Blame

(Sorry If this make no sense please pm or leave a question and ill do my best to answer it) I own a 81 corvette that has a gm crate motor 250hp that may have been put in around 1985-1995. The computer has no control over the motor other then to tell me the temp, psi, or gas lvl.

My troubles first started when the carb went out, I got it rebuilt and updated with better parts. Soon after I had it back on my fuel pump blew out and got replace. As I was setting the timing I notice my harmonic balancer was walking. So it too got replaced (the rubber broke which cause the outer part to spin freely.)

Seeing how I had the pulley system off I thought it be a good time to replace all the intake gasket seeing how it never leak in one spot which was where the carb went, it leak everywhere else. I end up breaking a bolt off in the intake and notice the bolt hole that hold the distributor went thru the intake I bought a new one. A Edelbrock rpm performance intake.

I also deleted the water pump fan and added a duel electric fan off a 94 camaro.

Ok flash forward to everything back on.
I pull spark plug 1 and put the motor to top dead center with the aid of a breaker bar. I adjusted the distributor to be set for first firing order. (18436572 ( please correct me if im wrong) I set the timing (after plugging the advance vac line.) To 4 degree above. I got the at idle 800-900 rpm. I turn the motor off unplugthe vac line and restarted the motor. She ran great better then before. (Please keep in mind the carb was set to bolt and play by the rebuilder). As the day went on it started to die when car was at a resting stop then gas was given to move but it cought itself and kept running everytime.

Now it regressed to back firing thru the carb. I pulled the plug 1 out and find top dead center. But it kept back firing thru the carb. So I 180 out to see if that fix it. It only served to make the motor back fire from both the carb and exhaust. So I 180 it back to get the back fire from the carb.

I live in jacksonville fl if anyone wish to see first hand. But can anyone offer any idea on what im doing wrong or what could of gone bad.

Blame

Forgot to add, every now and then the gauge that show oil psi with show no pressure but minutes later will show pressure after the car rested. Not sure if it the oil sending unit going bad or if the oil pump about to die.

Blame

Any tip will help, ran out of ideas and did not have many to start with.

billla

I suspect a lot of us are scratching our head a bit sorting through all the changes and potential issues.

I'm not sure how you're setting the timing - it sounds like you're just statically setting it to 4 degrees BTDC? Do you have a timing light?

SH-60B

Mine acted like that when a few lobes were rubbed off the cam..

73, Dark Blue 454

Some thoughts:

1) You sure your plug wires are indeed, routed to the correct plugs? (carefully double-check).

2) Also, forget the notion that the distributor is "180 degrees out". I've no idea how these garbage theories get legs.

3) Backfire through the carb is likely a timing issue. Also, 4 degree of lead at initial is pretty low. Bump her to 10 degrees as a baseline (though this won't help your problem)

4) No oil pressure for "minutes" after start up? Hopefully it's the gauge and not a problem with the distributor/oil pump shaft engagement.

5) Your new balancer,..you sure it has the correct timing mark? Gen-I SBC's used two different timing tabs clocked at two different locations which causes frustration.

6) Is your new fuel pump mechanical or electric? If electric, what pressure are you seeing at the carb? Too much pressure will overpower the needle & seat in the carb and cause all sorts of flooding problems (any fuel smell?)

7) What carb and distributor are you running?

8) Any reason the valve springs would be broken (recent over-rev, etc)?

Thinking out loud.

CaseyJones

First, make sure you have it on TDC. Remove the driver side valve cover. Rotate the engine until the #1 intake valve closes but before the #1 exhaust valve starts to open. There is TDC for sure. Check the timing mark and it should be coming up to the tab line. Go ahead and replace the cover. Now double-check the spark plug wires to be 100% sure the firing order is right for 18436572. If you put the distributor back in the same orientation as when you removed it, the timing should be close. Now it should be close to firing without backfiring from either end.

You mentioned weirdness with the oil pressure. I hope the distributor is seated completely in the intake and the oil pump is engaged correctly. I recently bought a good Corvette with a bad engine which had that very problem. The PO spun the bearings in it after messing with the distributor. So watch it carefully and notice any odd noises...

damoroso

A couple things come to mind. First, as was already suggested trace your wires and make sure you have them going from the cap to the correct spark plug in order. Then adjust the timing, and yes, 4 degrees is way low, bring 10-12 and start there. If you don’t have a timing light or a friend with one, this might be a good time to invest, they aren’t that expensive. Once your timing is set, make sure the distributor hold down is tight enough that the distributor doesn’t move. Sounds like it was set, then the timing changed, a loose distributor would easily do that! Finally, once the timing is addressed, then you can determine if the carb needs any adjustment. Once you verify timing, and that’s eliminated, you may be into valve train issues. I’m in Jax, if you can’t get it sorted, send me a PM and I may be able to look at it for you.

billla

There's quite a number of degrees where that's true.

The only way to verify TDC is to use a piston stop.

http://www.summitracing.com/parts/cca-4795/overview/

73, Dark Blue 454

First, a four stroke engine only fires every other crank rotation so there are two TDC's in the four strokes. He needs the TDC after compression stroke, so watch the intake valve. Once it closes, turn the crank by hand another half rotation (usually a bit less due to cam overlap) then watch the timing tab as you rotate for 0 degrees. Add another 10 degrees advanced and your initial timing is statically set. Then make sure the rotor on the distributor is pointing at the number one tower on the cap.

You may have to re-drop the distributor and you may have to align the oil pump shaft to the distributor with a long screwdriver.

After you've completed the above,..

One trick way to find exactly where the number one tower on the distributor is in relation to the rotor is,..

1) Pull the number one plug-wire from the plug.

2) Insert an old but working spark plug into the number one wire

3) Loosen the distributor's hold-down clamp

4) Get the rotor and cap aligned as best you can by sight

5) Turn the ignition key to the 'on' position

6) While grounding the old spark plug (away from the carb), turn the distributor cap back and forth and watch for a spark in the plug you're grounding.

7) Turn the key to 'off' then clamp the distributor where you obtained spark

Now you're set at 10 degrees initial timing.

(Again, all bets are off if you have a balancer and timing tab mismatch)

Good luck.

diehrd

He did say it idled ok and drove some before this happened , my bet is he hit operating temp and it started to fall on its face. From his own post he stated.


His timing was set with a vac advance plugged in ,, to 4 degrees or even 10 . So the instant he steps on the gas his vac drops off and his timing is falling off causing part if not all of his issue.

Pull and plug vac line to vac advance. Have someone sit in the car hold rpm at 2500 and set timing to 34 or 36 degrees and lock the dist down. Hook up vac advance and go drive it. If you still have issues post back

Blame

Everyone im sorry for this late reply work and lack of sleep put work on the vette on hold.


I grab a male end fitting for my air tools, a long rubber tube, a plastic bag , and a small zip tie. With this I removed plug 1 and place male fitting in then turn the motor by hand at balancer. When the bag inflated and I saw that the timing mark match I knew they were right. Which I was on the wrong strong stroke, but found out I had a vac leak plus bad tuning on crab.


The vac leak was on the tranny, I set the crab right set the distributor in the right place (was off by 3 teeth the whole time plus wrong stroke). It took a little bit of a try to get her to fire up but once on she ran. I adjusted the distributor to 8 degrees. After unplugging advance timing I started her up and had a tear fall.


My baby turn over with no trouble and sound really good. I like to thank all who posted I qrote most down for future use when the time comes. Thank you all again.

Haggisbash

You can find exact top dead centre this way as well but put some wash up liquid mixed with water on the end of the pipe to form a bubble, as the engine balances at TDC the bubble will be at its max inflation.

Blame

Plus I have pics of my some what finish for now motor bay if anyone like to pm me there email ill send you some pics.

maverickmk

Post the pictures here, I'm sure everyone would like to see them.

Blame

Might be best to just email them to someone and get them to post. Won't work with my tablet or laptop.

maverickmk

Sent you a PM.

maverickmk

Here ya' go Blame

Blame

Stage 2 of 5 and she look good. All the work im doing now will lead up to the new 383 lt1 carb motor swap.

7t9l82

wiring looks, interesting