88 monte carlo runny odd. Has been HEI converted and has demon carb, with throttle body spacer and edlebrock intake. The car for some reason backfires and the spits gas out of the carb. When idling and then accelerating, it backfires and spits. When going into second and accelerating hard it also does this. Not sure why? It's off its timing if that could be the problem. And another thing it does is shift about 10 to 20 seconds late going into second. Not sure why. If anyone could give me answers to how to fix this, I would greatly appreciate it. I'd hate to have to get rid of a classic.

Thanks.

 

First things first...

What Motor is in it?
What heads and valve train?...
Throttle plate spacer may have a vac leak and doesn't fit the intake correctly...
It sounds like a possible blown power valve in the carb....
2nd it could also be a bad intake valve..../to much backlash...
Is it hydraulic or solid lifters? could be a broken valve spring and or a bent pushrod or even a collapsed lifter....
Could also be the timing is to far advanced....
Could be a bad firing order.. (1 plug off)
It could also be a sign of a worn/bad timing chain....

I would start with rechecking the firing order....
18436572
also dbl check to see which way the rotor turns when you setup the firing order..

Maybe...when you re placed the distributor with the HEI...
You maybe 1 or 2 teeth off from TDC....
Did you bring #1 cylinder to TDC?

The late shifting is also possibly caused by an ill trans kick down setting and combined engine RPM


Hope this helps....
I'm sure others will chime in with more Ideas/Help...

 

From what I know about the car, it's the original 305, with no aftermarket parts, except the carb, throttle spacer, intake and it was fitted with a/c. I was told the car would be fine after running the gas through the motor. I'm now about two full tanks through and still nothing. I didn't do the HEI, but I know the timing is off. The backfires and spitting had stopped for a week but came back three days ago.

 

what cfm is the carb?

its probably to big for a stock 305...

im guessing it was more than likely a 2bbl carb originally...

if its a non SS monte.... It wasn't designed for a 4bbl carb....

How many miles on it?

You said the timing off?
That's the majority of the problem in my opinion...
Without actually seeing it in person...

 

Its a 4 barrel 550 cfm carb and is the base Monte Carlo. About 139000 miles. The timing is off. Could be fluids and spark plugs have any impact on it also?

 

Have you double checked the plug wires?

Firing Order: 1 8 4 3 6 5 7 2
Distributor Rotation: Clockwise
Cylinder Banks:
Right (Pass) 2 4 6 8
Left (Driver) 1 3 5 7

If that isn't it...

With the distributor swap chances are (like you said) the timing is off. Pull the coil + wire and remove cylinder #1 spark plug. Place your thumb over the spark plug hole and have someone 'tap' the starter a few times until you feel compression building in the cylinder. At that point rotate the engine by hand until you have the timing marks on the harmonic balancer line up with the timing tab. All engines are different (so timing will need to be dialed in after engine starts) but set the timing for about 6° BTDC. Pull the distributor cap and observe where the rotor is pointing. it should be pointing at the front right tower on the cap. If it isn't you need to pull and reinsert the distributor. A help is to use a long screwdriver and rotate the oil pump shaft so the openings are approx. at the 1:00 and 7:00 position. As you drop the distributor in rotate it about 2 teeth counterclockwise (before contacting teeth on cam) and the gears will 'walk' the distributor down into place. Rotate the base of the distributor as needed (shouldn't be much) to align the rotor with #1 tower on the cap. Snug the distributor down but leave loose enough to rotate with some resistance. Hook up your distributor wire, put #1 plug back in, hook up a timing light and torch it off. You may need to advance the initial timing to get a smooth idle, Those 305s can take up to about 10° advance but keep an ear out for pinging.

 

Great Info Mike!
Thanks!!!
I don't believe fluid and plugs will cause the misfire thru the carb... as Mike (03SSLE) explained its a definite timing issue... It may also be combined distributor offset and A stretched out worn timing chain... But you wont know that til your reset the distributor to the correct position. If the timing chain is also an issue.

 

I sure hope it isn't the timing chain. But I have a good feeling it is a great part with the fluids like you guys agreed with. The car sat for a year, so the timing is likely to be off. The previous owner didn't dial it in fully.

 

Oh, oops. I misread the last reply. So I just need to focus mainly on getting the timing fixed. But I was also told that setting the timing is hard when bad gas is present, which my car came with a half tank of bad gas.

 

If it's been sitting for any amount of time you'll definitely want to drain the tank and clean it. Fuel lines can be blown out with a little aerosol brake cleaner and a compressor. Check all rubber hoses if you haven't yet. It would be a good idea to rebuild the carb, but you might get away with popping the top of the carb to clean out the float bowls, air bleeds, needle seat assemblies (may just want to replace) and all the grunge in the bowl itself. You may also want to replace the accelerator pump, or at least trickle a couple drops of oil down between the shaft and carb body to help soften the diaphragm.

A once over on the wiring might uncover a few other tasks if any varmints made a home underhood while it was sitting.