Idle Issues...

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A bad ignition switch can cause backfires. The ignition system basically shuts down and back on for a split second. They're cheap and easy.
 
69swinger340391 said:
What about the reluctor air gap inside the distributor?

Also check for excessive side to side play in the distributor shaft.
Click to expand...


No side play in the shaft , I thought of that. I can go check the reluctor. I will also post pics. Should the advance mechanism open up all the way if i grab that and turn it? I noticed the slots that its sitting i can only get it to go half way. Didnt know if it had to much spring pressure on it for one to turn by hand of if something is binding I havnt got that far into the dizzy yet.
 
Was going to road test and put a video, i still my do so but I can get past why this is happening. No slack machanically, I'm thinking my light is hitting at a different time. But then again, thats why im on the forum :)


[ame]https://youtu.be/svsalEpdGXk[/ame]
 
Are the metering rods / power piston assembly adjusted properly in the carb? Float level set correctly? Have you had a vacuum gauge on the motor? Can you rig one in the cabin and watch it while you are driving and check the reading when it acts up? Noticed your pushrod question - Have the heads been milled - if so how much. I had a 340 that would backfire over 4500 rpm - was running non adjustable rockers, was getting into valve float due to milled heads and block - adjustable rockers fixed that. I'd pull the sending unit from the gas tank and check the sock/filter - see if it isn't plugged or collapsed.
 
Just saw your video - any issues with the distributor advance weights? No broken springs in the distributor? Is the vac advance diaphragm arm engaged in the advance plate? If the timing chain is known good I might try swapping in a different known good distributor, or go through yours to be sure it's 100%. And make sure your plug wires are good - not breaking down or crossed sending errant signals to your light. That timing is jumping around a bit. Some guys run a small collar on the end of the distributor shaft that stays in place with a set screw. It pushes down on the oil pump drive, keeping it from riding up the gear on the cam instead of driving the distributor and causing timing fluctuations. Seen it used on drag cars mostly. How's the oil pressure at idle? There were a bad batch of small block oil pumps on the market a few years back that would have like 60 psi at idle. The cam drives the pump and distributor and issues with the pump can cause timing issues.
 
airgrabber said:
Are the metering rods / power piston assembly adjusted properly in the carb? Float level set correctly? Have you had a vacuum gauge on the motor? Can you rig one in the cabin and watch it while you are driving and check the reading when it acts up? Noticed your pushrod question - Have the heads been milled - if so how much. I had a 340 that would backfire over 4500 rpm - was running non adjustable rockers, was getting into valve float due to milled heads and block - adjustable rockers fixed that. I'd pull the sending unit from the gas tank and check the sock/filter - see if it isn't plugged or collapsed.
Click to expand...

I adjusted the step up piston as described per rebuilt kit. If i remember correctly it was to back out the idle stop screws and allow butterfly to completly close. press down on the piston tab while holding the piston down and tighten.

Float was accordingly as well, first did it i had fuel coming up through the top. Set it back just a little to allow the seat to close and thats where ive left it.

I have not had a vacuum on it as i just moved last week and am still finding still. Last time i checked i believe it was in the 14-16 range on vacuum. I can pick up a gauge set today if i cant find mine and yes I have plenty of hose to bring in in the cab. Heads have not been milled or touched since ive owned it.

Will check the the sock today also.
 
airgrabber said:
Just saw your video - any issues with the distributor advance weights? No broken springs in the distributor? Is the vac advance diaphragm arm engaged in the advance plate? If the timing chain is known good I might try swapping in a different known good distributor, or go through yours to be sure it's 100%. And make sure your plug wires are good - not breaking down or crossed sending errant signals to your light. That timing is jumping around a bit. Some guys run a small collar on the end of the distributor shaft that stays in place with a set screw. It pushes down on the oil pump drive, keeping it from riding up the gear on the cam instead of driving the distributor and causing timing fluctuations. Seen it used on drag cars mostly. How's the oil pressure at idle? There were a bad batch of small block oil pumps on the market a few years back that would have like 60 psi at idle. The cam drives the pump and distributor and issues with the pump can cause timing issues.
Click to expand...

All, ive done to the dizzy so far is pop the cap to inspect. Looks clean and well. Looks can be deceiving. As I mentioned earlier, if i try to rotate to gain advance in the dizzy it only slides out about half way of the slots its sitting in. I wasnt sure if this was all it did or if it was to much force by hand... i need to get deeper in there and see whats up. Wires are good and set properly...
 
It can be pretty tough to get the full advance travel of the weights by hand.
Might be better if you can reach down in there and move the weights instead of trying to move them with the distributor shaft.
That one spring is a stock distributor is a tough little mother. (the garage door spring as we call it)
 
Just borrowed neighbors timing light. Turns out mine was junk. When its set to Zero no bounce. Advance the dial and it starts instantly. So, thats outta the way at least
 
I see what you mean. I clearly see misfires and double fires. Double fires are not actually double fires, but a firing in-between two regular firings. This is an induction cross-fire that usually originates in the plugwires having been run side-by-side, which is usually a no-no. Missfires can be for several reasons; 1) the voltage leaked away before it got to the plug, or 2) the plug shorted it away, or 3) it never got out of the cap in the first place.
I see in post #1, that a year ago the plugs and ignition were replaced. I'm assuming by ignition, you mean the plugwires? and maybe the cap? If not the cap then you need to inspect both the inside and the outside, for cracks, carbon tracks and moisture.
But; When I see this, I immediately flip my timing clamp, and if the problem persists, then I move the clamp to the #6 wire, and see if it's doing it too. If just one wire is doing it, separate it from other nearby ignition wires, to see if it quits. If it does , then the wire was probably picking up an induction crossfire. The wire may, or may not be bad.But if the problem remains, then it may be the sparkplug. Swap the plug to another hole and see if the problem follows it. If it does, it's junk.
But if the problem occurs with multiple wires, and cannot be traced to induction cross-fires, or a bad cap,then it may be the magnetic pick-up. I would rev it up slowly and watch the flashes and timing marks. If the timing marks are jumping all over the place and including backwards into a retard mode, then the polarity of the trigger may be reversed.But if the jumping never goes into retard, and remains about the same, then I would reset the reluctor gap, adding .003 to the gap, using a BRASS feeler gauge, or similar non-magnetic material. A good trigger will usually work from near zero gap to up to .020( and perhaps even more) without issue. But they have a sweetspot between .008 and about .015.If that doesn't do it, I would inspect the flyweight springs.
Now as to the timing marks;
Factory dampners have the long hashmarks at 10 degrees apart. Then there are 5 divisions between the long mark and the O mark, each representing 2 degrees. There is usually a 1 and a 0 straddling the 10 degree mark. I cannot recall ever seeing the number 5 on my dampner..Are you sure that you are seeing a 5?
 
Hard to tell with all the noise but here ya go... Each time i adjusted the timing i feel like it got better or worse. Could just be what i want to think... lol... Its not as bad as it was at all... but it sucks...


[ame]https://youtu.be/4r6JK4Z-GQQ[/ame]
 
Sent this to a friend that has several rods. He said its absolutley fuel/carb related... Not saying he is right... Just throwing it out there...
 
AJ/FormS said:
Afterfire, on deceleration is a whole nuther issue. Is that what I heard?
I thought we were talking about crappy running during and after a forced, WOT, 3-2 downshift.
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No afterfire on decel. We are talking about crappy running during a forced wot, 3-2. That's what its doing. Any gear, when you really get in it.. Runs like crap. The video sucks... but I'm in Texas and its an oven inside that thing even with the windows down. Decel is fine. it's only on the accel when it wot. Soon as I let off the throttle after its episode its back to normal.
 
For the record, I personally will not use a timing light with an advance dial on it. Too many stories of that circuitry corrupting the spark somehow, causing issues. I've got a 20+ year plain old Craftsman that, knock on wood, still works great...even when used with an MSD ignition.
 
Did I hear it backfire when you got off the pedal, on deceleration? I had a burnt exhaust valve do that...mine would pop out of the carb or exhaust...idled normal...an exhaust leak between the head and manifold would do that too...
 
Arg.... Can someone please tell me what voltage im looking for at the coil. "+" Terminal. I though it was 12V. Also there is a wire going from the positive side (about 6" long) to the bolt holding the bracket into the manifold. Near the end about the size of a tootsie roll is a black piece. Resistor? I would take a pic but its MIA right now...
 
Ok. I think ive figured out whats going on. I timed it today to about 11-12* at idle. Took it for a quick 5 min ride almost ran perfect. Didnt cut out at the WOT near as much. Then took it to the gym, 15 miles away and it ran ok. Headed home back to running so bad i didnt think it was going to make it home. Just out of curiosity I checked the timing. It's jumped from 12* to maybe 20* . Dizzy wont budge so i know thats tight. This leave what? Chain?
 
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