Help! My 62 corvette missing and back firing at speed

[Scotty]

Hi guys,
I am after some assistancead
My 62 Corvette with its 327 250 HP is having some major issues with surging at different speeds etc.
Whilst driving it a few weeks back at approx 60 mph the old girl just felt like the power died the only way to keep her running was by tickling the accelerator it was then surging and back firing, the engine would virtually stop. It would restart but at times on the side of the road would not even idle.
I have just had the carter carby rebuilt, I have replaced the coil and plugs. The car now starts and idles however when given some gas it boggs down again lacking power and wanting to stall, I haven't even had the old girl on the road as I know it wont go.
I note some play in the dizzy shaft? Should I continue and change all the spark plug leads? Has the harmonic balancer spun? Is the resistor no good? There as no noises from the engine it does not sound like its missing......
Help where do I start??
Cheers
Scotty

 

[Vettehead Mikey]

Have you checked points gap and condenser? Timing?

 

[Scotty]

Ok guys,
I have changed leads plugs rotor cap condenser checked timing however not sure what it should be as the motor has been rebuilt at some stage with 462 feullies on it.
Points are a struggle to get here in Australia the points that were in the dizzy look like they have a condenser on them and are bloody hard to get feeler gauges in there to regap??? Any help would be appreciated??
So little or no change still flat spotting when the car is given some gas however at idle runs like a dream.
Next I changed the resistor and gapped the points to what visually looks like 14thou. The car starts runs not more backfiring however now I have a little bog down under load I think a little more tweeking and im there......
Anyone know what I set the timing at??
Cheers
Scotty

 

[Vettehead Mikey]

Set the dwell to 30* +/- 2*. Gapping the points is a decent initial measurement, but dwell is far more important.

Don't know what the initial timing should be for your car but it's also possible that someone has reworked the advance curve making that irrelevant. Try advancing it 2* at a time until you hear detonation under acelleration, then back off 2*.

 

[vigman]

How old is the engine?

Specifically how old is the timing chain? But before going off the deep end…
Simple checks..
1) Pull the #1 plug, take a breaker bar ( ratchet ) and with the car in NEUTRAL crank till your timing mark is at TDC.
Take a LONG wood dowel and poke it down the #1 hole ( DO NOT USE METAL) If the piston is not UP go around 180 degrees.
See if the piston is in fact at TDC move the crank a few degrees ( 10 -15 ) and VERIFY you are at TDC. THEN verify if your harmonic pointer lines up. If not well your harmonic has spun.

2) Couldn't agree more with a METER measurement on dwell…. but I would ditch the points for a pertronix system.

3) If the car will not hold an idle, maybe you have a BIG vac leak somewhere…. crank the idle screw up so it will hold an idle.. hook up a external vac gauge and tell us the reading
18-20" good, below that… MEH.. so then one by one you have to cap off potential van leaks and see if that will come up. get a mighty van hand pump and check the distributor vac
advance.

4) Set timing (Note going back to step 1) When you have the engine @ TDC is the rotor point in gat the #1 cylinder?? If not there better be a damn good reason why… ALSO to check your timing chain…
As you turn the crank the distributor's ( cap off looking at the rotor ) movement SHOUD BE tight… If you can turn the crank for say 10 degrees and THEN the disturb moves…. go backwards and see if it's 10 ( or more ) and that tells you how sloppy your timing gear / chain is.

5) FIRST make sure you cannot twist the disturb by hand… some of these " gremlins " are due to the disturb not being locked down and the timing drifting. Next use a GOOD TIMING LIGHT~ Set timing 1st PLUG the line going to the vac advance and set for 10~12 degrees BTDC at a LOW idle…. Blip the engine a few times and watch the mechanical advance with might be an additional 20 degrees for a TOTAL ( when driving ) of 30-32 .. THEN plug the vac advance and that should give you a few more degrees @ idle


Play in the dizzy shaft… not a good thing at all...

 

[David Sr]

Basics..

Hi guys,
I am after some assistancead
My 62 Corvette with its 327 250 HP is having some major issues with surging at different speeds etc.
Whilst driving it a few weeks back at approx 60 mph the old girl just felt like the power died the only way to keep her running was by tickling the accelerator it was then surging and back firing, the engine would virtually stop. It would restart but at times on the side of the road would not even idle.
I have just had the carter carby rebuilt, I have replaced the coil and plugs. The car now starts and idles however when given some gas it boggs down again lacking power and wanting to stall, I haven't even had the old girl on the road as I know it wont go.
I note some play in the dizzy shaft? Should I continue and change all the spark plug leads? Has the harmonic balancer spun? Is the resistor no good? There as no noises from the engine it does not sound like its missing......
Help where do I start??
Cheers
Scotty

. Try to locate another carberator and swap out from a running car.this will probably fix the problem. Wrong gasket was probably use for rebuild. David Sr

 

[Scotty]

Still no good

Thanks for the assistance guys!
Ok I went to set the dwell after replacing the leads, plugs coil, dizzy cap, even the resistor, however setting the dwell at 30 the car ran like a pig it would not idle.
I cranked back the dwell to 16 and it ran smooth set the timing to about 2 degrees advanced took the car for a run but it was lacking power still.
I then placed another set of points in and I was able to set the dwell to 30 degrees I then adjusted the timing to approx 4 degrees advanced again took the car for a test run and ran sweet however a small amount of lag in the carby which was fine. stopped the car for approx 20 mins then started it again drove it down the road and yet again it is running like a pig on 3 cylinder's, no power what so ever and limped it home madmadmadmad I have just been an the garage again dwell at 29.8 timing at 4 degrees advanced at 600 to 650 rpm however upon giving it some gas it lets out a huge back fire boom enough to scare the people next door and just wont run at higher rpm. At idle it sounds sweet give it some gas and it all turns to shit!

Nearly time to give up :bash
I think its time I pull the dizzy out and have it rebuilt here in Australia.....

 

[vigman]

WOAH wait a sec….

OLD points ( bad ) new points good ( for a while ) … Hmmm seems THERMAL to me.
Things to check..
1) The dizzy timing adv plate moves smoothly ( might need a bit O cleaning & lube ).
2) The wire coming from the points down the Dizzy base to the coil… is it ORIGINAL? The ends MIGHT be coming apart ??
3) If memory serves there is also a ground braid from the dizzy advance plate to the dizzy can to keep that plate ( and the other side of the points grounded ).
4) Is the ballast resistor NEWER or original OE? MIght want to sub that out for test.

5) The KILLER…( on my 64 but I would guess yours is similar ) Under your brake master… down on the firewall are 2 connectors that go from the fuse panel thru the bulkhead of the firewall..
1 of these connectors ( over the years ) gets corroded, makes POOR contact , heats up and gets all melty.. and you loose connectivity ( read voltage drop, inability to deliver current ).

Do a search here for that topic… there have been some pictures posted as well… but if nothing else, worth popping the 2 ( 8 and 10 pin ?? ) connectors apart. inspect & clean.
USUALLY it gets so bad, that a no crank condition happens but mine was doing a similar random backfire complete loss of power on a HARD TURN.

When I replaced my engine side harness no more issues.. and I had slightly melty main power lines.
http://www.corvetteactioncenter.com/forums/c1-c2-general-technical-discussion/126676-help.html post #3

Worth a look!

Mike

 

[Vettehead Mikey]

I'd swap out the coil.

 

[Scotty]

Guys,
I ran the car again which was running sweet 30 on the dwell meter 4 degrees advanced at 650RPM 1 and 1/2 turns on the fuel idle mixture screws on the carby.
However it ran perfectly for approx. 20klms then came home assuming all is fix yeah!
Yeah until I took it out the following day, yes it ran sweet to its destination then when I stopped it went inside the store for 20 mins to by some goods came out and its running like a pig again....... Idles ok so I check the dwell at 30 check the timing at 4 degrees advanced and I haven't touched the carby all good so WTF. madad Anyway the only way I could get the car home was to change the point settings down to 14 which then advanced the timing to about 30 degrees, I did note that the carby was delivering a lot of fuel through the centre venturis primary side rather than through the jets, I assume that I have had a dicky carby rebuild or stuck float flooding the carby as during periods of giving the engine gas when its playing up it just breaks down has no power and backfires with excessive unburnt fuel. This does not occur when I changed the dwell setting to get me home however the idle rpm hits around 1100rpm.
Any suggestions?
Scotty

 

[Vettehead Mikey]

Fix the carb and stop playing with the dwell.

 

[Hib Halverson]

Set and leave the dwell at 28-32°.

Verify the timing mark by turning the engine over by hand to top dead center #1 then look to see the mark on the damper lines up with the index on the timing cover. If it doesn't, repair the engine such that it does.

Disconnect and plug the vacuum advance. Start the engine at set the timing at 8° BTDC. Reconnect the vac. advance.

Road test.

Other stuff to check:
fuel system and carburetor
primary ign. sys. voltage.
Plug wire resistance

P.S.: Stay away from "dicky carby rebuilds".