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Location: middleburg, fl
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back firing

can someone tell me what would cause my 1.8 to back fire?
shawn
Old 08-12-2002, 07:18 PM
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Have you checked your timing and advance? Are your valves adjusted.

Might also be your airflow meter. Could be set too rich or lean. There's an adjustment screw on top. It's best to have it hooked up to anr air/fuel ratio exhaust tester to get the right mixture.

Not sure which way to turn it to make it richer or leaner.

Be careful. If it backfires through the airflow meter you can F#%! it up and may end up buying a new one.

My last car, I used to fiddle with it. I sort of had a natural knack for tuning it just right. I think if it's too rich it will send out some white exhaust, to lean and it will back fire on deceleration.

I set it once by feel, listening and smelling. Took it to the shop for final adjustment and I was almost right on.

Check your hoses too.
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Old 08-12-2002, 07:40 PM
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i just changed my oil and adjusted my valves and it's done it since then.i'm almost positive that i adjusted them right,i even double checked them.i went step by step on adjusting them too
shawn
Old 08-12-2002, 07:47 PM
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shawn, sounds like the valves aren't adjusted properly, go through the steps till you get it right. you didn't mess with the air flow meter did you?
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Old 08-12-2002, 08:48 PM
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Shawn, What part of San Diego are you in? I know a great mechanic.
Mark
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Old 08-12-2002, 08:55 PM
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yes! i need advice too! i need to rough set the CO in order to be able to get the car to the shop that has a CO meter. the CO screw is in all the way, it seemed to make it run best there. what my car does is pop thru the exhaust on overrun, that is, when i speed up then let off the gas, still in the gear and coast (isn't that "overrun"?) or let the engine "brake" the car to slow it down. maybe i should just adjust until it doesn't pop? advice please.
Old 08-13-2002, 02:14 PM
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The screw adjustment on all 1.8L (l-jet) air flow meters is for idle only! I had the same problem on my 75' with "overrun backfires". I had to rebuild my dizzy, vac advance/retard check and replace all vacume lines for the dizzy and spend a couple hours to time it perfectly. It runs very smooth now and never backfires.
Old 08-13-2002, 02:43 PM
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dave i hat to correct you the airflow screw has an effect on all rpm ranges, try adjusting one rich and drive the highway the plugs would be black, i did it when setting mine

back to the orignal qusetion about back fire on overrun

check for vacuem leaks at the injector seals and the seals on the runners to the air distribution box as well as the decel valve if it is not working properly you draw a huge vacuemn that will suck a vacumn leak when you normally wont
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Old 08-13-2002, 04:33 PM
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guess i'll keep chasing the gremlin. in course of mechanical restoration, i put on new injector seals and intake manifold hoses and even hose clamps on 2 of the hoses. checked decel valve and hoses (will check and re-check). what does exhaust popping indicate? like too rich, too lean, too hot, too cold etc?

also mechanic wanna-be
Old 08-13-2002, 04:54 PM
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Deaccel valve supplies extra air on overrun to avoid backfire due to over rich mixture. Some d-jet systems had fuel cutoff on deaccel to prevent this (factory changed their minds off and on).
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Old 08-13-2002, 08:54 PM
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ok, i didn't start having the problem with back firing until i adjusted the valves, but i went step by step. this is what i did. "put the engine at tdc with the rotor at 12 o'clock on the notch of the distributor and adjusted the # 1 cylinder then i turn the engine so the rotor would go counter clockwise until the rotor was close to being at the 9 o'clock position for the # 2 cylinder and on to the # 3 and # 4" my biggest question is how do you know that you are exactlly at the 9 o'clock and 3 o'clock position. 12 o'clock and 6 are easy. i think that's what i messed up on to make it back fire.can anyone help me?
shawn
Old 08-14-2002, 03:07 PM
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now that i am getting info on the Ljet FI.can anyone tell me what would cause my car to idle at 2 rpm when it is started cold and slowly goes down below 1 rpm and it runs real rough until the engine warms up.i have no vacumm leaks that i can find.the way i check it was by spraying carb cleaner on all of the vacumm line connections. it's driving me crazy not knowing what it is.can anyone help me?
shawn
Old 08-14-2002, 03:25 PM
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Hi, as for checking to see if you are at 9 o'clock ect. there is a hole in the bottom of the bell housing. So if you start at TDC for #1 cylinder (look at TDC mark on the fan through the timing hole in fan housing) then rotate your engine 90 degres till you can see the TDC mark in the bell housing hole underneath the car. This should be exactly TDC for the # 4 Cylinder. Rotate another 90 degres till you see the TDC mark back in the fan housing/timing hole-TDC for #3 cylinder, another 90 degres for #2. I am pretty sure there is a tech article about it also. Hope this will help. Dave
Old 08-14-2002, 09:49 PM
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i'm no mechanic but i don't think it is that precise. you adjust the clearance when the valves are closed and therefore not "on a lobe" hope you get my drift. i adjusted mine basically same way but rotated engine/rotor clockwise (1-4-3-2). started with rotor at mark on dist rim, rotate about 90 degrees by eyeball. when valves are closed, there is alot of camshaft surface not lifting the valve. cam turns at 1/2 engine rev anyway.

(help dave darling, i'm fumbling!!!)
Old 08-15-2002, 11:11 AM
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Shawn,
I have a '75 1.8L and have noticed something similar. Here is what I have determined. The cold start system has two components during warm-up (ignoring the cold start valve which should only be on during cranking) the AAR and fuel enrichment controlled by the ECU based on Temp Sensor II. I have found that on my car, fuel enrichment stays on about 8-10 mins. Previous discussions of the AAR indicate that it should close in about 8-10 mins meaning that they would balance each other. My AAR actually closes in about 41/2 - 5 mins. This results in idle being high initially. Then falling when the AAR closes. Then coming back up again and steadying when enrichment shuts off.
Anyone else have any thoughts?
Old 08-15-2002, 01:20 PM
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thanks for the help.the back fire problem was the valves.(fixed that )the cold start problem was a vacumm leak(fixed that)
shawn
Old 08-22-2002, 07:30 PM
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