 Mild initial backfire, Question for the braintrust here... |
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| oakdalecurtis |
 Sep 9 2020, 05:54 PM
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#1
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Oakdalecurtis  Group: Members Posts: 1,325 Joined: 5-June 15 From: Oakdale, Ca Member No.: 18,802 Region Association: Central California 
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I have a stock, other than Fireball ignition, 76 2.0 for 20 years. Runs flawlessly. Recently when first started, as I back out of the garage, I get a few random mild backfire-like pops from the engine. As soon as I put the car in 1st and drive away, it never does it again. I have not had the valves adjusted for the last 10,000 miles and they make no noise, so I haven’t bothered. Could this initial backfiring be a sign that the valves finally need adjusting?
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| thelogo |
Sep 9 2020, 06:13 PM
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Senior Member Group: Retired Members Posts: 1,510 Joined: 6-April 10 Member No.: 11,572 Region Association: None |
Djet ..... Gremlins. But it still runs 50 years later
So dont mess with it. But they dont make noise so haven't bothered? Thats asking for it ! |
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| rjames |
Sep 9 2020, 07:29 PM
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#3
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I'm made of metal Group: Members Posts: 3,923 Joined: 24-July 05 From: Shoreline, WA Member No.: 4,467 Region Association: Pacific Northwest
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Go adjust your valves then if it still backfires it's likely too rich or too lean.
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| oakdalecurtis |
Sep 9 2020, 08:34 PM
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#4
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Oakdalecurtis Group: Members Posts: 1,325 Joined: 5-June 15 From: Oakdale, Ca Member No.: 18,802 Region Association: Central California
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QUOTE(thelogo @ Sep 9 2020, 05:13 PM)  Djet ..... Gremlins. But it still runs 50 years later So dont mess with it. But they dont make noise so haven't bothered? Thats asking for it ! Hey logo, you sound like my wife! She says that I’m always asking for it! |
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| porschetub |
Sep 9 2020, 10:15 PM
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#5
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Advanced Member Group: Members Posts: 4,697 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
QUOTE(rjames @ Sep 10 2020, 01:29 PM) Go adjust your valves then if it still backfires it's likely too rich or too lean. (IMG:style_emoticons/default/agree.gif) 10k is too long besides. |
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| oakdalecurtis |
Sep 10 2020, 01:18 AM
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#6
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Oakdalecurtis Group: Members Posts: 1,325 Joined: 5-June 15 From: Oakdale, Ca Member No.: 18,802 Region Association: Central California
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Go adjust your valves then if it still backfires it's likely too rich or too lean. [/quote] How can you tell if the mixture is too rich or too lean? |
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| mlindner |
Sep 10 2020, 04:21 AM
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#7
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Senior Member Group: Members Posts: 1,517 Joined: 11-November 11 From: Merrimac, WI Member No.: 13,770 Region Association: Upper MidWest
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I was told, rich backfires from exhaust, lean up through the intake.
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| rjames |
Sep 10 2020, 10:33 AM
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#8
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I'm made of metal Group: Members Posts: 3,923 Joined: 24-July 05 From: Shoreline, WA Member No.: 4,467 Region Association: Pacific Northwest
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[quote name='oakdalecurtis' date='Sep 10 2020, 12:18 AM' post='2849916']
Go adjust your valves then if it still backfires it's likely too rich or too lean. [/quote] How can you tell if the mixture is too rich or too lean? [/quote] To get it exactly right, you need a wideband O2 sensor to read what your AFR is at part load and WOT. Lots of options out there, but this is what I used PLX AFR |
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| Root_Werks |
Sep 10 2020, 11:11 AM
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#9
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Village Idiot Group: Members Posts: 8,315 Joined: 25-May 04 From: About 5NM from Canada Member No.: 2,105 Region Association: Pacific Northwest
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QUOTE(mlindner @ Sep 10 2020, 03:21 AM) I was told, rich backfires from exhaust, lean up through the intake. That sounds correct to me as well. Others have said, adjust your valve lash, it's past due. Probably something like a CHT or MPS that is finally starting to fail. |
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| 914_teener |
Sep 10 2020, 01:37 PM
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#10
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914 Guru Group: Members Posts: 5,197 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
QUOTE(oakdalecurtis @ Sep 9 2020, 04:54 PM) I have a stock, other than Fireball ignition, 76 2.0 for 20 years. Runs flawlessly. Recently when first started, as I back out of the garage, I get a few random mild backfire-like pops from the engine. As soon as I put the car in 1st and drive away, it never does it again. I have not had the valves adjusted for the last 10,000 miles and they make no noise, so I haven’t bothered. Could this initial backfiring be a sign that the valves finally need adjusting? Good for you for keeping a 76 stock. Don't know if some of the other posts are "braintrust worthy" As you probably already know the 76 is a little bit different animal than the others. A good 76 completely stock is worth more than most other 914-4's due to the low production numbers if that is your thing. Like a couple of others have posted,check you valve lash first....10k is a bit over time for not adjusting and is probably the likely cause. The next thing I'd check is a vaccum or slight exhaust leak. Don't know what distributor you are running but if a dual diaphram stock type on the dizzy I'd check those for leaks first. Post some pics if you can....very rarely do I see a good running stock 76, |
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| mrholland2 |
Sep 10 2020, 01:59 PM
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#11
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Senior Member Group: Members Posts: 750 Joined: 7-September 11 From: Santa Maria,CA Member No.: 13,531 Region Association: Central California |
QUOTE(oakdalecurtis @ Sep 9 2020, 04:54 PM) I have a stock, other than Fireball ignition, 76 2.0 for 20 years. Runs flawlessly. Recently when first started, as I back out of the garage, I get a few random mild backfire-like pops from the engine. As soon as I put the car in 1st and drive away, it never does it again. I have not had the valves adjusted for the last 10,000 miles and they make no noise, so I haven’t bothered. Could this initial backfiring be a sign that the valves finally need adjusting? Valves are noisy if too loose. They can also become too tight, which is very problematic. |
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| oakdalecurtis |
Sep 28 2020, 09:09 PM
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#12
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Oakdalecurtis Group: Members Posts: 1,325 Joined: 5-June 15 From: Oakdale, Ca Member No.: 18,802 Region Association: Central California
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Just got my teener back from a valve job. Mechanic said a few of the valves were “tight”, which he defined as opening a little too much. No more backfire on startup! (IMG:style_emoticons/default/piratenanner.gif)
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| Cairo94507 |
Sep 29 2020, 06:39 AM
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#13
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Michael Group: Members Posts: 9,734 Joined: 1-November 08 From: Auburn, CA Member No.: 9,712 Region Association: Northern California
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Great. Thanks for the follow-up to let us know what you did and that the issue was resolved. (IMG:style_emoticons/default/beerchug.gif)
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