I am about to go through a carb tune process with an LM2 AF meter, which should be fun.

However, I am just trying to set timing, idle and best lean idle with what I currently have and I continue to get pops in the exhaust at idle. I am hopeful that I will be able to tune that out, but I am wondering what would generally be considered the cause of those pops?

I have tightened all of my intakes, and exhausts. I don't think that I have any leaks. Tests with starter fluid don't yield any rise in rpm.

Is it running rich or lean at this point? Any help would be appreciated.

TIA

If popping is in exhaust I wouldn't think lean, and I wouldn't think intake leaks. Sure makes me think exhaust leak, but sounds like you've checked that. Typically lean pops out carbs, rich out exhaust.

How's the spark? Yellow, or nice fat blue?

I would be looking at timing lean can causing pre-det, rich is cold unless super rich like smell gas on dip stick rich not going to pop out the exhaust. Could be a floating valve?

Describe popping; what, where, when;
Does it sound like a gnat fart or a smooth bore report ?
What happens at 3500 in 3rd at throttle lift run-on ?
Does it go away at part throttle ?

Could be Fuel ( as in bad fuel delivery ); (crap in tank or fuel lines);
Could be incorrect jetting at your altitude; ( coupled with high idle )
Could be Air leak at base of carburator or manifold; vacuum leak;
Could be incorrect adjustment on crossbar linkage; (pre-loading one carb)
Could be Air being pulled into the exhaust;
Could be a crappy distributor;
Could be bad valve(s); valve guides, ( valve not seating properly );
Could be incorrect timing;
Could be incorrect valve adjustment;
Could be weak or broken valve spring;

You didn't mention what kind of induction (carburator(s) you're using, nor do you mention what kind of ignition system. You didn't mention what kind of exhaust
you are running ( dia, etc ).

All play a part in that gremlin.

Thanks for your input. Making sure I am on the right road.

you could have an air by-pass screw that needs to be addressed. as your engine pops at idle even with the linkage unattached, check the flow on each carb barrel with whatever type of uni-syn you are using. a distinct difference or more fluctuation between one reading and the others should help pin down the issue or at least eliminate one cause.

k

Carbs are synced fairly well. No fluctuations and all pulling the same on the snail. Will double check though. Thanks for the input.

do you have your choke plungers pinned down? maybe fuel is dripping from them. does your a/f read rich at idle?

Plungers removed and plugged with purpose built slugs from European in Hawthorne. I think those are taken care of.

I will actually have some time this weekend to look at the motor. Should be fun.

are you able to isolate it to a specific cylinder?

So this weekend I had a few hours and I was able to get out there and take another look-see.

I jacked up the rear, stuck her in 5th and rotated the engine. I took off the dizzy cap, and looked for the timing marks on both the flywheel and the fan. Both came up when the rotor was pointing to where #1 plugs into the cap.

Hmm... good I guess, but doesn't help me explain my rough running and crappy timing. Let alone the popping in the exhaust.

So I start to put everything back together, and I go to put the cap back on the dizzy, and it's just not locking into place. I flip it over and discover the notch is on the wrong side.

How the heck I did that and didn't notice is beyond me. I have had dizzys on and off motors hundreds of times. So I rotate her 'round and button everything back up and most of the popping is gone. I had tweaked the timing before I stopped last time, so I am sure it's still off, but it idled solid.

That cap must have been wiggling like a bobble-head doll, throwing my timing and spark all out of whack.

Such a damn rookie mistake. Repeating it here so others don't make the same mistake.

Anyway, was about to start over with carb sync and timing, when the misses told me that the washing machine took a crap. Oh well.....

nice find kapt. glad it was a simple fix...

Hey Kaos,
I have a similar setup on a 1.7 and I've having similar problems. However, its not the cap. The car pops at idle and runs like CRAP at 1/3 throttle. Seems to clear up between 2/3 and full throttle. Something tells me I didn't put the SVDA in right, or the plug wires are wrong. Would you be willing to take a picture of the SVDA in place and the location of each plug wire? Thanks!

I can, but not likely until tomorrow. However, I can describe it to you to see if that helps in the mean time.

For reference, 12 o'clock on the dizzy would be straight towards the front of the car.

I had to rotate my SVDA dizzy about 90 degrees because the vacuum canister would hit the tin. So on a 009 or 050, #1 would be at about 11 o'clock, but with the SVDA #1 is now at about 8 o'clock. #4 sits at 11 o'clock and so on.

I hope that helps and/or makes sense.

I can snap a pic tomorrow. I think I should have some time.

Update: I think my timing light is shot. Used one from my autoshop class and was able to get the timing set off of the flywheel, at least a little more accurately. Of course, I had a collapsed valve cover gasket, so it was spitting oil, but I digress....


Tomorrow I hope to do some more, and get set to best lean idle and see how it goes from there.

adjusted the timing off of the fly wheel. Much of the popping is gone and things are smoother. There is still some there from over run.

it bogs really badly off idle. I need to rev a bunch to get underway. Can't be good for the clutch. Tips?

I have a procedure from Mr.bubblehed to tune the carbs well, haven't gotten to that point yet. Just want to get things to a smoother state first. Tia

hey kapt, do you have too much accelerator pump squirt? did you balance with the bleed screws? then sync both carbs together? then reset your mixture screws to BLI? then recheck everything.....

Carbs are synced with the air bypass adjusted as discussed.

At BLI right now, but bogs on start off.

I haven't touched the accl pump nuts. should I back those off a bunch?

you could try it.... whar size are your venturies?

28 iirc. I need to check to confirm, but I am 90% sure.

hmmm..... those should give you plenty of velocity. im at a loss... for sure timing is correct? 28 degrees full advance? what kind of fuel pump are you using? regulator? are you using a fuel pressure gauge? should be about 2.5 psi....

ohhh what did you set your floats to? up position and down position.

does the bog feel like a rich condition or lean condition? or is it hard to tell?

fuel filter clean?

how does it rev with no load? like sitting in the driveway in neutral.

we'll get to the bottom of it

Hmm.... Let me get back to you on this one..... I think I am at 32 degrees, which would be too much.