I am both an idiot and a genius. 

"Bandit" (2bandit) 03/04/2018 at 19:55 • Filed to: None

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Recently I have been trouble shooing a weird thing where when there is no load on my engine (park/neutral) the revs climb to like 2500rpm but when the car is in gear it idles at a perfect 700rpm. I always assumed that this was the result of a vacuum leak, but could never figure out where the leak was coming from because I replaced all my hoses, gaskets, etc. One day I pulled all the hoses off the carb and tried to run the car with all ports open just for the heck of it, and against all typical tuning logic the car ran like normal. I am an idiot that I tuned my engine to run and drive sufficiently well on essentially zero vacuum pressure... but a genius because the car runs and drives on the worst tune ever. As for the source of the leak?

I’m almost positive there is a mismatch between the heads and the intake manifold that is causing a gap to be created that isn’t being sufficiently sealed with the standard gaskets, likely a result of the machining I had a shop do to these heads when I got them rebuilt. Not much I can do about this problem so I may as well just keep driving the car like normal.

Next steps for the car include finding a new front subframe that I can build up a new drivetrain on outside of the car to make a full engine swap really simple and to keep the car on the road while I buy and build everything. The goal is a modest LS with 350hp or so with hopefully a t56 6-speed, but I could settle for an automatic since it would swap right in with my current setup.

My bird IS the word > Bandit 03/04/2018 at 20:04

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That is really strange. You sure a thicker gasket couldn’t fix it?

MM54 > Bandit 03/04/2018 at 20:11

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How much did they shave the heads to end up with an intake that doesn’t mate? Could have the intake machined to fit if need be, though with an engine swap coming up it may not be worth it.

Bandit > My bird IS the word 03/04/2018 at 20:45

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Not positive, but truthfully I don’t want to start pulling the intake off the engine with my dreams of an engine swap coming up. This engine has just been a nightmare all around for me.

crowmolly > Bandit 03/04/2018 at 20:46

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Not trying to be a dick, but I kinda don’t buy that.

What are your timing specs? Initial, total, what the curve looks like.

Is the vacuum advance set up? You did disconnect and plug that when setting the timing, right? And which port is it plugged in to?

If you had a monster vacuum leak your power brakes would work like shit. Do they?

Demon-Xanth knows how to operate a street. > Bandit 03/04/2018 at 20:50

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Spray small amounts of carb cleaner at various places, have fire extinguisher type items at the ready, when the idle changes, that’s where your leak is.

TheHondaBro > Bandit 03/04/2018 at 20:51

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Ah, the classic “none-of-the-godawful-pictures-correlate-with-the-text-on-the-same-page” Haynes manual.

HFV has no HFV. But somehow has 2 motorcycles > Bandit 03/04/2018 at 21:22

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AN idius

My bird IS the word > Bandit 03/04/2018 at 21:24

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screw it then. These old blocks are not all they are cracked up to be anyway.

Bandit > crowmolly 03/04/2018 at 21:55

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Cant remember the timing but I did confirm it with a light and the typical suggested values for my camshaft. I have the vac advance set up in the correct way and have tested it with a vacuum tester (have used both ported and un-ported vacuum at different points in time). Brakes worked like ass, but I installed an electric vacuum pump to handle that because at the time I figured my cam was just too big to handle the brakes, but I was wrong. Hooking a vacuum gauge to the engine with everything buttoned up and “sealed” gave me a steady reading of 6 in.Hg and I should be seeing about 15-16 if I remember correctly.

Bandit > My bird IS the word 03/04/2018 at 21:57

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I’m absolutely sure a good portion of my problems can be blamed on my inexperience with old engines, my lack of money when I built the car, and my general stupidity back when I was younger and built the thing.

My bird IS the word > Bandit 03/04/2018 at 22:28

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You going to do something with the shaker? I am considering an LS but not for a long time.

LastFirstMI is my name > TheHondaBro 03/04/2018 at 23:34

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“Remove part x. Assembly is opposite of disassembly”. Very helpful, I hadn’t thought of that. Thanks Haynes.

Takuro Spirit > Bandit 03/05/2018 at 00:55

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When I wore a lobe off my camshaft due to lack of oil when I was young and dumb with my first Firebird, I had a shop replace it.

It ran like doodoo and idled high when I got it back and I had to get a Chilton manual from the library to find out why...

The shop has used the vacuum diagram on the radiator support to hook everything back up, but didn’t realize it had been replaced in a crash when my aunt had the car.

Replaced by one out of a 301 car. Mine was a 305. How. Did. They. Not. Notice??

I finally got it all hooked back up right, but I think it was at that point I swore I would never own a carbureted car ever again.

Bring on the LS swap, I say.

TheHondaBro > LastFirstMI is my name 03/05/2018 at 02:09

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Nah you gotta do the running man while you reassemble the part.

crowmolly > Bandit 03/05/2018 at 09:54

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Not sure if you want to get into this, so stop me if you want.

But what cam do you have? Still the stock converter?

This type of issue is not totally unheard of. Why I’m not sold about a manifold seal leak is because you mentioned it runs fine with no hoses attached. That makes me think something is wonky.

Bandit > crowmolly 03/05/2018 at 11:52

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Trans is a 700r4 with the stock converter out of a 91 caprice wagon. Camshaft is a comp cams XE268 http://www.compcams.com/v002/Pages/388/XE268H-10.aspx . Engine incase I didn’t specify it is a Pontiac 400, and I had the 6x heads rebuilt with new springs, deeper spring pockets, screw in rocker studs, and new lifters to accommodate the larger cam (engine was originally a very modest block out of a 74 catalina)

Bandit > Takuro Spirit 03/05/2018 at 11:57

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I’m just tired of dealing with carbs, priming the pumps, dealing with electric chokes, cold starts, you know the crap. I am just too impatient to not have fuel injection and a semi-functioning OBD system.

crowmolly > Bandit 03/05/2018 at 12:20

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Unless there’s some special Pontiac thing, you should be fine with that cam and power brakes. 6in Hg at idle with it is too low. IMO you should have twice that at least.

Do you remember where you got the timing numbers from? What dizzy are you running? HEI?

Bandit > crowmolly 03/05/2018 at 12:39

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Yeah, running a newer HEI distributor which luckily the factory had the wiring for since I have an ‘81 so it was plug and play. I don’t remember where I got my numbers from, probably my manual or a forum? But there is also a good chance I just tuned it to where it was happiest sounding. It’s been a long time since I’ve had a gun on it.

crowmolly > Bandit 03/05/2018 at 16:21

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Might want to get a light on it and see how much timing is in it. I think you may need more initial.