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68Sporto
Join Date: May 2004
Location: Denver area
Posts: 167
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65 356 Backfire
A friend has a '65 356 which he complained about running "crappy". Getting a bit worn out on my own 68 911 project I offered to help. First off, almost every nut and bolt on the carbs (Solex) were just a bit more than finger tight and gas was everywhere.
Took off both carbs, cleaned them up, cleaned the jets, tightened the cover on the accel pumps (really loose) and put everything back together with proper torque. It runs much better now and is easy to start. And it doesn't have gas all over the engine room. But, one cylinder backfires occasionally below about 2k rpm. Always the same cylinder. We adjusted idle mixture on all cylinders but no change. It was doing this before we worked on the carbs but the engine was running so rough we thought it was part of the overall problem. Less often it gives a muffler bang. If it matters, its the left side forward cylinder. Sorry I'm not familiar with 356 cyl numbers. What should we check? He's happy with it like it is because its a lot better but I would like to get rid of the backfire. Maybe avoid burning up a nice looking 356. Thanks, Tony
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Tony Porsche owner since 1967 1998 Boxster 1968 911 Sportomatic project |
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04-20-2006, 12:18 PM
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Registered
Join Date: Dec 2005
Location: Massachusetts
Posts: 54
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Sounds like a lean condition, it WOULD be for sure if you were running Webers. It's a little bit of work, but swap the jets from one car to the other and see if the backfiring moves with it. If yes, it's in the carb(s), if no, it's a tight valve or air leak . . . I think . . . worth a try. Whenever something drives me crazy, it usually take a crazy solution to fix it.
Luck, TC |
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04-21-2006, 04:08 AM
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Registered
Join Date: Mar 2003
Posts: 10,346
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The Maestro's Top 10 Reasons for a Backfire:
1. No tailpipes. 2. One tailpipe missing. Or one half a tailpipe missing 3. Leaking tailpipes 4. Hole in muffler 5. Leak at "J" tubes/muffler 6. Hole in J tubes 7. Blown exhaust gasket at head/J tube 8. Partially clogged idle jet (especially in Zeniths & Webers) 9. Carb dripping gas inside from various sources 10. Fouled plug And three or four more for good measure: 11. Burnt exhaust valve 12. Sometimes a leaking head/cylinder, but it makes the most noise on acceleration. 13. Too tight intake valves 14. Broken Valve Spring/popped seat/intake valve seized/not sealing 15. Extractor exhaust
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“IN MY EXPERIENCE, SUSAN, WITHIN THEIR HEADS TOO MANY HUMANS SPEND A LOT OF TIME IN THE MIDDLE OF WARS THAT HAPPENED CENTURIES AGO.” |
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04-21-2006, 04:42 AM
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