Tunning / Timing - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 6 (permalink) Old Oct 25th, 01, 10:29 AM Thread Starter
 
Join Date: Apr 2001
Location: Clermont, FL USA!
Posts: 21
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hey guys, could use some help. 327, I beleive is mostly stock, Edelbrock 600 carb, dual exhaust, HEI distributor. My car was backfiring when I floored it from a dead stop, sometimes through the exhaust mostly through the carb. I went out and bought a vaccum gauge and used it to set idle mixture. The most I could get was 15.5 to 16 psi..(normal?) This helped, dosen't backfire now just kinda bogs out like its lean. I've played with the timing a few times. How do you know what initail timing should be?, now I think it's set 6 degrees advanced. I also just purchased the rod, jet and spring set, I was hoping to get advice before playing with that stuff. If anyone can help, thanks.
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post #2 of 6 (permalink) Old Oct 25th, 01, 12:18 PM
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Hey Newbie...sounds like you're having fun.

A few thoughts. W

hen she backfires thru the carb, you can bet your timing is probably whacked...usually too advanced. 6 degrees initial sounds ok, but try 2 and see if it helps.

If not, I'd take a look at the mechanical advance mechanism...take it apart, clean it up,...it could be that it's not retracting fully when rpms go back down to idle speeds. Perhaps your new weaker springs aren't allowing the mechanical advance to return to 'low rpm' mode. Does your idle speed fluctuate?...if so, try stiffer springs.

Does it start ok, or does it have crank a while before firing up?

Lastly...pull the vacuum advance tube from the carb...suck on the end of it...see if the vacuum advance is leaking...if so, replace...you'll need too take distributor out, but no big deal. I leaky vac advance can cause craziness with timing, not to mention the vacuum leak itself.

These are some ideas...otherwise, I'm thinking timing chain issues...hope not though. Perhaps others have some thoughts. Good luck...let us know what you find.
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post #3 of 6 (permalink) Old Oct 25th, 01, 01:33 PM Thread Starter
 
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Well, the distributor is new, the only thing I didn't replace was the coil.

I do have a timing light and it dosen't seem to wander, and it seems to advance fine, although I don't know at what RPM it tops out at. I will check for leaks.

Starting is a little difficult in that I have to do the pump twice and hold the accelorator trick. Then I have to keep giving it gas a few minutes till it warms up a little or it idles a little rough and rpms drop low.

What possible issues could be with the timing chain? Anything I can check?

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post #4 of 6 (permalink) Old Oct 26th, 01, 11:09 AM
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Sleepy has very good suggestions.

In addition to, I would check to see if choke plate is closiing when cold, this would set fast idle, about 1400-1600 rpm, adjustable on pass side of carb. Then, after start-up, a choke pull-off and linkage are there on pass side, linkage may need adjustment to help maintain fast idle. The diapharm pulls the choke plate open against the spring pressure of the choke. Too much opening or not enough, will make the engine die.

Use vacuum gauge and set idle mixture screws for highest reading, depending on age/condition of engine, vacuum should be 16-20 in./H2O with stock camshaft. Reset curb idle to about 750-850 rpm.

Unplug vacuum line to distributor and set initial timing to 8-10 deg BTDC.

All this should get you in the ball park, one more thing, does it bog when you do an instant WOT? If it does, adjust the secondary return spring alittle tighter, adjustment is pass side, loosen the set screw then turn screwdriver slot CW about 1/2 turn to delay the secondaries from opening too quickly.

Alot of info to soak up, but read well and it'll work well.


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post #5 of 6 (permalink) Old Oct 26th, 01, 03:08 PM Thread Starter
 
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Well, I changed the 2ndairy jets one stage richer from stock calibration, and also 2 stages richer on the primaries between the jets and rods. Seems alot better and dosen't seem too rich. Still seems to lack power, and yes thats WOT from a complete stop. I'll try the secondary adjustment you mentioned.

Ok, this is probably a stupid question, but BTDC would be retarded, right? I just don't get the whole timing thing.

Unrelated question, does anyone know how much my car might way? 69 camaro, no ac, no heater core, original intake, pretty much bare bones.

Thanks, Khris.
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post #6 of 6 (permalink) Old Oct 29th, 01, 03:44 AM
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The only dumb question is the one NOT asked.

BTDC = Before Top Dead Center. As your engine spins, CW direction, looking at the front of with the hood open, the mark on the harmonic balancer, aligns with the "0" on the tab. This is TDC, providing the correct balancer and tab are mounted on the engine.

When viewing marks with a timing light, the mark on the balancer should be before "0" on the tab.

One wants the spark to be at the cylinder to ignite the air/fuel charge before the the compression stroke gets to TDC. This purpose is to get the flame started before the power stroke comes into play, allowing the engine to use all of its intended combustion pressure to make power.

If the spark arrives late, then, most is lost. Power is down, acceleration sucks, vacuum is less, car is a slug and you get the picture.


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