Went from poping from carb to backfiring out exhuast??? - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 6 (permalink) Old Jan 31st, 02, 01:34 AM Thread Starter
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I have posted two other topics in the troubleshooting section which had brought me to this problem last night. It used to not idle and pop out the carb, I opened the secondaries last night and now the car backfires out the exhuast and the plugs were pitch black and pretty wet. I am not a carb guy at all. I went to put the 650 back on and it was backfiring really bad. I assume I need new plugs. Somehow I fouled the plugs out with a rich condition right!! I went from lean and poping through the carb to rich and backfiring just by cracking the secondaries. I need help!!!!

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68 Camaro RS, Built 355, 274 Comp Cam, Sportsman II Heads 200 c.c. 2.02. Ported to Performer RPM Manifold and 1.75" Headers, 1.5 Roller Rockers, 650 Holley, Steel Crank, 4.11 Gears but no posi yet! TH350 tranny w/ shift kit.
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post #2 of 6 (permalink) Old Jan 31st, 02, 08:48 AM
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Try this,

Loosen your distributer, seat your mixture screws and open them 1 1/2 turns. Remove the number one plug and put a tissue in the hole crank the engine untill the tissue pops out. Your now at top dead center. turn your timing mark so it lines up and replace the spark plug. Start the car, plug vacume advance, and set the timing to 8 btc. This is a conservative starting point. Rev the engine and make sure your getting mechanical advance with the timing light. Now with a vacume gauge set your mixture screws to the highest vacume. If you have a low vacume check your carb to intake for leaks, this can be done by spraying carb cleaner around the base of the carb, if the rpms go up you have a leak, now tighten down your distributer just enough so you can still adjust it on a test drive. Drive it at full throttle, if no ping advance it an inch. do this untill you hear detonation and then back off the timing untill it's gone.
Now with the timing set, reset your carb mixture and your done!

hope this helps

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Stock 67 327 RS
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post #3 of 6 (permalink) Old Jan 31st, 02, 09:47 AM
 
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Eric,

You may have blown the diaphram on your power valve with the backfiring through the carb. If it is blown it will dump gas all the time and cause a severe rich condition.

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Kent
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post #4 of 6 (permalink) Old Jan 31st, 02, 10:06 AM Thread Starter
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My timing is set correct, it has been running awesome for a while now before I decided to try the 750. I really think it is a carb issue and not timing at all. With the size of the cam, I know we had to crack open the secondaries a fraction on the 650 and it ran great. I think I may have opened the secondaries to far or I know the back float was set to high and I wasn't able to adjust it before the plugs got fouled up. Somebody told me if the float was too high in the secondaries, and the secondaries were cracked open a bit then it could of been sucking fuel causing an extremely rich condition, which in turn fouled the plugs out. I should start with new plugs and a new powervalve for starters right. And lower the rear float, it was just at the top of the hole before I realized it. Thanks, Erik

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68 Camaro RS, Built 355, 274 Comp Cam, Sportsman II Heads 200 c.c. 2.02. Ported to Performer RPM Manifold and 1.75" Headers, 1.5 Roller Rockers, 650 Holley, Steel Crank, 4.11 Gears but no posi yet! TH350 tranny w/ shift kit.
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post #5 of 6 (permalink) Old Jan 31st, 02, 10:27 AM
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Erik,

The plugs are cheap but save some money and clean up the ones you have unless they are old to begin with. Replace the power valve and try to get the carb adjusted back to factory spec's when you do. Check out some of Holley's online info www.holley.com/HiOctn/TechServ/TechInfo/Trblsht.html

&
http://www.holley.com/HiOctn/TechSer.../TechInfo.html

By the way are these carbs vacuum or mechanical secondaries?

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...Dennis
"The '69, the '96 & the club"
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post #6 of 6 (permalink) Old Jan 31st, 02, 10:40 AM Thread Starter
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Tha carbs are mechanical secondaries. I know for a fact the factory specs won't work because we had to open the secondaries on the 650 to get it to idle right. The guy who built the engine and got it tuned correctly set up the 650, so I attempted to make the 750 setup just like the 650 setup. I think I was close except for the secondary float beinng to high and by the time I found out the plugs had pretty much took a dump. I will clean them up or buy a new set and try again. Thanks Erik

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68 Camaro RS, Built 355, 274 Comp Cam, Sportsman II Heads 200 c.c. 2.02. Ported to Performer RPM Manifold and 1.75" Headers, 1.5 Roller Rockers, 650 Holley, Steel Crank, 4.11 Gears but no posi yet! TH350 tranny w/ shift kit.
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