Still having problems. Re-set distributor to TDC, went to start car, started hard but now backfires through carb with gas and flames. What causes backfire of this magnitude, thinking improper detonation but why. Everything is fairly new, ran great last year and now has progressively gotten worse. Need help on this one, welcome all ideas.. Thanks guys.
Backfire though carb
rjg67rs
1 - 20 of 61 Posts
Still having problems. Re-set distributor to TDC, went to start car, started hard but now backfires through carb with gas and flames. What causes backfire of this magnitude, thinking improper detonation but why. Everything is fairly new, ran great last year and now has progressively gotten worse. Need help on this one, welcome all ideas.. Thanks guys.
Do u mean it was labouring when turning over on the starter?
If so , and assuming battery connections and starter are in good nic....indicates way to far advanced and not near TDC.
To back fire..that is the explosion in the cyclinder..firing..is taking place when the inlet valve is still open ot partly open....this then ignites the fuel in the manifold and carb...
This is the ONLY way carb backfire and flame is created
Cause..Dizzy timing way the hell out and/or cam not lined up on instal, and/or intel valve stuck, not closong /real bad valve seat.
Joined
·
6,338 Posts
I think you wiped an exhaust lobe.
Sent from my iPhone using Autoguide
Sent from my iPhone using Autoguide
no matter what I do with the distributor it will either not start, won't run or backfires through carb with gas an occasional flame. I think it is way too advanced but if I turn it back (clockwise is retarding right) it barely starts and doesn't run well.
I am wondering about that with the cam, how do you tell if I wiped a cam lobe. Can I check without removing cam? Could I possibly just watch rocker arms for movement or pull lifters. When it was sort of running the timing was jumping all over the place on the tab at about 2000 rpm's. Could it be the distributor? That's a brand new crane cam too, what would cause that. It was running fine last year and has started to get worse and worse this year, although I haven't ran it much.
I just don't know where to start first, how about a compression check?
I am wondering about that with the cam, how do you tell if I wiped a cam lobe. Can I check without removing cam? Could I possibly just watch rocker arms for movement or pull lifters. When it was sort of running the timing was jumping all over the place on the tab at about 2000 rpm's. Could it be the distributor? That's a brand new crane cam too, what would cause that. It was running fine last year and has started to get worse and worse this year, although I haven't ran it much.
I just don't know where to start first, how about a compression check?
Joined
·
15,378 Posts
Obviously something is breaking more and more each time you run it.
First check that nothing is askew... bent pushrod, damaged lifter, bent valve, etc. Pull the intake and look at the pushrods and the lifters and take a good look down at the cam lobes. If all seems OK, lash the valves cold, by disabling the ignition and bumping it over with the key, or a ratchet on the crank bolt.
Try to get a look at the cam gear and matching gear on the distributor... they may be incompatible and chewing one of them up.
Mayeb the carb is dumping fuel... pop it off the intake when you have the intake off and go through it.
First check that nothing is askew... bent pushrod, damaged lifter, bent valve, etc. Pull the intake and look at the pushrods and the lifters and take a good look down at the cam lobes. If all seems OK, lash the valves cold, by disabling the ignition and bumping it over with the key, or a ratchet on the crank bolt.
Try to get a look at the cam gear and matching gear on the distributor... they may be incompatible and chewing one of them up.
Mayeb the carb is dumping fuel... pop it off the intake when you have the intake off and go through it.
Joined
·
6,338 Posts
Yes, definitely do a compression check and yes, pull the valve covers and watch for equal movement on the rockers while turning it over with the coil wire grounded to prevent backfires. Second, If you can still get it to run/idle, disable plug wires one at a time to see if you can make the backfires stop. Why I think it could be the cam- back in the 80's every 327, 307, 350, 305 we knew of or touched ate a cam. The symptoms were always the same. Running fine, then backfiring through the carb and got far worse within 100 miles. I hope I am wrong.
Joined
·
6,338 Posts
In your other post you mention changing the timing and setting it at about 12 degrees (if I rmember right). I hope that was 12 with the vacuum advance line disconnected and plugged idling at approx 800-900?
If you are trying to set timing with the vac can connected you are going to make it way retarded. Still, more likely I think it is cam/valvetrain related.
If you are trying to set timing with the vac can connected you are going to make it way retarded. Still, more likely I think it is cam/valvetrain related.
I did set timing initially with vacuum hose off and plugged. This is what I did; installed new crane cam 268, timing chain and gears, new 2.02 heads, edelbrock rpm intake, summit carb, new lifters, kept original push rods and rocker arms. Set it up following mfg. specs, started it up and ran it like they said to break it in. Set the timing around 16 degrees initial and the car ran fine. It smoked but think that's the rings, I didn't do anything to lower end. This spring I started it up and it started to pop thru the exhaust but still ran ok. As this year has gone by, it has gotten worse, although I haven't driven it very much. Moved to NC and my car sat up north for almost 6 months. It is real bad now, I may have 25 miles or so on the setup. Also new wires, accell coil, points, condensor, plugs. When I pulled the #1 plug it was fouled pretty bad.
Is it possible that the distributor could be no good, when it was running today around 2,000 rpms I did notice the timing mark jumping around and then it backfired with a big flame so we shut it down.
Should I do a compression check first before dis-assembling intake?
Is it possible that the distributor could be no good, when it was running today around 2,000 rpms I did notice the timing mark jumping around and then it backfired with a big flame so we shut it down.
Should I do a compression check first before dis-assembling intake?
Joined
·
972 Posts
I would first change the points and condenser and check the rocker arms
Joined
·
6,338 Posts
I can not see a stock disti causing this kind of trouble. Especially since it was working fine. And you changed points, wires etc.
Sent from my iPhone using Autoguide
Sent from my iPhone using Autoguide
Joined
·
6,338 Posts
Compression test,obsrve rocker movements, then pull the intake and check all lifters, starting w #1 cyl.
Sent from my iPhone using Autoguide
Sent from my iPhone using Autoguide
Joined
·
972 Posts
Actually, a bad condenser will do exactly that- backfire through the carb or exhaust. Or the engine won't start. If you will replace them, get a uni set and either filler gauge it to 19 thou or 28 degrees on the dwell meter. After that, you reset your timing. Where are you located? Maybe someone can help you out. If you're anywhere near me, I'm willing to come look at it.
Nick
Joined
·
6,338 Posts
He claims he replaced it.
Sent from my iPhone using Autoguide
Sent from my iPhone using Autoguide
Joined
·
972 Posts
Back in the late 70s, It was a crapshoot to install a new condenser. It seemed like there was a bad batch from bluestreak and every second condenser was bad. 40 years as a tech, i've replaced a lot of NEW stuff, Most recently the signal switch on my gmc. After finishing the job I found out it was defective. So... what do I know
You're the second person to mention the condensor, the points and condensor are new so maybe I'll change them out, cheap enough to try. Is there any way to test them, if every other one is bad so to speak how do you know you have a good one or a bad one for that matter. I'm in NC, I think you're a little too far away, but thanks for the offer. If that doesn't work I'll start with a compression test and check rockers, then lifters. I'll let you know the outcome. Thanks everyone for their advice.
Joined
·
15,378 Posts
Mooresville! Yer in the center of NASCAR country! There's gotta be a thousand guys who could run by after todays race to help you out.
:thumbsup:
Tow it over by Penskes shop or Hendricks and park it on the side of the road with the hood up. SOMEBODY will stop and help.
:thumbsup:
Tow it over by Penskes shop or Hendricks and park it on the side of the road with the hood up. SOMEBODY will stop and help.
Joined
·
388 Posts
If you pulled the distributor I'd guess you're a tooth or two off....
What do u call jumping around?
Sloppy bushes and it is an old points dizzy will cause alsorts of weird crap.
Beg borrow a GM HEI, drop it in, set the total (intial+ cent) to 36 degs no VA and give it a run....dont run the 6mm leads on the HEI you will blow holes in the HT leads very quickly...then it will back fire all over the place.
Well, I replaced the points & condensor and lo and behold the car starts, was able to set the timing. Took it for a ride around the block and it started popping again when I got on it a little, popping through the muffler and bucked. Back in the garage and guess I'll look at the plugs and wires now and check compression. When revving engine timing does advance but not much, maybe the original distr may be on its way out. Should you be able to move the vacuum lever in the distributor, because it doesn't? Could I be blowing out the condensor?
Joined
·
306 Posts
I could be way off here, but you state the Car ran great last year, did this Catr sit in your garage, etc for an extended period of time!!! If so, wondering if you added STA-BILT to the Gas Tank, and ran it long enough for the product to reach the Carb. STA-<ILT can be purchased at any Auto Supply Store, and is designed to keep the Gas fresh, so that the Carb, fuel pump, and gas lines do not gum up thr fuel system..Inexpensive and the liguid is Red in Color, so it is easy to find on the shelve at the Parts Store. Again I may be way off, but this is something for you to think about for future long periods of not being started and driven, Apply's to anyone reading this, you think that you do not need that in your fuel system, think again, could save you hundreds of dollars in repairs and paying some one to figure out why the Car won't start.......Also suggest every one carry one or more Fire Extinguishers in your ride, in the cabin, not in the trunk. I have been there and done that, trust me...........................
1 - 20 of 61 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
