Engine Problem

[Zack]

OK guys, I thought all was well when i did my first start up but not so. The engine is backfiring slightly and you can hear it out both exhaust pipes. However, the engine runs beautiful and is advanced to 12 degrees timing. I am running a Skip White small base HEI distributor. It also has a tunnel ram with 2 edelbrock 500's. It is running very very rich and black smokes when i wrap it up and the fumes are so bad it burns my eyes. Could the carbs be causing the backfiring or ignition or a combination of both? I have a friend who is gonna put smaller jets in the carbs but i still don't understand the backfire problem. Any ideas????

 

[RPM]

First thing I would do is double check the firing order on your plug wires, and run it in the dark to see if you have any arc jumping from wire to wire. Jets won't make it rich at idle! Trash in a needle will make the floats high and cause it to run very rich.

 

[Zack]

First thing I would do is double check the firing order on your plug wires, and run it in the dark to see if you have any arc jumping from wire to wire. Jets won't make it rich at idle! Trash in a needle will make the floats high and cause it to run very rich.

Thanks Ron. I am 99% sure it is a ignition/firing problem. Tomorrow we are gonna do a compression test on every cylinder to rule out a valve problem. I will try the run in the dark test also. I will post what i find tomorrow if anything. Thanks again.

 

[Zack]

Ron, just went over and started it in total darkness. I looked all over and never saw any sparking anywhere. The firing order it spot on and the timing is at 12 degrees. This is very strange. You can hear it popping back out both pipes, it is not very bad just enough to hear. Also, it is not popping back out the carbs at all, only the exhaust. I have a NEW E-Coil coming to hook up with this HEI distributor. Right now i am using an old stock GM points style coil. Could this old style coil i am using be the problem?

 

[sstock]

Ron, just went over and started it in total darkness. I looked all over and never saw any sparking anywhere. The firing order it spot on and the timing is at 12 degrees. This is very strange. You can hear it popping back out both pipes, it is not very bad just enough to hear. Also, it is not popping back out the carbs at all, only the exhaust. I have a NEW E-Coil coming to hook up with this HEI distributor. Right now i am using an old stock GM points style coil. Could this old style coil i am using be the problem?

I assume you have the initial timing set 12 degrees BTDC (Advanced)with vacuum advance off correct?

 

[Zack]

I assume you have the initial timing set 12 degrees BTDC (Advanced)with vacuum advance off correct?

Yes but when i pulled the vacum line off it did not seem to make any difference.

 

[benT]

Don't just assume it's not a carb problem. I have dual edelbrock 500's as well and had an issue with similar symptoms. One of the Carbs had a bent needle. Edelbrock sent me a new one but it was a pain to diagnose.

 

[Zack]

Don't just assume it's not a carb problem. I have dual edelbrock 500's as well and had an issue with similar symptoms. One of the Carbs had a bent needle. Edelbrock sent me a new one but it was a pain to diagnose.

Wow, I guess that could potentially be my problem. These carbs were so far out it was insane. A buddy tuned them on the fly for me just to get it running but he said the jets are way too large. I have him lined up to go thru the carbs and get them right. They are both like new but the previous owner had them tuned for a blower.

 

[409T]

My 409 will act just like what you have described if I stet the float levels too high. As RPM said, dirt under the needle is a real common cause of this also.

 

[Mike]

Burning fuel in the headers?

Exhaust valves set too tight?

 

[2old2fast]

If those carbs were used on a blower, someone may have "modified" them?! Good luck if that's the case!!

dave

 

[Zack]

You guys have hit the nail on the head. Looking back at the overall first startup and noticing the fuel vapors seeping out from underneath the front carb base plate tells me that is probably 99% of my problem. This vacum leak looks to be the culprit at the moment. As Mike said, i am hearing the fuel burning in the exhaust. It is dumping a huge amount of fuel. I will post back tomorrow what i find this evening. I am not sure why the front carb is not sealing up but i will know tonight. Thanks again guys.

 

[fordsbyjay]

I bet 10 bucks your plugs are fouled now and thats why it is backfiring out the exhaust.. All the fuel is not burning in the cylinder so it is burning in the exhaust. Check the plugs then find out why it is running so rich (ie needle and seat in the carb). You can also pull the distributor cap and turn it over. Watch the rotor to make sure it is turning smooth. If it is all jumpy it could indicate cam or timing chain problems.

 

[Zack]

Thanks Jay. I am sure it has to do with the carbs and possibly the wrong coil now. I found a vacum leak on the manifold, fixed it and replaced both carb gaskets. Nothing changed. The exhaust gases are still burning my eyes and it is still popping out the exhaust. I back all the mixture needles out 2 turns and doesn't seem to make any difference. I will also change the plugs and see what that does. Thanks for all the suggestions guys, this problem is starting to get on my nerves, lol.

benT...........I did notice the pass side mixture needle on the rear carb is bent pretty good. So you think this could be the problem?

 

[benT]

Could be...on mine it was was dumping raw fuel in at all times...and it was the front carb which does not run much with my progressive linkage setup. Mine ran like sh*t and fouled out the plugs quickly. Once it was fixed, it ran smooth and was not running rich or lean,

 

[Zack]

Could be...on mine it was was dumping raw fuel in at all times...and it was the front carb which does not run much with my progressive linkage setup. Mine ran like sh*t and fouled out the plugs quickly. Once it was fixed, it ran smooth and was not running rich or lean,

Wow, I will call edelbrock tomorrow and get some new mixture screws coming. Thanks for the tip. I am getting to my wits end real fast with this.

 

[GT63]

Wow, I will call edelbrock tomorrow and get some new mixture screws coming. Thanks for the tip. I am getting to my wits end real fast with this.

Wow, I guess that could potentially be my problem. These carbs were so far out it was insane. A buddy tuned them on the fly for me just to get it running but he said the jets are way too large. I have him lined up to go thru the carbs and get them right. They are both like new but the previous owner had them tuned for a blower.

If those carbs were on a blower, I bet they had the secondary jets changed, the needles changed and the springs changed. Edelbrock has a chart in the manual on how to modify those carbs for blower use. They also have another chart on how to tune them. You may need to swap the jets, needles and springs back to the OEM parts and then tune from there.

 

[Zack]

If those carbs were on a blower, I bet they had the secondary jets changed, the needles changed and the springs changed. Edelbrock has a chart in the manual on how to modify those carbs for blower use. They also have another chart on how to tune them. You may need to swap the jets, needles and springs back to the OEM parts and then tune from there.

Yes, i know the guy who had them told me he changed the jets/rods/springs. So, i need to know do like you suggest and get it back to original. What if i unhook the secondaries? Would that help?

 

[2old2fast]

The jetting, rods , springs shouldn't have much effect at idle , altered idle orfices or idle air bleeds, leaking needle &seats, vacuum leaks , messed up idle adj. screws, timing off would be the place to start. If you ask around , someone may have the parts you need , I have all holley stuff, so , can't help you there. dave-

 

[Zack]

The jetting, rods , springs shouldn't have much effect at idle , altered idle orfices or idle air bleeds, leaking needle &seats, vacuum leaks , messed up idle adj. screws, timing off would be the place to start. If you ask around , someone may have the parts you need , I have all holley stuff, so , can't help you there. dave-

Thanks Dave. Things are looking towards the floats being way out of adjustment now. I will re-adjust them tonight and try it. I will also replace the bent idle mixture screw. If still no luck i will put the stock jets/ rods/springs back in. I cannot find any vacuum leaks. I have sealed the only one i found last night. Thanks for the help, i will post up tomorrow what i find tonight.