The 1947 - Present Chevrolet & GMC Truck Message Board Network
Page 1 of 2 1 2
Show 40 post(s) from this thread on one page

The 1947 - Present Chevrolet & GMC Truck Message Board Network (https://67-72chevytrucks.com/vboard/index.php)
-   The 1967 - 1972 Chevrolet & GMC Pickups Message Board (https://67-72chevytrucks.com/vboard/forumdisplay.php?f=3)
-   -   Need Help Dont No What Else To Do (https://67-72chevytrucks.com/vboard/showthread.php?t=727713)

C.20 01-16-2017 08:39 PM
Need Help Dont No What Else To Do
 
Hows everyone doing i got a problem with my 1971 chevy c20 350 sbc so recently after this snow storm in north carolina the truck would not turn on so me and my son did i tune up changed the cap,rotor,igniton module,spark plugs,wires the truck turned on we went down the road and all we got was horrible backfire so we thought it was the carb so we changed the carb and it still did it but it got better until u gave the truck alot of gas and it was back to backfiring i dont no what else to do if someone has some advice that will help us out a lot because its my sons daily driver!!

Shinysideup 01-16-2017 08:48 PM
Re: Need Help Dont No What Else To Do
 
Timing is off, or maybe fuel line/filter is clogged up.

Rickysnickers 01-16-2017 08:51 PM
Re: Need Help Dont No What Else To Do
 
Check for vacuum leaks, maybe .

too much stuff 01-16-2017 08:54 PM
Re: Need Help Dont No What Else To Do
 
Check your firing order on the plug wires

paul blair 01-16-2017 09:00 PM
Re: Need Help Dont No What Else To Do
 
Check fuel pump--filter--line

C.20 01-16-2017 09:46 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by Shinysideup (Post 7828772)
Timing is off, or maybe fuel line/filter is clogged up.
Replaced the filter already i havent checked the line will check tommorow

C.20 01-16-2017 09:47 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by paul blair (Post 7828790)
Check fuel pump--filter--line
replaced the fuel pump already and the filter havent done the line yet

C.20 01-16-2017 09:48 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by too much stuff (Post 7828779)
Check your firing order on the plug wires
alright im goona check again for this but wouldnt it always be back firing if the fireing order is off?

C.20 01-16-2017 09:49 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by Rickysnickers (Post 7828774)
Check for vacuum leaks, maybe .
im goona look into this tommorow

garyd1961 01-16-2017 09:57 PM
Re: Need Help Dont No What Else To Do
 
Check the firing order, also make sure the distributor cap is seated properly. It depends on which wires are crossed as to how it will or will not backfire.

C.20 01-16-2017 10:30 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by garyd1961 (Post 7828870)
Check the firing order, also make sure the distributor cap is seated properly. It depends on which wires are crossed as to how it will or will not backfire.
the firing order seems to be ok im goona check it again tommorow and im also goona check the cap and see if its sitting right

paul blair 01-16-2017 10:36 PM
Re: Need Help Dont No What Else To Do
 
Any unusual engine noise? How many miles on engine?

C.20 01-16-2017 10:41 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by paul blair (Post 7828918)
Any unusual engine noise? How many miles on engine?
nah no weird noises never had any weird noises once the storm hit it all hit the fan idk whats wrong with it

jocko 01-16-2017 11:37 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by C.20 (Post 7828751)
after this snow storm in north carolina the truck would not turn on
Can you elaborate on "would not turn on"? Would not crank? Would not fire/start? I assume the latter since you got backfiring (guess I just answered my own question, sorry...) The items you initially changed out sound like you had indications of no spark. You mentioned after a storm and ign module (as in HEI module?) - perhaps struck by lighting? I think if you changed the HEI module, it'd take care of any lightning damage. Hmm. More details please. It the backfiring load-dependent? Like, only when you let off the gas, for example? Or only when you step on the gas, etc? Sure sounds like a timing issue to me - but that wouldn't just change overnight after a storm. So, you may have two problems - perhaps module went out, and then, during reassembly, the plug wires or timing got crossed/set wrong(?) Backfiring is "normally" a timing/ignition issue - not a carb or fuel issue. Did you replace all the ignition components at the same time and then try to start, or one at a time and try to start? (I'd have done them all too... but that is how compound/self-induced issues can be masked). If it wouldn't start AT ALL (as in no ignition, but it did crank over) and then you changed all the ignition parts and it starts but backfires - my guess is something was messed up in the replacement process while the root problem was fixed.

wbc409 01-17-2017 12:38 AM
Re: Need Help Dont No What Else To Do
 
How often does it actually get cold enough to snow there? Did you let the truck warm up, is your choke working?

C.20 01-17-2017 02:19 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by jocko (Post 7828972)
Can you elaborate on "would not turn on"? Would not crank? Would not fire/start? I assume the latter since you got backfiring (guess I just answered my own question, sorry...) The items you initially changed out sound like you had indications of no spark. You mentioned after a storm and ign module (as in HEI module?) - perhaps struck by lighting? I think if you changed the HEI module, it'd take care of any lightning damage. Hmm. More details please. It the backfiring load-dependent? Like, only when you let off the gas, for example? Or only when you step on the gas, etc? Sure sounds like a timing issue to me - but that wouldn't just change overnight after a storm. So, you may have two problems - perhaps module went out, and then, during reassembly, the plug wires or timing got crossed/set wrong(?) Backfiring is "normally" a timing/ignition issue - not a carb or fuel issue. Did you replace all the ignition components at the same time and then try to start, or one at a time and try to start? (I'd have done them all too... but that is how compound/self-induced issues can be masked). If it wouldn't start AT ALL (as in no ignition, but it did crank over) and then you changed all the ignition parts and it starts but backfires - my guess is something was messed up in the replacement process while the root problem was fixed.
It backfires when i drive it mostly not when i start it turns right on no problem im running out of ideas

C.20 01-17-2017 02:20 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by wbc409 (Post 7829035)
How often does it actually get cold enough to snow there? Did you let the truck warm up, is your choke working?
not much dont snow much either but im running out of ideas im thinking it might be the distributor going

C.20 01-17-2017 02:22 PM
Re: Need Help Dont No What Else To Do
 
checked everything you guys told me check everything is good the only thing left i can think of is a warped manifold or a bad distributor

Alex V. 01-17-2017 02:35 PM
Re: Need Help Dont No What Else To Do
 
Is it a points-type distributor or HEI electronic?

C.20 01-17-2017 02:40 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by alex v. (Post 7829460)
is it a points-type distributor or hei electronic?
hei

wbc409 01-17-2017 02:41 PM
Re: Need Help Dont No What Else To Do
 
If you have a points distributor, you could have a bad condenser. I had a condenser go bad once, the truck backfired so hard it blew the end of the muffler off.

C.20 01-17-2017 02:57 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by wbc409 (Post 7829466)
If you have a points distributor, you could have a bad condenser. I had a condenser go bad once, the truck backfired so hard it blew the end of the muffler off.
im runnning hei

Deer_hunter_088 01-17-2017 03:00 PM
Re: Need Help Dont No What Else To Do
 
Dist gear could be warn, and it could have jumped a few teeth.

C.20 01-17-2017 03:02 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by Deer_hunter_088 (Post 7829480)
Dist gear could be warn, and it could have jumped a few teeth.
hm i didnt think of that it is a offbrand distributor

LongBox 01-17-2017 03:57 PM
Re: Need Help Dont No What Else To Do
 
A backfire strong enough to blow a muffler means unburnt gas was in the exhaust. this is because the engine was turning, but not firing. When it started firing again, the hot exhaust ignited the unburnt gas in the muffler. We used to do that on purpose when we was kids.

Since the last thing worked on seems to have been the ignition, time to go over the distributor very carefully, in an organized way. Is the wire from the coil connected correctly? Is the rotor seated on the plate on the top of the shaft. Is the centre contact in the cap there, and in good order. Is the centre contact on the rotor in good shape. I know these are new, but they can get out of whack.

Next, is each plug wire firmly seated in the cap? And at the plugs? Are the wires in good shape, with no issues with the insulation? Etc.Etc. Etc.

Deer_hunter_088 01-17-2017 04:20 PM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by C.20 (Post 7829483)
hm i didnt think of that it is a offbrand distributor
had an atv that did that, but the coil sparked bc of stator position, and it jumped timing, and it did EXACTLY what yours is doin. jumped like 3 teeth. pull dist and check On that style of atv, a lil raised pad acted as the rotor on your dist, so when it struck a certian point it fired, when the timing jumped, the valves would open at the wrong time, so it sparked wrong and ran like CRAP at idle, get up in rpms and it went away, but was a lil down on power.

volksworld 01-17-2017 04:48 PM
Re: Need Help Dont No What Else To Do
 
ok the backfire...is backfiring out the exhaust or popping back through the carb? back through the carb is typically a lean condition...what carb is on it? its possible that while cranking it when it was wet it crossfired and spit back thru the carb and damaged something...blew off a vacuum hose, damaged pcv valve or hose, power brake hose, carb gasket etc...now that its dry its running lean...also did you check the timing? if its way off or all over the place the timing chain could have skipped (original style plastic tooth ones were famous for that)...

Alex V. 01-17-2017 06:12 PM
Re: Need Help Dont No What Else To Do
 
What about the coil? I had similar symptoms after running my '85 out of gas - replaced everything but the coil (the fairly expensive part) and rebuilt the carb. to no avail, but IIRC a new coil fixed it right up.

C.20 01-17-2017 06:24 PM
Quote:
Originally Posted by volksworld (Post 7829553)
ok the backfire...is backfiring out the exhaust or popping back through the carb? back through the carb is typically a lean condition...what carb is on it? its possible that while cranking it when it was wet it crossfired and spit back thru the carb and damaged something...blew off a vacuum hose, damaged pcv valve or hose, power brake hose, carb gasket etc...now that its dry its running lean...also did you check the timing? if its way off or all over the place the timing chain could have skipped (original style plastic tooth ones were famous for that)...
Its a demon and we bought a new carb also and we checked the timing and it was fine
Posted via Mobile Device

C.20 01-17-2017 06:24 PM
Quote:
Originally Posted by Alex V. (Post 7829631)
What about the coil? I had similar symptoms after running my '85 out of gas - replaced everything but the coil (the fairly expensive part) and rebuilt the carb. to no avail, but IIRC a new coil fixed it right up.
Put a new coil in it
Posted via Mobile Device
Posted via Mobile Device

67 chevelle 01-17-2017 08:01 PM
Re: Need Help Dont No What Else To Do
 
check timing before you do anything

C.20 01-18-2017 12:40 AM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by LongBox (Post 7829515)
A backfire strong enough to blow a muffler means unburnt gas was in the exhaust. this is because the engine was turning, but not firing. When it started firing again, the hot exhaust ignited the unburnt gas in the muffler. We used to do that on purpose when we was kids.

Since the last thing worked on seems to have been the ignition, time to go over the distributor very carefully, in an organized way. Is the wire from the coil connected correctly? Is the rotor seated on the plate on the top of the shaft. Is the centre contact in the cap there, and in good order. Is the centre contact on the rotor in good shape. I know these are new, but they can get out of whack.

Next, is each plug wire firmly seated in the cap? And at the plugs? Are the wires in good shape, with no issues with the insulation? Etc.Etc. Etc.
will check on this tommorow im running out of ideas

71CHEVYSHORTBED402 01-18-2017 01:06 AM
Re: Need Help Dont No What Else To Do
 
Bad distributor is my guess.

dmjlambert 01-18-2017 01:33 AM
Re: Need Help Dont No What Else To Do
 
I read through the thread and don't think you mentioned yet, are you powering the HEI distributor with the stock resistor wire, or have you done the 12V solid wire modification to your wiring when you installed the HEI?

C.20 01-18-2017 01:48 AM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by 71CHEVYSHORTBED402 (Post 7830045)
Bad distributor is my guess.
thats what im thinking

C.20 01-18-2017 01:50 AM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by 67 chevelle (Post 7829730)
check timing before you do anything
pulled the first plug cranked it till it shot out of first looked at the rotor and it was pointing to number one

C.20 01-18-2017 01:50 AM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by dmjlambert (Post 7830074)
I read through the thread and don't think you mentioned yet, are you powering the HEI distributor with the stock resistor wire, or have you done the 12V solid wire modification to your wiring when you installed the HEI?
i did the mod to 12v

67 chevelle 01-18-2017 08:22 AM
Re: Need Help Dont No What Else To Do
 
Quote:
Originally Posted by C.20 (Post 7830089)
pulled the first plug cranked it till it shot out of first looked at the rotor and it was pointing to number one
has almost nothing to do with timing , check your timing

C.20 01-18-2017 10:50 AM
Quote:
Originally Posted by 67 chevelle (Post 7830182)
has almost nothing to do with timing , check your timing
I can't test it with a light because it doesn't have a mark were you can check it with the light
Posted via Mobile Device

C.20 01-18-2017 11:31 AM
Re: Need Help Dont No What Else To Do
 
So took the truck out this morning and when it shifts or gets to a certain rpm it backfires when I keep it at that certain rpm it backfires ALOT
Posted via Mobile Device


All times are GMT -4. The time now is 06:59 AM.
Page 1 of 2 1 2
Show 40 post(s) from this thread on one page

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2025, vBulletin Solutions Inc.
Copyright 1997-2025 67-72chevytrucks.com