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Old 02-08-2013, 04:06 PM   #16
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If your ignition timing is too retarded, you could be firing the gas mixture as it begins to exit via the exhaust valve, and actually burning in the hedder pipe adjacent to the cylinder head. This will make the hedder waaaay to hot. The engine will not run very well either. It could also be the result of a timing chain mis-alignment on the cam retard side, with the same results.
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Old 02-08-2013, 05:12 PM   #17
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Originally Posted by t_l75 View Post
MIKE80, how much did it cost fot yoou to get them coated? i am thinking of doing the header wrap, do you think that will be comprable?
I've had the headers for over 10 years and it cost a couple hundred bucks back then. Your best is to check with them for a quote. http://www.jet-hot.com/ordering/

I had a bad experience with header wraps once. I blew a heater hose and coolant got onto the wraps and ignited in my brand new 96' Trans Am. Luckily I had just pulled into a car wash and they extinguished the fire quickly for me before there was any damage. I never used wraps again.
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Old 02-08-2013, 05:17 PM   #18
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Quote:
Originally Posted by MIKE80 View Post
I've had the headers for over 10 years and it cost a couple hundred bucks back then. Your best is to check with them for a quote. http://www.jet-hot.com/ordering/

I had a bad experience with header wraps once. I blew a heater hose and coolant got onto the wraps and ignited in my brand new 96' Trans Am. Luckily I had just pulled into a car wash and they extinguished the fire quickly for me before there was any damage. I never used wraps again.
Wow, that sucked!
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Old 02-08-2013, 10:40 PM   #19
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Quote:
Originally Posted by PredatorC6 View Post
If your ignition timing is too retarded, you could be firing the gas mixture as it begins to exit via the exhaust valve, and actually burning in the hedder pipe adjacent to the cylinder head. This will make the hedder waaaay to hot. The engine will not run very well either. It could also be the result of a timing chain mis-alignment on the cam retard side, with the same results.
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Old 02-09-2013, 11:10 AM   #20
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Sweet thanks!! MIKE80, well that is good to know that the header wraps may not be the best option for me. Also, if the coating is gonna cost me a couple hundred more i might as well buy new headers that will have thicker flanges and tubing. Because even though the summit ones are fine, they definently are on the cheaper side.

Wildcatlock, wow that is some great info. I will definently try that out today and see how it goes. Could the air to fuel ratio be so off that it would be causing the huge backfire I am getting? Sidenote: my engine was running perfectly fine before. It would crank right over and then fire, idle and run perfectly fine. It started to backfire so i pulled the plugs. All of them were soaked in gas and black. I then assumed that it was a carburetor issue so i got it rebuilt. Still having the same issue even with the rebuilt carb.
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Old 02-09-2013, 11:43 AM   #21
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[QUOTE= Sidenote: my engine was running perfectly fine before. It would crank right over and then fire, idle and run perfectly fine. It started to backfire so i pulled the plugs. All of them were soaked in gas and black. I then assumed that it was a carburetor issue so i got it rebuilt. Still having the same issue even with the rebuilt carb.[/QUOTE]

Hmmmmmmmmm, Is it backfiring through the exhaust or back up through the intake?

What kind of carb are you running?

A good solid backfire up through one of the older holleys can blow a power valve causing a rich condition. The newer holleys have a check valve that prevents this.

Rochester carbs are known for a leak in the lower plug where they drill the air/fuel passageways. Brake Clean & JB Weld is the fix for that.

What kind of ignition?
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Old 02-09-2013, 11:44 AM   #22
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Quote:
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I gotta agree with Ivan here. Both a rich and a lean condition can cause the headers to get VERY hot very fast. if it is back fireing then your timing is most likely off also contributing to the heat.
I agree with both of you. The timing is most likely the culprit here.
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Old 02-09-2013, 01:08 PM   #23
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Quote:
Originally Posted by Junkman2008 View Post
Check the firing order of your plug wires for the backfiring problem. I bet you got two of them crossed up. Also check your timing. Bad timing affects temperature too.
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I agree with both of you. The timing is most likely the culprit here.
ToddG
Well damn, I got a few folks who agree with me on this one.
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Old 02-09-2013, 01:41 PM   #24
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A Racer once told me the wraps drastically limit the lifespan of the headers, as all of the heat is beeing held onto them ( also with engine shut down after driving ) - causing the tubes to decay slow by slow.
He didn`t suggest them to me for street car use unless i don`t care replacing them earlier as you wish.
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Old 02-10-2013, 12:07 AM   #25
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7TRoadster:
Through the intake. And a lot. Most of the time it spits a 3 foot tall fireball back up through the carb. Im using the rochester quadrajet and original HEI ignition. Carb just rebuilt. Im thinking its a valve thats off or sticking. Is this common to be happening on a brand new engine? The engine was running perfectly fine and then this randomly started happening. Could it have something to do with fuel? the engine was runnning fine then it sat for maybe 2 months without being turned over. Then this started happening.
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Old 02-10-2013, 06:53 AM   #26
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Quote:
Originally Posted by t_l75 View Post
7TRoadster:
Through the intake. And a lot. Most of the time it spits a 3 foot tall fireball back up through the carb. Im using the rochester quadrajet and original HEI ignition. Carb just rebuilt. Im thinking its a valve thats off or sticking. Is this common to be happening on a brand new engine? The engine was running perfectly fine and then this randomly started happening. Could it have something to do with fuel? the engine was runnning fine then it sat for maybe 2 months without being turned over. Then this started happening.
Starting to sound more and more like you have the dizzy 180 deg. out. You are trying to fire the cyl on the exhaust stroke instead of the compression stroke. When you set the balancer to TDC make sure both valves for #1 cyl are closed. If one is open or part way open then go around another turn. There are two turns of the crankshaft to one turn of the camshaft (i.e. piston goes up and down twice each time it fires). Check that first then procede.
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Old 02-10-2013, 07:13 AM   #27
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I am starting to think he has a wiped cam lobe .
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Old 02-10-2013, 09:52 AM   #28
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Quote:
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7TRoadster:
Through the intake. And a lot. Most of the time it spits a 3 foot tall fireball back up through the carb. Im using the rochester quadrajet and original HEI ignition. Carb just rebuilt. Im thinking its a valve thats off or sticking. Is this common to be happening on a brand new engine? The engine was running perfectly fine and then this randomly started happening. Could it have something to do with fuel? the engine was runnning fine then it sat for maybe 2 months without being turned over. Then this started happening.
Well there always seems to be a bug or two to work out of a new engine. The first of this thread you indicated you were trying to get a new engine running. I get this confused with the statement above that indicates it was running fine.........

I assume (correct me if I'm wrong) it was running fine before the rebuild. New engine in there now and not running or running for a few turns and backfiring out.

Before you disassemble the engine, some tests first may save you some work. Do a compression check, if you have a valve that is not closing or a flat cam lobe (as suggested earlier) it will show up here that will narrow down where you need to be checking too. Hydraulic or solid tappet cam? If all have roughly the same readings, it likely isn't a valve.

Any engine only needs 3 things to run, fuel, ignition and timing. You indicated spark plugs were wet and it's back firing, so your getting fuel. Ignition is also present as represented by the 3' plume of fire out the carb when it does back fire.

Soooooo, that leaves timing, engines have more than one type of timing. Cam timing, the cam turns at half the rate of the crank. Cam does one complete revolution for two revolutions of the crank. The timing marks on the cam sprockets need to be lined up in the number one firing position. This has been mentioned as a possible source already.

Valve timing is also a factor. It has to do with when the valves start to open/close in relation to crankshaft position. This is usually adjustable through different keys on the crank sproket. The above are mechanical settings, they are set static by the builder according to cam specifications and general assembly procedures. Once an engine is assembled these are generally not adjustable.

Ignition timing is by far the most complex of the timing family.
Ignition timing must work together with the engine timing the delivery of spark to each cylinder to make an engine run as expected. with others here, this is where you will likely find the backfire problem.

First bring the engine up on number one firing position, you have to be sure it is at the top of the compression stroke. The way to do that...........pull the plugs. Install a compression gauge in the number one cylinder. Rotate the engine slowly until you start to see compression on the gauge. Keep slowly rotating the engine until the timing mark is at the 0 position.

Pull the cap on the distributor and look at where the rotor is pointing. It should be pointed at the #1 spark plug wire. If necessary loosen the distributor and rotate one way or the other to align the rotor position with the #1 wire connection.

Firing order on SBC. * 18436572 * Install the wires sequentially around the distributor in the direction of rotation following the firing order. This should be close enough to fire the engine.

Ignition advance........ another subject of interest. Has to do with advancing the spark signal as engine rpm's increase to keep the spark happening at the top of the compression stroke. Without the advance the timing would retard as the engine turns faster rpm.

There are a couple of types of advance. Vacuum advance and mechanical advance are the two most common. Computers also have advance curve programs for ECU controlled ignitions.

I believe the HEI has both, mechanical and vacuum. There are books on how to dial these in. I'm not going there, but do a simple check to make sure the mechanical advance is not sticking and the vacuum advance pod isn't leaking.

The vacuum connection on the distributor should be connected to a hose connection on the carburetor. It needs to be plugged into venturi vacuum. Not usually at the base of the carburetor. Consult the service manual for the correct location to plug this in. I cannot remember which one it is on the Rochester. If this is plugged into manifold vacuum it is in the wrong place and it will advance your timing at idle. This is a potential source of your current back fire problem. Make sure this is correct.

For initially timing of the engine make sure the distributor vacuum advance is unplugged and capped at the carburetor. If all is correct the engine should fire and run allowing fine adjustment in timing at the distributor.

Long winded and some is likely information you already know. Just the same, some may be helpful.
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Old 02-10-2013, 04:30 PM   #29
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Lean mixture on british bikes (or any) produces very hot pipes and blueing of the pretty stainless steel or chrome. Not to mention it's dangerous for the motor...
Bill
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Old 02-10-2013, 07:37 PM   #30
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Well damn, I got a few folks who agree with me on this one.
Even a broken clock is right twice a day.
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