Does anyone know the difference between a 1968 400 vs 350 Distributor?

I have a 1968 Firebird with a 350 engine. My friend just rebuilt his 1968 firebird with a 400 engine and gave me his old distributor. Its a rebuilt one and in better condition than mine. Will it just drop in without any issues or do I need to swap the gear or anything else to make it work correctly?

I believe the differences would be in the advance curve each distributor is set up with. I'm sure both would physically interchange otherwise.

Yep, advance curve. Each app has different size weights and springs, but can be swapped around(mixed & matched) for custom set ups.

If yours is the OEM I would consider keeping it and rebuilding if You worry about numbers matching. The 400 uinits will work just fine. You can get a distributor advance kit and install new weights and springs the same time...something I would recommend regardless.

I put the 400 distributor in as it was and its still backfiring from the carburetor when I give it a lot of gas. I thought it was the timing chain as it was slacking so I replaced the timing chain and gears and same issues, backfiring out of carb and blowing smoke out exhaust. Do you think if I bought this fit for the 400 distributor it will fix my problems?
http://www.ebay.com/itm/Moroso-72310-Dis...039&vxp=mtr

Before you replace more parts I would recommend you do some more troubleshooting. Backfiring through the carb can be timing OR carb related. I'd put a vacuum gage on the intake manifold and adjust the carb to get the highest vacuum (15-20). It will also tell you if the ignition timing is off. Set your timing at 12 deg., dwell at 30. Pontiac engines seem to like 12 over the recommended 9. Once you know your carb is tuned, the timing is close, make sure your plugs, wires, ignition cab and rotor is good.

I'd put a vacuum gage on the intake manifold and adjust the carb to get the highest vacuum (15-20).
How do I adjust the carb to change the vacuum pressure? I have a 2 barrel carb..

It will also tell you if the ignition timing is off. Set your timing at 12 deg., dwell at 30.
12 degrees before 0(TDC) or after? Also I am new to these points distributors, how do I know set the dwell, I know its an Allen key screw inside behind the dwell cover but how do I know when its at 30

make sure your plugs, wires, ignition cab and rotor is good.
They are all brand new

I'd put a vacuum gage on the intake manifold and adjust the carb to get the highest vacuum (15-20).
How do I adjust the carb to change the vacuum pressure? I have a 2 barrel carb..
Plug the vacuum gage into the nipple thingy front of intake where your air cleaner vacuum hose plugs in. Run the car til warm and adjust mix screw/s in first until engine speed slows/vacuum on gage decreases, then back the screws out until vacuum is highest, just before reading drops again.

It will also tell you if the ignition timing is off. Set your timing at 12 deg., dwell at 30.
12 degrees before 0(TDC) or after? Also I am new to these points distributors, how do I know set the dwell, I know its an Allen key screw inside behind the dwell cover but how do I know when its at 30
Need a dwell meter, run engine, observe number, and use Allen wrench thru window on ignition cap to adjust. Google some of that stuff if you're unsure. Hope this helps.

Thank you. Ill try all your suggestions.

The reason I feel this is the timing and why I replaced the timing chain is My timing jumps a lot when I give her gas even when I take the advance module out of the equation by blocking off the hose.

I removed the stock fan and put an electric fan on the radiator. The fan has some weight to it. Do you think possibly I need to put the OEM fan back on? I wonder if its throwing off the balance.

The fan won't throw off your balance. Make sure your balancer isn't moving though, they do get loose. If it is loose, you'll have to recheck your timing marks to be sure you're TDC with #1 cyl. The timing on these engines is BTDC.

Still backfiring.......
Dwell is set at 25 it was at 35 and still backfiring.
Timing at 12 btdc
bought a vacuum gauge and connected it to the manifold and its jumping around a lot. It wont settle.
Should it be connected to a different port maybe the carb where the vacuum advance connects?
I drained the gas an put new gas in.

Can some give me the instructions to set the idle mixture? I have a 2 barrel carb with 2 screws in the front.
I think its carb related. When I sprayed carb cleaner in the carb while I revved it up it did not backfire....

You may have a lean condition causing backfiring through the carb. Hook up a tach and screw the idle screws in until the engine slows, then outward until you get a steady RPM reading and it won't go up any further. Then buy this: http://www.classicindustries.com/product/1968/firebird/parts/l582.html

The vacuum needle jumping tells me there's something wrong with your engine. Refer to this, it should help.
http://www.gregsengine.com/using-a-vacuum-gauge.html

I have a chilton manual it doesn't tell me how to adjust the idle mixture. Thank you for your help. I am going to set the idle mixture now and report back

I bought this an MSD Bushing & spring set but which bushings and springs do I use. Confusing....
http://www.pepboys.com/product/details/9954784/00348

Attached are the instructions.
How fast should I set the advance?
And the bushings Ill need to remove the distributor to install so Id like to get them right the first time if possible. It will be easy to change up the springs.

Appreciate all the help[ guys. I hope/pray I am getting close

I took the valve covers off and ran the car and notice the #8 rear push rod was not moving at all.

I took a video, see it here. http://youtu.be/gW2E8v1xV-8

The valve spring looks good and the push rod is good. I swapped the rocker arm, and push rod next to it and same thing. To take the spring off to see if its the problem will be a job as the AC is butting up against the head, had to the rear one....


So final thoughts before I tear the engine apart? Cam for sure?

Loosen the nut until the lifter clatters, tighten until clatter stops and go 1/4 turn more to see if it changes, if not, then you can assume your cam has a worn spot in it.

The push rod is not moving up and down. When I pushed the push rod down towards the lifter and it did moved up and down but only very slightly. Push rod is not worn at the bottom.

I did adjust the rocker with the car running. The looser I made the rocker the more it backfired out the carb. Is that a sign of something?

Ill check if oil is coming out of the top of the push rod.
If the cam is not pushing the pushrod up, the valve being stuck should not be suspect yet correct? Since is not engaging the valve.
I think my next logical step should be to remove the intake manifold and take a peak at the lift and cam. Correct?

Definitely the cam, it is completed rounded off. How does this happen?
I am considering putting a performance cam in and lifters.

You can see a couple pictures he I posted on my website
http://zetal.com/68firebird/

I'm considering just going stock to save any hassles. What do you think of this deal
http://www.ebay.com/itm/1968-1975-Pontia...c65&vxp=mtr

I believe someone replaced the cam in the past and did not break it in right. The #8 exhaust lobe is rounded and the lifter is mushroomed. It appears the rest of the lobes have excessive wear as well. I want to put an as close to stock cam with maybe a little more performance keeping the rest of the car stock and lifter kit in the car. I believe the previous owner may have installed a bigger cam and did not compensate for it and/or break it in properly and so this cause the rounding of the lobes and mushrooming of the lifters.

Anyone have any recommendations?
I may add headers later but for not I have stock exhaust

Getting the lifters out is going to be a PITA if they are mushroomed over, you may have to remove the cam then slid them down and out.

Thanks. I figured that after they did not come out easy from the top. Any advise on a cam?