Backfire under loads

[geezer#99]

When you’re turning the distributor is the vac advance hooked up?

[liftlawssuck]

Originally Posted by geezer#99

When you’re turning the distributor is the vac advance hooked up?

No it is not hooked up.

[geezer#99]

I’ve had motors that wouldn’t start unless you had the distributor in exactly the right spot.
How does it run when you’re at the sweet spot of about 29 degrees?
Does it run good. No backfiring. No pinging.

[liftlawssuck]

Originally Posted by geezer#99

I’ve had motors that wouldn’t start unless you had the distributor in exactly the right spot.
How does it run when you’re at the sweet spot of about 29 degrees?
Does it run good. No backfiring. No pinging.

It doesn't run that good at all. Don't know about the pinging yet. Definitely not smooth and never like any other motor I have ever got running. But yet when I put the new plugs in and started it up and got it all warm it ran pretty good. Started it the next day and was a total different animal. Won't idle in gear. Starts right up each time but just runs like crap.

I just remembered that the vacuum advance is adjustable so maybe I'll try to adjust so it comes in at idle. Not sure why though as it all worked before I started this all.

[geezer#99]

Have you looked in the carb while it’s idling?
Could be something in the needle/seat that makes it flood a bit.

Which Holley carb?

[liftlawssuck]

Originally Posted by geezer#99

Have you looked in the carb while it’s idling?
Could be something in the needle/seat that makes it flood a bit.

Which Holley carb?

Yes I have looked in while running and it's dry until accelerator pumps squirts.

Holley 1850

[geezer#99]

Likely time for a compression or leak down test.

And what intake?

[liftlawssuck]

Originally Posted by geezer#99

Likely time for a compression or leak down test.

And what intake?

I did a quick compression check and all were 120lbs and above. I haven't done a differential check yet.

Intake is Edelbrock Performer.

[geezer#99]

Is it an airgap type intake?
Compression is a bit low.
I think you mentioned checking the lifter pre-load. Did you reset them and if so how far?

[kazoocruiser]

Originally Posted by liftlawssuck

I did a quick compression check and all were 120lbs and above. I haven't done a differential check yet.

Intake is Edelbrock Performer.

Me thinks you might have to go back and put about 2 tablespoons of oil in the spark plug hole of the cylinder you are testing to see what a wet compression test indicates. Assuming that you did your initial test with the throttle open while cranking, 120 psi on a dry test indicates worn out rings, or the possibility of compression gas leaking past a valve. If your readings jump up dramatically with a wet test, it isn't the valves.

The other thing I would suggest is putting a vacuum gauge on a manifold source and using what it tells you to help sort out if you have a hidden problem. Watch the gauge to see whether the numbers jump around, climb, or stay stable.

https://www.motor.com/magazine-summa...-vacuum-gauge/

I didn't see it mentioned in the thread, but do you have any idea how many miles are on the "82 K10 with a 305"?

[geezer#99]

Good stuff Mr. Cruiser!
Might I add a visual chart to go with your link.
https://www.google.com/search?tbm=is...mc3ymmivPmJ9M:

[kazoocruiser]

I went back through the thread and didn't see that an oil change has been done.

You could pull the dip stick and see if the oil smells like gas.

I seem to recall that if the fuel pump develops a pinhole in the diaphragm, it can allow raw gas into the oil sump. There should be a small hole on the bottom of the pump you can look at to see if there is evidence of leakage, or wrap a rag around it and let the motor run for awhile, and take the rag off and smell for gas.

Diluted gas ruins oil sealing at the rings, and might account for your low compression readings.

ps, Thanks, geezer#99

[cadillac_al]

Whaere's all the Holly experts? Wouldn't this be a symptom of the classic Holly blown power valve?

[liftlawssuck]

Originally Posted by geezer#99

Is it an airgap type intake?
Compression is a bit low.
I think you mentioned checking the lifter pre-load. Did you reset them and if so how far?

It is not an airgap style intake.
When checking pre-load I just did the quick rocker arm check while running. I know it's not the correct way but it was a quick check that I have done over the years. However maybe you can tell how to properly adjust them after the lifters have been filled with oil? On aircraft engines we hold the lifter under pressure of some stroke to bleed off the oil then go from there. Same way here??

Originally Posted by kazoocruiser

Me thinks you might have to go back and put about 2 tablespoons of oil in the spark plug hole of the cylinder you are testing to see what a wet compression test indicates. Assuming that you did your initial test with the throttle open while cranking, 120 psi on a dry test indicates worn out rings, or the possibility of compression gas leaking past a valve. If your readings jump up dramatically with a wet test, it isn't the valves.

The other thing I would suggest is putting a vacuum gauge on a manifold source and using what it tells you to help sort out if you have a hidden problem. Watch the gauge to see whether the numbers jump around, climb, or stay stable.

https://www.motor.com/magazine-summa...-vacuum-gauge/

I didn't see it mentioned in the thread, but do you have any idea how many miles are on the "82 K10 with a 305"?

I didn't have the throttle wide open when doing comp check. Didn't know you had to.

I will get a vacuum gauge and see what it tells me.

I have no idea how many miles on it. I do know it has been apart from tell tale signs. Block and heads are different colors, chrome timing chain cover. Intake had been off before and just over all inside of motor is pretty clean. Doesn't show the age for what the odometer says. Odometer says 8xxxx.

Originally Posted by kazoocruiser

I went back through the thread and didn't see that an oil change has been done.

You could pull the dip stick and see if the oil smells like gas.

I seem to recall that if the fuel pump develops a pinhole in the diaphragm, it can allow raw gas into the oil sump. There should be a small hole on the bottom of the pump you can look at to see if there is evidence of leakage, or wrap a rag around it and let the motor run for awhile, and take the rag off and smell for gas.

Diluted gas ruins oil sealing at the rings, and might account for your low compression readings.

ps, Thanks, geezer#99

My son drained the oil and changed it. I'll ask him if it smelled. The fuel pump is new on it now. Previously who knows what happened????

Originally Posted by cadillac_al

Whaere's all the Holly experts? Wouldn't this be a symptom of the classic Holly blown power valve?

Power valve is new but I also swapped it out with same size known good carb with same results. Trying to eliminate things in my head.


I really appreciate the help with this and love the input from all!!

[geezer#99]

I reset the valves with the motor at idle. Use something to deflect the oil splash. Strips of cardboard work well.
Back off the nut until it clicks, tighten a touch until it’s quiet. Then tighten again to 1/2 turn. Go slow. Too fast and the motor might quit.
Manual likely says 1 turn. I do 1/2 turn.
Most important thing to watch for is how many turns out before it clicks.
If they’re set up too far you’ll lose compression and idle like crap.

[kazoocruiser]

Liftlawssuck I see you indicated "I didn't have the throttle wide open when doing comp check. Didn't know you had to."

Thanks for admitting that.

The idea behind testing with a wide open throttle is to minimize any restriction in the intake stream, which then doesn't allow for a full intake charge.

You might want to do the the test over, with a paper and pencil to write down your readings. I'd would like to see what the tests show you.

Anytime I have done a compression test, I use a screw-in type gauge. The ones where you hold a rubber snout against the hole seem like a useful gauge, but compression gas can get blown past the snout, and give you a false reading. With a screw-in style gauge, that is less likely to happen. You also want to verify that the rubber o-ring is on the adapter, and not missing, because 160 psi will push past it otherwise.

Disconnect power to the coil, wire the throttle plate wide open, or have whoever is helping you hold the throttle wide open. Crank the engine until the gauge doesn't read any higher, usually about 5 revolutions. The reading should jump about three times and then remain steady. If it climbs slowly to a final point, the cylinder is not sealing properly. That is when you write your initial findings down, and do a wet (with the oil added) test, then write those numbers down. What you are looking for is no more than 10% difference between any cylinders.

I used to use 2 gauges so I could do two dry tests at a time on adjacent cylinders, then do the wet test on the first cylinder, and use those revolutions to test the second cylinder on a dry test a second time while the checking the first cylinder. Easier to demonstrate than explain. You might be able to do the loan-a-tool program if you have access to AutoZone or some other place that offers it.

What you are looking for is consistent numbers across the entire engine.

The reason to write everything down is so you can refer back to a document instead of scratching your head after your test and trying to remember which cylinder indicated which number.

I'd go ahead and pull all of the plugs before doing testing, to allow the engine to freewheel during testing. That helps save the battery.

When you are done, make sure the throttle isn't still wired wide open. People don't and it isn't pretty when they start a motor that way. Don't forget to reattach the coil power.

And thanks for telling me that a fuel pump was replaced, and the oil has been changed. That eliminates the possibility of fuel-diluted oil. You will still need to do the wet-cylinder test to verify there isn't any damage if there was.

[geezer#99]

Might I add a couple things!
I jam the throttle open with a big screwdriver. One I can’t miss seeing when I’m done cranking.
And your first number you see on the gauge should be at least 65-70% of your final reading. That’ll tell you that you have a reasonably good cylinder.

[Pontiac1976]

I the balancer is the 305 it should be hollowed on the back side, since you dist. was mechanical weight wore. And timing chain and cover might have been wrong or changed, might have wrong balancer or the rubber seal ring slipped. this would make it hard to get TDC lined up right.

[kazoocruiser]

Originally Posted by Pontiac1976

I the balancer is the 305 it should be hollowed on the back side, since you dist. was mechanical weight wore. And timing chain and cover might have been wrong or changed, might have wrong balancer or the rubber seal ring slipped. this would make it hard to get TDC lined up right.

I was thinking about this some as well. If he has a two-piece balancer, maybe it is starting to delaminate. If the engine is rotated around to #1 TDC, the timing marks ought be be lined up. If they are not showing TDC, That might be contributing to some of this hard to fix ness.

I had a Toyota that had a pulley come apart at highway speeds, but before it did, I ran out of room on the distributor slot trying to get the ignition timing correct. It kept showing late. I think I even tried to reset the distributor in the block.

Geezer#99's link gives a way to check if the balancer is bad.

Checking the outer damper ring for movement
Damper line.jpgDraw a sharpie line as shown in the image below. When the timing light is pointed at the TDC line, the sharpie line will also be seen. By revving the engine and running it at different speeds, if the outer ring is loose, the line on the outer ring will be seen to move independently of the line on the inner hub. Over time the line may be seen to have separated as the outer ring has moved independently of the inner hub.

[geezer#99]

Originally Posted by kazoocruiser

I was thinking about this some as well. If he has a two-piece balancer, maybe it is starting to delaminate. If the engine is rotated around to #1 TDC, the timing marks ought be be lined up. If they are not showing TDC, That might be contributing to some of this hard to fix ness.

I had a Toyota that had a pulley come apart at highway speeds, but before it did, I ran out of room on the distributor slot trying to get the ignition timing correct. It kept showing late. I think I even tried to reset the distributor in the block.

Geezer#99's link gives a way to check if the balancer is bad.

Checking the outer damper ring for movement
Damper line.jpgDraw a sharpie line as shown in the image below. When the timing light is pointed at the TDC line, the sharpie line will also be seen. By revving the engine and running it at different speeds, if the outer ring is loose,
the line on the outer ring will be seen to move independently of the line on the inner hub. Over time the line may be seen to have separated as the outer ring has moved independently of the inner hub.

Sorta good theory but he proved his timing tab/balancer marks are accurate with a piston stop.
Back to the think tank!

[kazoocruiser]

Originally Posted by liftlawssuck

I took the tool to find TDC and located it and found the timing tab was correct with the mark on balancer.

I must have been asleep when this information was posted, because there it is. Don't work too hard on Labor Day frying hamburgers.

[kazoocruiser]

Hey, what about this theory? Worn out cam bearings. That would allow the cam to wobble around and make a mess of valve timing. Maybe an oil pressure test is a good idea.

[Wgesnerjr]

thinking pretty far out there with this one but it's worth checking.

I know there are some theories that a 4/7 plug swap makes more power and gives the engine a more even firing order. could this engine have one of these cams? you did say the P.O. messed with it.

http://garage.grumpysperformance.com...cam-swap.5508/

Try swapping the 4/7 plugs. maybe it works, maybe not.

Just trying to think outside the box.

[cadillac_al]

Well, never did read a plug gap, are they at .045"? Never saw a vacuum reading, is it at least over 16"? Never heard if the valves were adjusted. Could have a bad cam here as already suggested.

[kazoocruiser]

Anyone want to take a poll that this has become an abandoned thread?