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7 replies to this topic

#1 NoahDL88


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Posted 16 March 2004 - 01:13 AM

Tonight at 6:57pm EST, on March 15 2004, i got the new engine running for the first time. its first 20 minutes went off without a hitch, now the bad part.

When i juice the throttle, i get a backfire out the top of the carb, a very loud pop, my friend thinks that its the carb gasket letting in air and creating a vacuume leak, my professor thinks that its the timing, are they both right or is one the more likely candidate?

#2 ShawnW


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Posted 16 March 2004 - 01:27 AM

I would bet you are off a tooth on the disty. Is it timed with a timing light? 8 degrees BTDC if memory serves.

Congrats!!! Im getting close to being caught up with you.

#3 Turbone


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Posted 16 March 2004 - 01:28 AM

Well, if you time it and it still does it, you can rule out the timing issue. You can use some starter fluid and spray it around the base of the carb to see if there are any leaks.

#4 NoahDL88


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Posted 16 March 2004 - 01:31 AM

the timing is 180 out, so i switched the 2,4 plugs, i'm gonna redo it so its on right, but the timing seems just fine, maybe a little advanced but nothing extreme

#5 Snowman


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Posted 16 March 2004 - 01:33 AM

I would put my money on timing. 8 degrees BTDC is the factory spec. However, I think you will find that an engine with the modifications that you speak of will want a bit more timing (Heck, I just bumped my Webered-and-Delta-cammed ea82 up to 22 degrees today without any hint of detonation. Much below that and it ran like absolute crap.)

Also, is there an easy way to verify the cam timing on the ea81? When I first fired up my engine one of the cams was off a tooth and it backfired like crazy.

#6 ShawnW


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Posted 16 March 2004 - 01:53 AM

Its not cam timing this time. (ea81)

Timing can seem just fine but be a long way off as demonstrated by the "im at 22 degrees and it runs good" post.

I haven't seen mention of a timing light. Its time to break one out since you have the cool new engine and need to really know where you are setting it. Sorry to be a stickler on this one.

Was the carb on another engine before? Like do you have a history with it or is this a new edition to the family too?

#7 CIS Subaru

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Posted 16 March 2004 - 06:13 AM

This sounds suspiciously similar to a problem I had with my CIS project.
I never totally diagnosed it, but advancing the timing seemed to get rid of it.

More specifically, when I first got my CIS injected EA82 running, it would pop just like you describe. It would do this mostly when starting to move from a stopped position (throttle open wide, low rpm). I found that if I set the timing around 15 BTDC, the popping happened less and I got more power. 20 degrees gave great low-end power and virtually eliminated the popping, but caused detonation at higher rpm.

I now have my timing set somewhere around 13 degrees, and the popping just gradually stopped after about 1000 miles. I'm guessing it could have been related to my hacked PCV system or the custom work I did on the heads. I'm pretty sure that if I put the timing back to 8 degrees it will lose power and start popping again.

#8 NoahDL88


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Posted 16 March 2004 - 11:21 AM

all good info, when i get the chance, which may not be until thursday, i'm gonna redo the timing, ie get it not 180 out and try to advance the timing, i think i have it at 12-14 now i didn't want to go too far. but i'll inch it up and see if that helps. My pcv is old, i may pick up a new one and see if that helps too.

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