1986 Other Chevrolet Models 1986 C10 with 305

Tiny
ANDERSLAM2
  • MEMBER
  • 1986 CHEVROLET
  • V8
  • 2WD
  • AUTOMATIC
  • 100,454 MILES
Hello, I have a sbc 305 with everything stock, a week ago I was driving 45 down the road and all of the sudden the truck starts losing power and it backfires hard 4 times and shoots a bunch of debris out the exhaust. So when I was stopped I cut the exhaust at the y-pipe and it still is doing it. If you let it sit for a few minutes, it will start up and run fine for about 20-30 seconds then start loading up and running erratically, then when you try to give it some gas it will try to die and backfire. It just keeps doing this, is this a carb issue or a timing issue, or something else, any help would be appreciated, thanks
Do you
have the same problem?
Yes
No
Thursday, October 28th, 2010 AT 8:56 PM

12 Replies

Tiny
SERVICE WRITER
  • EXPERT
Put a timing light on it and if the timing is wacked then the pick up magnet on the distributor shaft is probably cracked and has moved. Either replace the distributor or install new shaft


http://www.2carpros.com/forum/automotive_pictures/30961_dist_2.jpg


IF timing is good check fuel pressure.
Was this
answer
helpful?
Yes
No
Friday, October 29th, 2010 AT 5:15 AM
Tiny
ANDERSLAM2
  • MEMBER
Ok so I took the fuel line off the carb and fuel pumping out, so fuels good, ill get the pickup in tomorrow and install that. Today I retimed the truck, brought 1st cylinder to tdc and set the distributor to cylinder 1. When cranking it still will not start, ive gotten it to backfire a few times but it wont start. I checked the spark and it was getting spark on 1, but we will see after I install that pickup. I also have a quadrajet off an 84 350 I will try, cause I heard mention that the carb might be shot. Also, when it was running (barely) I would stick the choke plate shut and it would kick and carry on dying, then I would let it off (full open) and it would run ok for 20 seconds, then start sputtering and dying again.
Was this
answer
helpful?
Yes
No
Sunday, October 31st, 2010 AT 7:00 PM
Tiny
ANDERSLAM2
  • MEMBER
Ok so, I have installed new timing gears and the chain, and set the distributor to fire at #6. I have also replaced the rotor, ignition module and magnetic pickup. Now when I try to start it, it spits fuel out of the carb in one spot or backfires, it is acting like it is 180 degrees out, thoughts? It is still doing the same thing, any response will be appreciated.
Was this
answer
helpful?
Yes
No
-1
Saturday, November 6th, 2010 AT 11:54 PM
Tiny
SERVICE WRITER
  • EXPERT
Is it still running okay for 20 seconds or so before it stalls out? OR has that changed?

IF this is the same, Then we need to determine what is being lost. Spark, fuel, timing/compression.

IF this is not running for the 20 sceonds, a second problem was created.
Was this
answer
helpful?
Yes
No
Sunday, November 7th, 2010 AT 3:34 AM
Tiny
ANDERSLAM2
  • MEMBER
No its not running now, I have read a forum online that a guy with the exact same truck having the same problem

im going to replace the cap and check the wiring to the vacuum advance.

Another note id like to add, I have the 4 wires in the back of the distributor, I dont think they were ever plugged in, but when I plug it in I get no spark, and when I leave it unplugged it gets spark.

When you try to start it it seems to get to one cylinder and shoots fuel out of the carb or backfires, depending on where I set the advance, so now its acting like its a 180 degrees out?
Was this
answer
helpful?
Yes
No
Sunday, November 7th, 2010 AT 9:18 AM
Tiny
ANDERSLAM2
  • MEMBER
Ok lets not worry about the esc, it wasnt hooked up in the first place, I am making some progress though, I think I am 1 cylinder off on my timing and will retime in a moment, but I can get it to stay running if I give it gas. Another possibility to the prior problem may be the idle air (warm idle) valve on the carb?
Was this
answer
helpful?
Yes
No
Sunday, November 7th, 2010 AT 11:34 AM
Tiny
SERVICE WRITER
  • EXPERT
Maybe a worn fuel pump shaft.

Do a fuel volume test, Or measure yours and compare to new.
Was this
answer
helpful?
Yes
No
Sunday, November 7th, 2010 AT 8:04 PM
Tiny
ANDERSLAM2
  • MEMBER
Ok I will check the fuel pump after work tomorrow. As for now it is running steadily, I have set the idle to 800 rpms in park, but when you put it in drive to takeoff it dies and once in awhile backfires when it does this. I will also check the tv cable.
Was this
answer
helpful?
Yes
No
Sunday, November 7th, 2010 AT 10:39 PM
Tiny
ANDERSLAM2
  • MEMBER
Ok so I ran into a mechanic down at the napa who had a stethascope on him and I listened to my motor as he revved it up. I either have a broken exhaust spring, or a bent exhaust valve on my passenger side. Will follow up when I have my covers off and check my springs.
Was this
answer
helpful?
Yes
No
Monday, November 8th, 2010 AT 8:01 PM
Tiny
SERVICE WRITER
  • EXPERT
That would make sense, One cyl not operating right.
Was this
answer
helpful?
Yes
No
Tuesday, November 9th, 2010 AT 6:10 PM
Tiny
ANDERSLAM2
  • MEMBER
Update. Alright so the engine is running ok at idle now, I have checked my valve springs, they are all good, which leads me to believe I may have burnt my exhaust valve when the cat backpressured. Now I have a new problem though. When you put it in drive or reverse (anything putting tension on the motor) it runs like crap again and dies, I checked the tv cable and it doesnt make any effect on it, its has the 700r4 with electronic shift. No vacuum modulator.
Was this
answer
helpful?
Yes
No
+1
Sunday, November 14th, 2010 AT 5:27 PM
Tiny
ANDERSLAM2
  • MEMBER
Im going to do a 350 swap in my truck, I dont feel like sinking money in this motor, lol I plugged that bad cylinder in and it backfired and caught my air cleaner on fire. Going to a built goodwrench 350 out of summit. 1500k flat top pistons, mild cam. Holley street avenger intake with 650 cfm edelbrock performer. Running 9-1 comp rat. With mallory dist, hooked to a 700r4 and running 3.73 spicer rear end. Once I tear the 305 apart well see what that exhaust valve is doing.
Was this
answer
helpful?
Yes
No
Wednesday, November 17th, 2010 AT 3:21 AM

Please login or register to post a reply.

Recommended Guides