63 bird running rough. Pls help

[6t3bird]

Hello all, my bird has been sitting to long (10 years) and I'm ready to determined to get her back on the road. I changed the plugs and timed it today but something isn't right and I just don't know what it is. She starts right up but timing or something feels off, it hesitates a little but when I hit the throttle and gas fumes burn my eyes a bit (in garage). Plugs are getting a little black so I leaned it out a little bit but not much better. I drained gas tank last year Maybe longer and filled with new gas, changed the fuel pump and filter.

Background info. Engine was rebuilt about 18ish years ago, tri power carbs just rebuilt, running a msd dist and spark box. I did the msd switch prob almost 10 years ago when car was running rough already and was chasing the problem. I gave up and left her in garage for past ten years occasionally starting once in a long while.

I'm 35 and restored car with my dad when I was 16 but he was the mechanic. Hes getting older and I'd love so fix this problem and take him for a ride and watch him light up. I know a bit but I'm stumped on this, any advice on what to look for but be appreciated. Thank you

[Rusty57]

I expect that all of your issues are related to deteriorated gasoline. Unless you put some type of preservative in the gas a year ago (my guess is that it was actually longer) most of the volatiles and aromatics have evaporated. I am actually surprised that it will run at all. If it was a fuel injected car I doubt if it would even start.

The reality is that even new gas will probably not solve the problems completely. I expect that the carburetor needs cleaned and rebuilt again.

[6t3bird]

Thanks for the response. I just put the rebuilt carbs on this morning so it's prob only ran 20 minutes or so. I can bypass the fuel tank easy enough and see if fresh gas makes a difference. I'll keep my fingers crossed and try tomorrow morning but I believe I'm chasing the same problem I had before I parked it. Thanks for info.

[ICON 1956]

You would need to remove the gas tank clean out entirely blow out the gas lines and you will need to go through the tri carbs. That is not an easy task to do. You have created a problem by leaving old gas which could have turned to varnish.. With the 10 % ethanol in your part of the US has made things worse. Do you have the shop manual ? read all you can to help understand how to work on the tri carbs. Leaving the car for such a long period of time will produce problems.
I would make a checklist and go through every step to resolve the issue in getting the car running properly. A quick tip: check the spark plug wires make sure they are not cracked and the boot make sure the contact is good.

[6t3bird]

[Rusty57]

Have you done a compression test? What vacuum reading do you get at idle and how steady is the needle?

I wonder if an intake valve is sticking. That problem could have existed 10 ears ago. This can happen due to the varnish from old gasoline. It could also be that whoever rebuilt the heads did not put enough clearance into the valve guides.

[6t3bird]

...well that was awful. Did a compression check, 3-4-8 were around 165 and the rest were only 65-75.

[jcbird63tb@gmail.com]

put a teaspoon of oil down the low cylinders and see if compression improves. At least you'll know if it is valves or rings

[Cliff Rankin]

Ok it looks Grim. Here’s my thoughts , the 390 is a tough old gal. Been sitting 10 years? Before you condemn it
Get out there and run it some. See what frees up. Throw a little atf or slick 50 or ? Run it ! Get it out , blow it out.
Up to temperature, not just once. I don’t think you will hurt her , with in reason. Let her warm up , lubercate
Expand and contract. You might be surprised.
Cliff

[Rusty57]

I vote for sticking valves.

Pull the valve covers and rocker arms. Squirt Marvel Mystery oil on each valve stem. Try to get some underneath the seal.

Let things soak overnight. Then hit the top of each valve stem with a hammer to determine if the valve moves down and then seats correctly.

Second choice as others noted is sticking rings. Pull the spark plugs and library soak each piston with Marvel Mystery oil. Let it soak for a couple of days. Each day turn the engine over by hand and re-soak the cylinders. Hopefully this will loosen any sticking rings.

It will smoke quite a bit when you start it up.