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Help... 72' 225 is kicking our butts
https://slantsix.org/forum/viewtopic.php?t=65305		 Page 1 of 1
Author:  Shadow9x99 [ Wed Sep 09, 2020 6:41 pm ]
Post subject:  Help... 72' 225 is kicking our butts
Hello Everyone! First time poster here. Me and my dad are old hats at working on old cars (well, dads hat is slightly older) but we're having a problem with the 225 /6 in my recently acquired '72 Valiant: it's popping through the carb under even the slightest load and we're about at our wits end.

It has what appears to be a "lean pop" back through the Holley 1920 1bbl carb at anything more than about 1/4 pedal. We've rebuilt the carb and had it on and off the car multiple times to recheck it. All seems to be functioning normally but we cannot correct this issue. We have adjusted the valve lash (.010" Intake & .020" Exhaust), Checked the timing (set to 0* BTDC with the vacuum advance unhooked), Put in new points (gaped at .020") & new condenser, and we have even pulled the manifolds and installed a new gasket, thinking it was a manifold leak around the intake runners. Still the popping continues!

We are at a point where options are few and the white cliffs of Dover look ever more promising with the passing of each day. Anyone ever experience anything like this with one of these leaning towers of power? This motor is the epitome of simplicity, and yet we cannot make it run. What are we missing?
Author:  Greg Ondayko [ Wed Sep 09, 2020 7:01 pm ]
Post subject:  Re: Help... 72' 225 is kicking our butts
I would say to recheck the firing order on the cap wires and also check to be sure the distributor is not 1 tooth retarded.

Bring up the tdc mark on the balancer for #1 and the rotor after twisting in should point to about 5 o'clock.



Greg
Author:  cpslntdchrg [ Wed Sep 09, 2020 7:05 pm ]
Post subject:  Re: Help... 72' 225 is kicking our butts
Welcome.
Well, when I bought my car it had a similar problem. Good idle, good high load but the engine kicked when on medium load (not sure if this is your situation too. My car is manual, so you could open it WOT without the transmission shifting). The way I fixed it was to buy a NOS (New old stock) 1920 carb in Ebay. Also, members like SlantSixDan might have an NOS carb, but again its probably the most expensive solution. I hope somebody can point you to a better direction, that probably will include checking worn parts (Worn throttle shaft, correct jets (did it failed the same way before rebuilding the carb), correct accelerator pump settings... etc...)

Another thing to check maybe timing. you might have a slipped harmonic balance mark, and you think the engine is on time but it is way advanced. If possible try to check TDC on cylinder 1 with the harmonic balance mark at 0 degrees (If this is the reason, maybe if you disconnect the vacuum and accelerate it wont kick as bad, as it will have less advance).

Good luck!

PD: This is a listing for a Holley 1920 NOS in ebay now, but it is freaking expensive!

https://www.ebay.com/itm/NOS-HOLLEY-192 ... SwSldcnPWM
Author:  ProCycle [ Wed Sep 09, 2020 7:31 pm ]
Post subject:  Re: Help... 72' 225 is kicking our butts
Cam chain jumped a tooth?
Author:  Badvert65 [ Thu Sep 10, 2020 5:00 am ]
Post subject:  Re: Help... 72' 225 is kicking our butts
This also sounds like it could be a burnt valve (intake).
Author:  emsvitil [ Thu Sep 10, 2020 6:03 am ]
Post subject:  Re: Help... 72' 225 is kicking our butts
Might be the ignition system...........

Bad plugs, wires, points, condenser.....
Author:  Greg Ondayko [ Thu Sep 10, 2020 9:42 am ]
Post subject:  Re: Help... 72' 225 is kicking our butts
Quote:
Cam chain jumped a tooth?

THat is also along the lines of possibility.

I thought that as well when I typed my original response.

Greg
Author:  Shadow9x99 [ Thu Sep 10, 2020 2:43 pm ]
Post subject:  Re: Help... 72' 225 is kicking our butts
I tried some of the suggestions when I got home today:

Timing mark is still at TDC
New condenser and points already installed
Compression checks out fine (probably no burnt valves)
A pretty nice set of aftermarket 7mm plug wires came with the car. Fairly confident they aren't bleeding spark.

99.99% sure the plug wires are where they need to be... but I did have them off to clean them (spark plug tube seals leaked on them over the years). I figured this was worth doublechecking...

And sure enough 3 and 4 were swapped. Switched them back and now it runs like a top again. I never would've guessed that because it still idled and ran under low load perfectly fine.

Thanks for the help everyone! I'll get some pictures up on the Slixer's Gallery tonight :)
Author:  Greg Ondayko [ Thu Sep 10, 2020 2:45 pm ]
Post subject:  Re: Help... 72' 225 is kicking our butts
Yay.

You got it.

Enjoy the ride!
Author:  wjajr [ Mon Sep 14, 2020 9:22 am ]
Post subject:  Re: Help... 72' 225 is kicking our butts
I my world so often these problems are caused by the one item that you believe to be correct.
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