deceleration backfire

[Duckhnter83]

I recently adjusted my valves on my car which is new to me but the lash is suppose to be set at .016 hot. before I adjusted them the car ran great. After now I have a backfire on deceleration and a little blue flame out the right header. Could this come from my lash being to tight maybe? Or would adjusting my lash cause the car to run lean? Any help would be great. I used the exhaust opening intake closing method.

[twisterf5]

I recently adjusted my valves on my car which is new to me but the lash is suppose to be set at .016 hot. before I adjusted them the car ran great. After now I have a backfire on deceleration and a little blue flame out the right header. Could this come from my lash being to tight maybe? Or would adjusting my lash cause the car to run lean? Any help would be great. I used the exhaust opening intake closing method.

most times it a header gasket leaking letting in air.

[Duckhnter83]

I would agree to that but what i don't understand is how one weekend it runs without popping or backfiring then I adjust valves and it starts backfiring. My gut tells me to loosen the valves up a little but I don't know if this would be right. I'll check the exhaust gaskets.

[Egoracing]

Did you happen to lean on the header while doing the adjustments?

[Duckhnter83]

Not that I recall.

[StuckInReverse]

Sounds like an cracked header or bad header gasket. Probably just a coincidence that it occurred the same week you adjusted valves.

[powerslide]

Header bolts need to be checked weekly. They tend to loosen themselves

[Duckhnter83]

I will definatly check the exhaust gaskets. My thought was I got an exhaust valve to tight and it was opening to soon and letting unburned fuel in the header causing the car to pop or backfire on deceleration.

[9car]

pop the valve cover off and run the valves again, 15 min you'll know if thats it or not

[Bubstr]

A little tip, if you don't already know it. Mark your Balancer at Top dead center and at every 90 degrees. put your pointer on the mark and follow the firing order, moving to the next mark and you will never be unsure if you set a valve on a ramp. It makes it fast too so all valves are set at close to the same temps. It's a good time for a plug check and that makes it easy to turn the crank with a ratchet. Write down if you have to tighten up a valve, it can be an early sign of wear in the valve train. It's also a good time to do a leak down test and record it. It will not only give you a progress report on your ring and valves, it gives you a baseline in case something happens internally. They don't all wear the same and if you feel something down on power, you know what it was and what it is now. The best part is it's only a couple minutes when all the plugs are out. Do it as you do the lash check. An ounce of prevention is worth a pound of cure. If you find one with too much leakage, listen to carb, exhaust and crank case to find what is leaking. If a valve tap with plastic hammer to dislodge any carbon if there and check again.

Another thing, all leak down testers are not the same. I could get mine to blow 2% on a tight cylinder and a friends registered 8% on the same hole. Use the same one all the time at the same incoming pressure.

Add checking oil for metal and sooner or later it will save you a lot of cash.

[Duckhnter83]

I checked the header gaskets last night and they weren't leaking so I took the headers off and inspected for cracks all good. Replaced header gaskets and put them back on. Still popping on decel and blue flames when it pops out both sides. Tonight I'm double checking my valve lasj again. If that doesn't cure it I guess I'll try making it run richer.

[crateracer16]

I had that happen to me last year and it ended up being a loose wire in my ignition system. It was always popping out of both pipes on decel.

[Duckhnter83]

What wire did you find loose

[merc123]

I had that happen last year. It took us a little while to track it down. Finally found the header was leaking out of the top on the middle ports. It was almost impossible to feel because of the air coming off the fan but we could hear it. Sounded like valves tapping. Resealed it and it stopped.

It would also do it in the shop if you reved it up and let it go real quick.

[jedclampit]

I recently adjusted my valves on my car which is new to me but the lash is suppose to be set at .016 hot. before I adjusted them the car ran great. After now I have a backfire on deceleration and a little blue flame out the right header. Could this come from my lash being to tight maybe? Or would adjusting my lash cause the car to run lean? Any help would be great. I used the exhaust opening intake closing method.

Will it do this in the garage or only when there is decel load on the engine?

If you have/had an exhaust valve too tight, it won't be long before you have, if you don't already , a poorly seating valve from the heat buildup @ valve head.Leakdown test as mentioned above will show if this is the case.

You may have an idle mixture screw open too far or a plugged/restricted air bleed on top of carb.

[crateracer16]

Power wire coming from the battery

[Duckhnter83]

Will it do this in the garage or only when there is decel load on the engine?If you have/had an exhaust valve too tight, it won't be long before you have, if you don't already , a poorly seating valve from the heat buildup @ valve head.Leakdown test as mentioned above will show if this is the case. You may have an idle mixture screw open too far or a plugged/restricted air bleed on top of carb.

Yes the car will do it in the garage if you rev it up and let off the throttle it will pop out both headers randomly. It also does it as you get off the gas on decel. The plugs look tan/ light brow like they should. Even replaced them with new ones. I'm lost on what to do. I re sealed the headers with high temp copper rtv and even checked for leaks I can't feel any. I'm afraid to jet it up any and start fouling plugs. Its got a 500 holley with 72 jets in it currently. On the throttle it runs great. I was also told that it could be normal for it to pop because your dumping all that fuel in then killing the air so it has to go somewhere. I do here other cars doing it from time to time but not all cars are doing it. any other thoughts?

[merc123]

A friend had a Dodge motor that would do it every time. Ran for 5 years with no problem and is sitting in the garage now waiting to go back in a car.

[Duckhnter83]

Well long story short we found the problem in the distributor the mechanical advance lockout was allowing the distributor to retard to about 17 degrees btdc when it should of been at 34 (this is when we checked it could of been more or less at any given time). I have never seen ignition retard. We ran two nights this way. I have now checked compression and there all at 100 except for 5 and 7 they are at 95. I didn't check the compression when I first got the engine I kick myself in the but now. But to me these numbers sound low I was thinking I should be up in the 150s+? the motor is built to be a 9:1 compression motor I was told. Here are some of the specs Gm 3.480 crank had been sent out and counter weights cut and nitride coated gm 350 block prepped 0 deck piston height is + 002 out 4.040 bore . Scat 2 -1cr5700 rod pushrods lingth 7.950 piston -7cc Felpro 1142 .041 thick 4.100 bore head gasket clevite ms-909p-10 main bearings rods torque 45 lbs .0047-.005 stretch mains 70 ft lbmain .0055 thrustRings total seal cr3690-45. Rod bearings clevite cb-663 p-10 .23 Side clearance bullet cam Chs 278/286-064f at .50 in 248 exh 256 1.5 rocker ratio exh 532 lift in 353 cam is in at 102 heads are done with stainless swirl polish valves true 76 cc lifters are bullet with ls9925spl with oil hole. Do you think my compression is low because the cam or do you think the motor is hurt? Needs new rings maybe valve job? I am baffled because all the compression numbers are within 5lbs of one another. I just dont want to tear my engine up anymore if it is hurt. The motor has maybe 300 laps on it on a 1/2 mile track.

[Bubstr]

Want a little tip? throw the compression gauge away and get a decent leak down tester. Compression gauges can be all over the place depending on cam overlap and turning speed while checking. The leak down if used every time you set valve lash will not only tell you if you have a weak cylinder but it can point you to what exactly is leaking, rings, valves intake or exhaust. It will give you a base line and tell you when the engine needs refreshed.

Always use only your leak down tester with the same compressor and regulator set the same and log it. All testers are not the same and not all air supplies are the same. Don't compare leak down percentages with your racing friends as they don't all read the same even if they are the same brand. Air presure, volume and orifice flow determine what each one reads. They can be 8% different and both be working well.

The results are worth their weight in gold. When you get a fresh engine, it will leak like a sieve. Rings aren't seated yet. After a race or two, it will be the tightest It will ever be and if everything is right the leak down percentage will slowly rise, till you need a refresh. A regular maintenance program of leak down, oil filter and valve lash checks can save you a ton of grief. If you know where it was and you know where it is, you know where it's going. It's always good to know. With these two things, I've found bad ignitions, burnt pistons, weak rings, roller lifters and rockers going bad, and valve springs giving up. The kinds of things that if you don't find them, they show up in a catastrophic way.