Float Adjustment Backfire
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New User
Joined: Feb 2010
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Float Adjustment Backfire
I was tuning my truck today (73 F100 360 FE Holley 600cfm Vac Sec) adjusting the timing and idle mixtures and got it running better.
I decided to check and adjust the float bowls. I only started on the front one and now cant get it to run without constant backfiring
Help!
I decided to check and adjust the float bowls. I only started on the front one and now cant get it to run without constant backfiring
Help!
Thread Starter
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New User
Joined: Feb 2010
Posts: 9
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Disregard...
I found two vacuum ports at the back of the manifold not capped. They must of blown off when it backfired because they were there when I started, thats where I put my Vacuum Gauge.
You live and you learn
I found two vacuum ports at the back of the manifold not capped. They must of blown off when it backfired because they were there when I started, thats where I put my Vacuum Gauge.
You live and you learn
Post Fiend
Joined: Mar 2004
Posts: 6,056
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From: Union, Washington
Is this a newer Holley with the backfire protector or an older model? If an older model you could now have a blown power valve.
I don't think I ever had a backfire from adjusting the float levels or any other carb adjustment got that matter. For that matter I don't think I ever had one while adjusting the timing either.
I don't think I ever had a backfire from adjusting the float levels or any other carb adjustment got that matter. For that matter I don't think I ever had one while adjusting the timing either.
Laughing Gas
Joined: Aug 2008
Posts: 840
Likes: 8
The term "backfire" always confuses me. I think it's supposed to mean firing back up through the carb, but it appears to also be used to mean an explosion out the exhaust.
I take it the OPs backfire was out the carb as he found vacuum lines blown off.
This type of backfiring occurs when the flame from cylinder igntion gets back past the intake valve and into the intake manifold. As valve timing doesn't change by itself, I'd say the most likely cause is the offending cylinder fired at the wrong time.
This could be from extremely mis-adjusted timing, or from crossfire. Bad plugwires or a distributor cap arcing (and maybe carbon tracking) might be the problem.
Or getting back to valves, it could be from a damaged intake valve.
I take it the OPs backfire was out the carb as he found vacuum lines blown off.
This type of backfiring occurs when the flame from cylinder igntion gets back past the intake valve and into the intake manifold. As valve timing doesn't change by itself, I'd say the most likely cause is the offending cylinder fired at the wrong time.
This could be from extremely mis-adjusted timing, or from crossfire. Bad plugwires or a distributor cap arcing (and maybe carbon tracking) might be the problem.
Or getting back to valves, it could be from a damaged intake valve.
