back fire through the carbs - Team Camaro Tech
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post #1 of 5 (permalink) Old May 5th, 02, 08:12 PM Thread Starter
Join Date: May 2002
Location: Lehi Utah USA
Posts: 11
I keep having a problem with backfiring through the carbs on my 350. I am running dual EB carbs at about 13 degrees advanced on initial timing. I don't know if it is the carbs or the timing giving me fits! I just moved and droped 1500 feet in elevation. The thing ran great and has given me fits since I unloaded it. Fouling plugs, backfireing through the carbs. I have changed the jets and am getting a handle on on fouling of plugs but have not got the backfiring taken care of.

[This message has been edited by roangle (edited 05-07-2002).]

[This message has been edited by roangle (edited 05-09-2002).]
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post #2 of 5 (permalink) Old May 6th, 02, 10:47 AM
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Join Date: May 2001
Location: Austin TX USA
Posts: 501
1) Too much initial?

2) Mechanical/centrifugal advance is binding or the springs are too weak to return the weights to static position?

3) Sloppy timing chain?

4) Broken valve spring(s)?

5) Vacuum leak?

Back to the fouled plugs...are they carbon fouled or real oily? Might go a bit hotter on the heat range scale.

[This message has been edited by Sleepy-69 (edited 05-06-2002).]
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post #3 of 5 (permalink) Old May 6th, 02, 12:02 PM
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Join Date: Mar 2001
Location: Tucson, AZ, USA
Posts: 122
As for the initial bas timing beinf too advanced....this depends on whethere or not you are using vacuum advance...
With vacuum advance...usually set base timing to about 10-12 degrees...
With-out vacuum advance you typically set the base timing up to about 18-20 degrees...
Make sure overall timing in either case max's out about 32 to 36 3000 to 3200 RPM..or whatever is under the detonation point..

At what point in driving is this backfire occuring?????? What do you have to do set make the back-fire act-up???
Is the engine over-running after you shut-off the ignition???

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post #4 of 5 (permalink) Old May 8th, 02, 09:32 PM Thread Starter
Join Date: May 2002
Location: Lehi Utah USA
Posts: 11
The plugs have been fouled by gas, I went one range hotter and they have lasted a little longer.
I added a bit to my first posting, but it only backfires right off the line if I put it under a good load. If I put my brake on and give it a little gas it will backfire or if I just try to excellerate hard. It also will backfire sometimes when starting. I am going to try to adjust the timing some tomorrow and will report my results.
Thanks again for your suggestions.

[This message has been edited by roangle (edited 05-09-2002).]
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post #5 of 5 (permalink) Old May 9th, 02, 11:33 PM Thread Starter
Join Date: May 2002
Location: Lehi Utah USA
Posts: 11
Well the backfire seems to be gone. I ended up with the initial timing set at 14 deg and it runs much better, it was at about 8 deg before.
Now for the plug fouling! I have been careful going to hotter plugs because I have heard that is a good way to hurt things. Would the altitude change cause that much problem and require hotter plugs? ( recently moved and dropped 1500 feet)
Thanks agian for any response.
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