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I'm begging... please help me trouble shoot this

78Suburban

78Suburban

1/2 ton status
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Jul 4, 2005
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Georgia
Well, I did the edelbrock swap today, hoping it would cure my problems.. I also swapped in some non fouled plugs (the old ones were BAD).. Cranked her up, and she runs ok without a load. Set timing to 10* BTDC. Drove it a little and if I really step into the gas, it backfires through the carb.. I think I also hear a bit of knocking coming from the top of the engine... I don't guess the valves are screwed up? I thought surely this carb would solve the problem. Is it possible that it could run and idle ok 180* out but mess up under load, or would it not even crank (I've heard mulitiple opinions on that)... I surely wish I could get somebody that knew what they were doing to look at it.. I really was hoping it would all be better after the swap.. It does seem to run a bit better, but still genreally underpowered, and BACKFIRING through the carb on occasion if I step into her under load.. If anyone can lead me to getting this bad boy running, you will be my hero forever :bow: .. This is the dizzy and wires off my old motor. I did the water spray bottle trick tonight and did see a bit of blue. But the motor acted the same way with the other dizzy and wires, and The old motor ran fine with this dizzy and wires..

I'm begging, please help me crack this case, before I loose all sanity... I've put so much time and money and hope into this truck only to be really discouraged.. Thank soooo much :bow: :bow: :bow: :bow: :bow:
James
 
just had this prob not too long ago.... its the timing. mine was 3 teeth off(advanced) from the P. owner. yank the distributor hook up a compression gauge and bump it over till you are at TDC for #1.set your rotor where it points to plug # 2 on the cap and align your oil pump shaft and voila! when you drop the dist the gears will mesh and fully seated the rotor will be pointing dead at cyl # 1. easy. just dont try to do it on an incline..... dont ask, it was 3 am and i had no help.:crazy:
 
I had this a similar problem last week after performing a tune-up on a friends '86 burb. It would "pop" through the carb when snapping the throttle. The first this I did was double check the plug wires. I found 6 and 8 to be crossed. Routed them correctly and it now runs great.
 
Check the wires for firing order, check the timing, if OK do a compresion test. If you have an intake valve starting to go it can cause the backfire in the intake...
 
I think I accidentally had the carb's full vaccume port hooked to the dizzy.. I'm gonna try to use the ported vaccume tomrrow and see if that solves my problem.. thank you paul :bow: :bow:
thanks,
James
 
Probably the timing

I bought my 2nd K5 last month. The guy that rebuilt the engine said he replaced the harmonic balancer. According to this guy, the timing marks no longer match up because of the different 350 balancer. :confused:

I have not checked this for myself. He said this caused problems after warm up. Difficulty restarting, poor running until he discovered it.

Did you replace the pushrods, lifters or anything like that? If you did, you may need to check the valve train for proper adjustment.
 
there are 2 differant 350 balancers so that is completely possible. either will work but the timing marks are in differant places
 
I had the same problem.


Pull the valve covers and make sure that all the rocker arms are adjusted corectly. A lose arm on the exhaust will cause the problem.:D:D:D:D:laugh::laugh:
 
jhellwig said:
I had the same problem.


Pull the valve covers and make sure that all the rocker arms are adjusted corectly. A lose arm on the exhaust will cause the problem.:D:D:D:D:laugh::laugh:
Click to expand...

How will I know if its loose? How do I properly tighten it.. I've swapped this motor in, and I've swapped intakes on a motor twice, but I've never actually had a set of valve covers off :o :o :o :o
thanks,
James
 
I hooked it up to ported vaccume, at it runs alot worse... won't hardly even drive.. and backfires through the carb... it basically chokes down in gear... idles really really choppy.. Why would it do worse with ported vaccume? Has my balancer or timing tab slipped way off? I'm going crazy.
thanks,
James
 
Take all of your plugs out so you can turn the engine over by hand.

Stick a thin screwdriver in the #1 spark plug hole and rotate the engine BY HAND until the screwdriver stops moving upwards. You may have to go back and forth with the crankshaft a couple times to get the exact TDC point.

Check the marks on your balancer to make sure it is now lined up with the 0° mark on your timing tab. If it's not, make a new mark on your balancer where it should be.

Now put all your plugs back in and start with the basics.
Cylinders are numbers 1-3-5-7 on the driver side, 2-4-6-8 on the passenger side.
Make sure you have all the wires in the right places and your firing order is correct (18436572) with the clockwise rotation of the dist.

Here's a good visual aid:
http://www.boxwrench.net/specs/chevy_sb.htm

If all that is right, then you can set your rocker arms. The easiest way is to do it while the engine is running. It's a bit messy but it works good. Loosen each rocker until you hear it start to click, then tighten it until it just stops clicking. Once you have does this to all 16 of them, shut off the engine and tighten each one an additional 3/4 turn.

Once that is done, you can set the timing using a timing light or the vacuum method linked earlier. Be sure you have the idle speed set properly, the vacuum advance disconnected and the hose plugged while you are setting the timing.

And once that is done, do a compression check to see if you have a burned valve that may be causing the backfire.
 
78Suburban said:
How will I know if its loose? How do I properly tighten it.. I've swapped this motor in, and I've swapped intakes on a motor twice, but I've never actually had a set of valve covers off :o :o :o :o
thanks,
James
Click to expand...

Pull the cover off of the cylinder head that is making the noise. Then take and shake the rocker arms(while the valve is closed). The should be able to move a very little but not rattle around or anything.

To tighten any offending arm just take a socket and tigten it until you can no longer move the push rod anymore. Then back it off slighly till you can move it. Basicaly just make it so that it feels like all the others. But make sure that the cam isn't trying to hold the valve open at that time.
 
With the vac on ported vacuum now the vac advance isn't doing much at idle anymore. Your timing is way retarded, try firing it up and turn the distributor to advnce the timing while it's running. You're going the right direction if the idle speed increases and the engine smooths out. Snug the hold down bolt and go for a drive...if it still feels a little doggy and you hear no pinging under load advance it a little more. Keep advancing the timing until you get slight pinging under load...then back it off a hair. Now hook the timing light to it and jot down how many degrees BTDC it's at. This is the 'sweet spot' for your motor.

As the timing chain ages and stretches the marks and stuff get a lot less reliable. I have always timed my junk this way. Each motor is pretty individual regarding timing, and each one has it's own sweet spot.

Before you do any of this double check the firing order and plug wires though. As mentioned it's pretty easy to get a few mixed up.

Rene
 
I had the problem with the wrong balancer. I pulled the oil pan to find TDC then put on some timing tape, which is like $4 from Summit. Then A cheap timing light is as good as a dial advance one.
 
so start turning that bad boy counter clockwise/ test driving it, untill she pings and back her off? I hope I can hear/detect pinging, because its straight piped.. I've got a feeling that if the balancer has slipped or the timing tab has slipped, if I ever do find that "sweet spot", it will be all the way off the timing mark. I surely hope I can get to the bottom of this.. and I hope I don't damage my motor playing with all this with my crappy old 1/8th tank of regular gas.. If this fails, I suppose I will try the rocker arm tightening next..
I'm also gonna try to get ahold of a vaccume gauge soon.
thanks,
James
 
If it's too advanced it'll crank hard when trying to start. Basically it's firing so early it's trying to turn the motor backwards. If you get any of this definitely back it off some. I never damaged any of the 40+ motors I've timed this way over the years. Just make conservative adjustments...

FWIW my friend used to have a '75 Pontiac Grand Prix, which he took to a tune up place once. We had always timed it by ear and he was really happy with the performance, but it had a high rpm problem occassionally. So he figured maybe if the 'pro's' tuned it up the problem would be solved. They charged him a couple of hundred bucks and the car literally fell on it's face when you stepped on it. They set the timing to the factory spec's...so we re-timed it ourselves and on their timing light it was 12-14 degrees more advanced than the factory spec's when we were happy with it.

Rene
 
79k20350 said:
there are 2 differant 350 balancers so that is completely possible. either will work but the timing marks are in differant places
Click to expand...

This is correct, i remember when i changed my motor out in my 85, we had to hunt for the balancer at a yard, because the old one diddnt work with the engine.
 
tRustyK5 said:
I never damaged any of the 40+ motors I've timed this way over the years.
Click to expand...

DANG.. I bet you've got a better ear for it than I do..lol :bow: :bow: :bow:
thanks,
James
 
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