was a loaner ended up checking  valve train   and that's what it was  , one valve stem "slightly" bent only hanging up occasionally cost a fortune to discover though    just thought I'd share 

[BSB67]

only had one car that backfired every now  and again thought it was the carb ,new carb still backfiring . then they thought it was dizzy , new one didn't fix it lucky that was a loaner ended up checking  valve train   and that's what it was  , one valve stem "slightly" bent only hanging up occasionally cost a fortune to discover though    just thought I'd share 

Certainly anything is possible.  I am curious, who is "they" in your comment?

Logic would suggest that a bent valve would stick all of the time.  How did it get bent? How did the piston look?  Pretty hard for the intake and piston contact.

Valve guides that are too tight (aftermarket or rebuilt heads) can cause the valves to stick open and cause grief.

Again, it is possible, but seems improbable.

[polywideblock]

"they"  were the mechanics that were working on my car  . engine was 4.2(253) Holden V8 , not  kissing the  piston .only "just" sticking but enough to let combustion into intake manifold ,  replacement(reco) heads fixed problem     don't build motors, just know what I was told . perhaps it was a tight guide  


   do you think  you could post these 50 reasons that you've seen for  backfires and actually help the OP       like i was trying to do    

[BSB67]

"they"  were the mechanics that were working on my car  . engine was 4.2(253) Holden V8 , not  kissing the  piston .only "just" sticking but enough to let combustion into intake manifold ,  replacement(reco) heads fixed problem     don't build motors, just know what I was told . perhaps it was a tight guide  


   do you think  you could post these 50 reasons that you've seen for  backfires and actually help the OP       like i was trying to do    

Not what I said.

Anyways, I think he only needs one.

Let's see.  It runs fine.  Switch the carb.  Now it does not run fine.  Hmmmm.....muffler bearing.

[A383Wing]

probably needs more pump squirt from the accelerator pump..sounds like a lean pop

[polywideblock]

 have been following this for a few threads   it didn't run fine it was backfiring through the old carb as well

         could it be a stuck "lean burn" valve or whatever its called in the stock 75 intake manifold 

[BSB67]

have been following this for a few threads   it didn't run fine it was backfiring through the old carb as well

         could it be a stuck "lean burn" valve or whatever its called in the stock 75 intake manifold 

Might want to read the first sentance of this thread.

[polywideblock]

from 24 jan

     "
I putting a "new" rebuilt TQ on my 400 this afternoon.

My old one was starting to leak around the gaskets coupled with a bit of backfire on hard acceleration (I do know this is a smogged 75, so "hard acceleration" is relative) and general lack of performance.

What else should I look for?

Any common TQ swap problems that I should be aware of?

I'm going to keep things stock so "super tuning" is not necessary.

Thanks! "

[polywideblock]

moot point anyway   

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