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Old 12-12-2018, 11:02 PM   #1 (permalink)
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Default Problems passing smog...due to rough idle

Hello folks,

I've been trying to get my beloved 88.5 Sammy smogged in CA, and I'm hitting some trouble. The tech did a sniff test and said it was clean as a whistle (as it should...just installed a new cat!) However, he said he couldn't do the test due to rough idle.

I checked and the Sammy idles around 800, dips slightly, then races to about 830...then slowly drops down to 800. Rinse and repeat. What could be wrong? Should I try another smog location?

Things of note:
  • Had the carb rebuilt and calibrated by GuaranteedCarburetors about half a year ago.
  • Replaced spark plugs, leads, distributor cap&rotor,ignition coil (my aftermarket tachometer works now instead of just spazzing out uncontrollably!)
  • Replaced fuel filter
  • Found clogged MCV jet, replaced that
  • It used to die at low idle, until I enriched the fuel/air mixture (bonus: can now hit [email protected] RPM now!)
  • Disconnected idle-up circuit
  • Disconnected EGR (plugged the hose from charcoal canister to carb)- made it run smoother
  • Adjusted timing to 10
  • Attached a vacuum gauge to manifold. Vacuum's at 21 at idle, but flutters by 3-4mm? If I rev up, the needle steadies. It fluttered much worse when I had the charcoal canister connected. When it automatically revs up, the flutter lessens.

What should be my next plan of attack? Someone suggested the distributor springs? Looking online about the vacuum readings point to worn valve guides? Even if it's worn valve guides, would it cause that revving pattern I described above?

Thanks for any insights in advance!

Last edited by Norad2000x; 12-12-2018 at 11:04 PM.
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Old 12-12-2018, 11:14 PM   #2 (permalink)
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Quote:
Originally Posted by Norad2000x View Post
Hello folks,


Thanks for any insights in advance!
Find a tech that understands what diagnostics are, instead of one who relys on guess work..

... Philip
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Old 12-12-2018, 11:22 PM   #3 (permalink)
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Sigh...I really wish there is someone around my area I could bring the Sammy to I live in the central coast area. I don't really know of anyone who would work on it. Most places are like, "A carbureted 89? Psh! Good luck!"
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Old 12-13-2018, 12:00 AM   #4 (permalink)
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Time to take the bull by the horns and start your own investigation...


Start by checking the engine health...

Compression test. fuel and spark disabled, throttle full open, and a fully charged battery..

If any low, repeat with tsp oil in cylinder..

report findings...

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Old 12-13-2018, 12:55 AM   #5 (permalink)
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4 or 5-Inch Fluctuation

If you notice the needle slowly fluctuating between four or five inches, chances are you have an ignition-related issue. Check your spark plug gap as this condition often indicates too narrow of a gap. Also, check your distributor cap and wires. If none of these areas are the culprit, you may need to adjust your idle mixture.

since you frigged with your idle mix, i suspect you have a carb thats not set correctly. Float level and mix screws need to be correct to get steady idle.

Rapid Vibration at Idle

If the needle vibrates rapidly between 14 and 20 inches of mercury, but then steadies as rpm increases, you may be dealing with worn valve guides. How fast the needle vibrates is telling of how many valve guides may be worn.

ok, ok, i'm old school and still use a vac gauge to diagnose carbed engines.
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