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Old August 18th, 2008, 04:58 PM   #1
Sandals
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backfire off load, timing?

OK all seems to be happy, but i dont think the timing is correct.

AMC 360, HEI dist, 4bbl carb

Where i have the motor timed right now it seems to be happy, starts easily, accelerates etc. with a vacuum gauge attached it seems to be reading a little low indicating bad timing.
When coming off the throttle from like 3K rpm's i'll get a nice backfire and pop, making me think it's too far retarded.

If i advance with the dist any at idle it starts to run really rough.

any ideas, i still suck at tuning motors
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Old August 18th, 2008, 05:41 PM   #2
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carb running too rich and fuel building up in the exhaust?
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Old August 18th, 2008, 05:47 PM   #3
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Pinhole leak in exhaust allowing unburned fuel to ignite while decelerating.
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Old August 18th, 2008, 06:04 PM   #4
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so i should actually get a decent exhaust before i worry about this then huh?

right now i have more than pinhole leaks
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Old August 18th, 2008, 07:53 PM   #5
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Have you run it on the road?
Mine runs rough when I'm cruising at 3k with very little load on the engine. Mine is a result of the vacuum advance pulling the timing ahead just a little too far when there is no load on the engine. The timing when it's loaded is great. Plug your vacuum advance and start there. It'll make tuning easier anyway. After you get that all sorted out, then re-attach your vacuum advance and see what the thing runs like. Vacuum advance is only supposed to work when the engine is at part throttle and slightly loaded. It pulls the timing ahead for better economy, etc. when at part throttle.
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Old August 18th, 2008, 07:56 PM   #6
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i've been timing it with the advance unplugged/plugged.

this was with it plugged in though after i think its timed

although it may all be for naught as i need to replace the accelerator pump so i can get gas in it to start it, as spraying starting fluid in it when it's a cold motor will get old really fast lol
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Old August 18th, 2008, 09:05 PM   #7
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fix your exhaust leaks then worry about tuning. my dodge does the same thing because of exhaust leaks. a bad exhaust leak lets the fuel ignite in the exhaust once you let off.
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Old August 18th, 2008, 09:11 PM   #8
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put 36 deg. mark on the balancer, and time at 2500 rpms.
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Old August 18th, 2008, 09:36 PM   #9
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if there's enough fuel in the air to ignite, you're running way too rich in my opinion.
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Old August 18th, 2008, 09:48 PM   #10
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if there's enough fuel in the air to ignite, you're running way too rich in my opinion.



Come tell that to my carb

it doesnt listen to me anymore :)
i'm rebuilding the bastard tomorrow anyway
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Old August 18th, 2008, 09:51 PM   #11
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vacuum line maybe
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Old August 18th, 2008, 10:56 PM   #12
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vacuum line maybe


I wish, all lines solid, all plugs good, everything passes brake clean spray test
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Old August 18th, 2008, 10:59 PM   #13
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Fix your exhaust, you'll be happy.
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Old August 19th, 2008, 07:28 AM   #14
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Fix your exhaust, you'll be happy.

easier said then done. 3 places so far wont touch it.
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Old August 19th, 2008, 08:01 PM   #15
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So, you need that y-pipe, then?
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Old August 19th, 2008, 08:08 PM   #16
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So, you need that y-pipe, then?


it would be a novel tool to fight the battle with
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Old August 19th, 2008, 08:12 PM   #17
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it would be a novel tool to fight the battle with
Okay, I'll find a big box and get it on the way this week.
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Old August 19th, 2008, 09:02 PM   #18
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Okay, I'll find a big box and get it on the way this week.

you can see if someones going to kzoo too.
If i dont end up spending a few days with queensryche i'm going to the westside to play
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Old August 20th, 2008, 12:40 AM   #19
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you can see if someones going to kzoo too.
If i dont end up spending a few days with queensryche i'm going to the westside to play
Well let me know what you figure out. If I send it there and then you don't make the trip, that's your problem.
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Old August 20th, 2008, 08:45 AM   #20
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If your taking it to Kzoo, somebody there should be able to put an exhaust on that thing in a couple hours.
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