Sprayed carb cleaner around the intake while running, no change in idle Posted using the Full Custom H.A.M.B. App!
A flat cam lobes it will give you lower compression on those cylinders and bad vacuum gauge readings. If you have an intake gasket leak on the underside of the manifold, its nearly impossible to detect with carb cleaner spray down. The spray down helps detect vacuum leaks on top. To determine an underside manifold leak, you first need to diagnose a vacuum leak and exhaust every possible elimination of the sources and then its a "diagnosis of exclusion" which means there's nothing else it can be. Have you tried a vacuum gauge and or service tachometer to watch while you are pulling plug wires. What the vacuum needle do? The fact that you say both that "it runs good" and that pulling those plug wires of those 4 cylinders has no change really stops the flow chart dead. One of them must be a false statement.
Factory or dual plane aftermarket intake? If so I'd say you have a vacuum or carb issue, the 4 cylinders listed (1,7,4,6) are all fed off one side of the intake on those. I'd say you have something causing a lean condition on that side, may not explain some of the other issues but that stuck out to me.
I hooked up a vacuum gauge to the pcv on the carb. But not while pulling the wires. I can also try that tomorrow. What should the vacuum gauge read? The intake is an edelbrock air gap. Posted using the Full Custom H.A.M.B. App!
check for a worn lobe on the cam. This will NOT show up by a compression test, and these engines are known for this type of problem.
Heard this before but I've run around with blown or no collector gaskets many times with no backfiring.
If the problem started after new plugs and wires I would find TDC on #1 and check rotor position. Pertronix can change timing when you install also. I would double check plug wire placement firing order 18436572 with odd cylinders on drivers side evens on passenger side. Don't forget to check power valve in holley with all the backfires. Posted using the Full Custom H.A.M.B. App!
The test for a worn cam lobe is running or dynamic compression test. Here's a very brief description if you want a little info http://student.ccbcmd.edu/~smacadof/CompressionTesting.htm The symptom shows up as " restricted intake or restricted exhaust" in that cylinder. It's up to you to determine if there is an actual restriction of carbon build up, mouse nest, mud daubers, potatoes in tailpipes or flat cam lobe. A running compression test and a static cranking compression test will show different things. Cylinder sealing versus cylinder breathing. But if you don't believe me, next time you are doing a cranking compression test and have a good baseline back off one of the rockers so it decreases the valve lift and simulate a lobe going flat and re do that cylinder cranking compression test. It will be lower. Up to you to notice it though.
Here's some ( you can find a lot more ) vacuum gauge diagnostics. http://www.international-auto.com/f...uges/tips-on-reading-gauges-vacuum-gauges.cfm
120 lbs. compression sounds like your test may have been done cold. A proper compression test is done on a warmed up engine. Fouling plugs can cause the backfire, or be the result of a weak ignition that fouls plugs and causes a backfire. I'd be checking each plug wire to ensure you're getting a good hot spark to the plugs, and replace the plugs too. Sounds like you may possibly have a weak ignition coil, or bad ground.
On the compression test it was done on a warm engine. Vacuum readings look good compared to whats on the chart in the link. I changed the cap and rotor and still have the backfire. Now looking at 24riverview's comments, after replacing the intake, the dizzy was off and I had several wicked backfires out of the carb before I got the timing right. Is it possible the left side of the carb (1,4,6,7) or intake was damaged from those backfires, giving me the problem I have now? Should I try to find another carb and replace it?
with it running, put a heat gun on each exhaust port at header/manifold--will tell if cylinder is firing or not. 1 and 7 on dr side-4 and 6 on pass side. 4 and 6 intake ports are close-1 and 7 are not.
Power valve can easily be damaged from backfires through carb. Posted using the Full Custom H.A.M.B. App!
could be a faulty petronox ignition. could be shorting out. if it were to short out it would be like closing the points on a points distributor. i have heard of condensers shorting out and causing backfire. think of what would happen if spark occurred in a cylinder that was not ready for ignition.
Dude, pushrods just dont bend. Before you start getting parts (carb, etc), you need to see why that happened first. Pull off the valve cover & see how much the rocker moves on the bent pushrod position. You may want to check the new pushrod just to make sure it didn't bend
Sticky valve is the most likely and common cause. However a valve stuck enough to bend a pushrod usually stays stuck. Maybe not but .... Floating valves and kissing pistons is another but valves bend with the pushrod and bent valves give low compression. Maybe it didnt bend the valve but I'd think there'd be more than just one pushrod bent. Backfire from crossed wires can bend pushrods if conditions and positions are just right. They can bend from fatigue too.
Pull the valve cover and see if the exhaust spring is broken near an end coil. This could give a good compression test, but, float the valve when some RPM is built up.
Make sure the vacuum line to the distributor is on the correct side of the carb, driver's side I think. I had something similar going on once before that did not make sense and that fixed it.
I have not checked for a broken spring yet, let me check the springs. I had the backfire before the pertronix was installed. Heat gun on the header? heat gun or one of those infrared thermometers? New pushrod did not bend Would a damaged power valve give me a backfire out of the exhaust? Are they easily damaged on Edel carbs?
First thing you need is a piece of paper and pen. Write down when you noticed the problem then list the what you had changed to create the problem. Sounds like you are chasing your tail and throwing parts at it. Go back to the basics most of which have been listed here. To change the intake you had to remove the distributor. You havent said anything about the timing? If you write down your info as you do your test you will be more likely to see whats going on. Take the info you have been given here and list your results of each. I am betting you will find your problem if not you will be able to give good info for others to help diagnois your problem.
I was using the wrong vacuum port on the carb, Thanks KeithDyer, but still receiving backfire. No Broken springs Yes I changed the intake and initially had timing issues, got the timing set at 36 degrees at 3k rpms. I'm thinking the problem is something simple that I'm overlooking, but I'm still stumped.
Even thought it was backfiring before the pertronix ignitor I still have the factory coil, is a high voltage coil necessary with ignitor?
The 1,4,6,7 problem needs to be corrected. Wicked backfire thru the carb MAY damage a carb beyond repair but is almost always cause for a clean & rebuild. A few pops or coughs thru the carb is different than a wicked backfire. These earlier backfires thru the carb is new information. I'd like to here it running with this 1,4,6,7 problem.
Uploaded to YouTube https://www.youtube.com/watch?v=aeEpEft_qSk&feature=youtube_gdata_player Posted using the Full Custom H.A.M.B. App!
Neat ride ! Now the sound quality on that may not be good on my end, it sounds like its running well enough to certainly have some change if 1-4-6 or 7 were canceled. In others words it doesn't appear to be running with those cylinders dead. It is deductive reasoning of IF - THEN only that leads to the conclusion - if the cylinder is canceled THEN no change is detected that cylinder must be doing nothing. Observational evidence says if 1-4-6-7 are doing nothing (dead) it won't run. I see it running Gotta scratch my head for a while
Thanks the headers out of those cylinders are very hot to the touch which makes me think the cylinder is working but as I said I pull a plug and no change in RPMs
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