Just for fun, what is wrong with this engine?

[Ele115]

This is just for fun. I already sorted this out. It took me way too long, I will be honest. WAAAAY TO LONG. Test and tune is in a few hours if it isn't raining. I am just doing this because hopefully a few of you get a kick out of this or learn from it. I hope, anyway. I DID already sorting this out....The car is a 1982 Diplomat with a 413. The engine is stock except for a cam and a really old Offenhauser intake with a Holley 4150. Stock valve train with double springs. The distributor is a stock Chrysler electronic unit from a 75 Fury Police car and the coil is a new Pertronix. It runs good, very strong but breaks up at full throttle under load, like in the burnout box. It's not backfiring, just a slight wheeze followed by a bog, not every time. Most times. 60 foot times are down. Compression is 160-180 on every cylinder. Vacuum is really low, like 4. It had been about 15 all summer. Gimme your educated guesses! You're going to love what this was.

 

[XfbodyX]

stock Chrysler electronic unit from a 75 Fury Police car and the coil is a new Pertronix

Ohm difference from unmatched ballast Id guess but probably wrong since you say "not every time" unless its the same time.

 

[Aspen500]

Idle vacuum was 15, then only 4. Hmmmm. Wild shot in the dark, guts fell out of the PCV valve? No? Told you it was a wild guess, lol.

 

[AMC Diplomat]

A squirrel put nuts in the intake

 

[69-]

Mice ate vac line(s).

 

[Ele115]

OK so this is odd but it makes sense. It ran really good, just a bit off. The vac gauge broke. I tried it on another car and it read even less vac. I tried another one and I had 15 in/hg give or take. Slightly smaller jets and freeing up one of the distributor weights fixed the top end problem. Just kind of mad I didn't suspect the gauge sooner. It ran too good to have such low vac. The simple things get you when you are looking for a big problem. I was fixated on the low vac reading and ran in circles. If I had ignored the gauge, which my mind wanted to do, I would have looked at ignition and AF mixture sooner. I don't think I ever saw a bad vac gauge before except the electronic ones. I need to clean the plugs and run it a few times really hard then take them out and see

 

[M_Body_Coupe]

Noooo...nooooo....too fast with the answer!!! LOL

I was going to suggest: too fat at WOT....the reason being: I am seeing something similar with my combo and it dips into the 10-11s (AFR) at WOT.

The similarity comes from you describing it like a RPM cutout, basically I can feel/hear a sort of "...rap...rap....rap...." once the secondaries open up on my TQ. Mind you, no surge, just an un-clean burn.

Well, anyways, that's what my theory is. I run a 1-3/8" primary TQ with 98 primary and 143 secondary jets, along with 2005 rods, which is all about 26%, 6%, 8% and 9% richer on idle, cruise, power and secondary power circuits.

Unfortunately I ran out ouf time this season to sort it all out following my re-install of the motor...spring will come...not fast enough, but it will!

 

[Aspen500]

In hindsight, with an actual 4" vacuum at idle, it wouldn't be idling, lol. I did have a vacuum gauge go bad once, so they do fail.

Sometimes diagnosing a vehicle, a person can forget to verify the accuracy of the test equipment. Remember chasing down a circuit with high resistance and after an hour of looking, discovered the high resistance was my DVOM not the circuit. DOH! Just then the Snap On truck pulled in so, toss the 20 year old meter in the circular file, pry the wallet open (WIDE open, it was Snap On afterall, lol) and buy a new meter.

 

[Ele115]

Noooo...nooooo....too fast with the answer!!! LOL

I was going to suggest: too fat at WOT....the reason being: I am seeing something similar with my combo and it dips into the 10-11s (AFR) at WOT."

You don't want that shot of extra fuel until the exact moment you are going to get that lean burp with the primaries wide open and the secondaries starting to open. On the 4160, you can change the power valve to open sooner or later. These have a secondary metering plate instead of a block like the primaries. I like the TQ a lot. If you take the time to set them up, they kick ass and your fuel in the bowl will be about 30 degrees cooler than other carbs. I don't currently have one that's ready to go. I used to do a lot of TQ's for monster trucks. People would just hand them to me or throw them in the trash because they were intimidated by them

 

[Aspen500]

What I remember about the TQ was, provided the main body isn't warped from some ape over torquing the screws mostly, AND nobody ever messed with the adjustments, they work excellent. Kind of like in my old Ford tech days and the VV carb. They work fine unless messed with. Once the adjustments were screwed up by someone trying to "fix" it, the carb was f****d. Only 2 things ever went wrong, and both easily repaired. The venturi diaphragm would go bad, and the metering rod would get gunked up and stuck. Zero reason to ever break the seals on the adjusting screws and nuts. Same pretty much applies to a TQ. Sorry for the novel, lol.

Nothing like the sound when the secondaries open on a TQ with an unsilenced air cleaner!

 

[80mirada]

The TQ going wide open was such a beautiful sound. They were actually really easy to tune, but most people who tried did everything wrong

 

[Ele115]

Or pried really hard on them and broke the plastic float bowl with their huge screw driver trying to pry the top off. "I needed a 650 dubbah pumpah anyway man!"