engine and drivetrain Backfire (pop) on 73tii...

[jgerock]

Should I bother checking valves & timing?

Don't let it intimidate you Scott. If you can, run thru the valve clearances before the engine gets warm.

As Bill mentions, adjusting the idle speed does not change the mixture (just like on a carburetor). Does the car have an 02 sensor - or do you have access to a portable unit?

[BillWilliams]

Neither of my cars pop or gurgle. My yellow car will as the weather changes and I have to do a slight adjustment to either richen or lean depending on if it is spring or fall.

If you feel the timing is on, you can try turning the small screw inside the tuna can about 1/32 of a turn and give it a whirl. Do this turn increment a few times and see if it helps or hurts.

If it hurts - go back to where you started and do the same in the other direction.

This small screw only adjusts air at idle but that is where the car is returning to when it starts to pop. If that does not help, call me.

Tiis do not pop if tuned correctly, PERIOD.

Is this the Charley?

[Scott Sislane]

Yes. That's Charlie!

[BillWilliams]

May want to start with fresh plugs, ensure the points are newish and gapped properly

[Scott Sislane]

I do not have an O2 sensor Jim. Great notes here. Bill, I may call for an SOS tomorrow afternoon.

[tlapham]

Don't forget, small exhaust leaks during deceleration can suck in cold air and cause a popping sound...

[Scott Sislane]

Don't forget, small exhaust leaks during deceleration can suck in cold air and cause a popping sound...

We'll check for that, thanks.

[willys]

Scott emailed me about this thread. I was the one that adjusted the idle screw outside of the tuna can. I always use an exhaust analyzer whenever I am adjusting anythingto do with air/fuel mixtures on my tii. I use an old heathkit purchased on ebay.

Scott, I am at the cape right now and heading back later today - home by 3. You are more than welcome to borrow it. If you have the tii manual it will tell you which way to turn the screw to enrich but it is pretty easy to tell by ear - more air=higher engine speed. It is a delicate balance between many parts. Popping on decel, assuming everything else is fine might mean an adjustment to the throttle cam as mentioned above. Feel free to email me when you are at the car and perhaps I can help via the phone.

Jeff

[Scott Sislane]

After reading all your helpful comments, and knowing what's transpired... I think it was running rich to begin with (plugs black), and by adjusting the idle screw simply brought the RPM's up at idle, keeping it from stalling, but the rich mixture remained.

My thought, is to return the idle screw to it's previous position (drop the idle slightly) and then under the lid, adjust for a leaner mixture, which should increase RPM's as well. Adjusting the screw clockwise (?) in 1/32nd increments to see what happens.

Does this sound right?

I like your picture here Jim.

[jgerock]

Scott -

The small screw only adjusts the mixture at idle - not across the entire RPM of the engine. I believe a clockwise turn of the screw ("in") = leaner. This opens the throttle plate at idle.

Backing off the screw (CCW or "out") makes the idle mixture richer. This closes the throttle plate at idle.

CAUTION: Before making any adjustments, let the engine warm up. This lets the warm up regulator on the injection pump get the engine up to operating temperature (engine will run a little richer during this period acting like a choke).

Note the cam-looking piece that the idle speed screw rests against. Below the housing is a coupling which connects the throttle body housing cam (NOT the butterfly flap) to the KF injection pump linkage. For the most part, that connection is what determines the air:fuel mixture across the range of the engine. Do not touch this coupling until other things are inspected.

I suggest you wait on adjusting the mixture until you can get hold of the portable Heathkit CO unit.

[Scott Sislane]

Thanks Jim.

[BillWilliams]

Scott,

Check your e-mail.

Just remember, the Heathkit will only tell you CO at idle - not off idle.

[Scott Sislane]

Well, Charlie made it up, we opened the can & adjusted the mixture screw just a hair clockwise, and in place reving his motor, it would not backfire (he said it would have before) but we took it out for a drive, and he could get it to do it, but not as often or frequently. We brought it back to the house & gave it another turn (like a c-hair) and off again for a test drive. Still on occasion, mostly in the motor there would be a very occasional "spat" (VERY TINY) if you rev'd over 3k & back down,and once on the test run a spat from the muffler. It's so minor compared to what I experience if my carbs are running too rich, it seems harmless. very tiny spat.

I was hesitant to to turn the screw too much, and marked it's original position. We didn't have enough time to do it properly, but Charlie says it's better than it was and now knows what's going on.

To get the timing light on the flywheel ball, we had to remove the air filter, which seemed to make it "hunt" so the RPM's would not stay put. Jim, guessing this is why you don't use that method. ?? So I didn't get the timing checked, which could also be affecting what's going on. The ball was also barely visible even after stick a few cotton swabs w/ solution on them to try & clean it off.

We changed the plugs before he left so he can check for any change in how they're doing.

Upon his departure, the tractor like sound of the motor made us realize we should probably have connected all 4 plug wires. 8-)

[BillWilliams]

Progress!

Give Charlie my best

[willys]

Nice job Scott - sorry I wasn't around to help.

Bill - above you mentioned that the Heathkit could only be used when adjusting the idle. I have used mine out on the road while driving in different situations and at different rpm's. I know the accuracy of the Heathkit testers are probably suspect but now I am curious if I should not be adjusting my settings when using it in this manner. Fortunately - the car runs fine and the plugs after 1000 miles look correct.

Jeff