I canceled 2,3,5,8 and you are right no change. Yes it's still backfiring Vacuum test shows 1" fluctuation at 18" I was meticulous in putting the new gaskets on, I'd say it's impossible to have a leak. Yes I followed the correct torque down procedure. I believe the vacuum gauge is about the same, but it does look more steady. I got the correct flame thrower coil so at least no issues starting now and the spark is strong as I got bit checking the cylinders So the problem is the same but now on the other side. I did not take the carb off the intake when changing the gasket, is anyone else thinking this is a carb issue? Posted using the Full Custom H.A.M.B. App!
Can you try another distributor or put points on your current one? A bad coil or high resistance in the plug cables can kill an ignition module. Double check the coil primary wires & make sure they are correct
Weird. Perhaps you have a piece of debris in the carb, was affecting one jet and now after moving it around has gone to the other.
Ok I have not read all of responses , but I did read your detailed problem, I had the same problem on my race car, I did all the usually ignition stuff , to no avail, I had a small hole in one of my header collectors ( merge style ) drove me nuts trying to find it , only happened under decelleraration , IMHO I would check for exhaust leaks , best of luck ! I changed the merge collectors and problem was gone thanks tintop ! Just read my statement at the bottom and it is very true always !
Copy on all that . I didn't see a specific answer to Did you do the same test for crankcase vacuum? I think salt flats gave it to you Take impossible out of your troubleshooting vocabulary when you do not have any history. Bouncing needle isn't a sign of perfect engine. After a intake manifold change, if there's a problem first thing to eliminate is potential vacuum leaks. Jostling the carb around may have something to do with problem switching sides. An exhaust leak will cause a backfire in the exhaust
The only thing that make sense (to me) is a bad pertronix. Maybe the magnet collar thing that goes on the shaft is missing a magnet??
If it and eddy carb I think it would be hard to have some crap move to the other side. Exhaust leak is not going to cause the engine to miss. Do the intake leak test again.
Yes I did the test with the valve covers and there was no pulling of air. I think I'll go to the muffler shop in the morning if it's not raining and have the exhaust leak repaired to see if that kills the backfire Posted using the Full Custom H.A.M.B. App!
It was raining like crazy yesterday, so I couldn't go. I'll go in the morning and update you guys. Posted using the Full Custom H.A.M.B. App!
I am going out on a limb and going say the exhaust leak , been there done that got the t-shirt to prove it ! Not trying to a smart ass know it all , use the Kiss method on this old stuff it works, hope all works out for you , thanks tintop
I went back and read the whole thread, I wonder about the low readings on #1 cyl, what's going on there, I had a 89 silverado with a 305 with a lot of miles on it, it ran great until one day it stuck a valve, bent the pushrod and the valve , it backfired all the time under load, I had to change the cylinder heads, have you done a leak down test yet, that will tell if is good or bad, if all the cylinders are within 3-10% of each other you are good to go, the leak down test must be done on a warm engine, when you put air to the cylinders , if you hear air coming out of carb it will be intake valve related, if air comes out the exhaust pipe it will exhaust related , compression test shows low on #1 , might be camshaft related, if you have dial indicator check how much lift you have compared to another high reading cylinder, remember that when doing a compression test that to get good readings the cam , ring seal , and valve seating must in general good condition, this shit is pretty simple stuff on a sbc , if the exhaust valve hung up for a split moment that could have bent the pushrod, was it the pushrod on the exhaust side? Might have bent the exhaust valve a bit ? What happens then it doesn't seal up and with your exhaust leak , it allow air in the exhaust under decel, with the unburnt gases from a bent exhaust valve you will create a backfire , the leak down test will tell u a lot more about your engine than a compression test, hope this helps a fellow hamber out .
Thanks I have not done a leak down test yet, if the exhaust leak is not the problem, then that will be the next step. Posted using the Full Custom H.A.M.B. App!
Did some one mill the shit out of the heads so that the intake won't sit flush??? Been there, seen that, not writing a book about it..... I was avoiding this thread since the last second opinion one.
It's an unknown 305, but the heads look normal from what I can see Posted using the Full Custom H.A.M.B. App!
Couldn't tell from the video, very noisey on my cell phone, but does it have a cam in it or is this just a stock unmolested engine? Sounded all most like open headers to me LOL, but my hearing ain't what it used to be...
So I would like to thank everyone for their responses and help. The muffler shop found a burnt collector gasket, about 60% of the gasket was missing from the passenger side and the driver side had about 10% of the gasket missing. They also added that my glasspacks sound empty and I need new mufflers. Looking back on everything I think I did have a couple of a different problems. The vacuum leak from the 1st intake gasket and the collector gasket were causing all the symptoms. Well on the drive home I really got on it hard and it never backfired! Again I thank everyone for their advice!!!
Dapirate, thanks for the detailed feedback on how you solved your problem. Now that you have fixed vacuum and collector leaks, are you now getting a steady reading on your vacuum gage? Have you diven it enough to be confident that #1 cylinder is no longer fouling the plug?
I just checked the #1 plug and it looks good, my guess is the cylinder wasn't firing due to intake gasket and it was just collecting fuel. The vacuum looks great holds steady at 20 And I can cancel cylinders by pulling the wires. Posted using the Full Custom H.A.M.B. App!
The Jalopy Journal
